Toshio Yanagiya

Ergometry for estimation of mechanical power output in sprinting in humans using a newly developed self-driven treadmill.

Abstract An evaluation of mechanical power during walking and running in humans was undertaken after developing a specially designed running ergometer (RE) in which the subjects gripped the handlebar in front of them keeping both arms straight and in a horizontal position. Ten subjects participated in comparisons of the mean horizontal pushing force (MFam) on the handlebar with the mean horizontal ground reaction force (MFfp) recorded by force platform under the RE during five different constant speeds of walking or running and sprint running with maximal effort. Mechanical power developed during sprint running on the RE was compared with a 50 m sprint. Mean linear velocity (Mv) of the RE belt was recorded by the rotary encoder attached to the axis of the belt. Mean mechanical power calculated from the handlebar setting (MPam=MFam × Mv) was compared to that calculated from force platform recordings (MPfp=MFfp × Mv). A high test-retest reproducibility was observed for both MFfp (r=0.889) and MFam (r=0.783). Larger values for the coefficient of variation for MFam (11.3%–15.8%) were observed than for MFfp (3.3%–8.2%). The MPam, which were obtained from five different constant speeds of walking, running and sprint running were closely correlated to those of MPfp (y=0.98x − 19.10,r=0.982, P < 0.001). In sprint running, MPam was 521.7 W (7.67 W · kg−1) and was correlated to the 50 m sprint time (r=−0.683, P < 0.01). It is concluded that the newly developed RE was useful in the estimation of mechanical power output during human locomotion such as when walking, jogging and sprinting.

Numerical study of ball behavior in side-foot soccer kick based on impact dynamic theory

This study examined the factors affecting the ball velocity and rotation for side-foot soccer kick using a numerical investigation. Five experienced male university soccer players performed side-foot kicks with various attack angles and impact points using a one-step approach. The kicking motions were captured three-dimensionally by two high-speed cameras at 2500 fps. The theoretical equations of the ball velocity and rotation were derived based on impact dynamic theory. Using the theoretical equations, the relationships of the ball velocity and rotation to the attack angle and impact point were obtained. The validity of the theoretical equations was verified by comparing the theoretical relationships with measurement values. Furthermore, simulations of the ball velocity and rotation were conducted using the theoretical equations. The theoretical relationships were in good agreement with the measurement values. The theoretical results confirmed the previously reported experimental results, and indicated that the impact point is more influential on the ball velocity than the attack angle and the attack angle is more influential on the ball rotation than the impact point. The simulation results indicated the following. The ball velocity produced by impact for all impact patterns is largely affected by the foot velocity immediately before impact but barely affected by the degree of slip between the foot and the ball. The ball rotation produced by an impact with a large attack angle is affected by the foot velocity immediately before impact and the degree of slip between the foot and the ball; however, these factors affect the ball rotation less than the attack angle.

Comparison of the Achilles tendon moment arms determined using the tendon excursion and three‐dimensional methods

The moment arm of muscle‐tendon force is a key parameter for calculating muscle and tendon properties. The tendon excursion method was used for determining the Achilles tendon moment arm (ATMA). However, the accuracy of this method remains unclear. This study aimed to investigate the magnitude of error introduced in determining the ATMA using the tendon excursion method by comparing it with the reference three‐dimensional (3D) method. The tendon excursion method determined the ATMA as the ratio between the Achilles tendon displacement during foot rotation from 15° of dorsiflexion to 15° of plantarflexion and the joint rotation angle. A series of foot images was obtained at 15° of dorsiflexion, the neutral position, and 15° of plantarflexion. The 3D value of the ATMA was determined as the shortest distance between the talocrural joint axis and the line of action of the Achilles tendon force. The ATMA determined by the tendon excursion method was smaller by 3.8 mm than that determined using the 3D method. This error may be explained mainly by the length change in the Achilles tendon due to the change in the force applied to it, as passive plantarflexion torque was different by 11 Nm between 15° of dorsiflexion and 15° of plantarflexion. Furthermore, the ATMAs determined using the 3D and tendon excursion methods were significantly correlated but the coefficient of determination was not large (R2 = 0.352). This result suggests that the tendon excursion method may not be feasible to evaluate the individual variability of the ATMA.

A Forefoot Strike Requires the Highest Forces Applied to the Foot Among Foot Strike Patterns

Ground reaction force is often used to predict the potential risk of injuries but may not coincide with the forces applied to commonly injured regions of the foot. This study examined the forces applied to the foot, and the associated moment arms made by three foot strike patterns. 10 male runners ran barefoot along a runway at 3.3 m/s using forefoot, midfoot, and rearfoot strikes. The Achilles tendon and ground reaction force moment arms represented the shortest distance between the ankle joint axis and the line of action of each force. The Achilles tendon and joint reaction forces were calculated by solving equations of foot motion. The Achilles tendon and joint reaction forces were greatest for the forefoot strike (2 194 and 3 137 N), followed by the midfoot strike (1 929 and 2 853 N), and the rearfoot strike (1 526 and 2 394 N). The ground reaction force moment arm was greater for the forefoot strike than for the other foot strikes, and was greater for the midfoot strike than for the rearfoot strike. Meanwhile, there were no differences in the Achilles tendon moment arm among all foot strikes. These differences were attributed mainly to differences in the ground reaction force moment arm among the three foot strike patterns.

The Influence of Position and Area of Shock Absorbing Material of Shoes on Ground Reaction Force during Walking

The purpose of this study was to identify the influence of position and area of shock absorbing material on ground reaction force. Seven subjects volunteered to participate in this study. These subjects were instructed to walk along a 8m long walkway at 1.0m/s (slow), 1.5m/s (medium), 2.0m/s (fast). These trials were repeated until three successful assignments. When subjects walked, they wore four kinds of shoes (Type1, Type2, Type3 and Type4). The differences of these shoes were position and area of shock absorbing material. Type1 did not contain the shock absorbing material at all. The other shoes were inserted the shock absorbing material in the heel region (Type2 and Type3), or between inside bottom and midsole (Type4). The area of the shock absorbing material of Type2 was smaller than that of Type3. The ground reaction forces from 6m to 7.8m of the walkway were recorded by the force plates. Walking velocity was measured by a laser apparatus. For each shoe condition, maximum values of vertical ground reaction force of the three trials were averaged, and the mean value was shown as GRFPEAK. GRFPEAK of all trials was normalized to that of Type1. For slow trial, GRFPEAK of all conditions was almost the same. On the other hand the walking at medium and fast, GRFPEAK of Type3 was only smaller than that of the others. Our results indicated that the increase of area of the shock-absorbing material is effective in the decrease of GRFPEAK. However, a significant difference was not found in each shoe.