If you want faster muscle gains, you may need to slow down your workouts. Scientists at Universidade Federal in São Paulo, Brazil, examined two groups of experienced weightlifters over a 12-week period. The first group performed Scott curls with a typical one-second eccentric (negative) motion. The second group performed the same exercise but took three seconds to lower the weight.
After 12 weeks, the participants in the slow-speed group had made almost five times more progression than the participants in the other group. In terms of muscle mass, the slow-speed group had done three times more mass than the high-speed group. The one-rep max of the slow group also increased considerably more than the lifters in the fast-negative group.