The Sensitivity of the Critical Resistance Model to Detect Sex-Related Differences in Fatigue During Submaximal Muscular Contractions

Abstract

Purpose Critical resistance (CR) is a fatigue threshold that, theoretically, estimates the highest sustainable resistance for repeated skeletal muscle contractions. Men are typically more susceptible to fatigue than women during sustained muscular contractions. Therefore, the purpose of this study was to compare the CR between men and women to determine the sensitivity of the CR model to detect sex-related differences in fatigue at submaximal intensities. Methods Ten men and 10 women completed one-repetition maximum (1RM) testing for the deadlift and repetitions to failure at 50%, 60%, 70%, and 80% of 1RM for the determination of CR. Repetitions to failure were then performed at the estimated CR. Results The men had a greater absolute 1RM (168 ± 27 kg vs. 115 ± 11 kg) and CR (62 ± 14 kg vs. 48 ± 6 kg), but a lower relative CR (percent of 1RM; 37 ± 6% vs. 41 ± 2%) and completed fewer repetitions at CR (45 ± 14 repetitions vs. 58 ± 12 repetitions) compared to the women. Conclusions The CR model was sensitive to detect sex-related differences in fatiguing muscular contractions of the deadlift. In addition, the men were more susceptible to fatigue than the women during performance of submaximal muscular contractions at CR, which may be related to sex-dependent physiological responses during fatiguing muscular contractions.

The Time Course of Changes in Neuromuscular Responses During the Performance of Leg Extension Repetitions to Failure Below and Above Critical Resistance in Women

“…Future studies should examine these parameters to determine the factor that differentiates the fatigue response when repetitions are performed below vs. above CR. In addition, this study examined the neuromuscular responses of women at intensities below and above CR; therefore, future studies should examine both men and women to determine whether any sex-related differences exist when repetitions are performed to failure at the CR fatigue threshold.

Practical Applications

Critical resistance is the highest sustainable resistance that can be completed for an extended number of repetitions (>35 repetitions) and is related to circulatory conditions within the working muscle (15,16,23,25). Typically, resistance training is prescribed at a relative percentage of 1RM and does not consider important factors related to submaximal performance capabilities such as individual metabolic system capacities (e.g., phosphocreatine stores and intracellular and extracellular buffering capacities) or muscle size (21).

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“…Critical resistance is the highest sustainable resistance that can be completed for an extended number of repetitions (.35 repetitions) and is related to circulatory conditions within the working muscle (15,16,23,25). Typically, resistance training is prescribed at a relative percentage of 1RM and does not consider important factors related to submaximal performance capabilities such as individual metabolic system capacities (e.g., phosphocreatine stores and intracellular and extracellular buffering capacities) or muscle size (21).…”

“…This mathematical modeling (critical force, critical power, and CR) defines the asymptotic nature of human movement capacities for power or force over time (23,24). Thus, theoretically, CR is the highest sustainable resistance that can be completed for an extended number of repetitions (.35 repetitions) and reflects the slope of the relationship between total work (resistance 3 repetitions completed 3 distance traveled) and total distance (repetitions 3 distance) completed (4,11,15,16,25,30). Previously, Monod and Scherrer (23) proposed the asymptote (critical force) for intermittent and continuous isometric contractions reflected the point of compromised blood flow because the intensity (as a % of maximal voluntary contraction) associated with the critical force was dependent on the muscle action performed (intermittent or continuous isometric contraction).…”

Applications of the Critical Power Model to Dynamic Constant External Resistance Exercise: A Brief Review of the Critical Load Test

“…to men for whole-body DCER exercises (Figure 5b,d), but not local muscle actions (Figure 5a,c), which may be related to differences in muscle size and, thus, intramuscular pressures that alter blood flow [41]. Thus, it appears the CL is specific to the muscle action (muscle group) and cadence for DCER exercise, and the modeling may also be sensitive to detect sex differences in submaximal performance capabilities.…”

“…In support of this hypothesis, the % 1RM of the CL has been shown to be greater for the whole-body deadlift exercise (~40% 1RM), where a pause between the concentric and eccentric phases resulted in an exercise more consistent with intermittent isometric exercise compared to local, bilateral leg extension exercise (~26% 1RM) without a defined pause between repetitions [36,37] (Figure 5). Furthermore, women have been shown to have a higher relative CL compared to men for whole-body DCER exercises (Figure 5b,d), but not local muscle actions (Figure 5a,c), which may be related to differences in muscle size and, thus, intramuscular pressures that alter blood flow [41]. Thus, it appears the CL is specific to the muscle action (muscle group) and cadence for DCER exercise, and the modeling may also be sensitive to detect sex differences in submaximal performance capabilities.…”