Influences of torque and joint angle on heart rate responses during isometric exercise in young men

Abstract

Objective: To evaluate the influence of joint angle on heart rate (HR) responses induced by isometric exercise. Method: Ten healthy men (23.8 ± 2.5 years old) underwent isometric maximum voluntary contraction (MVC) tests lasting 10 sec using an electronic dynamometer under the following experimental conditions: knee extension at angles of 60° and 90° and knee flexion at angles of 30° and 90° angles. Their HR was recorded at rest (65 sec), during MVC (10 sec) and during the recovery period (120 sec). The data on mean maximum torque (MMT) and HR variation (ΔHR) were analyzed using the Friedman test with the Dunn post-hoc test, and their correlation was analyzed using the Spearman test (α= 0.05). Results: 1) MMT was significantly higher at 60° and 90° knee extension than at 30° and 90° knee flexion (p< 0.05), while no significant differences were found between the two extension angles or between the two flexion angles; 2) ΔHR was similar under all the experimental conditions; 3) No correlation was found between MMT and ΔHR. Conclusion: The data suggest that the rapid increase in HR during the 10 sec of isometric MVC does not depend on the joint angle or the morphofunctional differences between the two muscle groups studied.