Apr 2015 18

The calf muslces

By: Dave Wheeler

Continuing an occasional series about the muscles of the body, today we're going to look at the calf muscles.


Pic by wikicommons.org


As the image shows, there are actually two muscles of the calves - the bulky gastrocnemius which has two heads running up the back of the lower leg, and the soleus which is a broad muscle lying underneath the gastrocnemius. Together, these muscles form what's called the triceps surae (tri = 3, because if you add up both heads of gastroc plus the soleus, there are 3 muscle masses there).

Both muscle combine down towards the foot into a single very strong tendon that we know as the achilles tendon, but which in anatomical terms is called the calcaneal tendon.


The gastrocnemius

The bulky 2-headed gastrocnemius, like the hamstrings, is one of a few muscles of the body that crosses two joints - the knee and the ankle. This is known as being biarticular ("bi" since the muscle crosses 2 joints; "articular" since the muscle articulates, or moves, 2 parts of the body.

Gastrocnemius actually starts (originates) from between the hamstring tendons at the back of the thigh bone, or femur.

The muscles run behind the knee to about halfway down the lower leg along the tibia (the larger and stronger bone of the lower leg).

So gastrocnemius is actually quite a short muscle - from about halfway down the lower leg it blends into the achilles tendon.

Interestingly, though the name gastrocnemius is translated from the Greek meaning "belly of the leg", it's actually quite thin compared to to the soleus beneath it.


The soleus

The soleus is deep to gastrocnemius, that is, it lies underneath it.

As I've mentioned already, soleus is a single broad, flat, thick muscle.

It's often the muscle that you feel if you run your fingers down the sides of your calf muscle - the fibres of soleus bulge out on both sides of gastrocnemius - on both the inside and outside of the leg.

Soleus also runs further down the leg than gastrocnemius before fusing into the achilles tendon.

The muscle contractions of soleus are very powerful - apparently, it's nicknamed "the second heart" because its contractions are so important in returning blood to the heart.


The actions of the calf muscles

Since both soleus and gastrocnemius become the achilles tendon which crosses the heel bone (the calcaneus), when the muscle contracts, it pulls the toes down towards the floor.

This action is known as plantarflexion (since it helps plant the forefoot and toes on the ground once the heel has struck during the gait cyle of walking)

But remember, the superficial gastrocnemius crosses 2 joints - it originates up on the femur, so when it contracts, it's also capable of flexing the knee.


The other function of the calf muscles - shock absorbers

one of the major functions of the calf muscles is to absorb the shock from walking and running.

With every footstep that you take when walking, 1½ times the force of your body weight spirals up your leg. So if you weigh 80kg (about 12½ stone) then 120,000 Newtons of force go spiralling up your body with every step. 

If you run, then the amount of force spiralling up the leg with every stride goes up to twice the weight of your body.

The soleus and gastrocnemius are the first shock-absorbers that that force comes through, so they absorb a lot of force in order to protect the knee joint.

Obviously, if the calf muscles are overtight (or, hypertonic) then they'll have the shock-absobency of a closed up "slinky"... none!


Tight calf muscles are common in runners, cyclists and walkers. As ever, if you think I can help, give me a call.