Build muscle With light weights
When people performed exercises that were less than 60 percent of their one-rep maximum to fatigue, they saw gains equivalent to their heavy-lifting counterparts over 6 weeks, explains study author Brad Schoenfeld, Ph.D., C.S.C.S.
The findings are surprising, since fitness experts will tell you that lifting light weights for a high number of reps targets your slow-twitch muscle fibers—the ones that offer endurance—and lifting heavy or explosively targets your fast-twitch muscle fibers—the ones that have the greatest potential for growth.
So what exactly is going on? Schoenfeld can’t say for sure until more research is done, but he believes that the participants may have actually increased the size of their slow-twitch muscle fibers due to more time under tension. That means men who can’t lift heavy due to injury can still increase muscle mass and strength at a comparable rate to men who can.
Even if you can lift heavy, you should consider lifting lighter loads once in a while, too, says Schoenfeld. You’ll maximize a muscle’s full potential, working both its fast-twitch and slow-twitch fibers. Plus, lighter loads put less stress on your joints, tendons, and ligaments than bigger loads, decreasing your risk of injury. Schoenfeld suggests training with lighter weights one day every week or every two weeks.