Neuromuscular fatigue and recovery in women at different ages during heavy resistance loading

To examine neuromuscular fatigue and recovery 23 women, divided into three different age groups, i.e. young women (YW); 30 years (25.0 +/- 1.4; n = 8), middle-aged women (MW); 50 years (48.0 +/- 3.7; n = 7) and elderly women (EW); 70 years (68.9 +/- 3.2; n = 8) performed a strenuous heavy resistance exercise protocol. The subjects performed a bilateral leg press exercise on the machine (David 210) for 5 sets by performing 10 repetitions in each set with the maximal load possible (10 RM). A recovery time of 3 minutes was allowed between the sets. Maximal voluntary neutral activation (integrated EMG), maximal bilateral isometric force, force-time and relaxation time curves of the leg extensor muscles were measured before, between the sets, and immediately after the loading as well as resting for 1 hour, 2 hours, 1 day and 2 days. The loading led to gradual decreases in maximal force in YW by 18.8 +/- 7.1% (p < 0.001), in MW by 30.9 +/- 14.8% (p < 0.01) and in EW by 13.7 +/- 11.9% (p < 0.01) so that the relative decrease in EW was smaller (p < 0.05) than the averaged decreases in YW and MW. Significant (p < 0.05) decreases also took place in the maximal IEMGs of the exercised muscles in all groups. The force-time curve shifted also significantly both in YW (p < 0.001) and in MW (p < 0.001), while only a slight change occurred in EW. Acute recovery in maximal force was significant (p < 0.05) during the first hour of rest in YW and in MW but the force values in all groups were still after two hours of rest significantly (p < 0.05) lower than the preloading values. After two days of rest the force values were 93.7 +/- 11.5% (ns), 90.6 +/- 19.2% (p < 0.05) and 94.6 +/- 17.1% (ns) from their initial force values in YW, MW and EW, respectively. The present results suggest that strenuous heavy resistance loading both in young and middle-aged as well as in elderly women may result in considerable acute fatigue in the neuromuscular system leading not only to the decreased force production capacity of the muscles but also some decrease in the voluntary neural activation of the exercised muscles. Because the degree of acute neuromuscular fatigue and the time needed for recovery may differ considerably, there is a need to optimize the contents and the frequency of different training sessions in order to create proper strength training and for rehabilitation programs to match with the individual requirements of young, middle-aged and elderly women.