Author(s): LUBIAK, S., HOWARD, M.A., SCHMIDT, J.T., PRAJAPATI, A.J., SHAH, N.M., PATEL, N.N., HERRING, E.K., FUKUDA, D.H., STOUT, J.R., KELLER, J.L., HILL, E.C., Institution: UNIVERSITY OF CENTRAL FLORIDA, Country: UNITED STATES, Abstract-ID: 307

INTRODUCTION:
Low-intensity aerobic exercise with blood flow restriction (BFR) augments indices of the exercise pressor reflex as evidenced by increased minute ventilation (V̇E) and heart rate (HR). There is, however, less known regarding aerobic exercise with BFR performed at the gas exchange threshold (GET). The purpose of this investigation was to examine the acute effects of cycling with and without BFR at the GET.
METHODS:
Fourteen (20.0 ± 1.0 yrs; 161.4 ± 7.3 cm; 61.3 ± 10.2 kg) aerobically trained (V̇O2max = 37.6 ± 3.4 ml˙kg-1˙min-1) women first completed a graded exercise test on a cycle ergometer with a verification bout to determine the GET and confirm V̇O2max. On the following visit, participants completed 2, randomly ordered 8-minute cycling bouts. After completing a 5-minute warm-up at 50 watts (W) with a cadence of 70 revolutions per minute (rpm), participants either started their first 8-minute bout without BFR or paused briefly to allow BFR to be applied bilaterally to the upper thighs at 60% of arterial occlusion pressure. Participants were instructed to maintain 70rpm throughout and BFR was only applied during exercise. Upon completion of the first bout, participants rested for 10 minutes passively and then completed the other condition. The final 5 minutes of each 8-minute bout (i.e., minutes 4-8 indexed as 1-5) were analyzed with separate two-way, 2 (Condition [GETBFR and GETNOBFR]) × 5 (Time [1,2,3,4,5]), Bayesian multilevel models with random intercepts and slopes to examine changes in V̇E and HR. The fixed effects were reported as the 95% high-density interval (95% HDI) and mean difference (Meandiff).
RESULTS:
There were significant interactions for V̇E (95% HDI: -3.2 to -1.5) and HR (95% HDI: -2.3 to -0.7). Follow-up Bayesian paired samples t-tests between Condition at each level of Time indicated that GETBFR provoked greater V̇E (95% HDI: 0.7 to 22.6; Meandiff range = 6.9 ± 0.8 to 12.9 ± 2.2 L/min-1) and HR (95% HDI: 0.1 to 20.0; Meandiff range = 7.4 ± 0.3 to 11.6 ± 1.0 bpm) responses at each time point than GETNOBFR. Follow-up simple main effects of Time at each level of Condition indicated that there were increases in V̇E during GETBFR between 1 vs 5 min (95% HDI: -20.6 to -0.4; Meandiff = 10.4 ± 1.8 L/min-1), but no changes during GETNOBFR. Additionally, HR increased from 1 to 4 and 5 min for GETBFR (95% HDI: -19.0 to -2.9; Meandiff = 10.9 ± 0.4 bpm and 95% HDI: -22.0 to -4.6; Meandiff = 13.2 ± 0.8 bpm, respectively) and GETNOBFR (95% HDI: -14.5 to -1.2; Meandiff = 7.7 ± 0.1 bpm and 95% HDI: -15.7 to -2.3; Meandiff = 8.9 ± 0.1 bpm, respectively).
CONCLUSION:
Applying BFR during an acute cycling bout at the GET increased V̇E and HR relative to cycling at the GET without BFR. These responses were likely attributable to a BFR-induced activation of group III/IV muscle afferent nerve endings which are sensitive to mechanical and metabolic perturbations thereby augmenting indices of the exercise pressor reflex.