It seems there is not much eccentric exercises cannot do between healing injured tissue, improving mobility and strength, and now possibly contributing to muscle size. We have long known muscles gain the majority of their strength after training because of the eccentric or lowering portion of any lift. Athletes who skip or speed through this portion of the lift do not benefit as much from the same exercise as those who focus equally on the lift and lowering of the exercise. New research compared the long term effects of strengthening either with a short or long duration eccentric or lowering phase.
A group of researchers put a group of participants, familiar with resistance training, through 2 workouts a week for 12 weeks (Pereira et al. Int J Applied Exercise Phys. 2016). The participants were placed in either a slow group, who performed a 4 second lowering phase, or a fast group, who performed a one second lowering phase of an upper body exercise. The exercise was performed for 3 sets of 8 repetitions to failure using either the slow or fast lowering phase, but every participant took 1 second to raise the weight. The researchers then measured strength, muscle size, and body composition (fat and fat free mass) at the end of the 12 weeks. As expected the slow group developed more strength than the fast group, but they also showed twice as much hypertrophy. This is the first study to report a relationship between eccentric loading and muscle growth.