Maximal oxygen uptake relative to plasma volume expansion

Area of Science:

• Exercise Physiology
• Sports Science
• Cardiovascular Research

Background:

• Debate exists regarding the impact of plasma volume (PV) expansion on maximal oxygen uptake (VO2max).
• Understanding the relationship between PV, stroke volume, and VO2max is crucial for optimizing athletic performance.

Purpose of the Study:

• To investigate the effects of two levels of plasma volume expansion on VO2max and exercise time to fatigue in untrained men.
• To determine if there is an optimal level of PV expansion for enhancing VO2max.

Main Methods:

• Nine untrained men underwent measurements of VO2max and exercise time to fatigue.
• Plasma volume was expanded using intravenous infusion of 6% dextran solution to two levels: PVX-1 (282 ml) and PVX-2 (624 ml).
• Stroke volume and hemoglobin concentration were monitored during exercise.

Main Results:

• PVX-1 significantly increased stroke volume (15%) and VO2max (4%) compared to normal levels, despite a slight reduction in hemoglobin.
• Exercise time to fatigue also increased following PVX-1.
• PVX-2 led to a greater reduction in hemoglobin (11%) and a return of VO2max and exercise time to normal levels.

Conclusions:

• Moderate plasma volume expansion (200-300 ml) can enhance VO2max and exercise performance in untrained men by increasing stroke volume with minimal hemodilution.
• Excessive plasma volume expansion (500-600 ml) results in significant hemodilution, negating performance benefits and returning VO2max to baseline levels.
• An optimal plasma volume exists for maximizing VO2max in untrained individuals, estimated to be 200-300 ml above their normal levels.