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Training calves with straight or bent legs? It makes a big difference in how much the major calf muscles are loaded. The muscle state responsible for this difference is called active insufficiency.
Muscles spanning two joints
Active insufficiency and
passive insufficiency occur when the range of motion of a joint is limited by a muscle that is already shortened or lengthened over another joint. Although the concepts mainly concern the range of motion of a joint, they also have two other consequences.
Active insufficiency and
passive insufficiency are also states in which a muscle, or a certain part of it, cannot exert maximum effort.
Active insufficiency and
passive insufficiency can apply when a muscle that spans two joints is put to work.
The simplest way to envision a muscle is as a rope connected to two ends of a hinge or pivot point. A rope that can contract or be stretched by an opposing force. A bit like “a rubber band with batteries.”
Some muscles span two joints/hinges. For example, the gastrocnemius, one of the calf muscles. The gastrocnemius is a so-called two-headed muscle. At the top (of the muscle), it attaches to two different points on the (bottom of the) thigh. At the bottom, both heads end in a shared attachment that runs over the ankle joint, known as the Achilles tendon.
In the (right) image next to this, you can see clearly how the muscle spans both joints. The advantage of this is that the gastrocnemius can not only help, for example, to stand on tiptoe but also to bend your leg at the knee. The downside is that both actions at the same time are much more difficult for the muscle.
Imagine the muscle again as a rubber band. What happens to this rubber band when you bend your knees? Then it becomes shorter. After all, the distance between both ends becomes smaller. Suppose you now point your feet downward, what happens then? Right, the muscle becomes even shorter because the attachment to the heel is brought towards the thigh.
Active insufficiency
Why is this important? Because a muscle that is already shortened over one joint cannot shorten maximally anymore. The muscle cannot then exert maximum effort when moving over the other joint.
Calf raises can be done standing or sitting. Standing, you do this by standing on the balls of your feet on a raised surface and holding a weight on the upper back/shoulders for resistance. Sitting, you do this with bent knees and the weight placed on the knees.
When sitting, the gastrocnemius is already shortened, so it cannot exert maximum effort anymore. If this were the only muscle to extend the ankle joint, then the conclusion would be clear: “Always do calf exercises standing.”
Training Calves: Why Standing?
Although in practice, this can be a good advice, it’s a bit more nuanced. People are pretty cleverly built. Evolution has ensured that you don’t have to depend on one muscle if it can easily be brought into an unfavorable position. In the images of the calf muscles, you can also see the soleus, which lies under and deeper than the gastrocnemius. This is attached at the top of the lower leg (instead of the thigh). At the bottom, it shares the attachment with the gastrocnemius. Some consider the gastrocnemius and soleus as a single muscle with three heads.
The soleus muscle only spans the ankle joint. This means that the soleus is not influenced by bending or straightening the knee. At least, not directly. Indirectly, this does have an effect. If the gastrocnemius cannot be fully engaged because the knee is bent and active insufficiency occurs, then the soleus must bear almost the entire load.
In other words: If you want to work both calf muscles, perform the exercises standing. If you want to isolate the soleus (as much as possible), train with bent knees.
Training Calves: Why Sitting?
Why would you want to isolate the soleus? That can be for aesthetic reasons. The muscle bellies of the gastrocnemius sit high on the calf and end in a long attachment. The muscle belly of the deeper lying soleus extends further down to end in a shorter attachment. I have colored them in the image next to/above for clarity. A highly developed gastrocnemius, but less developed soleus, makes the entire calf seem to start halfway down the lower leg. A better developed soleus adds thickness over a greater length.
Isolating the Gastrocnemius?
It is not possible to isolate the gastrocnemius. Firstly, you cannot bring the soleus into a mechanically unfavorable position in the same way. That does not mean it is impossible to make the gastrocnemius work harder than the soleus. After all, the gastrocnemius also helps to flex the leg. ‘Working harder’ here, however, does not mean ‘working hard’. The involvement of the gastrocnemius and its contribution to bending the knee are limited.
“Ideal Length of the Muscle”
The comparison of the muscle to a rubber band with batteries does not quite hold. Otherwise, a fully stretched muscle could deliver the most tension. That is not the case. Those ‘batteries’ in the rubber band, the sarcom
eres, work as it were like ‘active Velcro’. The muscle fiber is a long, thin cell. In that cell, there are threads with the thickness of 1/100th of a hair. These ‘myofibrils’ are formed by two chains of proteins, myosin and actin. These can grab each other at a further point and slide in and out of each other, allowing the muscle to contract and relax.
I called it ‘active Velcro’ because Velcro needs minimal overlap to allow both sides to grip each other. When a muscle is stretched too far, the overlap between the actin and myosin filaments is too small to generate maximum force.
So the muscle should not be already shortened or stretched too far to deliver maximum force. The optimal tension would be 1.2 times the tension at rest. With higher tension, passive insufficiency would occur [Levangie & Norkin].
Passive Insufficiency of the Gastrocnemius
So far, we have discussed
active insufficiency: a muscle that is already shortened over one joint and then has to contribute to movement of a second joint.
Passive insufficiency occurs when the muscle is already lengthened over one joint and then has to lengthen over a second joint. If full stretch over both joints has already been reached, then the muscle cannot exert maximum effort to shorten again from this position. The overlap between actin and myosin is too small for maximum contraction.
The gastrocnemius can also experience passive insufficiency. During calf training, however, active insufficiency occurs much more frequently.
Passive insufficiency of the gastrocnemius occurs when you have your thigh straightened and then want to point your toes towards the knee (or vice versa). Try it. Then bend your knee. You will feel that the stretch is immediately reduced at the back of the knee.
In strength training, you may encounter this when doing standing calf raises and fully lower the heels until a full stretch is achieved. If you want to push up from that position, the gastrocnemius cannot be maximally engaged, and the soleus must again bear a larger part of the load. However, sinking so low would likely result in your feet slipping off the device.
More Active and Passive Insufficiency
I took calves as the first example to illustrate the operation and consequences of
active and passive insufficiency. In subsequent articles, I will describe other muscle groups that deal with this principle.
Armed with this knowledge, you will immediately understand the influence of many variations of exercises on the engagement of different muscles (or muscle heads).
Sources
- Landin D, Thompson M, Reid M. Actions of Two Bi-Articular Muscles of the Lower Extremity: A Review. J Clin Med Res. 2016;8(7):489-94.
- suppversity.blogspot.com/2011/08/suppversity-emg-series-gluteaus-maximus
- Levangie, P., and C. Norkin. 22 Strength and Conditioning Journal August 2002 Joint: Structure and Function (2nd ed.). Philadelphia: F.A. Davis, 1992
