THE FORCE-FREQUENCY-RELATIONSHIP IS ALTERED IN REGENERATING AND SENESCENT RAT SKELETAL-MUSCLE

Maximal tetanic tension was elicited at 200, 150, and 150 Hz in contro l tibialis anterior muscles and at 150, 100, and 100 Hz in 14-day rege nerating muscles of young (3 months), adult (18 months), and old (31 m onths) Fischer 344/Brown Norway F1 rats, respectively. In contrast to young rats, increasing stimulation frequency from 50 to 150 Hz did not elicit significantly greater tetanic tension in control or regenerati ng muscles of old rats. At higher stimulation frequencies, tetanic fad e was prevalent in control and regenerating muscles of adult (250-300 Hz) and old rats (200-300 Hz), but was only present at 14 days of reco very in regenerating muscles of young rats (300 Hz). The decreased eff icacy of rehabilitative and physical medicine procedures in adult and elderly patients who have suffered skeletal muscle injury could be exp lained, in part, by the postulate that tetanic fade is indicative of i nadequate synaptic transmission. (C) 1998 John Wiley & Sons, Inc.