PROPERTIES OF SPROUTED RAT MOTOR UNITS - EFFECTS OF PERIOD OF ENLARGEMENT AND ACTIVITY LEVEL

The effects of short and prolonged partial denervation of lateral gast rocnemius muscles in sedentary and active rats (running) were examined , In PD muscles of sedentary animals the mean motor unit (MU) tetanic force after 30 days was not different than that measured after 90 days , Increased locomotor activity over the same period (voluntary running , approximate to 6 km/day) resulted in an increase in mean MU tetanic force of enlarged MUs (28%), The absence of a significant increase in mean muscle fiber area suggested an activity-related enhancement of mo toneuron sprouting, However, the small magnitude of this increase, rel ative to the potential for further sprouting, indicates the activity e ffect is not strong and may be partly due to fiber area changes not ev ident with whole muscle analysis. Nonetheless, these data demonstrate that daily locomotor activity can enhance the tension-generating capac ity of chronically enlarged MUs. (C) 1996 John Wiley & Sons, Inc.