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  • Author: Satoru Hashizume x
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Hiroaki Hobara, Sakiko Saito, Satoru Hashizume, Hiroyuki Sakata and Yoshiyuki Kobayashi

To understand the step characteristics during sprinting in lower-extremity amputees using running-specific prosthesis, each athlete should be investigated individually. Theoretically, sprint performance in a 100-m sprint is determined by both step frequency and step length. The aim of the present study was to investigate how step frequency and step length correlate with sprinting performance in elite unilateral transtibial amputees. By using publicly-available Internet broadcasts, the authors analyzed 88 races from 7 unilateral transtibial amputees. For each sprinter’s run, the average step frequency and step length were calculated using the number of steps and official race time. Based on Pearson’s correlation coefficients between step frequency, step length, and official race time for each individual, the authors classified each individual into 3 groups: step-frequency reliant, step-length reliant, and hybrid. It was found that 2, 2, and 3 sprinters were classified into step-frequency reliant, step-length reliant, and hybrid, respectively. These results suggest that the step frequency or step length reliance during a 100-m sprint is an individual occurrence in elite unilateral transtibial amputees using running-specific prosthesis.

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Ryota Akagi, Soichiro Iwanuma, Satoru Hashizume, Hiroaki Kanehisa, Toshimasa Yanai and Yasuo Kawakami

The purpose of this study was to investigate how the contraction-induced increase in distal biceps brachii tendon moment arm is related to that in elbow flexor muscle thickness, with a specific emphasis on the influence of the site-related differences in muscle thickness. The moment arm and muscle thickness were determined from sagittal and cross-sectional images, respectively, of the right arm obtained by magnetic resonance imaging of nine young men. The muscle thickness was measured at levels from the reference site (60% of the upper arm length from the acromial process of the scapula to the lateral epicondyle of the humerus) to 60 mm distal to it (every 10 mm; 7 measurement sites). At 80° of elbow flexion, the moment arm and muscle thickness were determined at rest and during 60% of maximal voluntary contraction (60%MVC) of isometric elbow flexion. Only the relative change from rest to 60%MVC in muscle thickness at the level 60 mm distal to the reference site correlated significantly with that of the moment arm. This result indicates that the contraction-induced increase in distal biceps brachii tendon moment arm is related to that in elbow flexor muscle thickness near the corresponding muscle-tendon junction.

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Atsushi Makimoto, Yoko Sano, Satoru Hashizume, Akihiko Murai, Yoshiyuki Kobayashi, Hiroshi Takemura and Hiroaki Hobara

Understanding the characteristics of ground reaction forces (GRFs) on both limbs during sprinting in unilateral amputees wearing running-specific prostheses would provide important information that could be utilized in the evaluation of athletic performance and development of training methods in this population. The purpose of this study was to compare GRFs between intact and prosthetic limbs during sprinting in unilateral transfemoral amputees wearing running-specific prostheses. Nine sprinters with unilateral transfemoral amputation wearing the same type of prosthesis performed maximal sprinting on a 40-m runway. GRFs were recorded from 7 force plates placed in the center of the runway. Peak forces and impulses of the GRFs in each direction were compared between limbs. Peak forces in vertical, braking, propulsive, and medial directions were significantly greater in intact limbs than those in prosthetic limbs, whereas there were no significant differences in peak lateral force between limbs. Further, significantly less braking impulses were observed in prosthetic limbs than in intact limbs; however, the other measured impulses were not different between limbs. Therefore, the results of the present study suggest that limb-specific rehabilitation and training strategies should be developed for transfemoral amputees wearing running-specific prostheses.

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Ryota Akagi, Soichiro Iwanuma, Satoru Hashizume, Hiroaki Kanehisa, Toshimasa Yanai and Yasuo Kawakami

The purpose of this study was to determine in vivo moment arm lengths (MAs) of three elbow flexors at rest and during low- and relatively high-intensity contractions, and to examine the contraction intensity dependence of MAs at different joint positions. At 50°, 80° and 110° of elbow flexion, MAs of the biceps brachii, brachialis and brachioradialis were measured in 10 young men using sagittal images of the right arm obtained by magnetic resonance imaging, at rest and during 20% and 60% of isometric maximal voluntary elbow flexion. In most conditions, MAs increased with isometric contractions, which is presumably due to the contraction-induced thickening of the muscles. This phenomenon was especially evident in the flexed elbow positions. The influence of the contraction intensities on the increases in MAs varied across the muscles. These results suggest that in vivo measurements of each elbow flexor MA during contractions are essential to properly examine the effects on the interrelationships between elbow flexion torque and individual muscle forces.