Time to Failure and Muscle Activation of a Fatiguing Contraction Alters with Practice and Age

Abstract

Alterations in muscle activation with repeat performances can prolong the time to failure of a submaximal fatiguing contraction. The influence of practice on time to failure of a fatiguing contraction with increased age is not understood. PURPOSE: The purpose was to compare the time to failure, muscle activation strategies and voluntary activation for a fatiguing contraction of young and old adults performed with the elbow flexor muscles. METHODS: Eight young adults (3 men and 5 women; mean ± SD; 20.5 ± 0.9 years) and 8 old adults (3 men and 5 women; 70.8 ± 4.0 years) performed sustained 3 isometric fatiguing contractions at 30% of maximal voluntary contraction (MVC) torque until the target force could no longer be achieved. One week separated each session. RESULTS: The time to task failure of the old adults increased between session 1 and 3 (9.4 ± 5 to 12.6 ± 5 min) but did not change for the young adults (5.8 ± 1.4 to 6.0 ± 1.7 min, session × age interaction, P < 0.05). Young adults were stronger than the old but strength was similar for each age group across sessions. MVC torque decreased similarly for the young and old adults after the fatiguing contractions. Voluntary activation was similar for young and old adults before the fatiguing contraction and decreased similarly for the both age groups when assessed during recovery of the 3 sessions. Twitch torque also decreased similarly after each fatiguing contraction for the young and old adults. RMS EMG (% MVC) for all elbow flexor muscles increased progressively during the fatiguing tasks for both age groups. However, the rates of the increase for the old adults in session 2 and 3 (2.6 ± 2 and 2.0 ± 1 %/min, respectively) were less than those of young adults (6.0 ± 3 and 4.3 ± 2 %/min, respectively, session × age interaction, P < 0.05). CONCLUSION: Practice of a fatiguing contraction enhanced the time to failure in old adults and this was accomplished with changes in muscle activation patterns.