Ski tours are an endurance sport. They make your heart, circulation and muscles work hard, so good health, a high fitness level and an honest assessment of your capabilities are required. On the mountain avoid having to rush and adopt a pace that avoids anybody in your group getting out of breath. Make sure you pace yourself and have enough energy for the return journey. 

Regular endurance and strength training make ski touring and mountaineering more enjoyable by improving your fitness. If you have been out of training for a while, after a sickness or at an advanced age, an examination by a sports physician can help you assess your physical limits.