Instantaneous heart rate increase with dynamic exercise: central command and muscle-heart reflex contributions

Area of Science:

• Cardiovascular Physiology
• Exercise Physiology
• Autonomic Nervous System Regulation

Background:

• The cardiac autonomic nervous system's response to cycling, both volitional and passive, is not fully understood.
• Investigating R-R interval (RRI) changes provides insight into cardiac regulation during different forms of cycling.

Purpose of the Study:

• To compare the effects of volitional unloaded cycling and passively induced cycling (PC) on RRI.
• To determine if electrical stimulation enhances the cardiac response during PC.

Main Methods:

• Recorded R-R intervals from 15 healthy volunteers during volitional and passive cycling.
• Used electrical stimulation with PC in 5 participants to increase mechanoreceptor activation.
• Measured RRI changes relative to pedal movement onset using electrocardiogram and electromyography.

Main Results:

• Volitional cycling caused the largest RRI decrease (-5.4%), especially with early movement initiation.
• Passive cycling alone did not significantly affect RRI.
• Passive cycling with electrical stimulation shortened RRI (-2.5%) but only when movement began in the first third of the cycle.

Conclusions:

• Volitional cycling elicits a robust cardiac response, reflected in significant RRI shortening.
• Passive cycling requires enhanced muscle activation (via electrical stimulation) to elicit a measurable cardiac response.
• The timing of movement initiation influences the cardiac autonomic response during cycling.