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.

This investigation employed a between-participant design comparing acute and chronic changes in brain-derived neurotrophic factor (BDNF), cathepsin B (CatB), insulin-like growth factor-1 (IGF-1), and interleukin-6 (IL-6) across four resistance training (RT) protocols differing in proximity to failure, while also examining inter-biomarker correlations. Thirty-eight resistance-trained men completed an eight-week intervention, training three times per week, allocated to one of four groups based on repetitions-in-reserve (RIR): 4–6 RIR, 1–3 RIR, 0–3 RIR, and 0 RIR. Serum was collected immediately before and after training on day 1 of weeks 1 and 7. The analysis revealed the main effects of Session for BDNF and IL-6 (posterior probability > 99%), indicating exercise-induced elevation independent of proximity to failure. Additionally, CatB demonstrated a Session × Week interaction (posterior probability > 99%), indicating a difference in the acute response between week 7 and week 1. No compelling evidence emerged for IGF-1 effects, and inter-biomarker correlations were weak and inconsistent. Notably, this is the first investigation to demonstrate RT-induced transient CatB elevation. These findings suggest that exercise-induced neuroprotective biomarker responses may be achieved while training relatively far from failure, potentially avoiding the neuromuscular fatigue, injury risk, and recovery demands associated with failure training.

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.