Submaximal exercise in the cold: does cooling potentiate the development of muscle injuries in the rat?

To test the effect of low ambient temperature on muscular strain and possib le development of muscle injuries, male Sprague-Dawley rats (n = 35) were e xercised at a speed of 15 m min(-1) on a treadmill at a 6 degrees inclinati on for 1.5 h in a warm (22 degrees C) or a cold (-10 degrees C) environment . Blood and tissue samples were collected 0 and 48 h postexercise. Blood gl ucose, lactate, pyruvate, cortisol, epinephrine (E) and norepinephrine (NE) were determined to investigate the effect on energy metabolism. To estimat e the degree of physical strain, possible muscle injury and regenerative pr ocesses of muscles in response to exercise in the cold, serum creatine kina se (CK), lactate dehydrogenase (LDH), muscle beta-glucuronidase and prolyl- 4-hydroxylase (PH) activities were measured. In addition, histology of the hindlimb muscles m. soleus and m. tibialis anterior was examined. In genera l, the circulating level of metabolic substrates during exercise were unaff ected by the exercise and independent of ambient temperature. Plasma cortis ol increased significantly during exercise (P < 0.01), but was unaffected b y the thermal strain. Of the myocellular enzymes, serum CK increased by 100 % (P < 0.01) and LDH by 93% (P < 0.05) during exercise in the cold compared with exercise in warm, indicating a higher physical strain. However, exerc ise in the cold did not result in muscle injuries as judged by the unaltere d muscular beta-glucuronidase, PH levels and muscle morphology. It is concl uded that the exercise type and intensity used caused stress that was indep endent of the ambient temperature. In addition, the rats were able to maint ain unaltered circulating levels of energy substrates also in the cold. Fin ally, exercise in the cold increased muscular strain but did not result in muscle injuries. (C) 1998 Elsevier Science Inc. All rights reserved.