title: Examination of Sex- and Limb-Specific Fatigue During Unilateral, Isometric Forearm Exercise
Creators: name: Voskuil, Caleb
Publisher: name: University of Kentucky Libraries
Year: 2021
Subjects: Kinesiology

description: The purpose of this study was to examine the effects of unilateral, isometric handgrip holds to failure for the dominant (Dm) and non-dominant (NDm) limb on ipsilateral ([IPS] exercised side) and contralateral ([CON] non-exercised side) performance fatigability. Twenty individuals participated in this study (Men [n =10]; Women [n = 10; Composite Demographics: Age: 22.2 years; Height: 174.4 cm; Body Mass: 75.0 kg) and completed three visits. Two, 6 s maximal voluntary isometric contractions (MVICs) for the Dm and NDm limb were performed during visit 1, followed by a familiarization of the fatigue test. Visits 2 and 3 included an isometric, handgrip hold to failure (HTF) fatigue test at 50% MVIC for either the Dm or NDm limb using a handgrip dynamometer (iWorx Systems Inc.; Dover, NH 03820). Prior to, and immediately after the HTF, a MVIC was performed on the IPS and CON sides. The fatigue test (Dm or NDm) was randomized between visits and the side tested first (IPS and CON) was randomized for pre-and post-tests, within and between each visit. The perceptual measures of Rating of Perceived Exertion (RPE) for the Active Muscle (AM) and Overall Body (O), along with the Numerical Pain Rating (NPR) for the AM and O were taken following each MVIC and the HTF. The test-retest reliability of the Dm and NDm hand pre-HTF MVIC demonstrated ‘excellent’ reliability (Dm: ICC = 0.936; NDm: ICC = 0.938) while the Dm limb HTF demonstrated ‘fair’ reliability (ICC = 0.553) with no systematic error for either the MVIC or HTF. Men and women demonstrated similar times for the HTF (Dm limb: 130.3 ± 36.8 s; NDm limb: 112.1 ± 34.3 s; p = 0.002), despite the men (46.07 ± 10.64 kg) demonstrating a significantly greater absolute MVIC force than women (30.52 ± 6.93 kg; p ≤ 0.001). Performance fatiguability (decrease in exercise performance) and facilitation (increase in exercise performance) was calculated a via a priori planned comparisons (%D = ((pre-HTV MVIC – post-HTF MVIC) / pre-HTV MVIC)*100)). Men, collapsed across limb, demonstrated IPS limb (%D = 22.9 ± 10.8%) performance fatiguability and CON limb facilitation (%D = -6.1 ± 6.9%) following the HTF, while women demonstrated differences in performance fatiguability between the Dm and NDm limbs in IPS (Dm: %D = 28.0 ± 9.4%; NDm: %D = 32.3% ± 10.1%; p = 0.027), but no significant changes in the CON limbs (Dm: %D = -1.6 ± 5.7%; NDm: %D = 1.7 ± 5.9%). Following the HTF, men (9.2 ± 1.1) demonstrated a greater RPE-AM value than women (7.4 ± 2.2; p = 0.031), but the RPE-O, NPR-AM, NPR-O demonstrated no differences. The perceptual responses for the Pre-/Post-HTF in men demonstrated increases in RPE-AM and RPE-O in both limbs; women demonstrated increases in the IPS side only. The NPR-AM and NPR-O measures demonstrated increases for the men in both limbs and the women in the IPS side only. In this study, women demonstrated less absolute grip strength than men and demonstrated greater Dm limb strength than NDm grip strength while the men demonstrated no difference between limbs. Sex-specific training programming and body composition differences may have influenced this finding as well as the finding that the RPE-AM for a 50% MVIC HTF was higher for the men than women despite similar times to failure. The Dm limb was more fatigue resistant than the NDm limb, possibly due to continual favoring of the Dm limb in everyday tasks. Similar performance fatiguability in the IPS limb was demonstrated for men and women, however, the men demonstrated facilitation in the CON limb while there were no CON limb changes for the women. The finding of facilitation may be due to central factors, such as interhemispheric excitatory signaling from the ipsilateral to the contralateral hemisphere, and peripheral factors such as post activation potentiation (PAP) elicited from myosin light chain phosphorylation. The PAP phenomenon occurs more frequently in type II muscle fibers. Thus, the sex-dependent differences seen in facilitation and perceptual responses may be related to a greater proportion of type II fibers for the men compared to the women.
description: © 2021 Caleb Christian Voskuil