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 plus or minus 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 ( Delta HR) 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: Delta HR showed higher values in MVC-10 versus MVC-5 (17 plus or minus 5.5 vs 12 plus or minus 4.2 bpm, p