Gamma Loop Dysfunction of the Quadriceps Femoris of Elderly Patients Hospitalized after Fall Injury

BACKGROUND AND PURPOSE: Gamma loop dysfunction may increase the risk of falls. Therefore, we evaluated gamma loop function in subjects hospitalized after fall injury and examined whether aging affects the gamma loop. METHODS: Maximal voluntary contraction (strength) of knee extension and integrated electromyography (I-EMG) of the quadriceps femoris were examined to evaluate the activities of alpha motoneurons before and after 20-min vibration applied to the quadriceps femoris. Mean percentage changes were calculated as: (previbration value-postvibration value)/previbration valuex100). As strength and I-EMG of both uninjured (UG) and injured limbs (IG) of patients with a history of falls resulting in hospitalization were examined in each group, the mean percentage changes of the 4 groups were compared with those of controls [young control group (YCG) and elderly control group (ECG)]. RESULTS: Mean percentage changes in strength of UG and IG were significantly different from YCG but not the ECG. Mean percentage changes in I-EMG for VL (vastus lateralis) and VM (vastus medialis)in IG were significantly different from YCG. However, I-EMG of RF of IG were not significantly different from YCG. Although mean percentage changes in I-EMG of UG were not significantly different from ECG, those for VL and VM of IG were different from ECG. CONCLUSIONS: As the gamma loop dysfunction exited in the uninjured limbs of subjects with a history of falls resulting in hospitalization, a dysfunctional gamma loop could be a risk factor for falling. Further studies are needed to identify the effects of aging on gamma loop function.