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Jesse W Young - One of the best experts on this subject based on the ideXlab platform.

  • Ontogeny of effective Mechanical Advantage in eastern cottontail rabbits (Sylvilagus floridanus).
    The Journal of experimental biology, 2019
    Co-Authors: Adam D. Foster, Michael T. Butcher, Gregory A. Smith, Gabrielle A. Russo, Rajaa Thalluri, Jesse W Young
    Abstract:

    Juvenile animals must survive in the same environment as adults despite smaller sizes, immature musculoskeletal tissues, general ecological naïveté and other limits of performance. Developmental changes in muscle leverage could constitute one mechanism to promote increased performance in juveniles despite ontogenetic limitations. We tested this hypothesis using a holistic dataset on growth and locomotor development in wild eastern cottontail rabbits (Sylvilagus floridanus) to examine ontogenetic changes in hindlimb muscle effective Mechanical Advantage (EMA). EMA is a dimensionless index of muscle leverage, equal to the quotient of average muscle lever length and the load arm length of the ground reaction force (GRF), effectively representing the magnitude of output force arising from a given muscle force. We found that EMA at the hip and ankle joints, as well as overall hindlimb EMA, significantly declined across ontogeny in S. floridanus, whereas EMA at the knee joint remained unchanged. Ontogenetic decreases in EMA were due to isometric scaling of muscle lever arm lengths alongside positive ontogenetic allometry of GRF load arm lengths - which in turn was primarily related to positive allometry of hindlimb segment lengths. Greater EMA limits the estimated volume of hindlimb extensor muscle that has to be activated in young rabbits, likely mitigating the energetic cost of locomotion and saving metabolic resources for other physiological functions, such as growth and tissue differentiation. An additional examination of limb growth allometry across a diverse sample of mammalian taxa suggests that ontogenetic decreases in limb joint EMA may be a common mammalian trend.

  • Ontogeny of effective Mechanical Advantage in Eastern cottontail rabbits (Sylvilagus floridanus)
    The Journal of Experimental Biology, 2019
    Co-Authors: Adam D. Foster, Michael T. Butcher, Gregory A. Smith, Gabrielle A. Russo, Rajaa Thalluri, Jesse W Young
    Abstract:

    Juvenile animals must survive in the same environment as adults despite smaller sizes, immature musculoskeletal tissues, general ecological naivete and other limits of performance. Developmental changes in muscle leverage could constitute one mechanism to promote increased performance in juveniles despite ontogenetic limitations. We tested this hypothesis using a holistic dataset on growth and locomotor development in wild eastern cottontail rabbits (Sylvilagus floridanus) to examine ontogenetic changes in hindlimb muscle effective Mechanical Advantage (EMA). EMA is a dimensionless index of muscle leverage, equal to the quotient of average muscle lever length and the load arm length of the ground reaction force (GRF), effectively representing the magnitude of output force arising from a given muscle force. We found that EMA at the hip and ankle joints, as well as overall hindlimb EMA, significantly declined across ontogeny in S. floridanus, whereas EMA at the knee joint remained unchanged. Ontogenetic decreases in EMA were due to isometric scaling of muscle lever arm lengths alongside positive ontogenetic allometry of GRF load arm lengths - which in turn was primarily related to positive allometry of hindlimb segment lengths. Greater EMA limits the estimated volume of hindlimb extensor muscle that has to be activated in young rabbits, likely mitigating the energetic cost of locomotion and saving metabolic resources for other physiological functions, such as growth and tissue differentiation. An additional examination of limb growth allometry across a diverse sample of mammalian taxa suggests that ontogenetic decreases in limb joint EMA may be a common mammalian trend.

  • Ontogeny of muscle Mechanical Advantage in capuchin monkeys (Cebus albifrons and Cebus apella)
    Journal of Zoology, 2005
    Co-Authors: Jesse W Young
    Abstract:

    Terrestrial locomotion requires that animals maintain postural stability against the flexing force of gravity. To counteract volume/area relationships that limit muscle force and may compromise stability, larger animals increase the effective Mechanical Advantage of their extensor musculature by walking on more extended limbs and showing allometric increases in extensor muscle lever arm lengths. Assuming these size-related principles are uniform, similar adaptations should characterize ontogenetic increases in size. Previous research on non-primate mammals has shown, however, that extensor muscle Mechanical Advantage is greater early in ontogeny and decreases with negative allometry during growth. This study extended this work by investigating patterns of relative elbow lever arm growth in two capuchin monkeys, Cebus albifrons and Cebus apella. Unlike previously studied mammals, growing capuchin monkeys face unique anatomical constraints, including relatively long limb bones and positively allometric limb growth. These constraints could augment the flexing torque of gravity at the limb joints and require compensatory increases in extensor muscle Mechanical Advantage as size increases through growth. Forearm length and the length of elbow extensor and flexor muscle lever arms were measured in longitudinal radiographic series of growing capuchin monkeys. In contrast to other mammals, all lengths scaled to body mass with positive allometry. Anatomical Mechanical Advantage (lever arm length/forelimb length) scaled with negative allometry, however, matching the non-primate mammalian trend. Greater muscle Mechanical Advantage during early locomotion may help young mammals overcome relatively weak extensor muscles and other growth-related limits on locomotor performance. Additional data on ontogenetic changes in gait dynamics and musculoskeletal growth are required to validate this hypothesis.

TA Wilson - One of the best experts on this subject based on the ideXlab platform.

  • Respiratory action of the intercostal muscles
    PHYSIOL REV, 2005
    Co-Authors: TA Wilson
    Abstract:

    The Mechanical Advantages of the external and internal intercostals depend partly on the orientation of the muscle but mostly on interspace number and the position of the muscle within each interspace. Thus the external intercostals in the dorsal portion of the rostral interspaces have a large inspiratory Mechanical Advantage, but this Advantage decreases ventrally and caudally such that in the ventral portion of the caudal interspaces, it is reversed into an expiratory Mechanical Advantage. The internal interosseous intercostals in the caudal interspaces also have a large expiratory Mechanical Advantage, but this Advantage decreases cranially and, for the upper interspaces, ventrally as well. The intercartilaginous portion of the internal intercostals (the so-called parasternal intercostals), therefore, has an inspiratory Mechanical Advantage, whereas the triangularis sterni has a large expiratory Mechanical Advantage. These rostrocaudal gradients result from the nonuniform coupling between rib displacement and lung expansion, and the dorsoventral gradients result from the three-dimensional configuration of the rib cage. Such topographic differences in Mechanical Advantage imply that the functions of the muscles during breathing are largely determined by the topographic distributions of neural drive. The distributions of inspiratory and expiratory activity among the muscles are strikingly similar to the distributions of inspiratory and expiratory Mechanical Advantages, respectively. As a result, the external intercostals and the parasternal intercostals have an inspiratory function during breathing, whereas the internal interosseous intercostals and the triangularis sterni have an expiratory function.

  • Respiratory Mechanical Advantage of the canine external and internal intercostal muscles.
    The Journal of physiology, 1999
    Co-Authors: A De Troyer, A Legrand, TA Wilson
    Abstract:

    1. The current conventional view of intercostal muscle actions is based on the theory of Hamberger (1749) and maintains that as a result of the orientation of the muscle fibres, the external intercostals have an inspiratory action on the lung and the internal interosseous intercostals have an expiratory action. This notion, however, remains unproved. 2. In the present studies, the respiratory actions of the canine external and internal intercostal muscles were evaluated by applying the Maxwell reciprocity theorem. Thus the effects of passive inflation on the changes in length of the muscles throughout the rib cage were assessed, and the distributions of muscle mass were determined. The fractional changes in muscle length during inflation were then multiplied by muscle mass and maximum active stress (3.0 kg cm-2) to evaluate the potential effects of the muscles on the lung. 3. The external intercostals in the dorsal third of the rostral interspaces were found to have a large inspiratory effect. However, this effect decreases rapidly both toward the costochondral junctions and toward the base of the rib cage. As a result, it is reversed to an expiratory effect in the most caudal interspaces. The internal intercostals in the caudal interspaces have a large expiratory effect, but this effect decreases ventrally and rostrally, such that it is reversed to an inspiratory effect in the most rostral interspaces. 4. These observations indicate that the canine external and internal intercostal muscles do not have distinct inspiratory and expiratory actions as conventionally thought. Therefore, their effects on the lung during breathing will be determined by the topographic distribution of neural drive.

  • Respiratory Mechanical Advantage of the canine external and internal intercostal muscles
    The Journal of Physiology, 1999
    Co-Authors: A De Troyer, A Legrand, TA Wilson
    Abstract:

    The current conventional view of intercostal muscle actions is based on the theory of Hamberger (1749) and maintains that as a result of the orientation of the muscle fibres, the external intercostals have an inspiratory action on the lung and the internal interosseous intercostals have an expiratory action. This notion, however, remains unproved. In the present studies, the respiratory actions of the canine external and internal intercostal muscles were evaluated by applying the Maxwell reciprocity theorem. Thus the effects of passive inflation on the changes in length of the muscles throughout the rib cage were assessed, and the distributions of muscle mass were determined. The fractional changes in muscle length during inflation were then multiplied by muscle mass and maximum active stress (3·0 kg cm−2) to evaluate the potential effects of the muscles on the lung. The external intercostals in the dorsal third of the rostral interspaces were found to have a large inspiratory effect. However, this effect decreases rapidly both toward the costochondral junctions and toward the base of the rib cage. As a result, it is reversed to an expiratory effect in the most caudal interspaces. The internal intercostals in the caudal interspaces have a large expiratory effect, but this effect decreases ventrally and rostrally, such that it is reversed to an inspiratory effect in the most rostral interspaces. These observations indicate that the canine external and internal intercostal muscles do not have distinct inspiratory and expiratory actions as conventionally thought. Therefore, their effects on the lung during breathing will be determined by the topographic distribution of neural drive. Although it is now well established that the interchondral portion of the internal intercostal muscles (the so-called parasternal intercostals) elevates the ribs and inflates the lung when it contracts (De Troyer & Kelly, 1982; De Troyer et al. 1996), the actions of the external intercostals and the interosseous portion of the internal intercostals remain uncertain. The current conventional view is based on the theory proposed 250 years ago by Hamberger (1749). According to this theory, the fibres of the external intercostals slope obliquely caudad and ventrally from the rib above to the rib below, and so their lower insertion is further from the centre of rotation of the ribs (i.e. the costo-vertebral articulations) than their upper insertion. Consequently, when this muscle contracts with its force equal and opposite at both insertions, the torque acting on the lower rib, which tends to raise it, is greater than that acting on the upper rib, which tends to lower it. The net effect of the muscle, therefore, would be to raise the ribs and to inflate the lung. In contrast, the fibres of the internal interosseous intercostals slope obliquely caudad and dorsally from the rib above to the one below so that their lower insertion is closer to the centre of rotation of the ribs than the upper one. As a result, the net effect of their contraction would be to lower the ribs and to deflate the lung. This theory, however, has not been verified, and computations based on the orientation of the muscle fibres and on descriptions of rib displacement in dogs (Margulies et al. 1989) have recently suggested that the actions of the external and internal intercostal muscles on the lung might vary between the dorsal and the ventral aspects of the rib cage as well as between the rostral and caudal interspaces (Wilson & De Troyer, 1993). In the present studies, we have examined the effects of the canine external and internal interosseous intercostals on the lung by using a standard theorem of mechanics, the Maxwell reciprocity theorem. When applied to the respiratory system (Wilson & De Troyer, 1992, 1993), this theorem predicts that the respiratory effect of a particular muscle (that is, the potential change in airway pressure - ΔPao - produced by the muscle contracting alone against a closed airway) is related to the mass (m) of the muscle, the maximal active muscle tension per unit cross-sectional area (σ), and the fractional change in muscle length (ΔL/L) per unit volume increase of the relaxed chest wall (ΔVL)Rel, such that: (1) For a machine, such as a lever, Mechanical Advantage is defined as the ratio of the force delivered at the load to the force applied at the handle. By analogy, the Mechanical Advantage of a respiratory muscle may therefore be defined as ΔPao/mσ and, according to eqn (1), could be evaluated by measuring (ΔL/(L ΔVL))Rel. In other words, a muscle that shortens during passive inflation would have an inspiratory Mechanical Advantage and would cause a fall in Pao when it contracts. Conversely, a muscle that lengthens during passive inflation would have an expiratory Mechanical Advantage and would cause a rise in Pao during contraction.

  • Mechanical Advantage of the human parasternal intercostal and triangularis sterni muscles.
    The Journal of physiology, 1998
    Co-Authors: A De Troyer, A Legrand, P A Gevenois, TA Wilson
    Abstract:

    1. Previous studies in dogs have demonstrated that the maximum change in airway pressure (DeltaPao) produced by a particular respiratory muscle is the product of three factors, namely the mass of the muscle, the maximal active muscle tension per unit cross-sectional area ( approximately 3.0 kg cm-2), and the fractional change in muscle length per unit volume increase of the relaxed chest wall (i.e. the muscle's Mechanical Advantage). In the present studies, we have used this principle to infer the DeltaPao values generated by the parasternal intercostal and triangularis sterni muscles in man. 2. The mass of the muscles and the direction of the muscle fibres relative to the sternum were first assessed in six cadavers. Seven healthy individuals were then placed in a computed tomographic scanner to determine the orientation of the costal cartilages relative to the sternum and their rotation during passive inflation to total lung capacity. The fractional changes in length of the muscles during inflation, their Mechanical Advantages, and their DeltaPao values were then calculated. 3. Passive inflation induced shortening of the parasternal intercostals in all interspaces and lengthening of the triangularis sterni. The fractional shortening of the parasternal intercostals decreased gradually from 7.7 % in the second interspace to 2.0 % in the fifth, whereas the fractional lengthening of the triangularis sterni increased progressively from 5.9 to 13.8 %. These rostrocaudal gradients were well accounted for by the more caudal orientation of the cartilages of the lower ribs. 4. Since these fractional changes in length corresponded to a maximal inflation, the inspiratory Mechanical Advantage of the parasternal intercostals was only 2.2-0. 6 % l-1, and the expiratory Mechanical Advantage of the triangularis sterni was only 1.6-3.8 % l-1. In addition, whatever the interspace, parasternal and triangularis muscle mass was 3-5 and 1-3 g, respectively. As a result, the magnitude of the DeltaPao values generated by a maximal contraction of the parasternal intercostals or triangularis sterni in all interspaces would be only 1-3 cmH2O. 5. These studies therefore confirm that the parasternal intercostals in man have an inspiratory action on the lung whereas the triangularis sterni has an expiratory action. However, these studies also establish the important fact that the pressure-generating ability of both muscles is substantially smaller than in the dog.

A De Troyer - One of the best experts on this subject based on the ideXlab platform.

  • Respiratory Mechanical Advantage of the canine external and internal intercostal muscles.
    The Journal of physiology, 1999
    Co-Authors: A De Troyer, A Legrand, TA Wilson
    Abstract:

    1. The current conventional view of intercostal muscle actions is based on the theory of Hamberger (1749) and maintains that as a result of the orientation of the muscle fibres, the external intercostals have an inspiratory action on the lung and the internal interosseous intercostals have an expiratory action. This notion, however, remains unproved. 2. In the present studies, the respiratory actions of the canine external and internal intercostal muscles were evaluated by applying the Maxwell reciprocity theorem. Thus the effects of passive inflation on the changes in length of the muscles throughout the rib cage were assessed, and the distributions of muscle mass were determined. The fractional changes in muscle length during inflation were then multiplied by muscle mass and maximum active stress (3.0 kg cm-2) to evaluate the potential effects of the muscles on the lung. 3. The external intercostals in the dorsal third of the rostral interspaces were found to have a large inspiratory effect. However, this effect decreases rapidly both toward the costochondral junctions and toward the base of the rib cage. As a result, it is reversed to an expiratory effect in the most caudal interspaces. The internal intercostals in the caudal interspaces have a large expiratory effect, but this effect decreases ventrally and rostrally, such that it is reversed to an inspiratory effect in the most rostral interspaces. 4. These observations indicate that the canine external and internal intercostal muscles do not have distinct inspiratory and expiratory actions as conventionally thought. Therefore, their effects on the lung during breathing will be determined by the topographic distribution of neural drive.

  • Spatial distribution of external and internal intercostal activity in dogs.
    The Journal of physiology, 1999
    Co-Authors: A Legrand, A De Troyer
    Abstract:

    1. The observation that the external and internal interosseous intercostal muscles in the dog show marked regional differences in Mechanical Advantage has prompted us to re-examine the topographic distribution of electrical activity among these muscles during spontaneous breathing. 2. Inspiratory activity was recorded only from the areas of the external intercostals with an inspiratory Mechanical Advantage, and expiratory activity was recorded only from the areas of the internal intercostals with an expiratory Mechanical Advantage. The expiratory discharges previously recorded from the caudal external intercostals and the inspiratory discharges recorded from the rostral internal intercostals were probably due to cross-contamination. 3. Activity in each muscle area was also quantified relative to the activity measured during tetanic, supramaximal nerve stimulation (maximal activity). External intercostal inspiratory activity was consistently greater in the areas with a greater inspiratory Advantage (i.e. the dorsal aspect of the rostral segments) than in the areas with a smaller inspiratory Advantage, and internal intercostal expiratory activity was invariably greatest in the areas with the greatest expiratory Advantage (i.e. the dorsal aspect of the caudal segments). 4. This topographic distribution of neural drive confers to the external intercostal muscles an inspiratory action on the lung during breathing and to the internal interosseous intercostals an expiratory action.

  • Spatial distribution of external and internal intercostal activity in dogs
    The Journal of Physiology, 1999
    Co-Authors: A Legrand, A De Troyer
    Abstract:

    The observation that the external and internal interosseous intercostal muscles in the dog show marked regional differences in Mechanical Advantage has prompted us to re-examine the topographic distribution of electrical activity among these muscles during spontaneous breathing. Inspiratory activity was recorded only from the areas of the external intercostals with an inspiratory Mechanical Advantage, and expiratory activity was recorded only from the areas of the internal intercostals with an expiratory Mechanical Advantage. The expiratory discharges previously recorded from the caudal external intercostals and the inspiratory discharges recorded from the rostral internal intercostals were probably due to cross-contamination. Activity in each muscle area was also quantified relative to the activity measured during tetanic, supramaximal nerve stimulation (maximal activity). External intercostal inspiratory activity was consistently greater in the areas with a greater inspiratory Advantage (i.e. the dorsal aspect of the rostral segments) than in the areas with a smaller inspiratory Advantage, and internal intercostal expiratory activity was invariably greatest in the areas with the greatest expiratory Advantage (i.e. the dorsal aspect of the caudal segments). This topographic distribution of neural drive confers to the external intercostal muscles an inspiratory action on the lung during breathing and to the internal interosseous intercostals an expiratory action. The current conventional view of intercostal muscle actions is based on the theory of Hamberger (1749) and maintains that as a result of the orientation of the muscle fibres, the external intercostals have an inspiratory action on the lung whereas the internal interosseous intercostals have an expiratory action. In the preceding paper, however, we have shown that in supine dogs, these muscles show marked topographic differences in Mechanical Advantage (De Troyer et al. 1999). Specifically, the external intercostals in the dorsal third of the rostral interspaces were found to have a large inspiratory Mechanical Advantage (i.e. a great ability to cause lung inflation), but this inspiratory Mechanical Advantage decreases rapidly toward the costochondral junctions and toward the base of the rib cage. Consequently, the muscles in the ventral portion of the caudal segments have an expiratory, rather than inspiratory Mechanical Advantage. The internal intercostal muscles in the dorsal portion of the caudal interspaces have a large expiratory Mechanical Advantage, but this Advantage decreases ventrally and cranially such that in the most rostral interspaces, it is reversed into an inspiratory Mechanical Advantage (De Troyer et al. 1999). These results imply that the actions of these muscles on the lung during breathing are largely determined by the topographic distribution of activity among them, rather than the orientation of the muscle fibres. A number of electrical recordings from intercostal muscles and nerves in anaesthetized cats (Sears, 1964; Bainton et al. 1978; Kirkwood et al. 1982, 1984; Greer & Martin, 1990) and dogs (De Troyer & Ninane, 1986) have shown that the external intercostals are active during inspiration. The muscles also appeared to display greater inspiratory activity in the rostral than in the caudal segments and greater inspiratory activity in the dorsal than in the ventral portion of the rib cage. In contrast, the internal intercostals were electrically active during expiration and displayed greater activity in the caudal than the rostral segments (Bainton et al. 1978; De Troyer & Ninane, 1986; Greer & Martin, 1990). In view of the distributions of Mechanical Advantage, such distributions of activity would suggest that the external intercostals have an inspiratory action on the lung during breathing and that the internal intercostals have an expiratory action. However, these descriptions of electrical activity are qualitative, and the sites where the recordings were made were not standardized. Consequently, the correspondence between the distributions of activity and the distributions of Mechanical Advantage can only be approximate, and no estimates can be made of the pressures contributed by the different muscle areas during breathing. More importantly, efferent discharges to the external intercostals in the caudal segments during expiration and to the internal intercostal in the second interspace during inspiration have also been recorded in decerebrate cats (Le Bars & Duron, 1984). As these discharges were recorded in animals performing forceful respiratory efforts against an occluded trachea, the possibility exists that they were the result of cross-contamination between the two muscle layers (De Troyer & Ninane, 1986). Yet such discharges would match, respectively, the expiratory Mechanical Advantage of the external intercostal muscles in the caudal segments and the inspiratory Mechanical Advantage of the internal intercostals in the most rostral segments, and this raises the possibility that these muscles may not have distinct effects on the lung during breathing. These issues prompted us to re-examine in detail the spatial distribution of activity among the canine external and internal intercostal muscles. The pattern of activation of the external intercostals in the caudal segments and of the internal intercostals in the most rostral segments was studied first. Selective muscle denervations were performed so that any cross-contamination could be identified. The distributions of external and internal intercostal activity along the rostrocaudal and dorsoventral axes of the rib cage were next assessed quantitatively by comparing for each muscle area the amount of activity recorded during breathing with that recorded during supramaximal, tetanic stimulation of the motor nerve. As the recordings were made in muscle areas with well-defined Mechanical Advantages (De Troyer et al. 1999), the respiratory function of each muscle could therefore be definitely established and the pressures contributed by the various areas could be estimated.

  • Respiratory Mechanical Advantage of the canine external and internal intercostal muscles
    The Journal of Physiology, 1999
    Co-Authors: A De Troyer, A Legrand, TA Wilson
    Abstract:

    The current conventional view of intercostal muscle actions is based on the theory of Hamberger (1749) and maintains that as a result of the orientation of the muscle fibres, the external intercostals have an inspiratory action on the lung and the internal interosseous intercostals have an expiratory action. This notion, however, remains unproved. In the present studies, the respiratory actions of the canine external and internal intercostal muscles were evaluated by applying the Maxwell reciprocity theorem. Thus the effects of passive inflation on the changes in length of the muscles throughout the rib cage were assessed, and the distributions of muscle mass were determined. The fractional changes in muscle length during inflation were then multiplied by muscle mass and maximum active stress (3·0 kg cm−2) to evaluate the potential effects of the muscles on the lung. The external intercostals in the dorsal third of the rostral interspaces were found to have a large inspiratory effect. However, this effect decreases rapidly both toward the costochondral junctions and toward the base of the rib cage. As a result, it is reversed to an expiratory effect in the most caudal interspaces. The internal intercostals in the caudal interspaces have a large expiratory effect, but this effect decreases ventrally and rostrally, such that it is reversed to an inspiratory effect in the most rostral interspaces. These observations indicate that the canine external and internal intercostal muscles do not have distinct inspiratory and expiratory actions as conventionally thought. Therefore, their effects on the lung during breathing will be determined by the topographic distribution of neural drive. Although it is now well established that the interchondral portion of the internal intercostal muscles (the so-called parasternal intercostals) elevates the ribs and inflates the lung when it contracts (De Troyer & Kelly, 1982; De Troyer et al. 1996), the actions of the external intercostals and the interosseous portion of the internal intercostals remain uncertain. The current conventional view is based on the theory proposed 250 years ago by Hamberger (1749). According to this theory, the fibres of the external intercostals slope obliquely caudad and ventrally from the rib above to the rib below, and so their lower insertion is further from the centre of rotation of the ribs (i.e. the costo-vertebral articulations) than their upper insertion. Consequently, when this muscle contracts with its force equal and opposite at both insertions, the torque acting on the lower rib, which tends to raise it, is greater than that acting on the upper rib, which tends to lower it. The net effect of the muscle, therefore, would be to raise the ribs and to inflate the lung. In contrast, the fibres of the internal interosseous intercostals slope obliquely caudad and dorsally from the rib above to the one below so that their lower insertion is closer to the centre of rotation of the ribs than the upper one. As a result, the net effect of their contraction would be to lower the ribs and to deflate the lung. This theory, however, has not been verified, and computations based on the orientation of the muscle fibres and on descriptions of rib displacement in dogs (Margulies et al. 1989) have recently suggested that the actions of the external and internal intercostal muscles on the lung might vary between the dorsal and the ventral aspects of the rib cage as well as between the rostral and caudal interspaces (Wilson & De Troyer, 1993). In the present studies, we have examined the effects of the canine external and internal interosseous intercostals on the lung by using a standard theorem of mechanics, the Maxwell reciprocity theorem. When applied to the respiratory system (Wilson & De Troyer, 1992, 1993), this theorem predicts that the respiratory effect of a particular muscle (that is, the potential change in airway pressure - ΔPao - produced by the muscle contracting alone against a closed airway) is related to the mass (m) of the muscle, the maximal active muscle tension per unit cross-sectional area (σ), and the fractional change in muscle length (ΔL/L) per unit volume increase of the relaxed chest wall (ΔVL)Rel, such that: (1) For a machine, such as a lever, Mechanical Advantage is defined as the ratio of the force delivered at the load to the force applied at the handle. By analogy, the Mechanical Advantage of a respiratory muscle may therefore be defined as ΔPao/mσ and, according to eqn (1), could be evaluated by measuring (ΔL/(L ΔVL))Rel. In other words, a muscle that shortens during passive inflation would have an inspiratory Mechanical Advantage and would cause a fall in Pao when it contracts. Conversely, a muscle that lengthens during passive inflation would have an expiratory Mechanical Advantage and would cause a rise in Pao during contraction.

  • Mechanical Advantage of the human parasternal intercostal and triangularis sterni muscles.
    The Journal of physiology, 1998
    Co-Authors: A De Troyer, A Legrand, P A Gevenois, TA Wilson
    Abstract:

    1. Previous studies in dogs have demonstrated that the maximum change in airway pressure (DeltaPao) produced by a particular respiratory muscle is the product of three factors, namely the mass of the muscle, the maximal active muscle tension per unit cross-sectional area ( approximately 3.0 kg cm-2), and the fractional change in muscle length per unit volume increase of the relaxed chest wall (i.e. the muscle's Mechanical Advantage). In the present studies, we have used this principle to infer the DeltaPao values generated by the parasternal intercostal and triangularis sterni muscles in man. 2. The mass of the muscles and the direction of the muscle fibres relative to the sternum were first assessed in six cadavers. Seven healthy individuals were then placed in a computed tomographic scanner to determine the orientation of the costal cartilages relative to the sternum and their rotation during passive inflation to total lung capacity. The fractional changes in length of the muscles during inflation, their Mechanical Advantages, and their DeltaPao values were then calculated. 3. Passive inflation induced shortening of the parasternal intercostals in all interspaces and lengthening of the triangularis sterni. The fractional shortening of the parasternal intercostals decreased gradually from 7.7 % in the second interspace to 2.0 % in the fifth, whereas the fractional lengthening of the triangularis sterni increased progressively from 5.9 to 13.8 %. These rostrocaudal gradients were well accounted for by the more caudal orientation of the cartilages of the lower ribs. 4. Since these fractional changes in length corresponded to a maximal inflation, the inspiratory Mechanical Advantage of the parasternal intercostals was only 2.2-0. 6 % l-1, and the expiratory Mechanical Advantage of the triangularis sterni was only 1.6-3.8 % l-1. In addition, whatever the interspace, parasternal and triangularis muscle mass was 3-5 and 1-3 g, respectively. As a result, the magnitude of the DeltaPao values generated by a maximal contraction of the parasternal intercostals or triangularis sterni in all interspaces would be only 1-3 cmH2O. 5. These studies therefore confirm that the parasternal intercostals in man have an inspiratory action on the lung whereas the triangularis sterni has an expiratory action. However, these studies also establish the important fact that the pressure-generating ability of both muscles is substantially smaller than in the dog.

A Legrand - One of the best experts on this subject based on the ideXlab platform.

  • Respiratory Mechanical Advantage of the canine external and internal intercostal muscles.
    The Journal of physiology, 1999
    Co-Authors: A De Troyer, A Legrand, TA Wilson
    Abstract:

    1. The current conventional view of intercostal muscle actions is based on the theory of Hamberger (1749) and maintains that as a result of the orientation of the muscle fibres, the external intercostals have an inspiratory action on the lung and the internal interosseous intercostals have an expiratory action. This notion, however, remains unproved. 2. In the present studies, the respiratory actions of the canine external and internal intercostal muscles were evaluated by applying the Maxwell reciprocity theorem. Thus the effects of passive inflation on the changes in length of the muscles throughout the rib cage were assessed, and the distributions of muscle mass were determined. The fractional changes in muscle length during inflation were then multiplied by muscle mass and maximum active stress (3.0 kg cm-2) to evaluate the potential effects of the muscles on the lung. 3. The external intercostals in the dorsal third of the rostral interspaces were found to have a large inspiratory effect. However, this effect decreases rapidly both toward the costochondral junctions and toward the base of the rib cage. As a result, it is reversed to an expiratory effect in the most caudal interspaces. The internal intercostals in the caudal interspaces have a large expiratory effect, but this effect decreases ventrally and rostrally, such that it is reversed to an inspiratory effect in the most rostral interspaces. 4. These observations indicate that the canine external and internal intercostal muscles do not have distinct inspiratory and expiratory actions as conventionally thought. Therefore, their effects on the lung during breathing will be determined by the topographic distribution of neural drive.

  • Spatial distribution of external and internal intercostal activity in dogs.
    The Journal of physiology, 1999
    Co-Authors: A Legrand, A De Troyer
    Abstract:

    1. The observation that the external and internal interosseous intercostal muscles in the dog show marked regional differences in Mechanical Advantage has prompted us to re-examine the topographic distribution of electrical activity among these muscles during spontaneous breathing. 2. Inspiratory activity was recorded only from the areas of the external intercostals with an inspiratory Mechanical Advantage, and expiratory activity was recorded only from the areas of the internal intercostals with an expiratory Mechanical Advantage. The expiratory discharges previously recorded from the caudal external intercostals and the inspiratory discharges recorded from the rostral internal intercostals were probably due to cross-contamination. 3. Activity in each muscle area was also quantified relative to the activity measured during tetanic, supramaximal nerve stimulation (maximal activity). External intercostal inspiratory activity was consistently greater in the areas with a greater inspiratory Advantage (i.e. the dorsal aspect of the rostral segments) than in the areas with a smaller inspiratory Advantage, and internal intercostal expiratory activity was invariably greatest in the areas with the greatest expiratory Advantage (i.e. the dorsal aspect of the caudal segments). 4. This topographic distribution of neural drive confers to the external intercostal muscles an inspiratory action on the lung during breathing and to the internal interosseous intercostals an expiratory action.

  • Spatial distribution of external and internal intercostal activity in dogs
    The Journal of Physiology, 1999
    Co-Authors: A Legrand, A De Troyer
    Abstract:

    The observation that the external and internal interosseous intercostal muscles in the dog show marked regional differences in Mechanical Advantage has prompted us to re-examine the topographic distribution of electrical activity among these muscles during spontaneous breathing. Inspiratory activity was recorded only from the areas of the external intercostals with an inspiratory Mechanical Advantage, and expiratory activity was recorded only from the areas of the internal intercostals with an expiratory Mechanical Advantage. The expiratory discharges previously recorded from the caudal external intercostals and the inspiratory discharges recorded from the rostral internal intercostals were probably due to cross-contamination. Activity in each muscle area was also quantified relative to the activity measured during tetanic, supramaximal nerve stimulation (maximal activity). External intercostal inspiratory activity was consistently greater in the areas with a greater inspiratory Advantage (i.e. the dorsal aspect of the rostral segments) than in the areas with a smaller inspiratory Advantage, and internal intercostal expiratory activity was invariably greatest in the areas with the greatest expiratory Advantage (i.e. the dorsal aspect of the caudal segments). This topographic distribution of neural drive confers to the external intercostal muscles an inspiratory action on the lung during breathing and to the internal interosseous intercostals an expiratory action. The current conventional view of intercostal muscle actions is based on the theory of Hamberger (1749) and maintains that as a result of the orientation of the muscle fibres, the external intercostals have an inspiratory action on the lung whereas the internal interosseous intercostals have an expiratory action. In the preceding paper, however, we have shown that in supine dogs, these muscles show marked topographic differences in Mechanical Advantage (De Troyer et al. 1999). Specifically, the external intercostals in the dorsal third of the rostral interspaces were found to have a large inspiratory Mechanical Advantage (i.e. a great ability to cause lung inflation), but this inspiratory Mechanical Advantage decreases rapidly toward the costochondral junctions and toward the base of the rib cage. Consequently, the muscles in the ventral portion of the caudal segments have an expiratory, rather than inspiratory Mechanical Advantage. The internal intercostal muscles in the dorsal portion of the caudal interspaces have a large expiratory Mechanical Advantage, but this Advantage decreases ventrally and cranially such that in the most rostral interspaces, it is reversed into an inspiratory Mechanical Advantage (De Troyer et al. 1999). These results imply that the actions of these muscles on the lung during breathing are largely determined by the topographic distribution of activity among them, rather than the orientation of the muscle fibres. A number of electrical recordings from intercostal muscles and nerves in anaesthetized cats (Sears, 1964; Bainton et al. 1978; Kirkwood et al. 1982, 1984; Greer & Martin, 1990) and dogs (De Troyer & Ninane, 1986) have shown that the external intercostals are active during inspiration. The muscles also appeared to display greater inspiratory activity in the rostral than in the caudal segments and greater inspiratory activity in the dorsal than in the ventral portion of the rib cage. In contrast, the internal intercostals were electrically active during expiration and displayed greater activity in the caudal than the rostral segments (Bainton et al. 1978; De Troyer & Ninane, 1986; Greer & Martin, 1990). In view of the distributions of Mechanical Advantage, such distributions of activity would suggest that the external intercostals have an inspiratory action on the lung during breathing and that the internal intercostals have an expiratory action. However, these descriptions of electrical activity are qualitative, and the sites where the recordings were made were not standardized. Consequently, the correspondence between the distributions of activity and the distributions of Mechanical Advantage can only be approximate, and no estimates can be made of the pressures contributed by the different muscle areas during breathing. More importantly, efferent discharges to the external intercostals in the caudal segments during expiration and to the internal intercostal in the second interspace during inspiration have also been recorded in decerebrate cats (Le Bars & Duron, 1984). As these discharges were recorded in animals performing forceful respiratory efforts against an occluded trachea, the possibility exists that they were the result of cross-contamination between the two muscle layers (De Troyer & Ninane, 1986). Yet such discharges would match, respectively, the expiratory Mechanical Advantage of the external intercostal muscles in the caudal segments and the inspiratory Mechanical Advantage of the internal intercostals in the most rostral segments, and this raises the possibility that these muscles may not have distinct effects on the lung during breathing. These issues prompted us to re-examine in detail the spatial distribution of activity among the canine external and internal intercostal muscles. The pattern of activation of the external intercostals in the caudal segments and of the internal intercostals in the most rostral segments was studied first. Selective muscle denervations were performed so that any cross-contamination could be identified. The distributions of external and internal intercostal activity along the rostrocaudal and dorsoventral axes of the rib cage were next assessed quantitatively by comparing for each muscle area the amount of activity recorded during breathing with that recorded during supramaximal, tetanic stimulation of the motor nerve. As the recordings were made in muscle areas with well-defined Mechanical Advantages (De Troyer et al. 1999), the respiratory function of each muscle could therefore be definitely established and the pressures contributed by the various areas could be estimated.

  • Respiratory Mechanical Advantage of the canine external and internal intercostal muscles
    The Journal of Physiology, 1999
    Co-Authors: A De Troyer, A Legrand, TA Wilson
    Abstract:

    The current conventional view of intercostal muscle actions is based on the theory of Hamberger (1749) and maintains that as a result of the orientation of the muscle fibres, the external intercostals have an inspiratory action on the lung and the internal interosseous intercostals have an expiratory action. This notion, however, remains unproved. In the present studies, the respiratory actions of the canine external and internal intercostal muscles were evaluated by applying the Maxwell reciprocity theorem. Thus the effects of passive inflation on the changes in length of the muscles throughout the rib cage were assessed, and the distributions of muscle mass were determined. The fractional changes in muscle length during inflation were then multiplied by muscle mass and maximum active stress (3·0 kg cm−2) to evaluate the potential effects of the muscles on the lung. The external intercostals in the dorsal third of the rostral interspaces were found to have a large inspiratory effect. However, this effect decreases rapidly both toward the costochondral junctions and toward the base of the rib cage. As a result, it is reversed to an expiratory effect in the most caudal interspaces. The internal intercostals in the caudal interspaces have a large expiratory effect, but this effect decreases ventrally and rostrally, such that it is reversed to an inspiratory effect in the most rostral interspaces. These observations indicate that the canine external and internal intercostal muscles do not have distinct inspiratory and expiratory actions as conventionally thought. Therefore, their effects on the lung during breathing will be determined by the topographic distribution of neural drive. Although it is now well established that the interchondral portion of the internal intercostal muscles (the so-called parasternal intercostals) elevates the ribs and inflates the lung when it contracts (De Troyer & Kelly, 1982; De Troyer et al. 1996), the actions of the external intercostals and the interosseous portion of the internal intercostals remain uncertain. The current conventional view is based on the theory proposed 250 years ago by Hamberger (1749). According to this theory, the fibres of the external intercostals slope obliquely caudad and ventrally from the rib above to the rib below, and so their lower insertion is further from the centre of rotation of the ribs (i.e. the costo-vertebral articulations) than their upper insertion. Consequently, when this muscle contracts with its force equal and opposite at both insertions, the torque acting on the lower rib, which tends to raise it, is greater than that acting on the upper rib, which tends to lower it. The net effect of the muscle, therefore, would be to raise the ribs and to inflate the lung. In contrast, the fibres of the internal interosseous intercostals slope obliquely caudad and dorsally from the rib above to the one below so that their lower insertion is closer to the centre of rotation of the ribs than the upper one. As a result, the net effect of their contraction would be to lower the ribs and to deflate the lung. This theory, however, has not been verified, and computations based on the orientation of the muscle fibres and on descriptions of rib displacement in dogs (Margulies et al. 1989) have recently suggested that the actions of the external and internal intercostal muscles on the lung might vary between the dorsal and the ventral aspects of the rib cage as well as between the rostral and caudal interspaces (Wilson & De Troyer, 1993). In the present studies, we have examined the effects of the canine external and internal interosseous intercostals on the lung by using a standard theorem of mechanics, the Maxwell reciprocity theorem. When applied to the respiratory system (Wilson & De Troyer, 1992, 1993), this theorem predicts that the respiratory effect of a particular muscle (that is, the potential change in airway pressure - ΔPao - produced by the muscle contracting alone against a closed airway) is related to the mass (m) of the muscle, the maximal active muscle tension per unit cross-sectional area (σ), and the fractional change in muscle length (ΔL/L) per unit volume increase of the relaxed chest wall (ΔVL)Rel, such that: (1) For a machine, such as a lever, Mechanical Advantage is defined as the ratio of the force delivered at the load to the force applied at the handle. By analogy, the Mechanical Advantage of a respiratory muscle may therefore be defined as ΔPao/mσ and, according to eqn (1), could be evaluated by measuring (ΔL/(L ΔVL))Rel. In other words, a muscle that shortens during passive inflation would have an inspiratory Mechanical Advantage and would cause a fall in Pao when it contracts. Conversely, a muscle that lengthens during passive inflation would have an expiratory Mechanical Advantage and would cause a rise in Pao during contraction.

  • Mechanical Advantage of the human parasternal intercostal and triangularis sterni muscles.
    The Journal of physiology, 1998
    Co-Authors: A De Troyer, A Legrand, P A Gevenois, TA Wilson
    Abstract:

    1. Previous studies in dogs have demonstrated that the maximum change in airway pressure (DeltaPao) produced by a particular respiratory muscle is the product of three factors, namely the mass of the muscle, the maximal active muscle tension per unit cross-sectional area ( approximately 3.0 kg cm-2), and the fractional change in muscle length per unit volume increase of the relaxed chest wall (i.e. the muscle's Mechanical Advantage). In the present studies, we have used this principle to infer the DeltaPao values generated by the parasternal intercostal and triangularis sterni muscles in man. 2. The mass of the muscles and the direction of the muscle fibres relative to the sternum were first assessed in six cadavers. Seven healthy individuals were then placed in a computed tomographic scanner to determine the orientation of the costal cartilages relative to the sternum and their rotation during passive inflation to total lung capacity. The fractional changes in length of the muscles during inflation, their Mechanical Advantages, and their DeltaPao values were then calculated. 3. Passive inflation induced shortening of the parasternal intercostals in all interspaces and lengthening of the triangularis sterni. The fractional shortening of the parasternal intercostals decreased gradually from 7.7 % in the second interspace to 2.0 % in the fifth, whereas the fractional lengthening of the triangularis sterni increased progressively from 5.9 to 13.8 %. These rostrocaudal gradients were well accounted for by the more caudal orientation of the cartilages of the lower ribs. 4. Since these fractional changes in length corresponded to a maximal inflation, the inspiratory Mechanical Advantage of the parasternal intercostals was only 2.2-0. 6 % l-1, and the expiratory Mechanical Advantage of the triangularis sterni was only 1.6-3.8 % l-1. In addition, whatever the interspace, parasternal and triangularis muscle mass was 3-5 and 1-3 g, respectively. As a result, the magnitude of the DeltaPao values generated by a maximal contraction of the parasternal intercostals or triangularis sterni in all interspaces would be only 1-3 cmH2O. 5. These studies therefore confirm that the parasternal intercostals in man have an inspiratory action on the lung whereas the triangularis sterni has an expiratory action. However, these studies also establish the important fact that the pressure-generating ability of both muscles is substantially smaller than in the dog.

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  • Ontogeny of effective Mechanical Advantage in eastern cottontail rabbits (Sylvilagus floridanus).
    The Journal of experimental biology, 2019
    Co-Authors: Adam D. Foster, Michael T. Butcher, Gregory A. Smith, Gabrielle A. Russo, Rajaa Thalluri, Jesse W Young
    Abstract:

    Juvenile animals must survive in the same environment as adults despite smaller sizes, immature musculoskeletal tissues, general ecological naïveté and other limits of performance. Developmental changes in muscle leverage could constitute one mechanism to promote increased performance in juveniles despite ontogenetic limitations. We tested this hypothesis using a holistic dataset on growth and locomotor development in wild eastern cottontail rabbits (Sylvilagus floridanus) to examine ontogenetic changes in hindlimb muscle effective Mechanical Advantage (EMA). EMA is a dimensionless index of muscle leverage, equal to the quotient of average muscle lever length and the load arm length of the ground reaction force (GRF), effectively representing the magnitude of output force arising from a given muscle force. We found that EMA at the hip and ankle joints, as well as overall hindlimb EMA, significantly declined across ontogeny in S. floridanus, whereas EMA at the knee joint remained unchanged. Ontogenetic decreases in EMA were due to isometric scaling of muscle lever arm lengths alongside positive ontogenetic allometry of GRF load arm lengths - which in turn was primarily related to positive allometry of hindlimb segment lengths. Greater EMA limits the estimated volume of hindlimb extensor muscle that has to be activated in young rabbits, likely mitigating the energetic cost of locomotion and saving metabolic resources for other physiological functions, such as growth and tissue differentiation. An additional examination of limb growth allometry across a diverse sample of mammalian taxa suggests that ontogenetic decreases in limb joint EMA may be a common mammalian trend.

  • Ontogeny of effective Mechanical Advantage in Eastern cottontail rabbits (Sylvilagus floridanus)
    The Journal of Experimental Biology, 2019
    Co-Authors: Adam D. Foster, Michael T. Butcher, Gregory A. Smith, Gabrielle A. Russo, Rajaa Thalluri, Jesse W Young
    Abstract:

    Juvenile animals must survive in the same environment as adults despite smaller sizes, immature musculoskeletal tissues, general ecological naivete and other limits of performance. Developmental changes in muscle leverage could constitute one mechanism to promote increased performance in juveniles despite ontogenetic limitations. We tested this hypothesis using a holistic dataset on growth and locomotor development in wild eastern cottontail rabbits (Sylvilagus floridanus) to examine ontogenetic changes in hindlimb muscle effective Mechanical Advantage (EMA). EMA is a dimensionless index of muscle leverage, equal to the quotient of average muscle lever length and the load arm length of the ground reaction force (GRF), effectively representing the magnitude of output force arising from a given muscle force. We found that EMA at the hip and ankle joints, as well as overall hindlimb EMA, significantly declined across ontogeny in S. floridanus, whereas EMA at the knee joint remained unchanged. Ontogenetic decreases in EMA were due to isometric scaling of muscle lever arm lengths alongside positive ontogenetic allometry of GRF load arm lengths - which in turn was primarily related to positive allometry of hindlimb segment lengths. Greater EMA limits the estimated volume of hindlimb extensor muscle that has to be activated in young rabbits, likely mitigating the energetic cost of locomotion and saving metabolic resources for other physiological functions, such as growth and tissue differentiation. An additional examination of limb growth allometry across a diverse sample of mammalian taxa suggests that ontogenetic decreases in limb joint EMA may be a common mammalian trend.