Ask a runner what the most important muscle is for running these days and I betcha 8 times out of 10 they’ll say their glutes. Maybe they’ll say the “core” - but the core is actually a group of muscles and more of a concept - there’s no commonly accepted definition of which muscles the core includes. Some people include all the torso muscles, some just the deep anterior musculature (transverse abdominus), some include the pelvic floor, the diaphragm, and even the glutes.
I’m not saying the glutes and core muscles are not important! Just that from my experience they seem to be an easy thing to blame when there could be a larger problem elsewhere.
The most important muscles are the calves, specifically the soleus.
The soleus is one of two muscles that make up the calf complex in the lower leg. The other is the gastrocnemius. Both S & G insert into the achilles tendon, which crosses the back of the ankle. They are our main plantarflexors at the ankle, providing our push off forces while running as well as controlling how fast our tibia (shin bone) moves forward over our foot in the stance phase of running.
One major difference between S & G is that the gastroc also crosses the back of the knee, where it assists the hamstrings in flexing/bending the knee. The soleus only crosses the ankle.
There is also a difference in the muscle fiber types. Endurance activities such as running and walking place more stress on the soleus (built of more slow twitch fibers), while sprinting places more stress on the gastroc (more fast twitch fibers) (O’Neill 2019).
Here’s why we think the soleus is the most important muscle for distance runners.
1. The peak load of the soleus is about twice as much as any other muscle while running.
In 2012, Dorn et al. showed the soleus itself has a peak load of up to 8 times body weight (BW) while running. The gastroc is up to 3 times BW, the quads 4-6 times BW, and the glutes 4 times BW. The more forces muscles have to withstand while running, the greater emphasis we should put on strengthening them.
2. We’re (typically) running slower than 4-minute mile pace.
Dorn et al. also found that the amount of work done by our muscles varies depending on our running speed.
When running less than 15 mph (4-minute mile pace) we increase our speed by pushing harder into the ground, mainly with our calves. This allows us to cover more distance with each stride.
At and above 15 mph we further increase our speed by increasing our leg turnover. This is accomplished by using a hip strategy with greater emphasis on the hip flexors, hamstrings, and gluteus maximus.
We see these concepts play out in the clinic with hamstring strains being more common with sprinters, and achilles issues more common with distance runners.
3. Many of the most common running-related injuries are associated with limited calf strength.
Significantly weaker calves have been linked to achilles tendinopathy, one of the most common running-related injuries. There is thought to be greater involvement of the soleus than the gastroc with achilles tendinoapthy. (O’Neill 2019).
Decreased calf strength is also associated with plantar fasciitis and medial tibial stress syndrome (shin splints), and is commonly something I include with management of stress fractures throughout the lower leg. The stronger the calf, the fewer loads to the achilles, plantar fascia, and medial tibia.
Now that we have determined our most important running muscle, it would behoove us to be incorporating regular strength training for our calves. Not only will we be able to run faster by pushing harder into the ground with each stride, but we may be able to prevent many of the common running-related injuries of the lower leg and foot.
O’Neill suggests building up to 2 times our body weight with calf exercises, to appropriately load the calves and best prepare them for the demands of running.
We rarely see runners loading their calves this much (perhaps why we see so many runners with achilles tendinopathy, plantar fasciitis, shin splints, & calf strains?). However, like with any loading to our bodies, a gradual increase in load is key to prevent other injuries from popping up.
Most calf strengthening exercises involve going into plantarflexion of the ankle, by coming up onto the toes and raising the heels. Heel raises are important. However, it is just as important to perform them correctly. When performing typical heel raises we want to keep a neutral rearfoot position, which requires ankle stability and control with optimal strength of the ankle evertors (peroneals) and inverters (posterior tibialis).
Here's a demonstration of a technique that you can use to make sure you perform your heel raises correctly.
We’ve also included some of our favorite calf strengthening exercises below.
Training the soleus is vital for runners, and is always included in our CPT Strength Training for Runners monthly subscription program. Click here to learn more
Be sure to share this info with a friend!
Dr. Kelton Cullenberg, PT, DPT
Cullenberg Physical Therapy and Performance
O'Neill S, Barry S, Watson P. Plantarflexor strength and endurance deficits associated with mid-portion Achilles tendinopathy: The role of soleus. Phys Ther Sport. 2019 May;37:69-76. doi: 10.1016/j.ptsp.2019.03.002. Epub 2019 Mar 9. PMID: 30884279.
Dorn TW, Schache AG, Pandy MG. Muscular strategy shift in human running: dependence of running speed on hip and ankle muscle performance. J Exp Biol. 2012 Jun 1;215(Pt 11):1944-56. doi: 10.1242/jeb.064527. Erratum in: J Exp Biol. 2012 Jul 1;215(Pt 13):2347. PMID: 22573774.