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

  • shortening induced depression of voluntary force in unfatigued and fatigued human Adductor Pollicis Muscle
    Journal of Applied Physiology, 2003
    Co-Authors: C J De Ruiter, A De Haan
    Abstract:

    The goals of this study were to investigate Adductor Pollicis Muscle (n = 7) force depression after maximal electrically stimulated and voluntarily activated isovelocity (19 and 306°/s) shortening ...

  • contractile speed and fatigue of Adductor Pollicis Muscle in multiple sclerosis
    Muscle & Nerve, 2001
    Co-Authors: C J De Ruiter, P J H Jongen, L H V Van Der Woude, A De Haan
    Abstract:

    The purpose of the study was to investigate differences in contractile speed, force, and fatigability of the Adductor Pollicis Muscle between 12 patients with multiple sclerosis (MS) and 8 sedentary control subjects matched for age and gender. There were no differences between the patients with MS and control subjects with respect to the percentage of maximal Muscle force that could be recruited during voluntary effort (95.5 +/- 3.9% and 98.2 +/- 2.0%, respectively, P = 0.10), the stimulation frequency/force and force/velocity relationships, the rates of force development and relaxation, fatigue resistance, and the recovery rate of Adductor Pollicis Muscle. However, previous results from the same group of MS patients showed that quadriceps femoris Muscle force and resistance to fatigue were reduced. Therefore, our data support the clinical experience that, in patients with MS, lower limb Muscle function is more or earlier affected than upper limb Muscle function.

  • the force velocity relationship of human Adductor Pollicis Muscle during stretch and the effects of fatigue
    The Journal of Physiology, 2000
    Co-Authors: C J De Ruiter, D A Jones, W J M Didden, A De Haan
    Abstract:

    1 We have examined the force-velocity characteristics of tetanically activated human Adductor Pollicis working in vivo, in the fresh and fatigued states. 2 The increase in force in response to stretch was divided into two major components. The first, steady, component persisted after the stretch and is concluded not to be a function of active cycling cross-bridges because it was not affected by either the velocity of the stretch or the level of Muscle activation. 3 The origin of the second, transient, component of the increased force seen during stretch is consistent with cross-bridge activity since it increased with increasing velocity of stretch and was proportional to the level of activation. 4 It is likely that both components of the stretch response make a significant contribution to Muscle performance when acting to resist a force. For the fastest stretch used, the contributions of cross-bridge and non-cross-bridge mechanisms were equal. For the slowest stretch, lasting 10 s and over the same distance, the force response was attributed almost entirely to non-cross-bridge mechanisms. 5 As a result of acute fatigue (50 % isometric force loss) there were only small reductions in the non-cross-bridge component of the force response to stretch, while the cross-bridge component decreased in absolute terms. 6 The transient component of the stretch response increased as a result of fatigue, relative to the isometric force, while the force during shortening decreased. The results are consistent with a decrease in cross-bridge turnover in fatigued Muscle.

  • temperature effect on the force velocity relationship of the fresh and fatigued human Adductor Pollicis Muscle
    Pflügers Archiv: European Journal of Physiology, 2000
    Co-Authors: C J De Ruiter, A De Haan
    Abstract:

    The purpose of the present study was to investigate the effect of Muscle temperature on the force/velocity relationship of electrically activated human Adductor Pollicis Muscle. Following immersion of the lower arm for 20 min in water baths of four different temperatures, the calculated Muscle temperatures were 37.1, 31.4, 25.6 and 22.2°C. At 22.2°C maximal isometric force was reduced to 79.3±2.9% of the force obtained at 37.1°C. Q 10 values for the maximal rates of force development and relaxation, and relaxation times, were about 2.0 between 37.1 and 25.6°C and increased to about 3.5 below 25.6°C. The Q 10 values of the maximal shortening velocity and the velocity for maximal power production were similar to those of the isometric speed parameters. The Q 10 for maximal power production increased from 2.0 above 31.4°C to 6.9 between 25.6 and 22.2°C. Following repetitive isometric contractions maximal power production was reduced to 60.0±1.7 and 90.5±1.0% at 37.1 and 22.2°C respectively. Fatigue decreased with cooling of the Muscle over the entire (37.1–22.2°C) temperature range.

  • temperature effect on the force velocity relationship of the fresh and fatigued human Adductor Pollicis Muscle
    Pflügers Archiv: European Journal of Physiology, 2000
    Co-Authors: C J De Ruiter, A De Haan
    Abstract:

    The purpose of the present study was to investigate the effect of Muscle temperature on the force/velocity relationship of electrically activated human Adductor Pollicis Muscle. Following immersion of the lower arm for 20 min in water baths of four different temperatures, the calculated Muscle temperatures were 37.1, 31.4, 25.6 and 22.2 degrees C. At 22.2 degrees C maximal isometric force was reduced to 79.3+/-2.9% of the force obtained at 37.1 degrees C. Q10 values for the maximal rates of force development and relaxation, and relaxation times, were about 2.0 between 37.1 and 25.6 degrees C and increased to about 3.5 below 25.6 degrees C. The Q10 values of the maximal shortening velocity and the velocity for maximal power production were similar to those of the isometric speed parameters. The Q10 for maximal power production increased from 2.0 above 31.4 degrees C to 6.9 between 25.6 and 22.2 degrees C. Following repetitive isometric contractions maximal power production was reduced to 60.0+/-1.7 and 90.5+/-1.0% at 37.1 and 22.2 degrees C respectively. Fatigue decreased with cooling of the Muscle over the entire (37.1-22.2 degrees C) temperature range.

C J De Ruiter - One of the best experts on this subject based on the ideXlab platform.

  • shortening induced depression of voluntary force in unfatigued and fatigued human Adductor Pollicis Muscle
    Journal of Applied Physiology, 2003
    Co-Authors: C J De Ruiter, A De Haan
    Abstract:

    The goals of this study were to investigate Adductor Pollicis Muscle (n = 7) force depression after maximal electrically stimulated and voluntarily activated isovelocity (19 and 306°/s) shortening ...

  • contractile speed and fatigue of Adductor Pollicis Muscle in multiple sclerosis
    Muscle & Nerve, 2001
    Co-Authors: C J De Ruiter, P J H Jongen, L H V Van Der Woude, A De Haan
    Abstract:

    The purpose of the study was to investigate differences in contractile speed, force, and fatigability of the Adductor Pollicis Muscle between 12 patients with multiple sclerosis (MS) and 8 sedentary control subjects matched for age and gender. There were no differences between the patients with MS and control subjects with respect to the percentage of maximal Muscle force that could be recruited during voluntary effort (95.5 +/- 3.9% and 98.2 +/- 2.0%, respectively, P = 0.10), the stimulation frequency/force and force/velocity relationships, the rates of force development and relaxation, fatigue resistance, and the recovery rate of Adductor Pollicis Muscle. However, previous results from the same group of MS patients showed that quadriceps femoris Muscle force and resistance to fatigue were reduced. Therefore, our data support the clinical experience that, in patients with MS, lower limb Muscle function is more or earlier affected than upper limb Muscle function.

  • the force velocity relationship of human Adductor Pollicis Muscle during stretch and the effects of fatigue
    The Journal of Physiology, 2000
    Co-Authors: C J De Ruiter, D A Jones, W J M Didden, A De Haan
    Abstract:

    1 We have examined the force-velocity characteristics of tetanically activated human Adductor Pollicis working in vivo, in the fresh and fatigued states. 2 The increase in force in response to stretch was divided into two major components. The first, steady, component persisted after the stretch and is concluded not to be a function of active cycling cross-bridges because it was not affected by either the velocity of the stretch or the level of Muscle activation. 3 The origin of the second, transient, component of the increased force seen during stretch is consistent with cross-bridge activity since it increased with increasing velocity of stretch and was proportional to the level of activation. 4 It is likely that both components of the stretch response make a significant contribution to Muscle performance when acting to resist a force. For the fastest stretch used, the contributions of cross-bridge and non-cross-bridge mechanisms were equal. For the slowest stretch, lasting 10 s and over the same distance, the force response was attributed almost entirely to non-cross-bridge mechanisms. 5 As a result of acute fatigue (50 % isometric force loss) there were only small reductions in the non-cross-bridge component of the force response to stretch, while the cross-bridge component decreased in absolute terms. 6 The transient component of the stretch response increased as a result of fatigue, relative to the isometric force, while the force during shortening decreased. The results are consistent with a decrease in cross-bridge turnover in fatigued Muscle.

  • temperature effect on the force velocity relationship of the fresh and fatigued human Adductor Pollicis Muscle
    Pflügers Archiv: European Journal of Physiology, 2000
    Co-Authors: C J De Ruiter, A De Haan
    Abstract:

    The purpose of the present study was to investigate the effect of Muscle temperature on the force/velocity relationship of electrically activated human Adductor Pollicis Muscle. Following immersion of the lower arm for 20 min in water baths of four different temperatures, the calculated Muscle temperatures were 37.1, 31.4, 25.6 and 22.2°C. At 22.2°C maximal isometric force was reduced to 79.3±2.9% of the force obtained at 37.1°C. Q 10 values for the maximal rates of force development and relaxation, and relaxation times, were about 2.0 between 37.1 and 25.6°C and increased to about 3.5 below 25.6°C. The Q 10 values of the maximal shortening velocity and the velocity for maximal power production were similar to those of the isometric speed parameters. The Q 10 for maximal power production increased from 2.0 above 31.4°C to 6.9 between 25.6 and 22.2°C. Following repetitive isometric contractions maximal power production was reduced to 60.0±1.7 and 90.5±1.0% at 37.1 and 22.2°C respectively. Fatigue decreased with cooling of the Muscle over the entire (37.1–22.2°C) temperature range.

  • temperature effect on the force velocity relationship of the fresh and fatigued human Adductor Pollicis Muscle
    Pflügers Archiv: European Journal of Physiology, 2000
    Co-Authors: C J De Ruiter, A De Haan
    Abstract:

    The purpose of the present study was to investigate the effect of Muscle temperature on the force/velocity relationship of electrically activated human Adductor Pollicis Muscle. Following immersion of the lower arm for 20 min in water baths of four different temperatures, the calculated Muscle temperatures were 37.1, 31.4, 25.6 and 22.2 degrees C. At 22.2 degrees C maximal isometric force was reduced to 79.3+/-2.9% of the force obtained at 37.1 degrees C. Q10 values for the maximal rates of force development and relaxation, and relaxation times, were about 2.0 between 37.1 and 25.6 degrees C and increased to about 3.5 below 25.6 degrees C. The Q10 values of the maximal shortening velocity and the velocity for maximal power production were similar to those of the isometric speed parameters. The Q10 for maximal power production increased from 2.0 above 31.4 degrees C to 6.9 between 25.6 and 22.2 degrees C. Following repetitive isometric contractions maximal power production was reduced to 60.0+/-1.7 and 90.5+/-1.0% at 37.1 and 22.2 degrees C respectively. Fatigue decreased with cooling of the Muscle over the entire (37.1-22.2 degrees C) temperature range.

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

  • temperature effect on the rates of isometric force development and relaxation in the fresh and fatigued human Adductor Pollicis Muscle
    Experimental Physiology, 1999
    Co-Authors: C J De Ruiter, D A Jones, A J Sargeant, A De Haan
    Abstract:

    The purpose of the present study was to investigate the effect of temperature on the rates of isometric force development and relaxation in electrically activated fresh and fatigued human Adductor Pollicis Muscle. Following immersion of the lower arm for 20 min in water baths of four different temperatures, Muscle temperatures were approximately 37, 31, 25 and 22 C. Maximal isometric force was reduced by 16.8 +/- 1.5 % at 22 C. The stimulation frequency-force and -rate of force development relationships were shifted to the left at lower temperatures. Q10 values for the maximal rates of force development and relaxation, and the times for 100 to 50 % and 50 to 25 % force relaxation, were about 2.0 between 37 and 25 C and about 3.8 between 25 and 22 C. However, the time for 50 to 25 % force relaxation had a relatively high Q10 value between 25 and 22 C (6.9) and this parameter also appeared to be more sensitive to fatigue compared to the other indices of relaxation. Nevertheless, the effect of fatigue on all parameters decreased with cooling over the entire (37-22 C) temperature range.

  • the measurement of force velocity relationships of fresh and fatigued human Adductor Pollicis Muscle
    European Journal of Applied Physiology, 1999
    Co-Authors: C J De Ruiter, D A Jones, A J Sargeant, A De Haan
    Abstract:

    The purpose of the study was to obtain force/velocity relationships for electrically stimulated (80 Hz) human Adductor Pollicis Muscle (n = 6) and to quantify the effects of fatigue. There are two major problems of studying human Muscle in situ; the first is the contribution of the series elastic component, and the second is a loss of force consequent upon the extent of loaded shortening. These problems were tackled in two ways. Records obtained from isokinetic releases from maximal isometric tetani showed a late linear phase of force decline, and this was extrapolated back to the time of release to obtain measures of instantaneous force. This method gave usable data up to velocities of shortening equivalent to approximately one-third of maximal velocity. An alternative procedure (short activation, SA) allowed the Muscle to begin shortening when isometric force reached a value that could be sustained during shortening (essentially an isotonic protocol). At low velocities both protocols gave very similar data (r2 = 0.96), but for high velocities only the SA procedure could be used. Results obtained using the SA protocol in fresh Muscle were compared to those for Muscle that had been fatigued by 25 s of ischaemic isometric contractions, induced by electrical stimulation at the ulnar nerve. Fatigue resulted in a decrease of isometric force [to 69 (3)%], an increase in half-relaxation time [to 431 (10)%], and decreases in maximal shortening velocity [to 77 (8)%] and power [to 42 (5)%]. These are the first data for human skeletal Muscle to show convincingly that during acute fatigue, power is reduced as a consequence of both the loss of force and slowing of the contractile speed.

  • shortening induced force depression in human Adductor Pollicis Muscle
    The Journal of Physiology, 1998
    Co-Authors: C J De Ruiter, A De Haan, D A Jones, A J Sargeant
    Abstract:

    1. The effects of single isovelocity shortening contractions on force production of the electrically stimulated human Adductor Pollicis Muscle were investigated in seven healthy male subjects. 2. Redeveloped isometric force immediately following isovelocity shortening was always depressed compared with the isometric force recorded at the same Muscle length but without preceding shortening. The maximal isometric force deficit (FD) was (mean +/- S.E.M.) 37 +/- 2% after 38 deg of shortening at 6.1 deg s-1. 3. The FD was positively correlated with angular displacement (r2 > 0.98) and decreased with increasing velocity of the shortening step. Stimulation at 20 Hz instead of 50 Hz reduced absolute force levels during the contractions to about 73% and the FD was decreased to a similar extent. Eighty-nine per cent of the velocity-related variation in the FD could be explained by the absolute force levels during shortening. 4. FD was largely abolished by allowing the Muscle to relax briefly (approximately 200 ms), a time probably too short for significant metabolic recovery. 5. At all but the highest velocities there was a linear decline in force during the latter part of the isovelocity shortening phase, suggesting that the mechanisms underlying FD were active during shortening. 6. Our results show that shortening-induced force deficit is a significant feature of human Muscle working in situ and is proportional to the work done by the Muscle-tendon complex. This finding has important implications for experimental studies of force-velocity relationships in the intact human.

  • shortening induced force depression in human Adductor Pollicis Muscle
    The Journal of Physiology, 1998
    Co-Authors: C J De Ruiter, A De Haan, D A Jones, A J Sargeant
    Abstract:

    The functional properties of skeletal Muscle during dynamic contractions have been extensively studied and often force-velocity characteristics are obtained by measuring the force or velocity at one Muscle length. The explicit, or more usually the implicit, assumption made is that once any initial alterations in series elasticity have taken place, the Muscle will settle into a phase of steady shortening, with the force sustained being determined only by the relative velocity. In practice, and especially with whole Muscle preparations, the force rarely reaches a constant value but declines throughout the shortening contraction. Whilst measurements made at one length may suggest a single force-velocity relationship (e.g. De Haan, Jones & Sargeant, 1989), in reality a family of curves can be obtained by making the measurements after varying degrees of shortening. This effect is well illustrated by the results of Joyce, Rack & Westbury (1969) and Joyce & Rack (1969) in cat soleus, where the force, or shortening velocity, at a certain Muscle length depends on the amount of preceding shortening. Since the measurement of force-velocity characteristics is central to much of Muscle physiology it is important to understand the mechanism and significance of this behaviour. The continued decline in force during sustained shortening contractions may be related to another widely recognized, but poorly understood, phenomenon of skeletal Muscle, that of shortening deactivation. From the work on isolated Muscle preparations (Abbott & Aubert, 1952; Marechal & Plaghki, 1979; Julian & Morgan, 1979; DeHaan et al. 1989) and single fibres (Sugi & Tsuchiya, 1988; Granzier & Pollack, 1989; Edman, Caputo & Lou, 1993), it has been known that isometric force redevelopment immediately following a single phase of isovelocity shortening is reduced compared with isometric force measured at the same Muscle length but without the preceding shortening. Whatever the mechanism of this force decrement, it is possible that the effect could be occurring during the shortening phase and thereby account for the progressive loss of force. The present study had two main objectives: first to see whether shortening deactivation could be demonstrated in human Muscle working in situ and second to see whether there is any link between shortening deactivation and the progressive loss of force seen during shortening at a constant velocity.

Maria Stokes - One of the best experts on this subject based on the ideXlab platform.

  • Muscle sounds during voluntary and stimulated contractions of the human Adductor Pollicis Muscle
    Journal of Applied Physiology, 1992
    Co-Authors: Maria Stokes, R G Cooper
    Abstract:

    The relationships between force, electromyography (EMG), and Muscle sounds recorded by acoustic myography (AMG) were investigated for both voluntary and stimulated isometric contractions in the Adductor Pollicis Muscle. Voluntary activity was performed at 10, 25, 50, 75, 85, and 100% of maximal voluntary contraction (MVC) force. Stimulated contractions were produced by supramaximal electrical stimulation of the ulnar nerve at the wrist at frequencies of 10, 20, 30, 50, 70, and 100 Hz. Contractions lasted for 4 s each, and were performed in random order with a 3-min rest between each. The voluntary and stimulation studies were performed in random order between subjects. Simultaneous recordings were obtained for force, force oscillation (from the differentiated force signal), and raw and integrated AMG (IAMG) and EMG (IEMG). During voluntary contractions, IAMG increased with force up to MVC (r2 = 0.99, P less than 0.001) in a curvilinear fashion and a similar relationship was seen between force and IEMG (r2 = 0.99, P less than 0.001). Conversely, during stimulated contractions as stimulation frequency increased, IAMG decreased in a fashion mirroring the frequency-force curve. The frequency of the AMG signal matched stimulation frequency and declines in total IAMG were due to reductions in amplitude of the AMG signal. The stimulation frequency-oscillation of force relationship was identical to that seen for stimulation frequency and IAMG. Integrated EMG increased linearly with stimulation frequency (r = 0.99). The stimulation results suggest that Muscle sounds reflect oscillation of Muscle fibers and that AMG signal characteristics are determined by motor control mechanisms rather than intrinsic contractile processes.

  • Muscle sounds during voluntary and stimulated contractions of the human Adductor Pollicis Muscle
    Journal of Applied Physiology, 1992
    Co-Authors: Maria Stokes, R G Cooper
    Abstract:

    The relationships between force, electromyography (EMG), and Muscle sounds recorded by acoustic myography (AMG) were investigated for both voluntary and stimulated isometric contractions in the add...

  • detection and severity of low frequency fatigue in the human Adductor Pollicis Muscle
    Journal of the Neurological Sciences, 1992
    Co-Authors: Rebecca Mellor, Maria Stokes
    Abstract:

    The sensitivity of electrical stimulation tests for detecting low frequency fatigue (LFF) and its duration were examined in the Adductor Pollicis Muscle of ten normal subjects. Supramaximal stimulation was applied to the ulnar nerve at the wrist and values for test stimulation force ratios of 10:100 Hz, 15:100 Hz and 20:50 Hz (2 sec at each frequency with 5 min rest between each ratio) were obtained for fresh Muscle. Fatigue was then induced by voluntary isometric contractions at 50% maximal voluntary force (MVC) repeated until only 30% MVC could be achieved. Contractions lasted 10 sec with 5 sec rest between each. The three test ratios were then repeated to monitor recovery at intervals up to 72 h after activity. High frequency forces returned to fresh values by 24 h but low frequency forces were all still significantly reduced. Forces at 10 and 15 Hz were still significantly reduced at 48 and 72 h (10 Hz > fatigue than 15 Hz). The low/high frequency ratios, calculated once 50 and 100 Hz forces had recovered, also demonstrated differences in revoery rates. Repeatability tests indicated that 10 Hz force was more variable than other frequencies and forces at all stimulation frequencies were repeatable on different days with a coefficient of variation of < 15%. Values for the 15:100 Hz ratio from fresh Muscle in 22 normal subjects were 0.48±8. The 15:100 Hz ratio is suggested as the most appropriate test ratio for detecting LFF since 15 Hz force is more sensitive than 20 Hz and more stable than 10 Hz.

  • stimulation frequency and force potentiation in the human Adductor Pollicis Muscle
    European Journal of Applied Physiology, 1992
    Co-Authors: S C Small, Maria Stokes
    Abstract:

    The effect of stimulation frequency on twitch force potentiation was examined in the Adductor Pollicis Muscle of ten normal subjects. The ulnar nerve was supramaximally stimulated at the wrist and isometric twitch force was measured from a 3-Hz train lasting 1 s. Test stimulation frequencies of 5, 10, 20, 25, 30, 40, 50 and 100 Hz were applied for 5 s each in random order (5 min apart) and the twitches (3 Hz) were applied immediately before and after (1 s) the test frequency and at intervals up to 5 min afterwards (10 s, and 1, 2 and 5 min). Poststimulation twitches were expressed as a percentage of the prestimulation twitch. Low frequency fatigue was not induced by the protocol since the 20:50 Hz ratio did not alter within each session. The degree of twitch potentiation was frequency dependent, with potentiation increasing up to 50 Hz [mean 173 (SD 16)%] but the effect was markedly less at 100 Hz [mean 133 (SD 25)%, P less than 0.01] for all subjects. The reduced potentiation at 100 Hz may have occurred due to high frequency fatigue produced by the 100-Hz test stimulation train. The optimal frequency of those examined in the experimental group was 50 Hz but this only produced maximal potentiation in six of the ten subjects and 100 Hz always produced less potentiation. These findings have implications for electrical stimulation of Muscle in the clinical setting.

R C Woledge - One of the best experts on this subject based on the ideXlab platform.

  • effects of voluntary activation level on force exerted by human Adductor Pollicis Muscle during rapid stretches
    Pflügers Archiv: European Journal of Physiology, 2004
    Co-Authors: S A Bruce, R C Woledge, Gladys L Onambele
    Abstract:

    We have observed the force resulting from sudden stretches (3-10 mm in 10-20 ms) of human Adductor Pollicis Muscle during voluntary contractions maintaining different proportions of the maximum voluntary force from 20% to 100%. The ratio of the peak force during stretch (S) to the voluntary force (I) just before the start of the stretch was calculated. The S/ I ratio was dependent both on the level of activation and the speed of the stretch. At all levels of activation S/ I increased exponentially with velocity towards a plateau value with an exponential constant of about 150 mm/s. The plateau values reached were dependent on activation level (P<0.02, linear regression, n=24). At 96% activation the plateau value of the S/ I ratio was 1.82+/-0.13 (mean+/-95% confidence limits); at 32% activation the value was 2.72+/-0.23.

  • a study of force and cross sectional area of Adductor Pollicis Muscle in female hip fracture patients
    Journal of the American Geriatrics Society, 1998
    Co-Authors: S K Phillips, S A Bruce, R C Woledge, A Young, D Levy, Finbarr C Martin
    Abstract:

    OBJECTIVES: To determine the extent of Muscle weakness in older female hip fracture patients compared with healthy older and young women; to determine the extent to which this weakness is caused by a decline of the force produced per unit area of Muscle rather than by a decline in Muscle bulk; and to investigate the mechanism of the decline in force per unit area. DESIGN: This was an open study of three groups of subjects, two age matched older groups and one young group. SETTING: University College London, Royal Free Hospital, and St. Thomas's Hospital, London. PARTICIPANTS: Twenty-nine older female hip fracture patients (mean age 85.6 ± 0.9 SEM), 18 healthy older women (mean age 84.7 ± 1.2 SEM), and 43 young women (mean age 28.9 ± 1.2 SEM). MEASUREMENTS: Adductor Pollicis Muscle maximum voluntary force (MVF) during isometric and pliometric contractions and cross-sectional area (CSA), body weight, height, and demi-span. RESULTS: Isometric MVF was lowest in the hip fracture group. In both older groups, isometric MVF and CSA were lower than in the young women. Only part of this weakness in the older groups could be explained by the smaller CSAs. The isometric force per unit area (MVF/CSA) was also lower in both older groups, the hip fracture patients again having the lowest values. Analysis of variance showed a significant difference between groups. The age-related declines in pliometric force were much less than the declines in isometric force. This resulted in an increase in the pliometric/isometric force ratio both for the hip fracture patients and for the healthy older women compared with that for young women. CONCLUSION: In comparison with the results from young women, the Adductor Pollicis Muscles of female hip fracture patients were even weaker than those of healthy older women when normalized for Muscle size. This decline in isometric MVF/CSA accounted for at least half of the overall weakness in the hip fracture patients. Inasmuch as pliometric force is maintained in situations where weakness is caused by a decline in the force produced per Muscle cross-bridge, this is the likely mechanism of the declines in isometric MVF/CSA observed in this study.

  • changes in maximal voluntary force of human Adductor Pollicis Muscle during the menstrual cycle
    The Journal of Physiology, 1996
    Co-Authors: S K Phillips, S A Bruce, A G Sanderson, Karen M Birch, R C Woledge
    Abstract:

    1. Muscle strength of the Adductor Pollicis (AP) was studied throughout the menstrual cycle to determine whether any variation in force is similar to the known cyclical changes in ovarian hormones. Three groups of young women were studied: trained regularly menstruating athletes (trained), untrained regularly menstruating (untrained) and trained oral contraceptive pill users (OCU). In addition a group of untrained young men was studied as controls. 2. Maximum voluntary force (MVF) of AP was measured over a maximum period of 6 months. Ovulation was detected by luteinizing hormone measurements or change in basal body temperature. There was a significant increase in MVF (about 10%) during the follicular phase of the menstrual cycle when oestrogen levels are rising, in both the trained and untrained groups. This was followed by a similar in MVF around the time of ovulation. Neither the OCU nor the male subjects showed cyclical changes in MVF.