Caloric restriction diminishes the pressor response to static exercise

Area of Science:

• Cardiovascular physiology
• Autonomic nervous system function
• Spaceflight analog research

Background:

• Astronauts experience reduced calorie intake and orthostatic intolerance upon return to Earth.
• The impact of caloric deficit on autonomic cardiovascular control during spaceflight analogs is not well understood.
• Head-down bedrest simulates spaceflight conditions, allowing investigation of its physiological effects.

Purpose of the Study:

• To investigate the effects of 6° head-down bedrest with caloric restriction (CR) on autonomic neural control.
• To assess autonomic responses during static handgrip (HG) and cold pressor (CP) tests under simulated spaceflight conditions.
• To compare the combined effects of bedrest and nutritional interventions on cardiovascular autonomic regulation.

Main Methods:

• A randomized crossover study involving nine healthy young men.
• Four two-week interventions: hypocaloric ambulatory, hypocaloric bedrest, normocaloric ambulatory, and normocaloric bedrest.
• Measurements included heart rate (HR), arterial pressure, and muscle sympathetic nerve activity (MSNA) during HG, post-exercise muscle ischemia, and CP.

Main Results:

• Caloric restriction attenuated HR, MSNA, and systolic blood pressure changes during handgrip exercise.
• Post-intervention responses during post-exercise muscle ischemia were similar across all groups.
• Caloric restriction increased diastolic blood pressure during cold pressor tests, with opposing heart rate trends between bedrest and caloric restriction.

Conclusions:

• Fourteen-day caloric/fat restriction attenuated muscle sympathetic nerve activity and pressor responses during isometric exercise to fatigue.
• The metaboreflex appears to maintain its integrity under these conditions.
• The findings suggest a potential reduction in the influence of the mechanoreflex and/or central command during simulated spaceflight with caloric restriction.