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In the context of a straight leg heel raise, the gastrocnemius plays a significant role in the movement due to its primary function of plantarflexion at the ankle joint. During this particular exercise, the gastrocnemius, which is a large muscle located at the back of the lower leg, is primarily responsible for lifting the heel off the ground while keeping the knee extended.

Research indicates that when the knee is straight, the gastrocnemius becomes the dominant muscle involved in the action of climbing up onto the toes, performing approximately 90% of the work in this motion. This is largely because the gastrocnemius is most activated when the knee is straight compared to when it is bent, where the soleus muscle, which is located beneath the gastrocnemius, takes on more of the workload. This distinct division of labor is crucial for understanding how different exercises engage the lower leg muscles, which is an important consideration for trainers when developing effective training programs.

The other percentages do not accurately reflect the muscular contribution of the gastrocnemius during a straight leg heel raise, as its activity is significantly higher typically closer to the 90% mark.