Prolonged Exercise in Highly Trained Female Endurance Runners

Abstract

The effects of prolonged exercise in a 21 ^°C dry bulb and 15^°C wet bulb environment at 65%-70% V̇O₂max were examined in seven highly trained females. The subjects, aged 22-35 years, underwent an initial incremental treadmill test to exhaustion, with assessment of V̇O₂max and related cardiorespiratory variables. One week later, under similar environmental conditions, subjects ran at approximately 65% V̇O₂max for 80 min on a motor-driven treadmill. Approximately 10 ml of venous blood was withdrawn 10 min prior and immediately prior to the onset of prolonged exercise, and at 20, 40, 60, and 80 min, and 20 min post-exercise. Venous blood was analyzed for glucose, lactate, osmolality, Na⁺, K⁺, protein, and hemoglobin (Hb). Hematocrit was measured and changes in plasma volume calculated. V̇O₂, V̇_E, respiratory exchange ratio, and heart rate were recorded at 17, 37, and 77 min. The percent body fat estimated from skinfold thicknesses was 19 ± 1%. The mean V̇O₂max was 59.3 ± 1.0 ml·kg·min^-1, with a mean max V̇_E STPD and heart rate of 78.75 ± 3.10 l·min^-1 and 175 ± 4 beats·min^-1, respectively.

No significant changes occurred in V̇O₂, V̇_E, % V̇O₂max, heart rate, venous lactate, plasma glucose, or plasma protein during the prolonged exercise. A significant decrease in respiratory exchange ratio was noted. Significant changes also occurred in hematocrit, Hb, Na⁺, K⁺, and osmolality. An interesting finding was the pre-exercise expansion of the plasma volume.

Key words

V̇O₂max - prolonged exercise - females - plasma volume