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Mechanical power and efficiency in running children
B Schepens1, P A Willems, G A Cavagna
1Unité de Réadaptation, Université catholique de Louvain, Place Pierre de Coubertin, 1, 1348 Louvain-la-Neuve, Belgium.
Insights
Children running mechanics show age-independent total mechanical power output (Wtot) at lower speeds due to compensatory internal and external power. However, children exhibit higher Wtot at high speeds.
Area of Science:
- Biomechanics
- Human Physiology
- Pediatric Exercise Science
Background:
- Understanding age-related differences in running biomechanics is crucial for pediatric sports science.
- Mechanical power output (Wtot) is a key determinant of running performance.
- Wtot comprises external power (Wext) for body movement and internal power (Wint) for limb movement.
Purpose of the Study:
- To investigate the effects of age and body size on Wtot during running in children (3-12 years) and adults.
- To analyze the contributions of Wext and Wint to Wtot across different running speeds.
- To compare the mechanical efficiency of running between children and adults.
Main Methods:
- Measured Wtot, Wext, and Wint during running in children and adults.
- Analyzed the influence of age, body size, and running speed on power outputs.
- Calculated mechanical efficiency based on positive work production and energy consumption.
Main Results:
- At low/intermediate speeds (<13 km/h), children's higher step frequency led to reduced mass-specific Wext and increased mass-specific Wint, making mass-specific Wtot age-independent.
- At high speeds, mass-specific Wtot was 20-30% higher in children than adults.
- Mechanical efficiency of positive work production was similar (0.40-0.55) in both groups.
Conclusions:
- Children's running Wtot is largely independent of age at sub-maximal speeds due to compensatory changes in internal and external power.
- Children exhibit higher mass-specific Wtot at high speeds, potentially due to greater center-of-mass deceleration.
- Running mechanical efficiency is comparable between children and adults.
Abstract:
The effect of age and body size on the total mechanical power output (Wtot) during running was studied in children of 3-12 years of age and in adults. Wtot was measured as the sum of the power required to move the body's centre-of-mass relative to the surroundings (the "external power", Wext) plus the power required to move the limbs relative to the body's centre-of-mass (the "internal power", Wint). At low and intermediate speeds (less than about 13 km h-1) the higher step frequency used by young children resulted in a decrease of up to 40-50% in the mass-specific external power and an equal increase in the mass-specific internal power relative to adults. Due to this crossed effect, the mass-specific Wtot is nearly independent of age. At high speeds the mass-specific Wtot is 20-30% larger in young children than in adults, due to a greater forward deceleration of the centre-of-mass at each step. The efficiency of positive work production, calculated as the positive mechanical power divided by the net energy consumption rate, appears to be similar in children and adults (i.e. 0.40-0.55).