During movement from plantar-flexion to dorsi-flexion the muscle-tendon-complex of the triceps-surae is
A contracting
B in steady state
C shortening
D lengthening
The correct answer and explanation is:
The correct answer is D: lengthening.
Explanation:
The triceps surae is a group of muscles located in the calf region of the lower leg, consisting of the gastrocnemius and soleus muscles, along with their corresponding tendons. These muscles play a critical role in plantar flexion, where the toes point downward, as seen when standing on tiptoe or pushing off during walking or running.
When transitioning from plantar flexion (toes pointing downward) to dorsiflexion (toes pointing upward), the triceps surae undergoes a lengthening contraction. This happens because the muscle fibers of the gastrocnemius and soleus, which were previously shortened during plantar flexion, now stretch as the foot moves into dorsiflexion. This process involves the elongation of the muscle fibers in response to the opposing force that is trying to flex the ankle joint in the opposite direction.
The lengthening contraction, also known as an eccentric contraction, occurs when the muscle is actively resisting a force while it is being stretched. In this case, as the foot moves from a plantar-flexed position to a dorsiflexed position, the triceps surae muscles must resist the motion and gradually elongate, which generates tension and helps control the ankle joint’s movement.
In contrast, a concentric contraction would occur if the muscle was actively shortening, as in the case of performing a plantar-flexion movement. During steady state, the muscle is neither shortening nor lengthening but rather maintaining its length under tension, which does not apply during the transition from plantar flexion to dorsiflexion.
Therefore, when moving from plantar flexion to dorsiflexion, the muscle-tendon complex of the triceps surae is lengthening, which is a critical action for controlling the rate of movement and maintaining stability during this transition.