SHORT-TERM RECOVERY FROM VOLUNTARY FATIGUE IN YOUNG AND OLDER MEN1644

Abstract

Fatigue and recovery from a period of intermittent isometric exercise have received little research attention in older adults. Here we report data from six old (80 ± 5 y) and four young men (27 ± 2 y) who performed a 50% of maximum voluntary contraction (MVC) quadriceps fatigue protocol as described by Bigland-Ritchie et al (JAP 61:42, 1986). MVC force, surface EMG, and electrically evoked contractile properties were recorded at the beginning and at every minute during the test. Subjects exercised until their MVC was reduced to ≈50%, or they could not continue. The same parameters were recorded post-fatigue at 1, 3, 5 and 10 minutes. In agreement with the study cited above, results from the young group showed a parallel decline in MVC and 50Hz tetanic force, whereas twitch amplitudes declined at a faster rate. In addition, by the end of the fatigue test, the integrated EMG(IEMG) of the 50% target force approached the MVC IEMG. The men in the old group showed similar responses to fatigue. During recovery, however, the MVC force of the young subjects returned to pre-fatigue levels (≥99%) by 10 min, but force was only ≈85% recovered (p≤0.05) for the old men. Similarly, peak twitch tensions tended to return to pre-fatigue values faster in the young than in the old. Target and MVC IEMGs recovered to near pre-fatigue values similarly in both groups. Results suggest that although the old men fatigue in a similar manner as the young, their force recovery is significantly reduced. Central drive, as measured by IEMG, does not seem to account for this age-related force depression during 10 minutes of recovery.