The study and application of the critical power (CP) concept has spanned many decades. The CP test provides estimates of two distinct parameters, CP and W′, that describe aerobic and anaerobic metabolic capacities, respectively. Various mathematical models have been used to estimate the CP and W′ parameters across exercise modalities. Recently, the CP model has been applied to dynamic constant external resistance (DCER) exercises. The same hyperbolic relationship that has been established across various continuous, whole-body, dynamic movements has also been demonstrated for upper-, lower-, and whole-body DCER exercises. The asymptote of the load versus repetition relationship is defined as the critical load (CL) and the curvature constant is L′. The CL and L′ can be estimated from the same linear and non-linear mathematical models used to derive the CP. The aims of this review are to (1) provide an overview of the CP concept across continuous, dynamic exercise modalities; (2) describe the recent applications of the model to DCER exercise; (3) demonstrate how the mathematical modeling of DCER exercise can be applied to further our understanding of fatigue and individual performance capabilities; and (4) make initial recommendations regarding the methodology for estimating the parameters of the CL test.

Fatigability varies depending on sex and contraction intensity during sustained exercise. This study examined the responses of time to task failure (TTF), performance fatigability (PF), and muscle oxygenation (SmO₂) in males and females during isometric handgrip holds to failure (HTF) at 30% and 60% maximum voluntary isometric contraction (MVIC). Males ( n = 12) and females ( n = 12) performed a pre-MVIC, handgrip HTF at randomly ordered percentages of MVIC (either 30% or 60%), followed by a post-MVIC on the dominant arm. During the HTF testing, the TTF and SmO₂ responses were recorded, and PF was determined from the pre- to post-MVICs. TTF for 30% MVIC HTF was greater than 60% MVIC HTF ( p < 0.001), but was not different between males and females ( p = 0.117). PF exhibited an inverse relationship with intensity for each sex, while males demonstrated greater PF than females for both 30% and 60% MVIC HTF. For the 60% MVIC HTF, males demonstrated greater desaturation than females (CI_95% = [−28.1, −2.6%], p = 0.021, d = 0.621), but not for the 30% MVIC HTF (CI_95% = [−12.2, 7.9%], p = 0.315, d = 0.621). Sex differences in PF and SmO₂ may be attributed to the differences in muscle mass, absolute strength, contractile properties, and muscle metabolism between males and females. However, these proposed differences between males and females may not fully inform exercise performance (e.g., TTF). Sex-specific fatigue responses may be affected by complex physio-psychological mechanisms, and therefore, additional investigations under diverse exercise conditions are required to better prescribe exercise for both males and females.

This study investigated the effects of fatiguing unilateral exercise on the ipsilateral, exercised, and contralateral, non-exercised limb’s post-exercise performance in males and females. Ten males and ten females performed a fatiguing, unilateral isometric leg extension at 50% maximal voluntary isometric contraction (MVIC) force. Prior to and immediately after the fatiguing tasks, MVICs were performed for the exercised and non-exercised limb, with surface electromyographic (sEMG) and mechanomyography (sMMG) amplitude (AMP) and mean power frequency (MPF) recorded from each limb’s vastus lateralis. There were no fatigue-induced, sex-dependent, differences in time to task failure (p = 0.265) or ipsilateral performance fatigability (p = 0.437). However, there was a limb by time interaction (p < 0.001) which indicated decreases in MVIC force of the ipsilateral, exercised (p < 0.001), but not the contralateral, non-exercised limb (p = 0.962). There were no sex-dependent, fatigue-induced differences in neurophysiological outcomes between the limbs (p > 0.05), but there was a fatigue-induced difference in sEMG MPF (p = 0.005). To summarize, there were no differences in fatigability between males and females. Moreover, there was insufficient evidence to support the presence of a general crossover effect following submaximal unilateral isometric exercise. However, independent of sex, the neurophysiological outcomes suggested that competing inputs from the nervous system may influence the performance of both limbs following unilateral fatigue.

Purpose: A square-wave verification bout to confirm maximal oxygen uptake (V̇O_2max) from a graded exercise test (GXT) has been recommended based on mean responses. This study used the test–retest reliability, mean, and individual differences between the highest V̇O₂ from the GXT (V̇O_2GXT) and verification bout (V̇O_{2verification}) to examine the efficacy of a verification bout in the determination of O_2max in healthy, recreationally trained, well-motivated men. Methods: Ten men (24 ± 4 yr) completed a GXT on a cycle ergometer followed by a submaximal verification bout to determine V̇O_2GXT and V̇O_{2verification}. After completion of the initial GXT, subjects rested for 5 min then performed the verification bout at 90% of the peak power output from the initial GXT. Analyses included a two-way repeated-measures ANOVA, intraclass correlation coefficients (ICC_2,1), standard errors of the measurement (SEM), minimal differences (MD), and coefficients of variation (COV). Results: There was no test (test 1 vs test 2)–method (GXT vs verification) interaction (P = 0.300) and no main effect for test (P = 0.690), but there was a main effect for method (P = 0.003). The V̇O_2GXT (46.0 mL⋅kg⁻¹⋅min⁻¹) was significantly greater than V̇O_{2verification} (43.9 mL⋅kg⁻¹⋅min⁻¹), collapsed across test. The V̇O_2GXT (ICC = 0.970, SEM = 1.63 mL⋅kg⁻¹⋅min⁻¹, MD = 4.51 mL⋅kg⁻¹⋅min⁻¹, COV = 3.54%) and the V̇O_{2verification} (ICC = 0.953, SEM = 1.87 mL⋅kg⁻¹⋅min⁻¹, MD = 5.17 mL⋅kg⁻¹⋅min⁻¹, COV = 4.25%) demonstrated “excellent” reliability. No subject exceeded the MD test–retest for V̇O_2GXT or V̇O_{2verification}. No subject had a V̇O_{2verification} that exceeded V̇O_2GXT by more than the MD, but two subjects had a V̇O_2GXT, which exceeded V̇O_{2verification} by more than the MD. Conclusions: The excellent reliability of V̇O_2GXT in addition to the examination of the individual differences between V̇O_2GXT and V̇O_{2verification} using the MD indicated that a standalone GXT was sufficient to determine V̇O_2max.