For many years I have believed that heating muscles in a hot tub or sauna after exercise interferes with muscle contractions and hampers muscular endurance. However, a study from the University of Otago in New Zealand shows that taking a sauna after workouts for three weeks helped athletes to exercise longer to exhaustion.
Trained runners sat in a humid sauna for 30 minutes at 89.9 degrees centigrade immediately after exercising, 12 times in three weeks. They then ran as hard as they could on a treadmill for about 15 minutes, to exhaustion. Sauna use increased run time to exhaustion by 32 percent, which would equal an improvement of approximately two percent in a full-length endurance time trial. Their blood volumes increased by more than seven percent, and higher blood volume increases endurance. If further research confirms these findings, athletes will be advised to use saunas or hot tubs after their workouts for several weeks before competition. Journal reference