INTRODUCTION: Earlier research described a linear relationship between the highest 1 min of oxygen consumption (Vo₂) during a recurring physical activity and incidence of decompression sickness (DCS) during research chamber exposures to high altitude. The current effort was designed to determine if that relationship holds true at a lower altitude.METHODS: Male subjects (20) were exposed without prebreathe to 22,500 ft (6858 m; 314 mmHg; 6.1 psi) for 4 h while seated, nonambulatory the entire time, with echo-imaging at 16-min intervals (Non-Amb Echo), breathing 100% oxygen. Average highest 1 min of Vo₂ and level of activity was determined. Results during Non-Amb Echo were compared with earlier research data acquired under identical conditions except for higher levels of activity.RESULTS: No DCS was reported or observed and no venous gas emboli were observed. Combined with earlier data, a strong linear relationship (r > 0.99) was observed between DCS incidence and level of activity.DISCUSSION: These results suggest physiological envelopes might be expanded or prebreathe time reduced for some high-altitude aircraft operations that involve very low levels of physical activity. They may also help to explain the higher DCS risk for inside observers vs. trainees during altitude chamber training. The data imply potential for update of altitude DCS risk prediction models by adjustment with quantified level of activity during exposure.Webb JT, Morgan TR, Sarsfield SD. Altitude decompression sickness risk and physical activity during exposure. Aerosp Med Hum Perform. 2016; 87(6):516–520.