Sprint, a study in progress since 2011, has a full name of Integrated Resistance and Aerobic Training Study. It evaluates a high-intensity, low-volume exercise protocol to minimize the loss of muscle, bone and cardiovascular function but also minimizing the time spent with daily exercise.
Despite the 2.5-hours of exercise allocated per day, crew members returning from 180-day missions have shown a 11-17% decrease in muscle strength, a 10% decrease in muscular endurance, and a drop in bone mineral density of 2-7%. Preventing these conditions is the overall goal of countermeasure development. Better countermeasures will be a critical requirement for longer missions to distant targets. Sprint aims to develop a higher-intensity, lower duration exercise program using the Advanced Resistance Exercise Device (ARED) and the Combined Operational Load Bearing External Resistance Treadmill (COLBERT).
To asses the protocol, crew members conduct regular measurements of VO2max, heart rate (HR) response to submaximal exercise and ventilatory threshold. Monthly ultrasounds of the thigh and calf are used to evaluate spaceflight-induced changes in the muscle volume. Post-flight data on muscle and bone mass is compared to pre-flight measurements and to data from control subjects that use the regular exercise protocol.