Age- and Sex-Related Differences in Motor Performance During Sustained Maximal Voluntary Contraction of the First Dorsal Interosseous

Abstract

Age and sex affect the neuromuscular system including performance fatigability. Data on performance fatigability and underlying mechanisms in hand muscles are scarce. Therefore, we determined the effects of age and sex on force decline, and the mechanisms contributing to force decline, during a sustained isometric maximal voluntary contraction (MVC) with the index finger abductor (first dorsal interosseous, FDI). Subjects (n = 51, age range: 19–77 years, 25 females) performed brief and a 2-min sustained MVC with the right FDI. Abduction force and root mean squared electromyographic activity (rms-EMG) were recorded in both hands. Double-pulse stimulation was applied to the ulnar nerve during (superimposed twitch) and after (doublet-force) the brief and sustained MVCs. Compared to females, males were stronger (134%, p < 0.001) and exhibited a greater decline in voluntary (difference: 8%, p = 0.010) and evoked (doublet) force (difference: 12%, p = 0.010) during and after the sustained MVC. Age did not affect MVC, force decline and superimposed twitch. The ratio between the doublet- and MVC-force was greater in females (0.33, p = 0.007) and in older (0.38, p = 0.06) individuals than in males (0.30) and younger (0.30) individuals; after the sustained MVC this ratio increased with age and the increase was larger for females compared to males (p = 0.04). The inadvertent contralateral, left force and rms-EMG activity increased over time (2.7–13.6% MVC and 5.4–17.7% MVC, respectively). Males had higher contralateral forces than females (p = 0.012) and contralateral force was higher at the start of the contralateral contraction in older compared with young subjects (difference: 29%, p = 0.008). In conclusion, our results suggest that the observed sex-differences in performance fatigability were mainly due to differences in peripheral muscle properties. Yet the reduced amount of contralateral activity and the larger difference in evoked versus voluntary force in female subjects indicate that sex-differences in voluntary activation should not be overlooked. These data obtained in neurological healthy adults provides a framework and help the interpretation and referencing of neurophysiological measures in patients suffering from neuromuscular diseases, who often present with symptoms of performance fatigability.

Self-Reported Fatigue After Mild Traumatic Brain Injury Is Not Associated With Performance Fatigability During a Sustained Maximal Contraction

“…Exclusion criteria included psychiatric disorder, neurologic disease (including previous TBI), and drug or alcohol abuse. Data from the control subjects were also used in an accompanying study (Sars et al, 2018). Experiments were designed in accordance with the declaration of Helsinki (World Medical Association, 2013) and approval of the experimental procedures was provided by the medical ethical board of the University Medical Center Groningen.…”

“…Next, group (mTBI) was added to the basic model as a fixed effect. Since sex and age can affect the time-related changes in force and EMG (Sars et al, 2018), we subsequently included these variables and their interactions to the model in a stepwise fashion. Model residuals were examined graphically for normality and heteroscedasticity (using quantile-quantile plots and heteroscedasticity plots) for all multilevel models.…”

Sex-Related Differences in Performance Fatigability Independent of Blood Flow Following a Sustained Muscle Action at a Low Perceptual Intensity

“…Furthermore, during the sustained muscle action at RPE = 2, the men decreased force nearly twofold more than the women (61.0% vs. 34.7%). These findings were typical of fatigue-related differences between men and women [17,28,33,35,36], but this is the first study to report a sex-related difference in performance fatigability following a muscle action anchored to a perception of exertion as opposed to a relative force value. Typically, sex-related differences are more pronounced following low-intensity than high-intensity sustained isometric muscle actions due to differences in the amount of muscle mass activated, which, in theory, leads to differences in muscle blood flow and neuromuscular responses between men and women [5,17,18,28,36].…”

“…Both sex-related differences (time to exhaustion and muscle activation) disappeared when repeated under an ischemic condition [5], which suggested that the differences were blood flow dependent [33]. Furthermore, Sars et al [35] recently hypothesized that sex-related differences in performance fatigability may be more influenced by peripheral factors such as fiber type distribution and intramuscular pressure than central factors such as neural drive and corticospinal excitability. Hunter [18] has previously described "…the magnitude of the sex-differences is specific to the task performed…" (p. 114).…”

Voluntary suppression of associated activity decreases force steadiness in the active hand

“…Participants sat in a chair with both forearms on the armrests and the elbows flexed at ~90°. In this position, participants held a force transducer in each hand with the index finger extended and parallel to horizontal bar (see Figure 2) (Sars et al, 2018; Wolkorte et al, 2015). The proximal interphalangeal joint of the index finger was taped to a C‐shaped plastic piece connected to a bar with strain gauges attached to the force transducer for measuring the voluntary index finger abduction force.…”