Toning Muscles vs. Bigger Muscles

Woman weight lifting, posing in studio, portrait

While toning is a common gym term, you can’t actually tone your skeletal muscles. Instead, you can target fibers located in your muscles to achieve a bigger or more defined appearance. Your body is made up of two different types of muscle fibers: slow-twitch and fast-twitch. Each muscle features a unique ratio of these fibers. The fast-twitch fibers have a larger diameter and can lead to bigger muscles, while your slow-twitch muscles are smaller and lead to smaller, more toned muscles. While you cannot change a fast-twitch into a slow-twitch or vice versa, you can perform exercises that target these muscle fibers differently to get bigger or more toned muscles.

Muscle Types

Every muscle in your body is composed of both slow-twitch and fast-twitch fibers. Slow-twitch fibers are used during aerobic activities. They are slow to contract but are very resistant to fatigue. Fast-twitch fibers are used during anaerobic activities that require power, speed or strength. These fibers contract quickly but fatigue easily. Your body starts by using your slow-twitch fibers, but if the activity is too strenuous, it recruits the fast-twitch ones.

Toning Versus Building

In the fitness world, toning generally means increasing your muscles' definition without adding excessive bulk. Building bigger muscles means increasing the diameter and mass of the muscle. Both toning and building mass come down to strengthening your muscles. When you tone your muscles, target your slow-twitch fibers by increasing endurance activites such as running, cycling and swimming laps. To build bigger muscles, on the other hand, do activities that push your body to the anaerobic level, such as sprinting.

Muscle Size

Genetics plays a major factor in the specific ratio in your body between fast-twitch and slow-twitch fibers. Unfortunately, you cannot gain or lose muscle fibers of either type, but you can train in a way that increases the mass of your fast-twitch muscle fibers, which leads to muscles that appear bigger.

Training Muscles

How you train directly affects whether you build bigger or more toned muscles. When you strength train for endurance, do higher reps with a lighter weight. To get bigger muscles, however, you want to cause hypertrophy in your fast-twitch fibers -- meaning increasing their diameter or thickness. When you strength train, do fewer reps with a heavier weight. To ensure that you are targeting your fast-twitch fibers, you want to reach muscle fatigue in fewer than 10 reps.