Maximal oxygen uptake has been used as a measure of physical fitness. This measure increases by approximately 25% when sedentary individuals become more physically active. Oxygen uptake measurement in the laboratory or estimation in fieldwork is complex and costly with finite risk. For the present study, 36 men and 32 women completed the Paffenbarger Physical Activity Index Questionnaire, including a sweat-inducing physical activity frequency question, and had measurement of oxygen uptake during pedal ergometry. Using maximal oxygen uptake as the measure of fitness, the authors found that the Paffenbarger Physical Activity Index, although more detailed, may be less valid than the simpler sweat induction frequency question for estimating fitness. The correlations observed between the sweat question and oxygen uptake were 0.54 for males, 0.26 for females, and 0.46 for the total group. The correlations between the Physical Activity Index and oxygen uptake were 0.26 for males, 0.08 for females, and 0.29 for the total group. The regression relationship (oxygen uptake = 1.92 X (sweat days) + 23.76; standard error of estimate = 8.63 ml/kg/min) is significant for sweat versus oxygen uptake. While the confidence interval limits the practical ability to predict individual values, low cost, absence of risk, and population validity suggest that fitness can be assessed rapidly and simply for epidemiologic studies with a simple "sweat" question.

The authors' modification of the Astrand-Rhyming Cycle Ergometer Test is of short duration, has low initial and peak work rates and was in an earlier study applied for population fitness testing (N = 587) at a survey center after other cardiovascular risk factor measures were obtained in the home. To add fitness testing in the home, the authors have designed a safe, brief 10 inch (25.4 cm) high step test for estimating maximal oxygen uptake (VO2max). Measured maximal oxygen uptake for step tests has been shown to be approximately 10% higher than that reported for cycle tests. All test instructions and stepping rates were included on a cassette tape; heart rates were monitored by a digital tachograph during the last 30 seconds of stepping. Maximal oxygen uptake was measured directly on a bicycle, estimated by the step test, and measured by the authors' bike test in 48 men and women aged 19-70 years who took part in a community fitness program in Pawtucket, Rhode Island in January-February 1983. No significant differences in maximal oxygen uptake were found between the bicycle protocols. The step test estimate of maximal oxygen uptake (VO2max) was significantly higher (12%) than directly measured VO2max, reflecting the expected difference between stepping and cycling. The correlation between direct and both estimates was 0.92. The cross-validation correlation between the estimates was 0.98. The authors' protocol provides accurate estimates of maximal oxygen uptake and is safe and suitable for in-the-home assessment of fitness of people aged 19-70 years for epidemiologic studies.

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We developed and validated assessments for total body water (TBW) and extracellular water (ECW) by using two resistance values of a new electric circuit model (CM) (two resistors; a capacitor and an inductor) with or without body mass. Fluid shifts occurring after 40 min of supine rest did not increase the validity of either estimate. CM estimates were valid; r = 0.941 to 0.969, low SE of estimates of 1.15-2.28 kg, nonsignificant mean differences (CM - dilution; %delta = -0.4 to 1.3%) that were close to the expected measurement errors for TBW (+/- 1%) and ECW (+/- 5%), and Bland-Altman pairwise comparisons that showed equivalence between methods. The CM estimates of TBW and ECW had marginally better validity than the previously published bioimpedance models. The advantage of the CM model is its assessments of multiple fluid spaces and that it does not require gender-specific equations. We conclude that CM estimate of TBW is acceptable, whereas further validation is needed before the ECW estimate should be used in a clinical or research setting.