Influence of eccentric actions on the metabolic cost of resistance exercise.

Maintenance of a low energy expenditure during exercise in space is important because of the confined environment of the space craft. Resistance exercise is receiving increased attention as an exercise countermeasure, and we have shown that training with concentric (con) and eccentric (ecc) muscle actions induces greater increases in strength than training with only con actions. This study determined if performance of both actions markedly increased the metabolic cost of resistance exercise. Seventeen middle-age males performed each repetition of a "warm-up" and four sets of the leg press exercise with only con (Group CON, n = 8) or with con and ecc (Group CON/ECC, n = 9) actions. Sets were separated by 3 min of rest and each was performed to failure by selecting a resistance that allowed performance of the prescribed number of repetitions (7 to 10). The net energy cost of exercise was estimated from oxygen consumption data that were obtained at rest before exercise, during exercise, and for 20 min of recovery. The total work performed during the con actions was about 290 J.kg-1 body weight for both groups. The energy cost for this work was about 3 x 10(-3) cal.J-1. The requirement for the CON/ECC group to also lower the load increased (p less than 0.05) the energy cost 14%. These results indicate that con actions are mainly responsible for the metabolic cost of resistance exercise. Because ecc actions enhance the resistance training-induced increases in strength that are evident with only con actions with minimal additional energy cost, we suggest that they be considered in exercise prescriptions for use in space.