(12) BLOOD FLOW RESTRICTION AMPLIFIES BIOMARKER AND CARDIOVASCULAR RESPONSES TO RESISTANCE EXERCISE IN RESISTANCE-TRAINED MEN

Few published data exist on how continuous lower-limb blood flow restricted resistance exercise (BFR+RE) alters the acute physiology of well-trained men. Measurement of stress biomarkers, metabolic factors, and cardiovascular metrics would provide insight into BFR+RE’s hemodynamic, endocrine, and metabolic effects.

Purpose: Measure salivary cortisol (sCort) and alpha-amylase (sAA) activity, blood lactate (bLa), heart rate (HR), systolic blood pressure (SBP), and diastolic blood pressure (DBP) during passive occlusion (pBFR), BFR resistance exercise (BFR+RE), and volume-matched free-flow resistance exercise (RE).

Methods: Eighteen resistance trained men (x̄±SD: age=23.8±3.5yr; relative back squat 1RM: 1.9±0.3kg•kg^-1bw) reported for anthropometric, back squat and leg extension one-repetition maximum (1RM) testing. Resting systolic blood pressures and proximal thigh circumferences were used to estimate full arterial occlusion pressure (eAOP). Visit two involved pBFR, where pneumatic BFR cuffs were inflated to 80% eAOP on participants’ proximal thighs for 10-minutes while seated in a leg extension machine. Then, 24-120hr later participants performed four sets of bilateral seated leg extensions at 30% 1RM for four sets to momentary task failure with 1-minute rest using the same 80% eAOP. After 72-120hr, participants matched the repetition performances from BFR+RE in the volume-matched, free-flow resistance exercise condition. A chest-strap HR monitor was worn for continuous monitoring, with blood pressure (BP) taken pre-exercise, immediately after each set, then 5 and 10min post- for all conditions. BP was measured at 2.5, 5, 7.5, and 10min during pBFR. Biomarkers bLa, sCort, and sAA were sampled pre-exercise, immediately post-, then 5 and 15min post- for all conditions. RMANOVA’s compared all variables, with Tukey’s HSD post-hocs. sCort and sAA were square root transformed to correct for non-normality. Significance was set a priori at p≤.05.

Results: All conditions elicited increases in HR above baseline, with BFR+RE greater than RE (p≤.05). Within-condition elevations in SBP only occurred during BFR+RE and RE (p≤.05), with no differences between the two. All conditions increased DBP above baseline, with higher values during BFR+RE than RE. Biomarker data are presented in Figure 1.

Conclusions: Compared to pBFR and RE, BFR+RE appears to have significantly amplified the acute autonomic nervous system (ANS) and hypothalamic-pituitary-adrenal (HPA) axis activity during resistance exercise as significantly greater sAA activity and sCort concentrations were present. There was no bLa response to pBFR, but when BFR is combined with RE (BFR+RE) greater bLa responses occurred than RE alone. Future work comparing BFR+RE to heavy load training (70% 1RM) is warranted. PRACTICAL APPLICATIONS: Applying BFR to low-load, lower body resistance exercise amplifies the acute metabolic and stress responses to training in men of a higher resistance training status.

Acknowledgements: The authors would like to acknowledge the support of this work by the Wu Tsai Human Performance Alliance and the Joe and Clara Tsai Foundation.