Heart rate variability in different intensities of static and dynamic exercises graded using similar heart rate

Abstract

The intensity and the type of the cardiovascular responses differ depending on the exercise type and intensity and the muscle groups involved. However, the responses in static and dynamic exercises are hardly comparable since the protocol used for grading the intensity of these exercises are different. Thus, we compared the cardiovascular autonomic responses in dynamic and static exercises of same muscle groups at increasing intensities graded using similar heart rate. 32 subjects performed dynamic and static exercises of lower limbs at 50% (HR50max) and 60% (HR60max) of their maximum achievable heart rates. Continuous ECG was recorded for 2 min during the exercise. Target heart rate specific single beat R–R intervals were extracted from the recorded ECG, and heart rate variability was determined. A factorial two way analysis of variance was conducted on the influence of two independent variables (load and exercise type) on the heart rate variability during different manoeuvres with baseline values taken as covariates. Exercise load had a main effect on HFnu and RMSSD. HFnu increased (p = 0.001) while RMSSD decreased (p = 0.025) with an increase in the exercise load. Exercise type also had a main effect on RMSSD with RMSSD being higher in dynamic exercise (p = 0.028). With increased load, LFnu decreased in dynamic exercise but was maintained in static exercise. Time domain parameter RMSSD decreases with an increase in the exercise load indicating a decrease in vagal modulation of heart rate with an increase in exercise load. RMSSD is more in dynamic exercise compared with static exercise indicating higher vagal modulation in dynamic exercise. However, increase in HFnu with exercise load may be due to the influence of increased ventilation on heart rate modulation.