Muscular contraction mode differently affects autonomic control during heart rate matched exercise

Area of Science:

• Exercise Physiology
• Autonomic Nervous System Regulation
• Cardiovascular and Respiratory Control

Background:

• The role of afferent feedback in exercise-induced cardiovascular and respiratory adjustments is not fully understood.
• Understanding autonomic control differences between exercise types is crucial for exercise prescription and understanding physiological responses.

Purpose of the Study:

• To compare autonomic cardiovascular and respiratory control during dynamic (DYN) and isometric (ISO) contractions at a similar low heart rate (HR).
• To investigate differences in physiological responses and heart rate variability (HRV) between DYN and ISO exercise.

Main Methods:

• A crossover study involving 22 healthy males performing voluntary DYN and ISO contractions of the quadriceps femoris muscle.
• Measurements included HR, blood pressure, rate pressure product, breathing frequency, minute ventilation, gas exchange, blood lactate, and HRV (SDNN, HF-Power, LF-Power, Sample Entropy).

Main Results:

• Despite equivalent HR (82 ± 8 bpm), ISO resulted in higher rating of exertion, blood pressures, and rate pressure product.
• Breathing frequency, minute ventilation, oxygen uptake, and carbon dioxide output were significantly lower during ISO.
• HRV analysis revealed significantly higher SDNN, HF-Power, and LF-Power during ISO, suggesting increased vagal and sympathetic influences and sympatho-vagal coactivation.

Conclusions:

• Cardiovascular control quality significantly differs between DYN and ISO exercise, even with similar HR.
• HRV analysis indicates a sympatho-vagal coactivation during ISO exercise.
• Further research is needed to determine the primary contributors (mechanoreceptor feedback, central command, or their interaction) to these distinct autonomic responses.