We studied the effects of physical training on antioxidant defences and susceptibility
to damage induced by exhaustive exercise in tissues of adult (12 mo) rats. Therefore,
untrained animals were sacrificed either at rest (n = 8) or immediately after swimming
to exhaustion (n = 8). Rats trained to swim for 10 weeks were also sacrificed, 48
hr after the last exercise, either at rest (n = 8) or after exhaustive swimming (n
= 8). Integrity of mitochondria and sarcoplasmic (SR) or endoplasmic (ER) reticulum
of liver, heart, and muscle was assessed by measuring mitochondrial respiratory control
and latency of alkaline phosphatase activity. Lipid peroxidation was measured by determination
of malondialdehyde and hydroperoxides. Additionally, the effect of training on tissue
antioxidant systems was examined by determining the glutathione peroxidase (GPX) and
glutathione reductase (GR) activity and the overall antioxidant capacity (CA). Membrane integrity was unaffected by training in liver and muscle, and improved
in heart of at rest animals, whereas lipid peroxidation was reduced in both liver
and heart. Glutathione peroxidase and glutathione reductase activity, and overall
antioxidant capacity were increased (p < 0.05) by training in liver and muscle. In
heart, antioxidant capacity was increased from 0.21 ± 0.01 to 0.33 ± 0.02 (p < 0.05),
but glutathione peroxidase activity remained unchanged (p > 0.05), and glutathione
reductase activity was decreased from 3.56 ± 0.08 to 2.27 ± 0.10 ?mol × min-1 x g-1 (p < 0.05). The exhaustive exercise gave rise to tissue damage irrespective of trained
state, as documented by similar loss of SR and ER integrity, and increase (p < 0.05)
in lipid peroxidation found in exhausted trained and untrained rats. However, the
above changes were elicited by exercise of greater duration in trained than in untrained
rats (340 ± 17 min and 233 ± 6 min, respectively). These findings support the view
that free radical-induced damage in muscle could be one of the factors involved in
muscle fatigue. If so, the increased endurance in trained rats should reflect lengthening
of the time required for the oxidative processes to sufficiently impair cell functions
so as to make further exercise impossible.
Key words
Exhaustive exercise - aerobic exercise - training - tissue antioxidants - fatigue
resistance
