Objective: To investigate heart rate response magnitudes during eccentric isokinetic exercise of the knee extensor muscles, at different angular velocities. Method: Ten healthy and active young volunteers underwent maximum eccentric contraction of the extensor muscle group of the dominant knee. An isokinetic dynamometer was used at velocities of 30º/s, 60º/s and 120º/s, randomly sequenced. The heart rate (HR) was obtained beat-by-beat, using a modified MC5 electrocardiogram lead, over 60s within the contraction, with five repetitions for each angular velocity, and over 120s after exercise effort. Mean HR for the 60s pre-exercise interval, peak HR attained at the end of exercise effort, HR variation (DHR) and peak torque were calculated. In addition, the pre-exercise mean HR over six minutes was compared with the recovery-period mean HR over six minutes. The results were compared using the Friedman and post hoc Dunn tests. The significance level was set at 5%. Results: No statistically significant differences were observed among the median values of resting HR (68bpm for 30º/s and 60º/s, 70bpm for 120º/s), peak HR (107 bpm for 30º/s, 103bpm for 60º/s and 100bpm for 120º/s), DHR (37bpm for 30º/s, 35bpmfor 60º/s and 27bpm for 120º/s) and peak torque (209.5N/m for 30º/s, 217.2N/m for 60º/s and 210.6N/m for 120º/s). The median HR values before and after exercise effort were the same (67bpm). Conclusion:The HR response magnitudes during eccentric muscular activity were similar, which indicates that the cardiac overload was the same for all the angular velocities studied.
heart rate; eccentric exercise; isokinetic; cardiovascular response; knee extensor muscles
