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Explaining differences in the metabolic cost and efficiency of treadmill locomotion in children
Gail Frost1, Oded Bar-Or, James Dowling
1School of Recreation Management and Kinesiology, Acadia University, Wolfville, Nova Scotia, Canada. gfrost@arnie.pec.brocku.ca
Insights
Children have a higher metabolic cost of locomotion than adults. This study found that muscle co-contraction, not mechanical power, significantly contributes to this age-related difference in energy expenditure during walking and running.
Area of Science:
- Exercise Physiology
- Pediatric Biomechanics
- Human Locomotion
Background:
- Children exhibit a higher metabolic cost of locomotion per kilogram of body mass compared to adults.
- Existing explanations for this age-related difference in energy expenditure are incomplete.
Purpose of the Study:
- To investigate the metabolic, kinematic, and electromyographic factors contributing to the age-related differences in the cost of locomotion.
- To identify predictors of net oxygen consumption (VO2) and efficiency in children of varying maturational stages.
Main Methods:
- Multidisciplinary approach analyzing metabolic (net VO2), kinematic (mechanical power, stride rate), and electromyographic (muscle co-contraction) data.
- Thirty children across three age groups (7-8, 10-12, 15-16 years) performed submaximal treadmill exercise at various speeds.
- Multiple regression analysis used to determine the relationship between independent variables (age, mechanical power, co-contraction, stride rate) and dependent variables (net VO2, efficiency).
Main Results:
- Age was the strongest single predictor of both net VO2 and efficiency.
- Muscle co-contraction, particularly in the thigh and leg segments, was a significant factor explaining age-related variations in metabolic cost.
- Mechanical power did not emerge as a significant predictor of the observed age-related differences.
Conclusions:
- Muscle co-contraction, potentially for joint stability, plays a crucial role in the higher metabolic cost of locomotion in children.
- Further research into growth-related factors, advanced mechanical work models, and measurement of elastic energy and isometric muscle costs may explain remaining variance.
Abstract:
The metabolic cost of locomotion at any given speed, when expressed per kilogram of body mass, is greater for children than for older individuals. Incomplete explanations for the age-related difference motivated this study, which used a multidisciplinary method to examine metabolic, kinematic and electromyographic data from three maturational groups of children. Thirty children aged 7-8 (n = 10), 10-12 (n = 10) and 15-16 (n = 10) years completed 4 min bouts of submaximal treadmill exercise at six speeds--two walking and four running--assigned in random order. Metabolic (net VO2), kinematic (total body mechanical power, energy transfer rates, stride rate) and electromyographic (co-contraction of agonist and antagonist muscles in thigh and leg segments) data were collected. Multiple regression analysis was performed with net VO2 or efficiency as the dependent variable and mechanical power, thigh and leg co-contraction, stride rate and age as independent variables. It was possible to explain up to 77% of the age-related variance in net VO2 and 62% of the variation in efficiency using combinations of these variables. Age was the best single predictor of both VO2 and efficiency. Co-contraction, possibly used to enhance joint stability, was an important component of the observed age-related differences, although mechanical power was not. Additional variance might be explained as specific growth-related factors affecting the metabolic cost of locomotion are identified, as mechanical work models improve, and as methods are developed to measure the effects of stored elastic energy and the metabolic cost of isometric muscle actions.