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Rupture of the anterior cruciate ligament (ACL) typically leads to surgical reconstruction followed by an extensive rehabilitation program. One of the most commonly experienced complications associated with ACL rupture and reconstruction is quadriceps muscle atrophy. A clear understanding of the exact mechanisms associated with ACL related atrophy remains undocumented. The purpose of the present study was to investigate maximum H-reflex to maximum M-wave ratio as well as quadriceps deficit for both isometric and isokinetic peak torques in a post ACL reconstruction population. Forty subjects volunteered for participation in this study. The experimental group comprised 20 subjects who had undergone patellar tendon graft reconstruction of a torn ACL. A matched control group of 20 subjects were also measured for comparative purposes. The results indicated the control group had significantly higher quadriceps to quadriceps ratio than did the ACL group [ f t j 8 ) = 9.05 p < .001]. In contrast, there was no difference in the H-max/M-max ratio for either group or leg. The strength findings of this study support previous findings. The spinal reflex results support the need for additional research in this area, specifically with more acutely injured subjects. K q w w d s :Anterior cruciate ligament; strength deficit; H-reflex

The results demonstrate different control strategies for young and elderly subjects between prone and standing body positions.

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The purpose of this study was to determine the ability of the elderly central nervous system to modulate spinal reflex output to functionally decrease a spinally induced balance perturbation. In this case, the soleus H reflex was used as the source of perturbation. Therefore, decreasing (down training) of the soleus H reflex was necessary to counteract this perturbation and to better maintain postural control. In addition to assessing the effect of this perturbation on the H reflex, static postural stability was measured to evaluate possible functional effects. Ten healthy young subjects (age: 27.0 +/- 4.6 yr) and 10 healthy elderly subjects (age: 71.4 +/- 5.1 yr) participated in this study. Subjects underwent balance perturbation on 2 consecutive days. On day 1 of perturbation, significant down training of the soleus H reflex was demonstrated in both young (-20.4%) and elderly (-18.7%) subjects. On day 2 of perturbation, significant down training of the soleus H reflex was again demonstrated in both young (-24.6%) and elderly (-21.0%) subjects. Analysis of static stability after the 2 days of balance perturbation revealed a significant 10.1% decrease in the area of sway in elderly subjects. In conclusion, this study demonstrated that healthy, elderly subjects compared with young subjects were equally capable of down training the soleus H reflex in response to a balance perturbation. Furthermore, the improvement in static stability through balance training may provide further evidence that balance can be retrained and rehabilitated in subjects with decreased reflex function.