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Cabrera, Marco E.; Bar-Or, Oded; Cabrera, M E.; Bar-Or, O; Minetti, Alberto E.; Ryschon, Timothy W.; Welsman, Joanne R.; Riddell, Michael C.

Medicine & Science in Sports & Exercise: May 2001 - Volume 33 - Issue 5 - p S1
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From the energetic point of view, an exercising human can be compared to a machine such as an automobile. A machine transforms one form of energy into another to perform work. Similarly, humans convert chemical energy to mechanical energy at a rate appropriate to sustain muscle contraction. A “better machine” would be capable of sustaining high speeds for longer time and with lesser fuel consumption than a “standard machine”. A more efficient biological machine would be able to sustain heavy exercise with lower excess VO2 (i.e., slow component) and lower muscle lactate levels.

From the metabolic stand point, children have lower muscle lactate levels, faster VO2 kinetics, and less O2 deficit than adults at the same relative work rate, suggesting less anaerobic energy contribution for a given task. Children reach both lower peak lactate levels and muscle Pi/PCr than do adults during incremental exercise, suggesting less reliance on non-oxidative energy sources. These observations may suggest that children are “better machines” than adults. However, recent studies claim that many of these differences may be related to the approach/method employed to analyze the data. Moreover, other factors (e.g., size, gait, speed of walking/running, mechanical energy storage/recovery) play a role in determining the body's mechanical and metabolic efficiencies especially at high exercise intensities. Thus, a crucial question remains: Are children's mechanical and metabolic efficiencies greater than those of adults?

The symposium will focus on reviewing and comparing existing data and interpretations to foster discussions that may lead to better understanding of the biological and mechanical factors affecting whole-body efficiency in children and adults.

©2001The American College of Sports Medicine