Vascular volume changes during cycling and stepping in women at two hydration levels

Summary

Five female Caucasians were studied in a hot, wet environment (32.2‡ C dry bulb, 30‡ C wet bulb) during both cycle ergometer exercise and block stepping at exercise intensities (30–40% of the subjects's $\dot V$O₂ max) which produced similar heart rates. During each type of exercise, the women were studied once following 24 h water deprivation and once 60 min after ingestion of an amount of water equal to 1% of their body weight. Venous blood samples were obtained before, and at 10 min intervals during each of the four 60-min exercise sessions. Hemoconcentration and osmoconcentration were observed during both types of exercise, with more rapid increases in these variables occurring during ergometer exercise compared to block stepping. While the fluid status manipulation was effective in altering the pre-exercise osmolalities by an average of 9 mosmol·kg⁻¹, it had little effect on vascular volume dynamics during either type of exercise. Similarly, increases in heart rate and body temperature during exercise were not altered by the water balance of the subject. The pattern of vascular volume changes during exercise in women, therefore, seems more sensitive to exercise mode than to pre-exercise water balance.