Effects of a World Record Unsupported Ski Trek Across Greenland (The G2 Expedition) on Physical Performance and Body Composition

摘要

Prolonged exhaustive physical exertion is often predicted to result in reduced performance capacity ('overtraining'), through mechanisms of tissue breakdown and inadequate time for full recuperation. This is of importance in military operations, where sustained performance is a typical requirement. We had the opportunity to test the hypothesis that highly motivated men pushed to the limits of their endurance capacity would suffer physical breakdown. Two, 25 year old, Norwegian Navy, Sea, Air and Land Soldiers, (SEALS) completed an unsupported 2928 kilometer south-to-north ski-trek across Greenland in 86 days. The trek involved ski-marching, for 9 hours a day, pulling sleds (150 kg starting load) with all of their food, fuel and supplies. Both SEALs ate an energy-dense diet estimated at 6000 kcal per day. The two volunteers were tested 14 days pre- and 4 days post-trek using anthropometric, physiological, and performance measures. Pre-trek testing showed them to be aerobically and anaerobically fit and to have high lean body masses. Total daily energy expenditure (TDEE), based on doubly-labeled water, reached 6750 and 8260 kcal/d for the two men during the most demanding phase of the trek and other samples showed TDEEs of; 3500 to 4940 kcal/d. Both men lost body weight, with the changes primarily reflecting loss of fat energy stores, finishing the trek with fat stores of approximately 13% body fat. Most physical performance measures showed no significant loss of physical capacity as a result of prolonged exertion. However, anaerobic tests were significantly impaired following the trek, probably reflecting a detraining effect and possibly including some component of fast twitch muscle loss as previously reported in other prolonged military ski treks.