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  • Author: Yoshiyuki Kobayashi x
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A Comparison of Computation Methods for Leg Stiffness During Hopping

Hiroaki Hobara, Koh Inoue, Yoshiyuki Kobayashi, and Toru Ogata

Despite the presence of several different calculations of leg stiffness during hopping, little is known about how the methodologies produce differences in the leg stiffness. The purpose of this study was to directly compare K leg during hopping as calculated from three previously published computation methods. Ten male subjects hopped in place on two legs, at four frequencies (2.2, 2.6, 3.0, and 3.4 Hz). In this article, leg stiffness was calculated from the natural frequency of oscillation (method A), the ratio of maximal ground reaction force (GRF) to peak center of mass displacement at the middle of the stance phase (method B), and an approximation based on sine-wave GRF modeling (method C). We found that leg stiffness in all methods increased with an increase in hopping frequency, but K leg values using methods A and B were significantly higher than when using method C at all hopping frequencies. Therefore, care should be taken when comparing leg stiffness obtained by method C with those calculated by other methods.

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Differences in Spring-Mass Characteristics Between One- and Two-Legged Hopping

Hiroaki Hobara, Yoshiyuki Kobayashi, Emika Kato, and Toru Ogata

Although many athletic activities and plyometric training methods involve both unilateral and bilateral movement, little is known about differences in the leg stiffness (K leg) experienced during one-legged hopping (OLH) and two-legged hopping (TLH) in place. The purpose of this study was to investigate the effect of hopping frequencies on differences in K leg during OLH and TLH. Using a spring-mass model and data collected from 17 participants during OLH and TLH at frequencies of 2.0, 2.5, and 3.0 Hz, K leg was calculated as the ratio of maximal ground reaction force (F peak) to the maximum center of mass displacement (ΔCOM) at the middle of the stance phase measured from vertical ground reaction force. Both K leg and F peak were found to be significantly greater during TLH than OLH at all frequencies, but type of hopping was not found to have a significant effect on ΔCOM. These results suggest that K leg is different between OLH and TLH at a given hopping frequency and differences in K leg during OLH and TLH are mainly associated with differences in F peak but not ΔCOM.

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Normative Spatiotemporal Parameters During 100-m Sprints in Amputee Sprinters Using Running-Specific Prostheses

Hiroaki Hobara, Wolfgang Potthast, Ralf Müller, Yoshiyuki Kobayashi, Thijs A. Heldoorn, and Masaaki Mochimaru

The aim of this study was to develop a normative sample of step frequency and step length during maximal sprinting in amputee sprinters. We analyzed elite-level 100-m races of 255 amputees and 93 able-bodied sprinters, both men and women, from publicly-available Internet broadcasts. For each sprinter’s run, the average forward velocity, step frequency, and step length over the 100-m distance were analyzed by using the official record and number of steps in each race. The average forward velocity was greatest in able-bodied sprinters (10.04 ± 0.17 m/s), followed by bilateral transtibial (8.77 ± 0.27 m/s), unilateral transtibial (8.65 ± 0.30 m/s), and transfemoral amputee sprinters (7.65 ± 0.38 m/s) in men. Differences in velocity among 4 groups were associated with step length (able-bodied vs transtibial amputees) or both step frequency and step length (able-bodied vs transfemoral amputees). Although we also found that the velocity was greatest in able-bodied sprinters (9.10 ± 0.14 m/s), followed by unilateral transtibial (7.08 ± 0.26 m/s), bilateral transtibial (7.06 ± 0.48 m/s), and transfemoral amputee sprinters (5.92 ± 0.33 m/s) in women, the differences in the velocity among the groups were associated with both step frequency and step length. Current results suggest that spatiotemporal parameters during a 100-m race of amputee sprinters is varied by amputation levels and sex.