(12) IDENTIFYING SEX-DIFFERENCES IN NEUROMUSCULAR PATTERNS OF RESPONSE DURING UNILATERAL AND BILATERAL FATIGUING BODY WEIGHT SQUATS

Abstract Details: Prior studies demonstrated that during submaximal exercise, women exhibit a greater resistance to fatigue than men, however, the mechanisms mediating these differences remain unclear.

Purpose: The purpose of this study was to examine sex differences in the neuromuscular patterns of response during unilateral (UL) and bilateral (BL) bodyweight (BW) squats to failure.

Methods: This study recruited 10 males (age=24.0±4.4yrs; weight=78.1±12.5kg; hheight=176.8±5.8cm; 241.0±110.8 min of resistance exercise per week) and 9 females (age=25.8±3.3yrs; weight=68.0±9.6kg; hheight=164.3±6.4cm; 255.0±117.6 min of resistance exercise per week) to perform UL and BL BW squats at full range of motion until failure, in random order on separate days. The BW squats were completed by starting in a standing position, lowering to 90-degree knee flexion, and returning to a standing position. For the UL squats, the participants placed their non-working leg on a bench behind them. The participants squatted until volitional failure or were unable to maintain proper squat form. Electromyography (EMG) was used to assess neuromuscular excitation (EMG amplitude, AMP) and peripheral fatigue (EMG mean power frequency, MPF) of the non-dominant vastus lateralis for each repetition (reps) during the fatiguing task. Repetitions were normalized to the total repetitions to failure, and raw neuromuscular values were averaged together to generate 10% increments of time-to-task failure (TTF). The EMG AMP and EMG MPF 10% increments were then normalized to the value at 10% and examined with separate 2(Sex: Males vs Females) x 2(Condition: BL vs UL) x 10(Repetition:10-100%) mixed factorial ANOVAs. The repetitions completed were examined with a 2(Sex: Males vs Females) x 2(Condition: BL vs UL) mixed factorial ANOVA where UL represents the sum of repetitions completed by both legs.

Results: The EMG AMP results indicated no significant 3-way or 2-way interactions (p >0.05), but a significant main effect for Repetition (p< 0.001). Post-hoc pairwise comparisons demonstrated that compared to the value at 10%, the values at 30-50% (p=0.009-0.016) and 70-100%(p< 0.001-0.012) TTF were significantly greater. For EMG MPF, the results indicated no significant 3-way or 2-way interactions (p >0.05), but a significant main effect for Repetition (p< 0.001). Post-hoc pairwise comparisons demonstrated that compared to the value at 10%, 30-50% (p< 0.001) and 70%-100% (p< 0.001-0.002) TTF were significantly lower. Analysis for Repetitions completed demonstrated no Sex by Condition interaction (p=0.601) but a significant main effect for Condition (p=0.006). Post-hoc pairwise comparisons demonstrated that the participants performed significantly more repetition during the BL (282.2±281.2reps) than the UL condition (62.8±43.9reps).

Conclusion: Under submaximal conditions, men and women exhibited a similar increase in neuromuscular excitation (EMG AMP) and development of peripheral fatigue (EMG MPF) in response to submaximal fatiguing exercise. Our finding suggested that under submaximal conditions, men and women exhibited similar patterns of neuromuscular responses, regardless of exercise modality. PRACTICAL APPLICATION: Under submaximal conditions, exercise-induced fatigability may be more attributable to perception of fatigue than excitation-contraction coupling failure. Practitioners may use athletes’ ratings of perceived exertion to determine fatigability from submaximal exercise, regardless of sex.

Acknowledgements: None