Muscle Oxygenation, Performance, and Perceived Fatigability During Low-Intensity Isometric Exercise: Effects of Anchoring Strategy, Blood Flow Restriction, and Sex

ABSTRACT: Kwak, M, Benitez, B, Mitchinson, CJ, Snell, ER, and Bergstrom, HC. Muscle oxygenation, performance, and perceived fatigability during low-intensity isometric exercise: Effects of anchoring strategy, blood flow restriction, and sex. J Strength Cond Res XX(X): 000-000, 2025-This study investigated the effects of low-intensity isometric exercise modality and sex on muscle oxygen saturation (SmO2), rating of perceived exertion (RPE), pain, performance fatigability (PF; change in maximal voluntary isometric contraction), and time to task failure (TTF). Fifteen healthy men (22.7 ± 4.7 years) and 15 women (22.5 ± 4.4 years) completed 3 isometric exercise conditions: (a): RPE-Clamp at RPE = 3, (b) torque-matched blood flow restriction (BFR), and (c) torque-matched NON-BFR. No significant differences in TTF (p = 0.198) were found across conditions or between sexes. SmO2 was generally highest in the RPE-Clamp condition and lowest in BFR. At task failure during BFR, men exhibited significantly lower SmO2 than women (p = 0.001), though no sex differences were found at other time points or in other conditions. Rating of perceived exertion and pain increased significantly over time in both BFR and NON-BFR conditions (p < 0.001), regardless of sex. Performance fatigability was significantly greater in BFR and NON-BFR than in RPE-Clamp (p < 0.01), with no difference between BFR and NON-BFR (p = 1.000). Men demonstrated greater PF than women in BFR (p = 0.001) and NON-BFR (p = 0.011), but not in RPE-Clamp (p = 0.720). These findings suggested that BFR exercise performed with sustained isometric contractions under relatively moderate cuff pressure may not induce greater fatigability than NON-BFR exercise. However, fatigability may be influenced by sex-related differences in absolute target torque. Although the RPE-Clamp condition, characterized by lower muscular stress and fatigability, may represent a viable option for clinical and early-rehabilitation settings, its training efficacy requires further investigation.