Validity of an anthropometric estimate of thigh muscle cross-sectional area.

This study examined the validity of an anthropometric estimate of thigh muscle cross-sectional area using magnetic resonance imaging (MRI). The anthropometric model assumed that a cross section of the thigh could be represented as a circle with concentric circular layers of fat-plus-skin, muscle, and bone tissue. On 18 healthy, active men and women (mean +/- SD age = 23 +/- 5 yr), total thigh circumference (CT) was measured with a fiberglass tape, fat-plus-skin thickness was measured over the quadriceps (SQ) using calipers, and the distance across the medial and lateral femoral epicondyle (dE) was measured with calipers. Direct measurements of each tissue were obtained by planimetry of an MRI image taken at the same site as the circumference and skinfolds. Thigh muscle cross-sectional area (AM) was estimated as follows: [equation: see text] Mean +/- SD AM from MRI and anthropometry were 121.9 +/- 35.1 cm2 and 149.1 +/- 34.1 cm2 (r = 0.96, SEE = 10.1 cm2), respectively. Errors in the anthropometric approximations of AM were due to an overestimate of the total thigh cross-sectional area and an underestimate of fat-plus-skin compartment. Because of the close relationship between MRI and anthropometric estimates of AM, zero-intercept regression was used to produce the following final equation, applicable for use in populations studies of young, healthy, active men and women: [equation: see text]

Ambulatory foot contact monitor to estimate metabolic cost of human locomotion.

The rate of metabolic energy expenditure during locomotion (Mloco) is proportional to body weight (Wb) divided by the time during each stride that a single foot contacts the ground (tc) (Nature Lond. 346: 265-267, 1990). Using this knowledge, we developed an electronic foot contact monitor. Our objective was to derive and cross-validate an equation for estimation Mloco from Wb/tc. Twelve males were tested [age = 19.4 +/- 1.4 (SD) yr, Wb = 78.4 +/- 8.0 kg] during horizontal treadmill walking (0.89, 1.34, and 1.79 m/s) and running (2.46, 2.91, and 3.35 m/s). Measured Mloco was defined as the total rate of energy expenditure, measured by indirect calorimetry, minus the estimated rate of resting energy expenditure. The equation to estimate Mloco was derived in six randomly selected subjects: Mloco = 3.702.(Wb/tc) - 149.6 (r2 = 0.93). Cross-validation in the remaining six subjects showed that estimated and measured Mloco were highly correlated (r2 = 0.97). The average individual error between estimated and measured Mloco was 0% (range -22 to 29%). In conclusion, Mloco can be accurately estimated from Wb and measurements of tc made by an ambulatory foot contact monitor.

Accuracy of physical working capacity (PWC170) in estimating aerobic fitness in children.

Physical working capacity, the workload at a heart rate of 170 bpm (PWC170), has been utilized as a marker of maximal oxygen uptake. The precision of PWC170 in predicting VO2max in children has not been fully evaluated. In this study, 35 children (18 boys and 17 girls, mean ages 10.5 and 9.9 years, respectively) underwent maximal cycle testing to assess the relationship between VO2max and PWC170. These measures correlated closely in absolute terms (r = 0.71 and 0.70 for girls and boys, respectively), but the relationship was weaker when both were expressed per kg body weight (r = 0.65 and 0.48, respectively). When VO2max was calculated from the regression equation of VO2max versus PWC170, the mean error from measured VO2max was 3.4 ml.kg-1.min-1 (SD 2.5) for the girls and 2.8 ml.kg-1.min-1 (SD 2.6) for the boys. These findings indicate that although mean predictability of VO2max from PWC170 is good, the variability is wide, with a 10-15% error at one standard deviation. PWC170 provides only a crude estimate of VO2max and should not be used to predict individual maximal aerobic power.

Validity of self-assessed physical fitness.

This study compared self-ratings of components of physical fitness with objective measures of physical fitness. We made comparisons in two groups of male infantry soldiers (n = 96 and n = 276) and one group of older male military officers (n = 241). To obtain self-ratings of physical fitness, we asked subjects, "Compared to others of your age and sex, how would you rate your (a) endurance, (b) sprint speed, (c) strength, (d) flexibility?" Subjects responded to each of the four questions on a five-point scale. Self-ratings of endurance were systematically related to three measures of aerobic capacity, including VO2max, peak VO2, and two-mile run time (r = 0.29 to 0.53). Self-ratings of sprint speed showed only weak relationships to measures of anaerobic capacity assessed by the Wingate test, push-ups, and sit-ups (r = 0.10 to 0.17). Strength ratings were systematically related to measures of maximal strength (r = 0.28 to 0.53). Upper body strength measures were more closely associated with the self-ratings of strength than were measures of lower body strength. Responses to the flexibility question were systematically related to measures of hip/low back flexibility (r = 0.30 and 0.48) but not to other measures of flexibility. Apparently, physically active subjects can approximately classify their aerobic capacity, muscle strength, and some types of flexibility.

Metabolic and performance responses to uphill and downhill running in distance runners.

Distance running performance is slower on hilly race courses than flat courses even when the start and finish are at the same elevation, resulting in equal amounts of uphill and downhill running. The physiological mechanism limiting performance on these courses is not known. We examined the effects of uphills and downhills with 11 trained male distance runners running three 30 min self-paced competitive races on a treadmill. Race courses consisted of five, 6 min stages. Percent grades were: course A (0, 0, 0, 0, 0), course B (0, +5, 0, -5, 0) and course C (0, -5, 0, +5, 0). Pace, oxygen consumption (VO2), heart rate (HR), blood lactate (LA), and rating of perceived exertion (RPE) did not change significantly (P greater than 0.05) over stages on the control course A. Pace changed inversely with percent grade on courses B and C. The increase in downhill running pace was inadequate to maintain a level VO2 during the race. LA increased on the uphill stages even though running pace decreased. The running paces for courses B and C were slower (P less than 0.05) than course A by 2.8% and 2.4%, respectively. Runners do not maintain constant energy expenditure when racing on hilly courses. Lactate accumulated on uphill stages even though pace decreased. Running pace increased on downhills but not enough to maintain a constant VO2.

Mechanical efficiency during cycling in prepubertal and adult males.

Previous studies have indicated that values for mechanical efficiency during cycle exercise in prepubertal subjects are similar to those in adults. Few studies have directly compared these groups, however, and earlier reports did not consider the importance of assessing efficiency at similar relative exercise intensities. Nineteen prepubertal boys and 21 college men underwent cycle exercise testing for determination of delta efficiency (the energy required to increase workload), related to both absolute work load and relative work intensity (percent VO2max). No significant differences in either of these measures were observed between the two groups. Mean delta efficiency between workloads of similar relative intensity was 23.2% for the prepubertal subjects and 22.5% for the adults (p greater than .05). Between equal absolute workloads the values were 23.2 and 26.5%, respectively (p greater than .05). These findings support earlier contentions that the efficiency of muscular contraction during exercise is comparable in pre- and post-pubertal subjects.