Effect of Exercise Duration on Post-Exercise Hyperemia During Moderate and Heavy Intensity Handgrip Exercise

Abstract

Compared to the mean blood flow response during dynamic handgrip exercise, there is a transient overshoot in muscle blood flow early in recovery which has been used as evidence to suggest that blood flow is inadequate for the metabolic requirements of the exercise. If muscle blood flow is limited during handgrip exercise, one might reason that progressive increases in exercise duration would lead to greater increases in post-exercise blood flow, consistent with the results of post-occlusive studies. PURPOSE: To examine the effect of progressively increasing exercise duration on recovery blood velocities following moderate (MIE) and heavy intensity (HIE) handgrip exercise. METHODS: Five male subjects (30.6 ± 6.2 yrs, ± SD) participated in this study. Maximal voluntary contraction (MVC) force was determined using a handgrip dynamometer. MIE and HIE was set at 5% and 10% of each subject's MVC. Subjects exercised for either 3, 5, 7, or 9 min at a fixed duty cycle (33%). No more than 3 trials were performed each visit. Blood velocities were measured in the brachial artery at rest, during exercise, and recovery (5 min) using Doppler ultrasound. For each exercise duration and intensity, the 5 highest peak velocities during the last 15 s of exercise and the first 5 cardiac cycles after the last contraction were determined. The area under the curve (AUC) for recovery blood velocity was used as an index of total post-exercise hyperemia. RESULTS: For each exercise duration, the mean and peak blood velocities were higher (p<0.05) during HIE than MIE, as expected. Within condition comparisons indicated that peak blood velocities during exercise were higher (p<0.05) than recovery peak blood velocities; no difference was observed with increasing exercise duration. AUC was similar between exercise durations within MIE (range; 772 to 910 ml) and HIE (range; 1304 to 1575 ml). CONCLUSIONS: For handgrip exercise corresponding to 5 and 10% MVC, the peak blood velocities achieved during exercise compared to recovery are independent of exercise duration. In addition, the similar total post-exercise hyperemia in spite of increasing exercise duration suggests that the transient overshoot in blood flow during early recovery does not reflect a blood flow limitation during exercise but rather, blood flow is adequate for the metabolic requirement.