This study examined post-occlusive reactive hyperemia (PORH) and muscle metabolic responses via near-infrared spectroscopy-vascular occlusion tests (NIRS-VOT) under four experimental conditions: (1) rating of perceived exertion (RPE)-Clamp, (2) blood flow restriction (BFR), (3) NON-BFR, each involving low-intensity, sustained isometric forearm flexion, and (4) PASSIVE BFR, a passive occlusion without exercise. Eighteen healthy young adults (11 males, 7 females) completed a sequence of pre-VOT, an experimental intervention, and post-VOT on separate days. During each intervention, time to task failure (TTF), percent changes in muscle oxygenation (SmO ₂ ), and performance fatigability (PF) were also assessed. RPE-Clamp exhibited a significant, positive change in SmO ₂ compared to negative changes in other conditions ( p < 0.003). PF did not differ between NON-BFR and BFR ( p = 1.000), but both were greater than RPE-Clamp and PASSIVE BFR, with RPE-Clamp greater than PASSIVE BFR ( p = 0.022). No differences were observed in TTF across conditions ( p = 0.455). Desaturation rate (oxygen extraction rate; slope 1) ( p < 0.001) and ischemic stimulus (MinSmO ₂ ) ( p = 0.001) were greater pre- than post-VOT. Reperfusion slope (slope 2) showed no significant differences by time ( p = 0.119) or condition ( p = 0.448). Peak SmO ₂ (MaxSmO ₂ ) was higher pre- than post-VOT ( p = 0.017), with NON-BFR ( p < 0.001) and BFR ( p = 0.005) greater than PASSIVE BFR. Area under the curve (AUC) above baseline SmO ₂ did not differ by time ( p = 0.695) but was greater in NON-BFR than PASSIVE BFR ( p = 0.010). Despite the distinct SmO ₂ responses and fatigue profiles across conditions, immediate post-intervention occlusion following prolonged isometric exercise or occlusion may have reduced oxygen extraction capacity and facilitated metaboreflex-induced sympathetic overactivity, collectively attenuating PORH.

Background: Surface mechanomyographic (sMMG) signals have been used to examine sex-specific differences in the mechanical behavior of muscle during fatiguing exercise. However, studies often utilize simple amplitude- and frequency-based analyses, which only reveal the static components of the sMMG signal. Methods: Thus, a wavelet-based analysis was used to examine changes in the spectral intensity of the non-dominant limb’s vastus lateralis during a fatiguing, maximal, unilateral isometric leg extension in recreationally active men (n = 11) and women (n = 10). Relative changes in spectral intensities and instantaneous mean frequency (IMF) were examined using linear mixed-effect models. Time-to-task failure was compared using an independent sample t-test. Results: The neuromuscular responses demonstrated parallel decreases in IMF (p < 0.001). Further, there were parallel, nonlinear, decreases in spectral intensity across wavelets (p < 0.001) and there were no sex differences in time-to-task failure (p = 0.15). Conclusions: These data showed no sex-specific differences in exercise fatigability or muscle mechanics during fatiguing exercise of the leg extensors. However, when collapsed across sex, wavelet-specific changes in spectral intensity over time reveal novel insights into the interplay between low- and high-frequency components during fatigue.

Recommendations for endurance exercise prescription are often based on percentages of heart rate (HR) or the volume of oxygen consumption ($\dot{\mathrm{V}}$O₂) maximum or reserve that is extrapolated to a power output (P) or velocity. Previous work has demonstrated dissociations of the expected responses to exercise anchored to the critical heart rate (CHR) compared with the P associated with CHR. However, it is unclear if similar dissociations due to reductions in P to maintain the designated intensity would be present during exercise anchored to the $\dot{\mathrm{V}}$O₂ associated with CHR ($\dot{\mathrm{V}}$O₂CHR). The purpose of this study was to examine the patterns in physiological ($\dot{\mathrm{V}}$O₂, HR, P, respiration rate [RR], muscle oxygen saturation [%SmO₂]), neuromuscular (electromyographic and mechanomyographic amplitude [EMG AMP, MMG AMP], mean power frequency [EMG MPF, MMG MPF]), and perceptual (rating of perceived exertion [RPE]) responses during exercise at $\dot{\mathrm{V}}$O₂CHR ($\dot{\mathrm{V}}$O₂-clamp). On separate days, ten participants (age: 25 ± 4 yr) performed a graded exercise test and four constant P trials at 85–100% of peak P (PP) to derive CHR and $\dot{\mathrm{V}}$O₂CHR. Responses were recorded during a trial to exhaustion at $\dot{\mathrm{V}}$O₂CHR (32.86 ± 7.12 mL·kg⁻¹·min⁻¹; T_Lim = 31.31 ± 21.37 min) and normalized in 10% intervals of T_Lim to their respective values at PP. The one-way repeated-measures ANOVA with post hoc, Bonferroni-corrected, pairwise comparisons indicated differences (p < 0.001) from baseline for HR (mean ± SD %change = 8 ± 3%), RR (43 ± 38%), P (−15 ± 5%), EMG MPF (10 ± 8%), and RPE (65 ± 38%), but no differences (p = 0.077–0.955) for %SmO₂ (−17 ± 53%), EMG AMP (−3 ± 16%), MMG AMP (40 ± 61%), and MMG MPF (1 ± 7%). The loss in performance observed during $\dot{\mathrm{V}}$O₂-Clamp exercise may provide a quantification of the inefficiency associated with the $\dot{\mathrm{V}}$O₂ slow component phenomenon. The neuromuscular responses suggested constant muscle excitation despite the reductions in P, but the metabolic and perceptual responses suggested a combination of feedforward and feedback mechanisms regulating T_Lim. Future studies should further examine responses to the $\dot{\mathrm{V}}$O₂-Clamp exercise at a uniform threshold.

Background: Fatigue thresholds such as the gas exchange threshold (GET) and respiratory compensation point (RCP) describe unique physiological responses. This study investigated the reliability of, and sex-dependent responses for, the GET and RCP across absolute, relative, and normalized expressions of volume of oxygen consumption ($\dot{\mathrm{V}}$O₂), power output (PO), heart rate (HR), and rating of perceived exertion (RPE). Methods: A test–retest graded exercise test (GXT) protocol was conducted on healthy, recreationally trained males (n = 9) and females (n = 9) to determine the GET and RCP ($\dot{\mathrm{V}}$O₂). Linear regression was used to identify the PO, HR, and RPE at the GET and RCP. Separate 2 [test (1, 2)] × 2 [sex (male, female)] mixed-model analysis of variance (ANOVA) examined systematic error across test and sex (p > 0.05). Separate reliability analyses were conducted for each variable for males and females using intraclass correlation coefficients (ICC_2,1), minimal differences (MDs), standard errors of measure (SEMs), and coefficients of variation (CVs). Results: Absolute and relative expression of PO and $\dot{\mathrm{V}}$O₂ at the GET and RCP reflected “excellent” relative reliability (R = 0.816–0.978) across sex. Absolute and normalized expression of HR and RPE at the GET and RCP demonstrated “good” to “poor” relative reliability (R= −0.093–0.886) across sex. The SEMs and MDs were relatively small with CVs at or below 10% across thresholds. Absolute PO and $\dot{\mathrm{V}}$O₂ for the GET and RCP were greater for males than females, while females demonstrated greater normalized RCP as well as absolute and normalized HR and RPE at the RCP. Conclusions: Although the relative reliability for HR and RPE at the GET and RCP was, in some cases, limited, these variables demonstrated acceptable absolute reliability and, therefore, have applicability to monitor and prescribe exercise intensities. Current exercise prescription techniques may neglect the unique sex-dependent perceptual and cardiovascular responses at the GET and RCP.