Pre-exhaustion Exercise Differentially Influences Neuromuscular Fatigue Based on Habitual Physical Activity History

Harlan, KG, Merucci, RB, Weaver, JJ, Windle, TC, and Malek, MH. Pre-exhaustion exercise differentially influences neuromuscular fatigue based on habitual physical activity history. J Strength Cond Res 35(3): 739-745, 2021-Although there is anecdotal evidence of a potential physiological benefit of pre-exhaustion exercise to enhance muscular recruitment, few studies have systematically examined the effect on neuromuscular activity. Moreover, a subject's habitual physical activity history may, in part, contribute to the muscle's response on a subsequent workbout after a single pre-exhaustion workbout. To date, no studies have examined the effect of pre-exhaustion exercise on the electromyographic fatigue threshold (EMG(FT)). The purpose of this study, therefore, is to determine whether pre-exhaustion exercise influences the EMG(FT). Specifically, we were interested in determining whether or not there is a dichotomous response to pre-exhaustion exercise based on the individual's habitual physical activity history. Thus, we hypothesized that healthy active subjects would have reduced EMG(FT) values, whereas elite runners would have increased EMG(FT) values as a result of the pre-exhaustion exercise. Eight healthy college-aged men (mean +/- SEM, age = 24.5 +/- 0.3 years; body mass = 83.1 +/- 3.0 kg; and height = 1.80 +/- 0.02 m) and 9 elite runners (mean +/- SEM, age = 23.4 +/- 0.7 years; body mass = 70.3 +/- 2.7 kg; and height = 1.79 +/- 0.03 m) participated in current study. Each subject visited the laboratory on 2 occasions separated by 7 days and performed the single-leg knee-extensor ergometry test. For one of the visits, the subjects performed the Thorstensson test (50 continuous, concentric knee extensions) before the single-leg knee-extensor ergometry. The EMG(FT) was measured on both visits for all subjects. For healthy subjects, we found that the EMG(FT) was significantly reduced after performing the 50 isokinetic knee extensions (control: 27 +/- 6 W vs. Thorstensson: 21 +/- 6.0 W; p = 0.001), whereas for elite runners, there was no significant mean differences between the 2 visits (control: 38 +/- 3 W vs. Thorstensson: 39 +/- 2 W; p = 0.813). These results suggest that 50 repetition of isokinetic muscle action, as a method of pre-exhausting the quadriceps femoris muscles, may be influenced by the subject's habitual exercise history.

Automated summary

This study investigated the influence of pre-exhaustion exercise on the electromyographic fatigue threshold (EMG(FT)), finding that EMG(FT) values decreased in healthy active subjects but remained unchanged in elite runners. These results suggest that the impact of pre-exhaustion exercise may be influenced by the subject's habitual exercise history.