From Movement guides
Muscle matters
All muscle isn't built the same. What Type 1, 2A, 2X and 2B fibres are each good at, why size doesn't equal power, and how training and genetics shape the muscle you carry.
Published
by Adarsh Gopal
Think of everything you’ve seen muscle do — a gymnast’s twist, a strongman’s deadlift, a sprinter’s start, a marathoner’s stride, a climber pasted to a wall. All muscle clearly isn’t built the same.
Something different is happening when Federer hits the ball, Kipchoge runs a marathon record, Bolt dashes 100 metres, Ramdev swaps orifices while holding a casual downward dog, Arnold curls a heavy dumbbell, or the Mountain crushes Pedro Pascal’s skull. More size does not necessarily translate into more force or power in racquet or track-and-field sports. In combat and strength sports, on the other hand, size categories are a must for competition to be fair.
Size isn’t the point
Federer doesn’t need Arnold’s arm to hit a 160 km/h forehand. Kipchoge doesn’t need Bolt’s shoulders or hamstrings to be quick over long distances. Bolt didn’t need Arnold’s quadriceps to be fast. You get the idea. Muscle comes in all shapes and sizes, and you don’t need big muscles to generate power or to be strong. Being physically strong can take many shapes and forms, and strength can mean different things to different people.
Muscles come with names: Type 1, Type 2A, Type 2B and Type 2X. Each is great at a specific task. Depending on what a person trains for and is good at, they’ll carry different amounts of each.
What each fibre is good at
Different fibres suit different activities. Some need action in the blink of an eye; others need slow, repetitive movement; and then there’s everything in between, which is a lot. Type 2 is built for quick, intense bursts — and within Type 2 there are sub-classes suited to different kinds of intense work. Type 1 is for longer durations, where resisting fatigue is the priority. Some people are predisposed to pack on more Type 2, others more Type 1.
| Trait | Type 1 (slow-twitch) | Type 2A (fast) | Type 2X (fast) | Type 2B (fast) |
|---|---|---|---|---|
| Speed of fatigue | Slowest to fatigue | Faster | Faster still | Fastest |
| Speed of contraction | Slow | Fast | Faster | Fastest |
| Metabolic type | Oxidative | Oxidative | Glycolytic | Glycolytic |
| Representative myosin | MYH7 | MYH2 | MYH1 | MYH4 |
Traits, not just types
Strength, speed, endurance, robustness, size, and the ability to hold a length without discomfort are all individual traits that muscle can be trained to improve or adapt to. You can carry varying amounts of each. The best athletes have a cocktail of all of them — and how much of each varies with individual genetics, tolerance and training style.
All of this is possible because muscle becomes extremely competent at the stimulus you give it — and only at the stimulus you give it. That stimulus is training. You can make a muscle shift from 2A to 2X, or from Type 1 toward Type 2 and back. It comes down to genetics and stimulus: your body adapts to whatever you throw at it, and the composition of your muscle will reflect that.
The takeaway
Exercise and genetics are the two things that decide how much and what kind of muscle you carry. Fight gravity in every way you can. Slow things down when gravity is pulling you down (the eccentric), speed them up when gravity is trying to keep you down (the concentric), and simply fight to hold a challenging position (the isometric). Tempo and exercise selection are the crucial choices. The rest are your variables: volume (how much of each movement), intensity (how much weight or height), rest (between sets and sessions) and frequency (how often you train a movement). Together they determine the muscle you carry, how you look, and how useful your training is for everyday life and sport. Like everything else, variety is the key to longevity, versatility and quality of life.