Muscle fatigue in response to low-load blood flow-restricted elbow-flexion exercise: are there any sex differences?

Sex differences in muscle fatigue following isokinetic muscle contractions

Muscle fatigue is a limiting factor of human performance. It is unclear whether sex-based differences in fatigability exist during dynamic exercise of varying velocities of contraction. We aimed at exploring sex differences in muscle fatigue elicited by maximal isokinetic muscle contractions performed at different angular velocities. Twenty-six healthy participants (13 men: 23.2 ± 1.5; 13 women: 21.9 ± 3.0 years) were tested for concentric knee-extension at slow, moderate and fast angular isokinetic velocity (60, 180 and 300º.s^-1, respectively), on non-consecutive days. The impact of sex on fatigue resistance and consecutive recovery for each isokinetic condition was explored by calculating the percent change in maximal voluntary isometric contraction (MVIC) and in rate of torque development (RTD), from pre- to post-isokinetic exercise (30 repetitions). The isokinetic fatigue index was also determined. No sex differences were obtained in response to isokinetic contractions completed at 60º.s^-1. After performing muscle contractions at 300º.s^-1, women had a significantly greater loss in MVIC than men (- 18.4 ± 5.5 vs. - 12.9 ± 3.8%; p = 0.009) and larger decreases in work output during isokinetic exercise (- 34.2 ± 8.9 vs - 27.5 ± 10.6%; p = 0.017). Recovery of initial MVIC strength was greater for women post-exercise at 180º.s^-1 (15.6 ± 4.1% vs. 6.7 ± 9.5; p = 0.003). No differences were found between sexes in any condition for RTD from pre- to post-fatigue. These results suggest the presence of a sexually dimorphic fatigability in response to dynamic (isokinetic) contractions favouring men at higher absolute velocities of contraction.

The acute and early phase effects of blood flow restriction training on ratings of perceived exertion, performance fatigability, and muscular strength in women

BACKGROUND: Blood flow restriction (BFR) resistance training (RT) has garnered recent interest, but female-specific data remains scarce. OBJECTIVE: The purpose was to examine the effects of 2-wks of low-load concentric, isokinetic, reciprocal forearm flexion and extension training, with and without BFR on perceptual responses, performance fatigability, and muscular strength. METHODS: Twenty women were assigned to a BFRT or a non-BFRT group. Each group trained at 30% of concentric peak moment. Each session consisted of 75 concentric, isokinetic, reciprocal forearm flexion extension muscle actions. RPEs were recorded following each set. Pretest and posttest maximal voluntary isometric contraction (MVIC) force was measured, and percent decline was defined as performance fatigability. RESULTS: The RPE values (p< 0.05) increased across sets. Strength (collapsed across muscle action) increased (p< 0.05) from 0-wk (23.7 ± 3.2 Nm) to 2-wk (26.8 ± 2.7 Nm). Independent of group and muscle action, performance fatigability (p< 0.05) increased from 0-wk (10.9 ± 5.0%) to 2-wk (14.1 ± 4.4%). CONCLUSIONS: 2-wks of low-load concentric, reciprocal forearm flexion and extension training resulted in similar training-induced changes in perceptual responses, performance fatigability, and muscular strength between BFRT and non-BFRT. These findings may reduce concerns of increased perceptual responses following BFRRT compared to non-BFRRT.

INDICATORS OF NEUROMUSCULAR FATIGUE IN LEG PRESS EXERCISE IN MEN AND WOMEN

ABSTRACT Introduction Muscle fatigue is characterized by reduced ability to produce maximum strength or power, and may differ between men and women. Changes in velocity of movement during exercise, and in the ability to produce strength after exercise, may help when comparing fatigue in men and women. Objective To analyze the differences between men and women in relation to number of repetitions, kinetics, kinematics and isometric force-time curve performance, and their respective muscle activation in horizontal leg press exercises. Methods Fifteen men and fifteen women underwent isometric force-time curve (Cf-t) and electromyographic (EMG) assessments before and after performing horizontal leg press exercises. The exercises were performed in three sets until voluntary exhaustion, at 70% maximal repetition. During the exercises, kinetic and kinematic variables were obtained by means of two force transducers, a linear position potentiometer and accelerometer adapted for the horizontal leg press and synchronized by a signal conditioning plate. Results The mean propulsive velocity significantly reduced between the first and last repetition of each series, with a similar reduction for men (-12.4 to -29.2%) and women (-29.2 to -35.6%). The same pattern was observed for the other kinetic and kinematic variables. The maximum voluntary contraction and peak force development rate also decreased for both men (-15.1 ± 8.7% and -26.9 ± 21.2%, respectively) and women (-13.9 ± 10.4% and -28.2 ± 11.5%, respectively). Conclusion Based on the different variables used to quantify the effect of fatigue during and after horizontal leg press exercises, the research found practically no differences between men and women. Level of evidence II; Comparative prospective study.