According to existing research, the three main requirements for promoting gains in muscular size and strength are mechanical tension, muscular damage, and metabolic stress. While all of these factors are involved in promoting muscular hypertrophy, mechanical tension is often thought to be the most important, although recent research casts doubt about that. Mechanical tension is induced in trained muscles by the amount or level of resistance applied to the muscles. In simple terms, using heavier weights increases mechanical tension and promotes gains in muscular size and strength. The tension applied to the muscles in converted from a physical to a chemical signal in muscles that initiate increased muscle protein synthesis, as well as other changes. Most bodybuilders have understood that lifting heavier weights usually leads to increased muscle size. This is the entire basis of the venerated Progressive Resistance Principle, where attempts are made to always add more weight to promote muscle gains. You read about bodybuilding champions such as 8-time Mr.Olympia, Ronnie Coleman, who was known for lifting humongous poundages in the heyday of his bodybuilding competition days, which lead to one of the most massive physiques in bodybuilding history. It seems to make sense that Ronnie would have developed such mass based in his heavy style of training.
On the other hand, you see other athletes, such as elite powerlifters and Olympic Weightlifters, most of whom are undeniably strong, yet often don't show a level of muscle mass comparable with even mediocre bodybuilders, much less champions such as Coleman. Clearly, it's obvious that mechanical tension developed by lifting heavy isn't all there is to building muscle mass. As noted in a past article in this publication, you can get stronger, yet not develop muscle mass commensurate with that added strength. One reason for this is that other factors besides muscle mass are involved in the acquisition of strength. For example, neuromuscular factors play a large role in producing notable feats of strength. Indeed, when a person begins to lift weights, strength gains proceed that of muscular gains. This initial strength results from an increased connection between muscles and the brain that didn't exist to the same extent prior to beginning regular exercise, especially resistance training. Any apparent muscle gains that appear within the first three months of training are more due to a type of muscle swelling, rather than the development of real muscle. That begins to happen around the fourth month of training.
Another apparent paradox related to mechanical tension as a cause of muscular growth are recent findings that lifting much lighter weights, but using a higher number of repetitions along with training to muscular failure, can result in gains that are similar to lifting much heavier weights and not training to failure. This doesn't . . .