The response of the peroneal muscles to sudden inversion of the ankle during standing was investigated. The variation of the inversion angle with time was measured by means of a potentiometer attached to a specially designed test apparatus. During the tests, volunteers were subjected to sudden and unexpected inversion of their ankle, during which the surface EMG of the peroneal muscles was also recorded. Two groups were tested, one of normal subjects and one consisting of subjects with recurrent ankle sprains. There were 8 females and 3 males in each group. The subjects in the second group, who suffered from recurrent ankle sprains, had been asymptomatic during the last 2 months prior to the tests. For each subject in the two groups, both ankles were tested. The results indicated a latency time ranging from 60 to 80 ms for both groups. It was concluded that the reflex contraction of the peroneal muscles due to a sudden stretch inversion motion has no role in protecting the ankle joint during sprain and that this protection is mainly provided by the passive tissues.
Eli Isakov, Joseph Mizrahi, Pablo Solzi, Zev Susak, and Moshe Lotem
Oleg Verbitsky, Joseph Mizrahi, Arkady Voloshin, July Treiger, and Eli Isakov
The goal of this research was to analyze the effects of fatigue on the shock waves generated by foot strike. Twenty-two subjects were instrumented with an externally attached, lightweight accelerometer placed over the tibial tuberosity. The subjects ran on a treadmill for 30 min at a speed near their anaerobic threshold. Fatigue was established when the end-tidal CO2 pressure decreased. The results indicated that approximately half of the subjects reached the fatigue state toward the end of the test. Whenever fatigue occurred, the peak acceleration was found to increase. It was thus concluded that there is a clear association between fatigue and increased heel strike–induced shock waves. These results have a significant implication for the etiology of running injuries, since shock wave attenuation has been previously reported to play an important role in preventing such injuries.
Margaret K.Y. Mak, Oron Levin, Joseph Mizrahi, and Christina W.Y. Hui-Chan
Calculation of joint torques during the rising phase of sit-to-stand motion is in most cases indeterminate, due to the unknown thighs/chair reaction forces in addition to the other sources of uncertainties such as joint positioning and anthropometric data. In the present study we tested the reliability of computation of the joint torques from a five-segment model; we used force plate data of thighs/chair and feet/ground reaction forces, in addition to kinematic measurements. While solving for joint torques before and after seat-off, differences between model solutions and measured data were calculated and minimized using an iterative algorithm for the reestimation of joint positioning and anthropometric properties. The above method was demonstrated for a group of six normal elderly persons.