Fluid replacement and glucose infusion during exercise prevent cardiovascular drift.

Area of Science:

• Exercise Physiology
• Cardiovascular Regulation
• Sports Science

Background:

• Cardiovascular drift during prolonged exercise is characterized by a decline in stroke volume and cardiac output.
• The influence of hydration status on these physiological responses is not fully understood.

Purpose of the Study:

• To investigate whether preventing dehydration through fluid replacement mitigates cardiovascular drift during endurance exercise.
• To examine the impact of hydration on stroke volume, cardiac output, and heart rate responses.

Main Methods:

• Endurance-trained subjects performed 2-hour cycling trials at 70% VO2max in a euhydrated state.
• Two conditions were tested: no fluid (NF) replacement and full fluid replacement (FR) to prevent body weight loss.
• Measurements included heart rate, stroke volume, cardiac output, oxygen uptake, and rectal temperature.

Main Results:

• In the NF trial, stroke volume declined 15% and cardiac output 7% (P<0.05), while heart rate increased 10%.
• In the FR trial, stroke volume was maintained, and cardiac output increased 7% (P<0.05) with a 5% heart rate increase.
• After 2 hours, rectal temperature was higher and stroke volume/cardiac output were lower in the NF trial compared to FR.

Conclusions:

• Preventing dehydration with adequate fluid replacement effectively prevents cardiovascular drift during prolonged exercise.
• Maintaining hydration is crucial for sustaining stroke volume and cardiac output during endurance activities.
• Dehydration exacerbates cardiovascular strain during prolonged exercise.