Heart rate responses during isometric exercises in patients undergoing a phase III cardiac rehabilitation program.

BACKGROUND the magnitude of cardiovascular responses is dependent on the static and dynamic components as well as the duration and intensity of the contraction performed. OBJECTIVE to evaluate the heart rate responses to different percentages of isometric contractions in 12 patients (63 ± 11.6 years) with coronary artery disease and/or risk factors for coronary artery disease that were participating in a phase III cardiac rehabilitation program. METHODS heart rate variation (ΔHR) was evaluated during maximum (MVC, five and ten seconds in duration) and submaximal (SMVC, 30 and 60% of MVC-5, until muscle exhaustion) voluntary contraction, using a handgrip dynamometer. Additionally, the representative index of cardiac vagal modulation (RMSSD index) was calculated at rest (pre-contraction), at the final 30 seconds of SMVC and during recovery (post-contraction). RESULTS ΔHR showed higher values in MVC-10 versus MVC-5 (17 ± 5.5 vs 12 ± 4.2 bpm, p<0.05) and the SMVC-60 vs SMVC-30 (19 ± 5.8 vs 15 ± 5.1 bpm, p<0.05). However, results for CVM-10 showed similar ΔHR compared to results for CVSM (p> 0.05). RICVM at rest decreased (p<0.05) during SMVC-30 (30% = 27.9 ± 17.1 vs 12.9 ± 8.5 ms) and SMVC-60 (60% =25.8 ± 18.2 vs 9.96 ± 4.2 ms), but returned to the baseline values when the contraction was interrupted. CONCLUSIONS in patients with coronary artery disease and/or risk factors for coronary heart disease, low intensity isometric contraction, maintained over long periods of time, presents the same effect on the responses of HR, compared to a high intensity or maximal isometric contraction of briefly duration.