How should we train the calf muscles?

How can we design a strength training program that will maximize the growth of the calf muscles (triceps surae)? What factors do we need to take into consideration, and how do each of these factors affect the different variables within the training program?

What information do we need?

We can use the research literature to enhance our training programs if we search for information about the gross anatomy, regional anatomy, and internal moment arm lengths of a muscle, in addition to its working sarcomere lengths, and susceptibility to muscle damage. Each of these factors provides information that is useful for different reasons (read more).

• Gross anatomy describes the locations of the attachments of the muscle to the skeleton. Learning the basic anatomy of a muscle helps us figure out suitable exercises, and also helps us see how we might alter them to target different muscles within a group.
• Regional anatomy describes the way in which a muscle divides into several internal regions, and this tells us whether we are going to need multiple exercises to train the muscle.
• The internal moment arm lengths of a muscle determine its leverage on the joint, and therefore its contribution to a joint moment, relative to other agonist muscles. This allows us to see where peak force in an exercise joint range of motion needs to be, to target one muscle within a group (or one region of a muscle). We can alter the point where peak force occurs by our exercise selection and by our choice of external resistance type.
• The working sarcomere lengths describe the lengths of the sarcomeres inside a muscle over its joint angle range of motion. It allows us to see if the muscle can experience (1) active insufficiency (and so will be trained poorly by exercises involving peak forces at very short muscle lengths), and (2) stretch-mediated hypertrophy (and so will be trained more effectively by exercises involving peak forces at very long muscle lengths).
• The susceptibility of a muscle to damage is how easily a muscle is damaged by a workout. It is affected by: (1) muscle fiber type proportion, (2) its level of voluntary activation, and (3) the working sarcomere lengths of its muscle fibers. The amount of muscle damage that a muscle experiences after a workout is the main determinant of the frequency (and volume) we can use for training it, and it also influences our choice of exercises (single-joint vs. multi-joint, single-limb vs. multi-limb, and full vs. partial range of motion).

#1. Anatomy

Relative muscle sizes

The calf muscles are variously known as the gastrocnemius-soleus complex, the triceps surae, and the calves. The group comprises the gastrocnemius (medial and lateral heads) and the soleus, in addition to the much smaller plantaris, which is not present in all humans. The three larger calf muscles vary substantially in size, with the soleus being by far the largest. Indeed, one study found that the soleus, the medial gastrocnemius, and the lateral gastrocnemius accounted for approximately 52%, 32%, and 16% of total calf muscle volume, and approximately 62%, 26%, and 12% of total calf muscle physiological cross-sectional area, respectively. Other research has often reported similar results. Thus, despite the fact that it lies deep to the lateral gastrocnemius and is therefore less apparent to view, the soleus actually provides the greatest contribution to calf muscle size.

Origins and insertions

The large soleus muscle originates on the posterior surfaces of the tibia and fibula (the shin bones). Consequently, it crosses (and therefore plantar-flexes) the ankle, but does not cross the knee (and thus cannot perform any action at this joint). As indicated by its name, the medial head of the gastrocnemius originates from the medial supracondylar ridge and the adductor tubercle, on the posterior surface of the femur (the thigh bone above the knee joint), while the lateral head originates on the posterior surface of the lateral femoral condyle. Both heads insert via the Achilles tendon into the posterior surface of the calcaneus, at the foot of the ankle. Since the gastrocnemius crosses over the rear of the knee joint as well as over the rear of the ankle joint, it can flex the knee (and thereby act as a synergist with the hamstrings) as well as plantar-flex the ankle (and thereby act as a synergist with the soleus).

Tendons and subtendons

Although all three calf muscles insert into the Achilles (calcaneal) tendon (and are therefore treated as having the same insertion), they do each have subtendons that differ in their behavior and mechanical properties, which allow the muscles to operate somewhat independently from one another. In particular, the Achilles tendon can be easily subdivided into two structurally-distinct parts: (1) a proximal part, which originates from the gastrocnemius, and (2) a distal part, which originates from the soleus. The arrangement of these two parts can vary between individuals, which may affect the extent to which each muscle is used during certain exercises and movements. Also, while the two parts do join at the point where the gastrocnemius subtendon meets the subtendon from the soleus, the tendinous fibers from each muscle actually form three, unique fascicles of the Achilles tendon. These three fascicles twist around one another, such that the fibers from the medial gastrocnemius are superficial, the fibers from the lateral gastrocnemius are deep, and the fibers from the soleus are found in the central part of the tendon. Practically, this means that, despite their apparently common insertion point, the three calf muscles likely enjoy a relatively high degree of independence during normal activities such as walking.

Practical implications

In practice, the calf muscles can be subdivided into three parts: the soleus, the medial gastrocnemius, and the lateral gastrocnemius. The single-joint soleus, which plantar-flexes the ankle, is the largest single muscle, making up more than half of the calves by volume. The gastrocnemius is a two-joint muscle that flexes the knee (thereby acting as a synergist to the hamstrings) as well as plantar-flex the ankle. Its medial head is much larger than its lateral head. Although the calf muscles have a common tendon, it is formed of intertwined tendinous fascicles, which allow the individual muscles to function somewhat independently.

#2. Regional anatomy

Anatomy and innervation

Anatomical investigations into the medial gastrocnemius have revealed it to contain a single, unipennate region, with muscle fascicles running from origin to insertion. Yet, it can appear bipennate because of the central location of the tendon, which means that fascicles on the lateral and medial sides of the muscle curve inwards towards the insertion. Although similar data for the lateral gastrocnemius are scarce, it seems likely that it displays a fairly similar appearance. In contrast, anatomical studies of the soleus have revealed two separate regions, a bipennate anterior region and a (typically) unipennate posterior region. Even so, substantial inter-individual variation exists. Thus, it is more likely that the larger soleus will display distinct regions (and therefore benefit from multiple exercises) than the two gastrocnemius heads.

Muscle activation

Muscles can subdivide into functional regions that are activated in response to the need to perform different tasks. While this likely occurs in tandem with the varying internal moment arm lengths of the various regions (because muscles and regions of muscles seem to be recruited in line with their mechanical advantage), it also requires motor units to control muscle fibers that are grouped within those regions. Thus, muscle activation must also be localized, according to the task that is being performed. Several investigations using surface electromyography (EMG) have found evidence that the human medial gastrocnemius muscle displays regional activation, and that such regional activation is linked to the performance of specific, different tasks. Additional, similar evidence has been uncovered with the use of functional MRI scans. However, there are also some conflicting reports suggesting that there is no such division of the muscle into regions.

Practical implications

In practice, the calf muscles display evidence of regional anatomy and activation, but which regions are activated in response to which movements is unknown. It is more likely that there are anatomically separate regions within the soleus than within each of the gastrocnemius heads.

#3. Internal moment arm lengths

As plantar-flexors, the calf muscles have plantar-flexion internal moment arms. The lengths of these internal moment arms can theoretically change with ankle angle. Some research has found that calf muscle plantar-flexion internal moment arm lengths do not change substantially with ankle joint angle. However, other studies have found that calf muscle plantar-flexion internal moment arm lengths increase with increasing plantar-flexion angle, thereby being greatest at shortest muscle lengths. Unfortunately, since the calf muscles share a common insertion point on the Achilles tendon, little work has been devoted to understanding differences in the internal moment arm lengths of each individual muscle, and how these might alter with changing joint angles.

It seems likely that the calf muscles evolved to function optimally when walking, and this is reflected in their tendency to display long internal moment arm lengths for plantar-flexion in a range around neutral. During the walking gait cycle, the ankle joint begins at a moderate level of plantar-flexion at ground contact, reaches a moderate level of dorsiflexion during the early stance phase, then reverses to a high level of plantar-flexion by late stance. Even so, when walking, the calf muscles are mainly active during the first half of the stance phase, and are largely inactive thereafter. They do not act to propel the body center of mass forwards at the end of the gait cycle, as occurs during running. Thus, force production is required mainly in the range around neutral.

Curiously, some studies have found that hip rotation angle can affect the relative activation of the medial and lateral gastrocnemius muscles during plantar-flexion. Specifically, while the medial gastrocnemius is normally much higher in activation than the lateral gastrocnemius (most likely due to its larger size), internally rotating the hip (such that the toes point inwards) can increase the contribution of the lateral gastrocnemius to force production by increasing its activation. Similarly, externally rotating the hip (such that the toes point outwards) can increase the contribution of the medial gastrocnemius to force production by increasing its activation. This effect may occur due to changes in the internal moment arm lengths of the affected muscles, or perhaps for other reasons.

Practical implications

In practice, the calf muscles all seem to have their longest plantar-flexion internal moment arm lengths in neutral (or at short lengths), which may be adaptive for walking (or running). Whether these moment arm lengths differ between muscles is unclear. Internally rotating the hip (pointing the toes inwards) may increase the contribution of the lateral gastrocnemius to plantar-flexion, while externally rotating the hip (pointing the toes outwards) may increase the contribution of the medial gastrocnemius. The reasons for this are unknown.

#4. Working sarcomere lengths

Some limited research has investigated the working sarcomere length ranges of the gastrocnemius and soleus muscles. This research suggests that the two muscle groups seem to contain sarcomeres that work on the ascending limb, plateau, and descending limb of the length-tension relationship. Yet, the gastrocnemius seems to start lower down the ascending limb (which gives it greater potential for experiencing active insufficiency) and also seems to extent further down the descending limb (which also gives it greater potential for experiencing stretch-mediated hypertrophy).

When comparing the muscles of the quadriceps, those muscles that contain sarcomeres that reach further down the descending limb of the length-tension relationship (such as the vastus medialis) experience greater hypertrophy when exposed to active stretching (eccentric training). Therefore, we should expect the gastrocnemius to display greater increases in muscle fiber length and diameter after training than the soleus. Yet, this does not happen. In fact, the soleus displays a greater increase in size than the gastrocnemius. This could be explained in two ways. Firstly, it is possible that our current measurements of sarcomere length ranges are inaccurate, and that the soleus actually has sarcomeres that reach further down the descending limb of the length-tension relationship than the gastrocnemius. Secondly, it is possible that the proportionally greater size of the soleus leads its motor units to be recruited to a preferentially greater degree than the gastrocnemius during submaximal voluntary contractions of the calf muscles (although eccentric training often uses maximal efforts, it rarely involves full recruitment).

Practically speaking, bodybuilders have used the phenomenon of active insufficiency for many years, by training the soleus using seated calf raises. This position shortens the gastrocnemius, which is a knee flexor (but does not affect the length of the soleus, which is not). Since both of these muscles display active insufficiency at short lengths, it is feasible that this exercise will put the gastrocnemius into a greater degree of active insufficiency than the soleus throughout more of the exercise range of motion, and thereby allow the soleus to contribute to a greater extent.

Practical implications

In practice, each of the calf muscles contain sarcomeres that work on the ascending limb, plateau, and descending limb of the length-tension relationship. Thus, they can experience active insufficiency and stretch-mediated hypertrophy. Whether the gastrocnemius or soleus can be targeted preferentially by using active stretch (larger ranges of motion or eccentric training) is currently unclear. It is feasible that the soleus might be targeted by using calf raises with a flexed knee, since this shortens the gastrocnemius and may put it into active insufficiency.

#5. Susceptibility to muscle damage

Comparisons with other muscles reveal that the calf muscles recover more quickly from a standardized workout than any other muscle, with the sole exception of the quadriceps. This may be the result of several factors.

First and foremost, the calf muscles are famous for being the most slow twitch muscles, although it is actually only the larger soleus that is extremely slow twitch, with current estimates ranging between 70 and 96% of type I muscle fibers. In contrast, the gastrocnemius has a somewhat more balanced fiber type, with estimates ranging between 50 and 70% of type I muscle fibers. Even so, this is still toward the upper end of the range for human muscles. When muscles contain a large proportion of slow twitch muscle fibers, they are very difficult to damage, because their oxidative nature is highly protective against the accumulation of calcium ions, which is what triggers the release of the muscle-damaging proteases.

Secondly, while the calf muscles are easier to activate voluntarily than the quadriceps, they are not as easy to activate voluntarily as many other, smaller muscles. Thus, their most easily-damaged muscle fibers (which belong to the highest-threshold motor units) are rarely trained. Their activation does not seem to be particularly affected by knee angle. Yet (and counter-intuitively), it seems to be easier to activate the calf muscles during movements involving both knee extension and ankle plantar-flexion than during single-joint plantar-flexion exercise. This greater voluntary activation seems to occur mainly as a result of increased soleus muscle activation. Yet, gastrocnemius muscle activation does not appear to be negatively affected by knee extension force production, despite it being a knee flexor, and therefore an antagonist to the knee extensors. Consequently, it is feasible that most commonly-used calf training exercises (such as seated and standing calf raises) actually involve lower levels of calf muscle voluntary activation than might be achieved during multi-joint exercises such as deadlifts.

Practical implications

In practice, the calf muscles recover more quickly than most other muscles in the body, with the sole exception of the quadriceps. This is likely mainly the result of their prevailing slow twitch fiber type, but may also occur due to a lower level of voluntary activation than some other muscles, which is particularly noteworthy during direct calf training exercises such as calf raises.

What is the takeaway?

The calf muscles can be subdivided into three parts: the soleus, the medial gastrocnemius, and the lateral gastrocnemius. The single-joint soleus, which plantar-flexes the ankle, is the largest single muscle, making up more than half of the calves by volume. The gastrocnemius is a two-joint muscle that flexes the knee (thereby acting as a synergist to the hamstrings) as well as plantar-flex the ankle. Its medial head is much larger than its lateral head. Although the calf muscles have a common tendon, it is formed of intertwined tendinous fascicles, which allow the individual muscles to function somewhat independently. Although the calf muscles display evidence of regional anatomy and activation, which regions are activated in response to which movements is unknown.

The calf muscles all seem to have their longest plantar-flexion internal moment arm lengths in neutral (or at short lengths), which may be adaptive for walking (or running). Whether these moment arm lengths differ between muscles is unclear. Internally rotating the hip (pointing the toes inwards) may increase the contribution of the lateral gastrocnemius to plantar-flexion, while externally rotating the hip (pointing the toes outwards) may increase the contribution of the medial gastrocnemius. The reasons for this are unknown.

Each of the calf muscles contains sarcomeres that work on the ascending limb, plateau, and descending limb of the length-tension relationship. Thus, they experience active insufficiency and stretch-mediated hypertrophy. Whether the gastrocnemius or soleus can be targeted preferentially by active stretch (larger ranges of motion or eccentric training) is unclear. It is feasible that the soleus might be targeted by using calf raises with a flexed knee, since this shortens the gastrocnemius and may put it into active insufficiency.

The calf muscles recover more quickly than most other muscles in the body, with the sole exception of the quadriceps. This is likely mainly the result of their prevailing slow twitch fiber type, but may also occur due to a lower level of voluntary activation than some other muscles, which is particularly noteworthy during direct calf training exercises such as calf raises.