(52) EFFECT OF ISOMETRIC FATIGUING TASK MODALITY ON PERFORMANCE FATIGABILITY AND REACIVE HYPEREMIA RESPONSES

Purpose: The near-infrared spectroscopy-derived reperfusion slope provides a direct assessment of skeletal muscle reperfusion rate, a key microvascular response associated with exercise capacity and overall cardiovascular health. This study aimed to compare performance fatigability (PF) and reactive hyperemia (RH) responses following three distinct isometric fatiguing task conditions. Methods: Fourteen males (22.6±4.9yr, 178.2±6.2cm, 78.6±9.9kg) and fourteen females (22.7±4.5yr, 163.0±6.3cm, 62.5±10.2kg) completed the following three isometric forearm flexion hold-to-failure tasks at an elbow joint angle of 100° on separate days: (1) a task anchored to a rating of perceived exertion of 3 (RPE-clamp), (2) a task anchored to a constant torque corresponding to the first 1-sec torque level (T_1sec) during the RPE-clamp trial (non-blood flow restriction [BFR]), and (3) a task performed at the same torque level as non-BFR trial but with BFR at 40% arterial of occlusion pressure. Vascular occlusion tests (VOTs) and maximal voluntary isometric contractions (MVICs) were assessed pre- and post-task to evaluate RH and PF, respectively. The VOT included a 2-min baseline rest period, followed by 5-min of complete occlusion and a 3-min reperfusion phase. RH was assessed as the resaturation slope (%·s^-1) within the first 10-sec after cuff deflation. PF was quantified as the percent change in MVIC from pre- to post-fatigue. Separate, mixed factorial ANOVAs were used to examine RH (condition x sex x time) and PF (condition x sex), with Bonferroni post hoc t-tests. An independent t-test compared T_1sec between sexes. Results: RH showed no significant three- or two-way interactions, main effects for time or sex. However, a main effect for time (p< 0.001) indicated lower RH during post-VOT (4.3±1.6 %·s^-1) than pre-VOT (5.2±1.9%·s^-1). For PF, there was no significant condition x sex interaction, but significant main effects for condition (p< 0.001) and sex (p=0.006) were observed. PF was greater (p< 0.001) in BFR (-31.3±14.7%) and non-BFR (-30.9±14.7%) compared to the RPE-clamp (-14.1±7.9%), with no significant difference between BFR and non-BFR conditions. Additionally, males (-30.3±15.4%) exhibited greater PF than females (-20.6±13.1%), and the T_1sec was also greater (p< 0.001) in males (23.7±8.6 N·m) than females (12.0±6.3 N·m). Conclusions: The ability to adjust force level to maintain an “easy” perceptual intensity during RPE-clamp task likely resulted in the lower PF compared to constant-force conditions (both BFR and non-BFR). The greater absolute torque level (T_1sec) in males than females likely led to greater intramuscular pressure, blood flow restriction, and increased metabolite accumulation, ultimately resulting in greater PF. However, regardless of the exercise intervention, the post-exercise attenuation of RH compared to pre-exercise may reflect the distinct characteristics of isometric fatiguing exercise, which restricts reperfusion during exercise and promotes the further accumulation of intramuscular metabolites across all three conditions. This may have continuously triggered the metaboreflex, leading to increased sympathetic activity, vasoconstriction, and peripheral resistance. Practical Applications: Isometric fatiguing exercise inherently leads to accumulation of intramuscular metabolites; however, the additional external occlusion in the BFR condition may not further influence post-exercise microvascular function. Acknowledgements: None