We routinely write about the benefits of using super-slow reps for gaining muscle size. This style of training — 3 to 10 seconds on the positive part of the rep and 3 to 10 seconds on the negative part of the rep — has been shown to produce good muscle growth. But we also preach constantly changing up your training. One study from the National Institute of Health and Nutrition (Tokyo) found that when subjects followed a super-slow leg-training program for 13 weeks, it increased their leg muscle size but decreased their muscle force during a cycling test. In other words, while super-slow training may be beneficial for muscle growth, it can compromise muscle strength to some degree. So be sure to change up your training style at least every 4 to 6 weeks to maximize muscle growth and strength.