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table des matière 74.  Houle-Leroy, P., T. Garland, Jr., J. G. Swallow, and H. Guderley. 2000. Effects of voluntary activity and genetic selection on muscle metabolic capacities in house mice Mus domesticus.
Journal of Applied Physiology 89:1608-1616.

Selective breeding is an important tool in behavioral genetics and evolutionary physiology, but it has rarely been
applied to the study of exercise physiology. We are using artificial selection for increased wheel-running behavior to
study the correlated evolution of locomotor activity and physiological determinants of exercise capacity in house mice. We
studied enzyme activities and their response to voluntary wheel running in mixed hindlimb muscles of mice from generation
14, at which time individuals from selected lines ran more than twice as many revolutions per day as those from
control (unselected) lines. Beginning at weaning and for 8 wk, we housed mice from each of four replicate selected lines
and four replicate control lines with access to wheels that were free to rotate (wheel-access group) or locked (sedentary
group). Among sedentary animals, mice from selected lines did not exhibit a general increase in aerobic capacities: no
mitochondrial [except pyruvate dehydrogenase (PDH)] or glycolytic enzyme activity was significantly (P < 0.05) higher
than in control mice. Sedentary mice from the selected lines exhibited a trend for higher muscle aerobic capacities, as
indicated by higher levels of mitochondrial (cytochrome-c oxidase, carnitine palmitoyltransferase, citrate synthase,
and PDH) and glycolytic (hexokinase and phosphofructokinase) enzymes, with concomitant lower anaerobic capacities,
as indicated by lactate dehydrogenase (especially in male mice). Consistent with previous studies of endurance train-ing
in rats via voluntary wheel running or forced treadmill exercise, cytochrome-c oxidase, citrate synthase, and carni-tine
palmitoyltransferase activity increased in the wheel-access groups for both genders; hexokinase also increased
in both genders. Some enzymes showed gender-specific responses: PDH and lactate dehydrogenase increased in
wheel-access male but not female mice, and glycogen phosphorylase decreased in female but not in male mice. Two-way analysis of covariance revealed significant interactions between line type and activity group; for several enzymes, activities showed greater changes in mice from selected lines, presumably because such mice ran more revolutions per day
and at greater velocities. Thus genetic selection for increased voluntary wheel running did not reduce the capability of
muscle aerobic capacity to respond to training.

Copyright 2000 the American Physiological Society