When the triceps contracts what does the biceps do?

Answer 1

When you contract your bicep, the tricep is relaxed as it is intended to resist against a force in the complete opposite direction. As it is relaxed, it stretches because the insertion point of the muscle in the forearm experiences a pull and the tendon is stretched around the bend of the elbow. There may be a very small contraction in the tricep, to stabilise the contraction of the bicep.

Answer 2

Same as any other muscle. Details bit too elaborate for here but I'll give it a go. Micro filaments within the muscle join and pull each other together. This causes the muscle to shorten and contract. When the muscle relaxes, the filamants break apart and the muscle returns to resting length.

For more detail, look up Sliding Filament Theory, currently the most superior theory regarding muscle contraction.

Answer 3

The bicep contracts when bending the arm. The only action of all skeletal muscles (ie those that are attached to and act on bones) that produces movement is to contract. In the case of bending the arm, the biceps contract, thereby bringing the bones of the lower arm and upper arm closer together, and therefore bending the arm. At the same time, the triceps, which are on the other side of the upper arm, relax (ie do nothing) so as to let the biceps work. Many muscles are used in simple movements in a stabilising manner to support the primary movers, which accounts for the feeling that other muscles are tensing.

Answer 4

Yes they do. As they oppose the action of the other, they are referred to as "an antagonistic pair of muscles".

Answer 5

The triceps and biceps are antagonistic muscle groups; the triceps straighten the arm and the biceps pull it in the opposite way. Therefore, when the triceps contract, the biceps lengthen.