Plasma volume and renal function during and after ultramarathon running.

Plasma volume (PV) and renal function were studied in eight subjects for 3 d prior to and 6 d after a 56 km footrace. Immediately following the race, PV, creatinine clearance, and urine flow were unchanged from pre-race values. Over the subsequent 3 d, PV increased due initially to a 17 g influx of serum albumin and an associated increase in plasma sodium content, which persisted throughout the study period. A reduction in urine sodium secretion occurred during the race day. Creatinine clearance increased after the race and remained elevated for 48 h. Increases serum enzyme activities, C-reactive protein concentration, serum uric acid content, and plasma creatinine concentration and production suggest muscle damage. We suggested the following. First, the persistent post-exercise plasma volume expansion is initiated by an influx of albumin into the intravascular space with an associated increase in plasma sodium content. A decrease in urine sodium excretion during the race day would contribute to the latter. Second, the interpretation of post-race changes in serum constituents must take account of changes in plasma volume. Third, there is an increase in creatinine clearance, indicating an increase in glomerular filtration rate, after both standard and ultramarathon running. This may be caused by the products of muscle cell damage although the physiologic mechanism for this is unclear.

Assessment of the 2.4 km run as a predictor of aerobic capacity.

Since the 2.4 km run time test is routinely used in military training programmes as an indicator of aerobic capacity and its possible improvement, an attempt was made to: (i) establish a regression equation of VO2max v. 2.4 km run time in a group of 20 young military volunteers; and (ii) determine whether this equation could be used to predict VO2max reliably from the 2.4 km time obtained from another group. Before and after training, VO2max was measured in all subjects using a treadmill test, and 2.4 km run time was determined in the field. Linear regression equations using the 2.4 km run time as the independent variable accounted for 76-92% of the variance in VO2max, while the standard error of the estimate varied from 2.24-2.91 ml/kg/min. In the second test group, the directly measured VO2max was 59.89 +/- 0.99 ml/kg/min, while the mean value estimated from the regression equation of the first group was 59.61 +/- 1.16 ml/kg/min (P less than 0.001). It was concluded that, in the population studied, the 2.4 km run time in the field reliably predicts VO2max measured during treadmill exercise in the laboratory.