The effects of cryotherapy on muscle damage in rats subjected to endurance training.

Sixty 60-day-old Sprague-Dawley male rats were subjected to exhaustive and non-exhaustive exercise treatment over a period of 3, 5 and 7 weeks. Moderate exercise consisted of running on the treadmill at 10% grade at 10 m/min for 20 min for 5 days per week, while exhaustive running consisted of running at 10% grade at 15 m/min with an increase of 5 m/min every 5 min for 5 days per week. Half of the exercised rats were subjected to immersion in 4 degrees C water for 5 min after each exercise bout. Histological analyses of the gastrocnemius showed that ultrastructural damage of myofibrils occurred after 5 weeks of exhaustive running and 7 weeks of moderate running. With post-exercise immersion in 4 degrees C water for 5 min, the occurrence of ultrastructural damage advanced by 2 weeks in both treatments. It was concluded that the application of cryotherapy to the exercise groups was deleterious. Muscle damage occurred earlier in the treatment group and the degree of damage was also more serious over the same time period. This study supports the recommendation that the use of cryotherapy to reduce pain and haematoma formation should be coupled with rest for at least 48 hours.