Training to maximize economy of motion in running gait.

Recent reviews of how training affects running performance have indicated, to varying degrees, that running economy (RE) is a determinant of running performance. However, the literature suggests that the relationship between training-induced changes in biomechanics and RE is still largely unknown. While there is some evidence that high intensity interval training, plyometrics, and altitude/hypoxia training can improve economy, it remains unclear how these improvements are mediated. In addition, although it is clear from the literature that meaningful differences in RE exist among runners, the causes for the inherent differences are not clear. Consequently, suggestions are made to explore more individualized and integrated models of the determinants of performance that might better explain the interrelatedness of gait, RE, V.O2max, and peak performance.

The size-independent oxygen cost of running.

PURPOSE: The purpose of this investigation was to determine whether differences in running economy among children, adolescents, and adults can be explained by differences in resting metabolism, mass, and stature. METHODS: Participants were 36 children, 23 adolescents, and 24 adults. Mass-specific gross oxygen cost per minute ([OV0312]O(2gross) x M-1), mass-specific gross oxygen cost per kilometer (VO(2gross) x M-1), mass-specific net oxygen cost per kilometer (VO(2net) x M-1), and a dimensionless index called the size-independent cost (SIC) were compared for level treadmill running at speeds ranging from 1.6 to 3.1 m.s-1. SIC was defined as the net oxygen cost to move a mass of 1 kg a distance equal to stature (mL x kg-1). RESULTS: Children generally had higher [OV0312]O(2gross).M-1, VO(2gross) x M-1, and VO(2net) x M-1 than adolescents who similarly had greater costs than adults. When SIC was used to control for size-related differences in resting metabolism, mass and stature the costs of children and adults were similar (0.323 +/- 0.034 and 0.338 +/- 0.035 mL x kg-1, respectively, P = 0.54). However, adolescents had significantly higher SIC (0.360 +/- 0.026 mL x kg-1, P < 0.001) than both children and adults. Analysis of data from the literature indicated SIC peaks around 15 yr of age and changes were parallel to changes in the ratio of leg length to stature. CONCLUSIONS: We conclude that when resting metabolism and the dimensional effects of mass and stature are controlled, the running economy of adolescents is greater than in children and adults, which are similar. Therefore, differences in [OV0312]O(2gross) x M-1, VO(2gross) x M-1, and VO(2net) x M-1 among children, adolescents, and adults do not solely reflect qualitative differences in running performance.

A theory for normalizing resting .VO(2) for differences in body size.

PURPOSE: The purpose of this paper was two-fold: 1) to present a method of normalizing data for differences in body size that is consistent with the dimensional relationship between mass and power, and can be universally applied to subjects of any age, sex, or size without statistical cross-validation; and 2) to apply the model to data gathered from boys, girls, men, and women to determine whether or not age- and sex-dependent differences in resting .VO(2) exist. METHODS: Mass, percent body fat, and resting .VO(2) were measured in 39 boys, 40 girls, 40 men, and 40 women. RESULTS: Dimensional analysis predicted .VO(2) = a fat-free mass (FFM)2/3, with a defined as the size-independent metabolism of FFM. Bivariate correlation revealed the association between .VO(2) and FFM in children was consistent with biological similarity but not in men and women. Group mean .VO(2).FFM(-2/3) (mL.min(-1).kg(-2/3)) was significantly greater in children (21.7 +/- 2.62) than adults (16.7 +/- 2.30). Also, .VO(2).FFM(-2/3) of female subjects was significantly lower than male subjects in children (girls: 21.0 +/- 2.46; boys: 22.5 +/- 2.61) and adults (women: 15.0 +/- 2.39; men: 16.5 +/- 2.21). CONCLUSIONS: The dimensional paradigm indicated that mass exponents not equal to 2/3 simultaneously factor out size-dependent and size-independent differences that accompany differences in size. Therefore, size-independent comparisons can only be made using the theoretical mass exponent of 2/3. Also, the experimental results indicated that structural changes accompanying growth must be different from those hypothesized to be the cause of 3/4 scaling in adult animals of different size and species.

A dimensional paradigm for identifying the size-independent cost of walking.

PURPOSE: The purpose of this investigation was to present an alternative paradigm to that of dividing the rate of oxygen consumption by body mass (VO2.M-1, mL.min-1kg-1) for comparing walking economy in humans. METHODS: The paradigm used dimensional analysis and similarity theory to derive a measure of size-independent cost (SIC), defined as the net oxygen cost to move a mass of one kilogram a distance equal to stature. Mass-specific gross oxygen cost per kilometer, mass-specific net oxygen cost per kilometer, and SIC were used to analyze results from 184 subjects who performed level treadmill walking. Subjects were 63 children, 40 adolescents, 42 adults, and 39 seniors (approximately equal numbers of male and female subjects) walking at treadmill speeds from 0.9 to 1.8 m.s-1. RESULTS: Comparisons of metabolic cost between children and the older groups were dependent on the measure of metabolic cost and speed. At each speed, VO2gross.M-1 was higher in children than in older groups, whereas VO2net.M-1 of children was higher at 1.1 and 1.3, but similar at 0.9 m.s-1. SIC of children was similar at 1.1 and 1.3 m.s-1 but lower than the older groups at 0.9 m.s-1. CONCLUSIONS: Higher mass-specific metabolic costs of children were explained by differences in standing metabolism and stature. When these variables were considered, children had similar or lower metabolic costs than older subjects. Alternatives to using mass alone to normalize locomotor economy are warranted.