Final answer:
During a vertical jump, the concentric contraction of the gastrocnemius and soleus muscles at the ankle is responsible for plantar flexion, lifting the heel and propelling the body upward. correct answer is B .
Step-by-step explanation:
The muscle that is activated at the ankle during lift-off from the ground when performing a vertical jump is the concentric contraction of the gastrocnemius and soleus. This is the action that contributes to plantar flexion, where the heel is lifted off the ground, and the toes are pointed downward, propelling the body upwards.
During a vertical jump, it is crucial for these muscles in the back of the leg to contract in a concentric manner, which means they shorten and generate force. The gastronemius and soleus muscles attach to the calcaneus bone via the Achilles tendon. These muscles pulling on the Achilles tendon cause the foot to plantar flex, generating the force required for the propulsive movement to jump. This opposes dorsiflexion where muscles such as the tibialis anterior are involved in lifting the front of the foot.