The Experts below are selected from a list of 72 Experts worldwide ranked by ideXlab platform

William O. Hancock - One of the best experts on this subject based on the ideXlab platform.

  • the kinesin 5 chemomechanical cycle is dominated by a two heads bound state
    Journal of Biological Chemistry, 2016
    Co-Authors: Geng-yuan Chen, Keith J Mickolajczyk, William O. Hancock
    Abstract:

    Single-molecule microscopy and stopped-flow kinetics assays were carried out to understand the microtubule polymerase activity of kinesin-5 (Eg5). Four lines of evidence argue that the motor primarily resides in a two-heads-bound (2HB) state. First, upon microtubule binding, dimeric Eg5 releases both bound ADPs. Second, microtubule dissociation in saturating ADP is 20-fold slower for the dimer than for the monomer. Third, ATP-triggered mant-ADP release is 5-fold faster than the Stepping Rate. Fourth, ATP binding is relatively fast when the motor is locked in a 2HB state. Shortening the neck-linker does not facilitate rear-head detachment, suggesting a minimal role for rear-head-gating. This 2HB state may enable Eg5 to stabilize incoming tubulin at the growing microtubule plus-end. The finding that slowly hydrolyzable ATP analogs trigger slower nucleotide release than ATP suggests that ATP hydrolysis in the bound head precedes Stepping by the tethered head, leading to a mechanochemical cycle in which processivity is determined by the race between unbinding of the bound head and attachment of the tethered head.

  • processivity of the kinesin 2 kif3a results from rear head gating and not front head gating
    Journal of Biological Chemistry, 2015
    Co-Authors: Geng-yuan Chen, David F.j. Arginteanu, William O. Hancock
    Abstract:

    Abstract The kinesin-2 family motor KIF3A/B works together with dynein to bidirectionally transport intraflagellar particles, melanosomes and neuronal vesicles. Compared to kinesin-1, kinesin-2 is less processive and its processivity is more sensitive to load, suggesting that processivity may be controlled by different gating mechanisms. We used stopped flow and steady-state kinetics experiments, along with single-molecule and multi-motor assays to characterize the entire kinetic cycle of a KIF3A homodimer that exhibits similar motility to full-length KIF3A/B. Upon first encounter with a microtubule, the motor rapidly exchanges both mADP and mATP. When AMPPNP was used to entrap the motor in a two-head-bound state, exchange kinetics were unchanged, indicating that rearward strain in the two-head-bound state does not alter nucleotide binding to the front head. A similar lack of front-head gating was found when intramolecular strain was enhanced by shortening the neck linker domain from 17 to 14 residues. In single-molecule assays in ADP, the motor dissociates at 2.1 s-1, 20-fold slower than the Stepping Rate, demonstrating the presence of rear-head gating. In microtubule pelleting assays the KDMt is similar in ADP and ATP. The data and accompanying simulations suggest that, rather than KIF3A processivity resulting from strain-dependent regulation of nucleotide binding (front-head gating), the motor spends a significant fraction of its hydrolysis cycle in a low affinity state, but dissociates only slowly from this state. This work provides a mechanism to explain differences in the load-dependent properties of kinesin-1 and kinesin-2.

Rita Santosrocha - One of the best experts on this subject based on the ideXlab platform.

  • peak ground and joint forces in step exercise depending on step pattern and Stepping Rate
    The Open Sports Sciences Journal, 2009
    Co-Authors: Rita Santosrocha, Antonio Veloso, Maria Lourdes Machado, Maria J Valamatos, Carlos Ferreira
    Abstract:

    The assessment of biomechanical loading is quite important for exercise prescription and injury prevention in the scope of Exercise Biomechanics. The study of ground reaction forces, joint forces and joint moments of force at ankle, knee and hip, allows the understanding of the magnitude of external and internal loading experienced by the lower ex- tremity joints and the pattern of force-absorbing adjustments while performing a dynamic activity. The main purposes of this study were to compare the peak values of those forces, during the ascending and the descending phases of four Step- Exercise patterns (basic-step, knee-lift, run-step and knee-hop), performed at varying Stepping-Rate conditions (125, 130, 135 and 140 beats per minute), in a group of 18 skilled females. The results showed that vertical ground reaction forces and joint forces at ankle varied from: 1.6-1.7 BW (body weight) in basic-step, 1.3-1.6 BW in knee-lift, 1.7-2.1 BW in run- step and, 1.0-1.8 BW in knee-hop; vertical joint forces at knee and hip varied from: 1.5-1.7 BW in basic-step, 1.2-1.5 BW in knee-lift, 1.5-2.0 BW in run-step and, 0.8-1.8 BW in knee-hop. Significant greater values were found in run-step for all parameters. No significant differences were found among conditions of Stepping-Rate. The anterior-posterior forces varied from 0.2-0.6 BW considering the four movements. Significant greater values were found in the two propulsive move- ments. Also, these forces increased with faster Stepping-Rates. The joint moments of force varied from 0.1-1.0 Nm/BW considering the four movements. Significant greater values were found: at ankle, in basic-step and run-step; at knee, in run-step and knee-hop (ascending-phase); and at hip, in run-step. No significant differences were found among conditions of Stepping-Rate, at ankle and at knee (decending-phase). Joint moments increased with faster Stepping-Rates at knee (as- cending-phase) and at hip. The results suggest that experienced steppers are capable of Stepping at different cadences, with generally similar patterns of kinematics and kinetics. We concluded that lower extremity internal loading can be ef- fectively controlled by varying Stepping-Rate during Step classes.

  • analysis of ground reaction forces in step exercise depending on step pattern and Stepping Rate
    Journal of Strength and Conditioning Research, 2009
    Co-Authors: Rita Santosrocha, Antonio Veloso, Maria Lourdes Machado
    Abstract:

    The analysis of ground reaction forces (GRFs) helps one understand the magnitude and pattern of loading experienced by the body while in contact with the ground in locomotor actions. The GRFs reflect a general indicator of mechanical loading on the musculoskeletal system, establishing the "whole-body biomechanical intensity" of physical activity and allowing the comparison between different activities. Our purposes were to analyze the GRFs produced by step exercise particularly-the force profile, average GRF, peak GRF, impulse, and loading Rate-on the ascending and descending movements in 18 skilled women, investigating the differences that exist between 4 Stepping-Rate conditions and between 4 step patterns. Two force platforms were used. These differences were studied using analyses of variance with repeated measures. Our results show that experienced subjects were able to deal with the increase of movement cadence in terms of external load, maintaining the GRF values at the same levels as the ones obtained for quick walking and modeRate step running, activities that are considered safe. The results indicate that lower-extremity external loading can be effectively controlled by varying the Stepping Rate during step classes. With the correct use of this mechanical control, this activity could be included in exercise and rehabilitation programs. The knowledge about the magnitude of loading helps in selecting proper Stepping Rates and proper movements for inclusion in classes.

  • osteogenic index of step exercise depending on choreographic movements session duration and Stepping Rate
    British Journal of Sports Medicine, 2006
    Co-Authors: Rita Santosrocha, Carla Sofia Oliveira, Antonio Veloso
    Abstract:

    Background: Step exercise has been promoted as a low impact physical activity recommended for the improvement of cardiorespiratory and muscular fitness. This recreational activity might also be recommended to improve bone health since mechanical load plays an important role in the normal development of the skeleton. Methods: Our main purpose was to characterised 100 step sessions and to calculated osteogenic index (OI) according to Turner and Robling: OI (one session) = peak ground reaction force(BW)*ln(number of loading cycles+1). Results: Main results (mean±SD) were as follows: OI was 12.0±0.8; peak ground reaction force (GRF) was 1.40±0.10 times body weight (BW); session duration was 38.6±8.3 min; Stepping Rate was 134.6±4.7 beats per minute (bpm); the movements performed most often were marching, knee hop, side leg, L step, and over the top; and the number of loading cycles was 4194.1±1055.2. OI and GRF increased significantly when Stepping Rate was higher than 135 bpm. This Stepping Rate might be used as a reference for higher intensity classes. A frequency of two to three sessions per week of step exercise is recommended. Conclusions: Despite the benefits that have been stated when step classes are structured correctly and adapted to the participants, further research is needed concerning biomechanical load, exercise prescription, and injury prevention.

Antonio Veloso - One of the best experts on this subject based on the ideXlab platform.

  • peak ground and joint forces in step exercise depending on step pattern and Stepping Rate
    The Open Sports Sciences Journal, 2009
    Co-Authors: Rita Santosrocha, Antonio Veloso, Maria Lourdes Machado, Maria J Valamatos, Carlos Ferreira
    Abstract:

    The assessment of biomechanical loading is quite important for exercise prescription and injury prevention in the scope of Exercise Biomechanics. The study of ground reaction forces, joint forces and joint moments of force at ankle, knee and hip, allows the understanding of the magnitude of external and internal loading experienced by the lower ex- tremity joints and the pattern of force-absorbing adjustments while performing a dynamic activity. The main purposes of this study were to compare the peak values of those forces, during the ascending and the descending phases of four Step- Exercise patterns (basic-step, knee-lift, run-step and knee-hop), performed at varying Stepping-Rate conditions (125, 130, 135 and 140 beats per minute), in a group of 18 skilled females. The results showed that vertical ground reaction forces and joint forces at ankle varied from: 1.6-1.7 BW (body weight) in basic-step, 1.3-1.6 BW in knee-lift, 1.7-2.1 BW in run- step and, 1.0-1.8 BW in knee-hop; vertical joint forces at knee and hip varied from: 1.5-1.7 BW in basic-step, 1.2-1.5 BW in knee-lift, 1.5-2.0 BW in run-step and, 0.8-1.8 BW in knee-hop. Significant greater values were found in run-step for all parameters. No significant differences were found among conditions of Stepping-Rate. The anterior-posterior forces varied from 0.2-0.6 BW considering the four movements. Significant greater values were found in the two propulsive move- ments. Also, these forces increased with faster Stepping-Rates. The joint moments of force varied from 0.1-1.0 Nm/BW considering the four movements. Significant greater values were found: at ankle, in basic-step and run-step; at knee, in run-step and knee-hop (ascending-phase); and at hip, in run-step. No significant differences were found among conditions of Stepping-Rate, at ankle and at knee (decending-phase). Joint moments increased with faster Stepping-Rates at knee (as- cending-phase) and at hip. The results suggest that experienced steppers are capable of Stepping at different cadences, with generally similar patterns of kinematics and kinetics. We concluded that lower extremity internal loading can be ef- fectively controlled by varying Stepping-Rate during Step classes.

  • analysis of ground reaction forces in step exercise depending on step pattern and Stepping Rate
    Journal of Strength and Conditioning Research, 2009
    Co-Authors: Rita Santosrocha, Antonio Veloso, Maria Lourdes Machado
    Abstract:

    The analysis of ground reaction forces (GRFs) helps one understand the magnitude and pattern of loading experienced by the body while in contact with the ground in locomotor actions. The GRFs reflect a general indicator of mechanical loading on the musculoskeletal system, establishing the "whole-body biomechanical intensity" of physical activity and allowing the comparison between different activities. Our purposes were to analyze the GRFs produced by step exercise particularly-the force profile, average GRF, peak GRF, impulse, and loading Rate-on the ascending and descending movements in 18 skilled women, investigating the differences that exist between 4 Stepping-Rate conditions and between 4 step patterns. Two force platforms were used. These differences were studied using analyses of variance with repeated measures. Our results show that experienced subjects were able to deal with the increase of movement cadence in terms of external load, maintaining the GRF values at the same levels as the ones obtained for quick walking and modeRate step running, activities that are considered safe. The results indicate that lower-extremity external loading can be effectively controlled by varying the Stepping Rate during step classes. With the correct use of this mechanical control, this activity could be included in exercise and rehabilitation programs. The knowledge about the magnitude of loading helps in selecting proper Stepping Rates and proper movements for inclusion in classes.

  • osteogenic index of step exercise depending on choreographic movements session duration and Stepping Rate
    British Journal of Sports Medicine, 2006
    Co-Authors: Rita Santosrocha, Carla Sofia Oliveira, Antonio Veloso
    Abstract:

    Background: Step exercise has been promoted as a low impact physical activity recommended for the improvement of cardiorespiratory and muscular fitness. This recreational activity might also be recommended to improve bone health since mechanical load plays an important role in the normal development of the skeleton. Methods: Our main purpose was to characterised 100 step sessions and to calculated osteogenic index (OI) according to Turner and Robling: OI (one session) = peak ground reaction force(BW)*ln(number of loading cycles+1). Results: Main results (mean±SD) were as follows: OI was 12.0±0.8; peak ground reaction force (GRF) was 1.40±0.10 times body weight (BW); session duration was 38.6±8.3 min; Stepping Rate was 134.6±4.7 beats per minute (bpm); the movements performed most often were marching, knee hop, side leg, L step, and over the top; and the number of loading cycles was 4194.1±1055.2. OI and GRF increased significantly when Stepping Rate was higher than 135 bpm. This Stepping Rate might be used as a reference for higher intensity classes. A frequency of two to three sessions per week of step exercise is recommended. Conclusions: Despite the benefits that have been stated when step classes are structured correctly and adapted to the participants, further research is needed concerning biomechanical load, exercise prescription, and injury prevention.

Makoto Ayabe - One of the best experts on this subject based on the ideXlab platform.

  • assessment of minute by minute Stepping Rate of physical activity under free living conditions in female adults
    Gait & Posture, 2011
    Co-Authors: Makoto Ayabe, Junichiro Aoki, Hideaki Kumahara, Hiroaki Tanaka
    Abstract:

    Abstract Background The minute-by-minute Stepping Rate (MMSR) is a unique index of the walking speed. The MMSR under free-living conditions remains unclear. Purpose The purpose of the present investigation was to clarify the physical activity (PA) levels based on MMSR under free-living conditions. Methods A total of 85 female volunteers, age from 21 to 91 year, wore a pedometer with a uni-axial accelerometer (Lifecorder, Kenz, Japan) for 7 days consecutively in order to determine the number of steps, the intensity of PA (light intensity PA; LPA, modeRate intensity PA; MPA, and vigorous intensity PA; VPA), and the MMSR. Thereafter, the daily time spent in PA at −1 (min day −1 ) was calculated. All experiments were conducted in March 2007. Results The number of steps, the time spent in LPA, MPA, VPA, PA at −1 were 9275 ± 3453 steps day −1 , 71 ± 25 min day −1 , 34 ± 22 min day −1 , 4 ± 6 min day −1 , 295 ± 88 min day −1 , 16 ± 12 min day −1 , and 4 ± 6 min day −1 . The time spent in PA at −1 positively associated with age ( p −1 negatively associated with age ( p Conclusion The time spent in PA at −1 MMSR differs across different age-groups under free-living conditions in female adults. The clinical significance with regards to the age-associated changes in MMSR remains unclear.

  • minute by minute Stepping Rate of daily physical activity in normal and overweight obese adults
    Obesity Research & Clinical Practice, 2011
    Co-Authors: Makoto Ayabe, Junichiro Aoki, Hideaki Kumahara, Eiichi Yoshimura, Sakiko Matono, Takuro Tobina, Akira Kiyonaga, Keizo Anzai, Hiroaki Tanaka
    Abstract:

    Summary The relationship between minute-by-minute Stepping Rate under free-living and obesity remains unclear. The purpose of the present investigation was to compare the levels of physical activity (PA) based on the minute-by-minute Stepping Rate under free-living conditions between normal weight (NW) and overweight and obese (OV) individuals. A total 40 volunteers participated in the present investigation. These participants were divided into NW or OV according to the body mass index ( −2 or 25kgm −2 ). All participants wore a pedometer with a uni-axial accelerometer (Lifecorder-EX 4sec, Kenz, Japan) for 7 days continuously. The Lifecorder determined the number of steps and time spent in PA at −1 according to the minute-by-minute Stepping Rate. The OV group took a significantly fewer number of steps per day in comparison to that in the NW group ( p p =0.01). Furthermore, the OV group spent a significantly shorter time in PA at a 100stepsmin −1 of the Stepping Rate compared with that in the NW group ( p −1 of Stepping Rate in comparison to the NW individuals.

Geng-yuan Chen - One of the best experts on this subject based on the ideXlab platform.

  • the kinesin 5 chemomechanical cycle is dominated by a two heads bound state
    Journal of Biological Chemistry, 2016
    Co-Authors: Geng-yuan Chen, Keith J Mickolajczyk, William O. Hancock
    Abstract:

    Single-molecule microscopy and stopped-flow kinetics assays were carried out to understand the microtubule polymerase activity of kinesin-5 (Eg5). Four lines of evidence argue that the motor primarily resides in a two-heads-bound (2HB) state. First, upon microtubule binding, dimeric Eg5 releases both bound ADPs. Second, microtubule dissociation in saturating ADP is 20-fold slower for the dimer than for the monomer. Third, ATP-triggered mant-ADP release is 5-fold faster than the Stepping Rate. Fourth, ATP binding is relatively fast when the motor is locked in a 2HB state. Shortening the neck-linker does not facilitate rear-head detachment, suggesting a minimal role for rear-head-gating. This 2HB state may enable Eg5 to stabilize incoming tubulin at the growing microtubule plus-end. The finding that slowly hydrolyzable ATP analogs trigger slower nucleotide release than ATP suggests that ATP hydrolysis in the bound head precedes Stepping by the tethered head, leading to a mechanochemical cycle in which processivity is determined by the race between unbinding of the bound head and attachment of the tethered head.

  • processivity of the kinesin 2 kif3a results from rear head gating and not front head gating
    Journal of Biological Chemistry, 2015
    Co-Authors: Geng-yuan Chen, David F.j. Arginteanu, William O. Hancock
    Abstract:

    Abstract The kinesin-2 family motor KIF3A/B works together with dynein to bidirectionally transport intraflagellar particles, melanosomes and neuronal vesicles. Compared to kinesin-1, kinesin-2 is less processive and its processivity is more sensitive to load, suggesting that processivity may be controlled by different gating mechanisms. We used stopped flow and steady-state kinetics experiments, along with single-molecule and multi-motor assays to characterize the entire kinetic cycle of a KIF3A homodimer that exhibits similar motility to full-length KIF3A/B. Upon first encounter with a microtubule, the motor rapidly exchanges both mADP and mATP. When AMPPNP was used to entrap the motor in a two-head-bound state, exchange kinetics were unchanged, indicating that rearward strain in the two-head-bound state does not alter nucleotide binding to the front head. A similar lack of front-head gating was found when intramolecular strain was enhanced by shortening the neck linker domain from 17 to 14 residues. In single-molecule assays in ADP, the motor dissociates at 2.1 s-1, 20-fold slower than the Stepping Rate, demonstrating the presence of rear-head gating. In microtubule pelleting assays the KDMt is similar in ADP and ATP. The data and accompanying simulations suggest that, rather than KIF3A processivity resulting from strain-dependent regulation of nucleotide binding (front-head gating), the motor spends a significant fraction of its hydrolysis cycle in a low affinity state, but dissociates only slowly from this state. This work provides a mechanism to explain differences in the load-dependent properties of kinesin-1 and kinesin-2.