Muscle Types

Andrew Huberman has discussed various types of muscles and their functions in detail.

Flexors and Extensors

Muscles are divided into flexors and extensors. When you engage in any movement, whether it's lifting weights, yoga, or simple daily tasks like picking up a pen, you use both types of muscles. For example, the bicep acts as a flexor when you bring your wrist closer to your shoulder, while the tricep serves as an extensor when you move your wrist away. Additionally, the abdominal muscles act as flexors for the spine, bending it forward, whereas the muscles in the lower back are extensors, allowing you to arch your back or look up 1.

Muscle Fiber Types

There are two primary types of muscle fibers: fast twitch and slow twitch. Fast twitch fibers are usually larger and contract quickly, making them suitable for activities that require bursts of strength or speed. However, they fatigue more quickly. Slow twitch fibers, on the other hand, are smaller, packed with mitochondria, better for endurance, and contract more slowly. Each muscle in the body has a mix of both types, but the ratio varies from one muscle to another and from one individual to another. For instance, the soleus muscle in the calf is predominantly slow-twitch, aiding in posture and continuous activity, while the gastrocnemius muscle in the calf predominantly consists of fast twitch fibers, useful for powerful movements 2.

These insights help in understanding how muscles function and respond to different types of movement and training.