To understand how different forms of weight training affect the human body, you first have to realize that there are different types of muscle fibers being exerted.
There are two categories of muscle fibers: Fast-twitch muscle fibers and slow-twitch muscle fibers1, and they each serve a purpose.
Per the National Academy of Sports Medicine, fast-twitch muscle fibers support quick and powerful movements while slow-twitch muscle fibers support endurance activities. You can think of fast and slow-twitch fibers like the tortoise and the hare. Fast-twitch fibers tire out as quickly as they can move, while slow-titch fibers support well-paced activities and are much more fatigue-resistant.
According to celebrity trainer and founder of the NWMethod, Nicole Winhoffer, you’ll see different results if you’re lifting fewer repetitions of heavier weights than if you were to do more reps of lighter weights because you’re working different muscle fibers, and exercising them differently.
“Lifting heavier requires larger dominant muscle groups (ie. bicep, tricep, quad, and glute) to complete more work and recruit more muscle fibers to lift the load,” Winhoffer explains. This means that these targeted muscle groups will bulk up. When you lift more reps of lighter weights, you encourage slow-twitch muscle fibers, building a more even tone over time.
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