The soleus is the muscle on the outside of your calf. This muscle is smaller than the gastrocenemius and generally less powerful. With that in mind, it’s a vital muscle to work out especially if you want your calves to appear wider and you want to maximize the diamond shape. Unfortunately, it’s difficult to work both the soleus and the gastrocnemius at the same time. I’ll explain why below.
The soleus activates when the knee is almost full flexed, meaning it’s approaching or at a ninety degree angle. While the soleus is activated, the gastrocnemius is inactive, meaning that it’s pretty much impossible to work both. When I work out, I like to do calves every day. In order to give each muscle additional recovery time, I’ll rotate between working the gastrocnemius and soleus daily. This has allowed me to build stronger and more powerful calves than I would have been able to otherwise. There is, however, one exercise that’ll hit both of these muscles and I’ll mention it below.
The main exercise that is used to work the soleus is the seated calf extension. As I said, this exercise places minimal stress on the stronger gastrocnemius, so I recommend using slightly less weight than you’d do with normal calf extensions. You can start with your foot in a flexed state and then go all the way to full extension to utilize the full range of motion.
You’ll also find that the soleus is hit pretty hard in the barbell lunge. This is primarily on the back leg because the foot enters an extension as the lunge is completed. Most of the stress on the soleus happens on the return, where the weight has to be stabilized and balanced on the ball of your foot.
Calf extensions at a 45 degree angle will hit the soleus and gastrocnemius fairly equally and are great for building overall leg mass. While this exercise, like I said, is good for building leg mass, using it means you can not rotate between your different muscles. On top of that, you’ll have to work in one rep range for both muscles. This is not optimal because they contain different levels of fast and slow twitch fibers.
In regard to slow and fast twitch fibers, the soleus is primarily composed of fibers in the slow twitch range. This means that it is less explosive but is more capable of endurance. With that in mind, you should work the soleus in the high rep range while the gastrocnemius should be worked in the low rep range. This is why it is important to separate the workouts for these different calf muscles.