Daniel J. Mccann

Phosphocreatine kinetics in humans during exercise and recovery

System linearity was assessed for exercise induced changes in energetics of forearm exercise. 31P-NMR spectroscopy techniques, with 12.5-s serial measurements of [PCr], [Pi], [ATP], and [H+] were employed during exercise and recovery transitions in four untrained men for moderate (1.7 W) and heavy (3.6 W) exercise. Signal averaging was applied and data were analyzed by regression analysis using a first-order exponential model. The time constants for both [PCr] and [Pi] responses to moderate exercise and recovery were not different both within and between nuclei ranging from 32 to 35 s (P > 0.05). The time constants derived from moderate exercise and recovery, when employed to construct predictive equations for heavy exercise and recovery, did not adequately describe [PCr] dynamics. Underestimation of the net hydrolysis of PCr during heavy exercise was associated with increases in [H+] as predicted by the creatine kinase equilibrium reaction (CKeq). Calculation of [ADP] by CKeq revealed steady state [ADP] was achieved during moderate exercise and during recovery for both intensities much earlier than during heavy exercise. We conclude that the metabolic system does not behave as a linear system. Therefore, the time constant and the net change in [PCr].W-1 must themselves be determined by work dependent combinations of other system variables.

Peak torque per unit cross-sectional area differs between strength-trained and untrained young adults

It is unclear whether gender differences in the relative strength of the upper and lower body are due to differences in muscle mass distribution or dissimilarity of use. There is also controversy as to whether prolonged resistance training increases strength per unit cross-sectional area (CSA). To help resolve these questions, maximum isometric torque per unit muscle and bone (M+B) CSA was measured in the upper arm and thigh of 26 trained (13 males; 13 females) and 26 untrained (13 males; 13 females) young adults. Muscle and bone CSA values were calculated from limb circumferences and skinfolds. Maximal isometric torque values were recorded by a LIDO isokinetic dynamometer. There was no significant difference (P > 0.05) in mean upper arm or thigh torque per unit M+B CSA between the trained males and trained females, or between the untrained males and untrained females. However, mean torque per unit M+B CSA was significantly higher for the trained subjects of both genders compared with the untrained subjects of both genders for the upper arm (28.9%; P < 0.0001) and thigh (18.8%; P < 0.0001). These results suggest that muscle quality (peak torque/CSA) is equal between genders, and that the increase in muscle strength per unit area that occurs with resistance training is not gender-dependent.

Wet bulb globe temperature index and performance in competitive distance runners.

In 1974 two sets of heat stress guidelines, each based on the wet bulb globe temperature (WBGT) index, were designed for mens National Collegiate Athletic Association (NCAA) Championship Division I distance running competitions. One set of guidelines was established to minimize the chance of heat injury during distance running events. A second set was designed to predict heat stress related performance decrements. During the time the heat injury guidelines were used (1974-1993), no heat injuries were reported. The purpose of this study was to assess the accuracy of the performance decrement guidelines and determine whether the WBGT indices were linearly related to mens championship distance running performance. WBGT index data were collected during the 1500-, 3000-steeplechase (SC), 5000-, and 10,000-m events at mens NCAA Division I Track and Field Championships held from 1974 to 1981 (excluding 1975). These data were compared to the average running performance of the top six finishers in each event. Analysis of the accuracy of the NCAA performance decrement guidelines revealed four unexpected performances out of 28 predictions. Pearson product-moment correlation and linear regression analyses between the WBGT indices and performance revealed statistically significant linear relationships for the 3000-SC and 10,000-m events (P < 0.05). A significant linear relationship was also found when the 1500-, 3000-SC, 5000-, and 10,000-m results were pooled (P < 0.05). In conclusion, the NCAA guidelines were effective in preventing heat injury and fairly successful in predicting performance. However, a linear relationship between WBGT indices and distance running performance did not exist in all running events.

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.

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.

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.

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.