The effects of a single sprint interval training session on the rapid onset vasodilation response to a single contraction

Abstract

The blood flow increase at the onset of exercise is due to rapid onset vasodilation (ROV) and can impact exercise tolerance. Potassium (K+) released from skeletal muscle fibres and muscle contraction-induced mechanical compression of arterioles are primary mechanisms of ROV linking contraction strength to ROV magnitude. Whether a single sprint interval training (SIT; essentially maximal effort exercise) session increases the ROV response at exercise onset remains unknown. We tested the hypothesis that a single SIT session would increase ROV. Twelve participants (20.72  2.7 yrs, 6F) performed single, 2-sec forearm contractions at 20%, 40%, and 60% of maximal voluntary contraction (MVC) force prior to and 10 minutes following forearm SIT and matched duration rest. The SIT session consisted of 8 x 20-sec maximal rhythmic (2-sec contraction/2-sec relaxation) forearm exercise with 10-sec rest intervals. Forearm blood flow (FBF; Doppler and echo ultrasound), muscle excitation (EMG; electromyography), and arterial blood pressure (ABP; finger photoplethysmography) were measured. Forearm vascular conductance (FVC), which quantifies vasodilation, was calculated as FBF/MAP x 100. Results are mean ± SD. Peak increase in FVC (ml·min−1·100 mmHg−1) following a single contraction was greater Post vs. Pre for SIT at all contraction intensities (20% MVC 181.9 ± 58.9 vs. 118.2 ± 54.6; 40% MVC 264.6 ± 83.6 vs. 192.7 ± 39.5; 60% MVC 323.7 ± 99.4 vs. 230.1 ± 61.8; all P<0.05). There was no Post vs. Pre difference for control. Contraction impulse was not different Post vs. Pre within or between SIT and Control (all P>0.05). In contrast, muscle excitation (EMG, % of maximal millivolt (mV) muscle excitation) during single contraction was greater Post vs. Pre in all contraction intensities for SIT (20% MVC 24.2% vs. 18.0%; 40% MVC 48.7% vs. 38.7%; 60% MVC 69.0% vs. 56.0%, all P<0.05) and at 40%, but not 20% or 60% MVC, for control (40% MVC 48.7% vs. 36.2%, P<0.05; 20% MVC 19.38% vs. 21.35%, P>0.05; 60% MVC 57.09% vs. 56.62%, P> 0.05). In conclusion, a single SIT session of forearm exercise increases ROV. A greater EMG response to achieve the same contraction impulse post SIT suggests lingering fatigue may necessitate increased muscle excitation to achieve contraction impulse. This may implicate a greater muscle fibre release of K+ (a vasodilator) as the mechanism for increased ROV following a single session of SIT.