While some climbers prefer steep outdoor crags with tough-to-negotiate overhangs, other climbers prefer the relative safety of indoor climbing. Whichever type of climbing you prefer, the muscles used are very similar. Climbing is a whole-body activity, but there are some muscles that must work harder than others to pull your body upward against gravity.
The main muscle used in climbing is your lats, short for latissimus dorsi, which is located on the side of your back. This large, wing-shaped muscle is responsible for pulling your arms downward and inward as you pull yourself upward using your arms. Climbers develop this muscle by performing lat pull downs or chinups using a variety of hand positions and resistance training methods.
Located on the front of your upper arm, the biceps brachii -- literally two-headed arm muscle -- is responsible for bending your arm. Commonly referred to as your biceps, the biceps work in conjunction with your lats to pull your body upward. Due to their relative small size, the biceps often fatigue before the larger and more powerful lats. Strong biceps are especially important on steep routes or when tackling an overhang.
There are numerous muscles that are responsible for flexing your fingers and your forearms so that you can grip the rock. These muscles are collectively called your forearm flexors and include muscles such as flexor carpi ulnaris, flexor carpi radialis and flexor pollicis longus. Long or strenuous climbs can leave these muscles engorged with blood and feeling very tight and fatigued. Climbers call this sensation getting pumped. Once your forearms are pumped, it is only a matter of time before your grip will fail and you will either fall or need to take a hands-free break before continuing your climb.
Gastrocnemius and Soleus
Climbers spend a lot of time balancing on very small toe-holds and often have to support their entire body weight on one foot. Climbing shoes are designed to keep your foot rigid and provide a stiff lever from the tips of your toes to your powerful calf muscles. Your have two major calf muscles -- gastrocnemius and soleus. If you spend a lot of time on the tips of your toes, you may find your calf muscles begin to shake with fatigue. Climbers euphemistically call this condition disco leg as it looks like you are tapping your foot to fast music.