Exercise responses to heart rate clamped cycling with graded blood flow restriction

Objectives: To quantify the acute effects of graded blood flow restriction on the interaction between changes in mechanical output, muscle oxygenation trends and perceptual responses to heart rate clamped cycling.Design: Repeated measures.Methods: Twenty-five adults (21 men) performed six, 6-min cycling bouts (24 min of recovery) at a clamped heart rate corresponding to their first ventilatory threshold at 0 % (unrestricted), 15 %, 30 %, 45 %, 60 % and 75 % of arterial occlusion pressure with the cuffs inflated bilaterally from the fourth to the sixth minute. Power output, arterial oxygen saturation (pulse oximetry) and vastus lateralis muscle oxygenation (near-infrared spectroscopy) were monitored during the final 3 min of pedalling, whilst perceptual responses (modified Borg CR10 scales) were obtained immediately after exercise.Results: Compared to unrestricted cycling, average power output for minutes 4-6 decreased exponentially for cuff pressures ranging 45-75 % of arterial occlusion pressure (P < 0.001). Peripheral oxygen saturation averaged similar to 96 % across all cuff pressures (P = 0.318). Deoxyhemoglobin changes were larger at 45-75 % versus 0 % of arterial occlusion pressure (P < 0.05), whereas higher total haemoglobin values occurred at 60-75 % of arterial occlusion pressure (P < 0.05). Sense of effort, ratings of perceived exertion, pain from cuff pressure, and limb discomfort were exaggerated at 60-75 % versus 0 % of arterial occlusion pressure (P < 0.001).Conclusions: Blood flow restriction of at least 45 % of arterial occlusion pressure is required to reduce mechanical output during heart rate clamped cycling at the first ventilatory threshold. Whilst power decreases non-linearly above this pressure threshold, higher occlusion levels ranging 60-75 % of arterial occlusion pressure also accentuate muscle deoxygenation and exercise-related sensations.(c) 2023 The University of Western Australia. Published by Elsevier Ltd on behalf of Sports Medicine Australia. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).