A running coach says this is the most important muscle you’re probably not strengthening

Person's bare legs below the knees seen from behind. They stand on tip toes and are wearing white trainers.

There’s a good chance that, not only have you not been strengthening this muscle, you might not even know its name.

“The soleus is the one muscle that is active throughout the whole gait cycle when you run,” says running coach James Stirling, who goes by London Fitness Guy on Instagram.