Lower extremity vascular responses to preexercise intermittent passive stretch and treadmill exercise
Authors: Caldwell Jacob , Bekkedal Lukas , Luff Macy , Holliday Andrew , Lisowski Connor , Johnson Grace , Fenn Sarah 
Published: May 2023

Intermittent passive stretch induces local tissue hypoxia with subsequent increases in micro- and- macrovascular shear-rate, a powerful stimulus for nitric oxide generation in endothelial cells. Acute aerobic exercise stress has been associated with decreased endothelial function of the active limb. Whether intermittent passive stretch can reduce endothelial injury and improve endothelial function if performed before exercise has yet to be shown. This work investigated the impact of preexercise intermittent passive stretch on popliteal artery flow-mediated vasodilation (FMD) and the post occlusive reactive hyperemic (PORH) response within the gastrocnemius after aerobic exercise. We hypothesized that preexercise intermittent passive stretch of the calf muscles would prevent a decline in micro- and- macrovascular function after treadmill exercise. Sixteen healthy college-aged males and females participated in a single laboratory visit and underwent a PORH test with near-infrared spectrometry and FMD test to assess micro- and- macrovascular function. Participants were split into a PS group and a sham-control group performing minimal stretch. Intermittent passive calf stretching was performed by having participants place their foot in a splinting device for a 5-minute stretch, 5-minute relaxation period, repeated four times. Pre, post treatment, and post exercise time points were used in this investigation for analysis with a two-way repeated measures ANOVA and significance set at (P≤0.05). Following the treatment protocol, participants completed a VO2 peak test to calculate 65% VO2 peak and ran at this intensity for 30-minutes with post measurements taking place after a brief 10–20-minute recovery period. PORH with the NIRS revealed that microvascular responsiveness was preserved with the passive stretch group (pre: 0.053±0.009 %/s-1), (post: 0.051±0.013 %/s-1). There was a significant reduction (p=0.05) in the sham control group (pre: 0.072± 0.015 %/s-1), (post: 0.051±0.007 %/s-1) after treadmill exercise. Flow mediated vasodilation of the popliteal artery showed similar responses. In the passive stretch group, %FMD (pre: 7.58±0.88 %), (post: 6.40±1.21 %; p=0.27) and shear normalized FMD did not significantly decline after exercise (pre: 7.24E-04±1.50E-04), (post: 5.05E-04±1.25E-04; p=0.83). In the sham-control group %FMD (pre: 9.31±0.72 %), (post: 4.73±1.24 %; p<0.001) and normalized FMD were significantly reduced (pre: 1.06E-03± 1.58E-04), (post: 5.06E-04±1.97E-04; p<0.001). Passive stretch prior to acute exercise preserved popliteal artery endothelial function and gastrocnemius microvascular reperfusion. This vasoprotection was not shown in the sham-control group after acute exercise. Passive stretch is an easy low-cost method to maintain vascular function in the face of an acute exercise stress. Future work investigating adaptations to long term training when combined with preexercise stretch would be a valuable next step. University of Wisconsin- La Crosse Start up funds This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.