Changes in Fatigue Are the Same for Trained Men and Women After Resistance Exercise

Paul W. Marshall; Emily Metcalf; Amanda D. Hagstrom; Rebecca Cross; Jason C. Siegler; Roger M. Enoka

Disclosures

Med Sci Sports Exerc. 2020;52(1):196-204. 

In This Article

Abstract and Introduction

Abstract

Purpose: To measure changes in fatigue and knee-extensor torque in the 48 h after trained men and women completed a full-body resistance exercise session.

Methods: Eight trained women (mean ± SD: age, 25.6 ± 5.9 yr; height, 1.68 ± 0.06 m; mass, 71.0 ± 8.6 kg) and eight trained men (age, 25.5 ± 6.2 yr; height, 1.79 ± 0.05 m; mass, 86.4 ± 9.8 kg) performed a full-body resistance exercise session based on real-world athletic practice. Measurements were performed before and after the exercise session, as well as 1, 24, and 48 h after the session. Fatigue and pain were measured with standardized self-report measures. Maximal isometric contractions with the knee extensors and superimposed femoral nerve stimulation were performed to examine maximal torque, rate of torque development, voluntary activation, and muscle contractility. Two sets of 10 isokinetic contractions (60°·s−1) with the knee extensors were performed during the protocol with use of near-infrared spectroscopy to assess muscle oxygenation. EMG were recorded from two quadriceps muscles during all isometric and isokinetic contractions.

Results: Fatigue was increased from baseline for both sexes until 48 h after training (P < 0.001). Maximal torque and evoked twitch amplitudes were similarly reduced after exercise for men and women (P < 0.001). Voluntary activation and EMG amplitudes were unchanged after the training session. Muscle oxygenation was 13.3% ± 17.4% (P = 0.005) greater for women during the isokinetic repetitions, and the values were unchanged after the training session.

Conclusions: This is the first study to show similar changes in the fatigue reported by trained men and women in the 48 h after a training session involving full-body resistance exercises. Sex differences in muscle oxygenation during exercise do not influence the reductions in muscle force, activation, or contractility after the training session.

Introduction

Fatigue is a common self-reported symptom after exercise that is associated with impaired cognitive and physical function in the hours and days after match-play or training.[1] The examination of fatigue after different training protocols, such as resistance exercise, is important in the competitive sports environment where there is difficulty understanding how best to prescribe training sessions.[2] The assessment of fatigue after a training session that involves full-body resistance exercises, as used in athletic practice, has received relatively little attention, despite most sports science practitioners (84% to 97%) using self-report measures of fatigue and overall wellness to monitor athlete recovery and adjust weekly exercise prescription.[2,3]

Moreover, there appears to be no information on sex differences in fatigue and recovery after resistance exercise in trained individuals. Evidence from single-limb studies suggest that men exhibit greater reductions in muscle force and contractility after isometric and slow-velocity concentric contractions due to a combination of muscle characteristics (e.g., relative area of type II muscle fibers) and rates of adjustment in cardiovascular attributes (e.g., heart rate, blood pressure).[4,5] Furthermore, men exhibit greater reductions in work, sprint time, and maximal strength after interval sprint (cycling, running) sessions.[6–8] In contrast, sex differences are not observed after moderate-to-high velocity concentric or eccentric contractions with a single limb.[9–11] It is difficult to extrapolate these findings to athletic practice, where resistance training sessions include a combination of slow- and high-velocity contractions, as well as eccentric contractions. Critically, it is not known whether any sex differences in force capacity translate to differences in the fatigue reported by men and women after a session of full-body resistance exercises.

A few studies have examined fatigue and the associated changes in muscle force after full-body resistance exercise, and all have been performed on men.[12–14] These findings suggest that there is a mismatch between the recovery of fatigue and measures of muscle force after resistance exercise sessions similar to that observed in athletic practice. Thus, changes in muscular force do not appear to be an appropriate surrogate for the fatigue experienced by individuals after resistance exercise. Fatigue appears to require at least 48 h to recover back to the levels measured before exercise, whereas measures of muscle force (e.g., maximal force, rate of force development) and neuromuscular properties that establish force capacity (e.g., voluntary activation, spinal reflexes, twitch-evoked estimates of contractility) return to baseline levels within 24 h after training.[12–14]

It seems that only three studies have examined sex differences in changes in muscle force after performing a single exercise (squat or leg-extension exercise) with a similar intensity (range, 67% to 90% maximal strength), volume (three to six sets), and rest–interval scheme to real-world practice.[15–17] The three studies measured changes in knee extensor torque, but report different outcomes for sex differences in the decreases in muscle torque and the associated physiological adjustments (e.g., muscle contractility and activation). For example, one study reported delayed recovery of torque in women for up to 72 h after exercise,[17] whereas the other studies reported no sex difference,[16] and greater reductions for men.(15) None of these studies acquired self-reported measures of fatigue. Thus, sex differences in fatigue and knee extensor torque after full-body resistance exercise, including the adjustments that contribute to the reductions in torque, are unclear.

The purpose of our study was to measure fatigue and knee-extensor torque over the 48 h after trained men and women completed a training session involving full-body resistance exercises. We measured the knee extensors due to their key role in all sprint and jump activities. As potential explanatory variables for sex differences in knee-extensor torque, we measured muscle contractility and activation. Moreover, based on studies suggesting sex differences may be explained by cardiovascular adjustments that alter muscle perfusion,[4,5,18,19] we used near-infrared spectroscopy (NIRS) during sets of isokinetic contractions performed to estimate muscle tissue oxygenation. We hypothesized that men and women would report similar levels of fatigue after the training session with both groups recovering within 48 h, but that men would exhibit greater reductions in maximal torque and rate of torque development (RTD) due to more substantial decreases in muscle contractility and oxygenation.

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