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. 2009 Nov;179(8):921-31.
doi: 10.1007/s00360-009-0374-0. Epub 2009 Jun 17.

Exhaustive exercise training enhances aerobic capacity in American alligator (Alligator mississippiensis)

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Exhaustive exercise training enhances aerobic capacity in American alligator (Alligator mississippiensis)

John Eme et al. J Comp Physiol B. 2009 Nov.

Abstract

The oxygen transport system in mammals is extensively remodelled in response to repeated bouts of activity, but many reptiles appear to be 'metabolically inflexible' in response to exercise training. A recent report showed that estuarine crocodiles (Crocodylus porosus) increase their maximum metabolic rate in response to exhaustive treadmill training, and in the present study, we confirm this response in another crocodilian, American alligator (Alligator mississippiensis). We further specify the nature of the crocodilian training response by analysing effects of training on aerobic [citrate synthase (CS)] and anaerobic [lactate dehydrogenase (LDH)] enzyme activities in selected skeletal muscles, ventricular and skeletal muscle masses and haematocrit. Compared to sedentary control animals, alligators regularly trained for 15 months on a treadmill (run group) or in a flume (swim group) exhibited peak oxygen consumption rates higher by 27 and 16%, respectively. Run and swim exercise training significantly increased ventricular mass (~11%) and haematocrit (~11%), but not the mass of skeletal muscles. However, exercise training did not alter CS or LDH activities of skeletal muscles. Similar to mammals, alligators respond to exercise training by increasing convective oxygen transport mechanisms, specifically heart size (potentially greater stroke volume) and haematocrit (increased oxygen carrying-capacity of the blood). Unlike mammals, but similar to squamate reptiles, alligators do not also increase citrate synthase activity of the skeletal muscles in response to exercise.

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Figures

Fig. 1
Fig. 1
Mean oxygen consumption rate (a), carbon dioxide production rate (b) and respiratory exchange ratio (c) before (Pre-ex), during (0.5–2.0 km h−1) and after (recovery) a graded treadmill exercise test for alligators from different exercise groups, run, swim and sedentary (sit). All groups showed a significant increase in formula image with speed. The run group showed no trend towards increasing formula image with increasing treadmill speed, and hence, displayed lower RERs than the swim and sedentary (sit) groups. Error bars are SE
Fig. 2
Fig. 2
Mean mass-specific peak oxygen consumption rate recorded during a graded treadmill exercise test for alligators from different exercise groups, run, swim and sedentary (sit). Run and swim groups had significantly higher formula image peak than the sedentary (sit) group. Uppercase letters above error bars indicate significant differences between groups derived from Kruskal–Wallis rank sums test (α = 0.05) followed by Wilcoxon rank sums test with Bonferroni correction (α = 0.0167). Error bars are SE
Fig. 3
Fig. 3
Mean mass-specific ventricular wet mass (a) and mean haematocrit (b) for alligators from different exercise groups, run, swim and sedentary (sit). Uppercase letters above error bars indicate significant differences between groups within each metric derived from ANOVA followed by SNK post hoc test (α = 0.05) (for haematocrit, fractional values were arcsine square root transformed). Error bars are SE
Fig. 4
Fig. 4
Mean lactate dehydrogenase (LDH) and citrate synthase (CS) activities for skeletal muscles at 30°C for subsets of alligators from different exercise groups, run, swim and sedentary (sit). DP diaphragmaticus, CF caudofemoralis, GC gastrocnemius, SC splenius capitis. Aerobic (CS) and anaerobic (LDH) enzyme activity appeared unaffected by exercise training. Error bars are SE

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