Sports science in English
from A to Z

Depending on the actions that they perform, muscles (see muscular system) are divided into several types.

• Tonic and phasic: tonic muscles are used to maintain muscle tone, that is they allow keeping the tone to win antigravity forces, also involuntarily. Phasic muscles, instead, are responsible for voluntary movements: usually those movements that we make with our limbs.
• Flexor, extensor, adductor, abductor and rotator: when a joint’s function is to move to and from different bone segments on the same level, the muscles placed before it allow the flexion by contracting (flexor muscles). On the contrary, the muscles placed behind the joint are responsible for allowing the extension (extensor muscles), moving away non-articular bone segments. In the most mobile joints, the articular mechanics occurs through the work of pairs of muscles that make opposite movements. There are also muscle groups which make possible the approach (adductors) or separation (abductors) from the median axis of the body, and muscles that allow internal or external rotation (rotator muscles).
• Protagonist, antagonist and synergistic: a muscle producing a movement with its contraction is called protagonist of that movement, whereas a muscle making the opposite movement is said antagonist. The muscles that contribute together to express a given movement are called synergistic muscles. Each type of activity involves a combined action of protagonist and synergistic muscles together with the antagonist muscles that must relax to not impede the contraction.