Go heavy or go home. That’s the mantra bros live by — except those that go to Planet Fitness. It implies that the only way to gain muscle is to lift heavy, all the time. As for light weights, leave ’em for the boys.
While lifting heavy is a cornerstone for building muscle, lifting lighter weights is beneficial too. To understand why, it’s important to make sense of how muscles grow.
How Muscles Get Bigger
Muscles are composed of long, fiber-like strands called fascicles. These fascicles house smaller strands called muscle fibers. And inside of these are more strands called myofibrils.
Lifting heavy weights, say on Monday, colloquially known as International Chest Day, causes tiny tears in the myofibrils. This is one reason you may feel sore the next day.
Your immune system responds by releasing proteins called cytokines to fix the damaged areas. Surrounding the muscle fiber is a layer of satellite cells. These are your muscle stem cells.
The cytokines order the satellite cells to start multiplying and send them to the muscle tears to start the repair process. Once there, they fuse with the fibers regenerating the muscle fiber and increasing the size of the muscle.
The Size Principle
The functional units of skeletal muscle are motor units. These motor units possess different characteristics and are categorized as type 1 (slow-twitch) or type 2 muscle fibers (fast-twitch).
Type 1 muscle fibers don’t fatigue easily, but they’re not that powerful. This fiber type tends to respond better to longer duration sets requiring lighter weights. Type 2 muscle fibers, on the other hand, fatigue quickly but are more powerful. They tend to be more responsive to short sets with heavier weights.
Your nervous system activates these muscle fibers based on how much force you need to produce. It starts with the smaller, Type 1 muscle fibers which are recruited under low force conditions until it needs to activate the larger Type 2 muscle fibers as the force requirements increase.
And because lifting heavy weights results in more muscle fiber activation, and therefore the opportunity for muscle growth, it’s commonly deemed superior for building muscle compared with lifting light weights.
Light Weights vs Heavy Weights
A 2016 meta-analysis looked at nine studies to determine if lifting light weights to muscular failure resulted in similar gains to that of using heavy weights.
Heavy weight, or high-load training, was defined as lifting weights greater than or equal to 65% of a person’s one-rep max. Light weight, or low-load training, was defined as lifting weights less than or equal to 60% of a person’s one-rep max.
The resistance training protocols analyzed in the study were carried out for a minimum of six weeks and measured muscle strength or muscle growth.
After analyzing the studies, the researchers found no significant differences between the high- and low-load groups in muscle strength or growth. They did, however, find a trend for increased muscle size and strength with the high-load training compared to low-load.
This research provides evidence that muscle growth can occur with a variety of repetition schemes and weight variations provided that the low-load training is carried out to muscular failure. In fact, some of these studies reached upwards of 30 or more reps, with some as high as 100.
A Combination Is Best
For those looking to maximize their gains in the gym, it’s best to train across a variety of rep ranges.
Focusing on the “hypertrophy range” (6-12 reps) is a good strategy for putting on size, but you can also benefit from high (15-20 reps) and low (1-5 reps) repetitions. This ensures full stimulation across the spectrum of muscle fibers.
Regardless of the rep range, however, it’s important to continually push yourself. For example, if you’re performing 20 reps of an exercise, that 20th rep should feel difficult, almost as if you couldn’t do one or two more.