When people think of the calf muscle complex or “triceps surae,” they often focus on the large, superficial gastrocnemius muscle due to its prominent location and shape. However, the complex also includes another crucial muscle: the soleus. Positioned deep beneath the gastrocnemius, the soleus plays a vital role in ankle function and plantarflexion, making it a key driver of locomotion and a major force producer in the lower limb.
For runners, the soleus muscle is arguably the most important component of the calf complex due to its significant contribution to both push-off and acceleration, as well as its role in maintaining lower limb stability during the running gait cycle. The soleus can generate forces up to eight times a person's body weight during high-speed running, thanks to its large cross-sectional area and muscle fiber orientation. Unlike the gastrocnemius, which crosses both the ankle and knee joints (making it a biarticular muscle), the soleus is a uniarticular muscle. This means its effects are confined to the ankle joint, as it attaches distally to the Achilles tendon and does not influence knee motion. The primary function of the soleus is plantarflexion of the ankle, and it is particularly active when the knee is flexed, whereas the gastrocnemius is less active when the knee is bent.
Another reason the soleus is crucial for runners is its composition of Type I or “slow-twitch” muscle fibers. These fibers are well-suited for high-volume training due to their high mitochondrial and myoglobin content. The soleus's aerobic nature makes it more resistant to fatigue, playing a significant role in endurance running.
Training the Soleus for Optimal Performance
To optimize the performance of the soleus, it’s important to tailor your training specifically to this muscle. Since the soleus acts exclusively on the ankle joint as a plantar flexor, exercises should target it while the knee is flexed. This position minimizes the involvement of the gastrocnemius, which crosses both joints. The seated calf raise is an effective exercise for isolating the soleus, as it ensures that the soleus is the primary muscle engaged in plantarflexion.
When designing a training program for the soleus, consider factors such as frequency, intensity, volume, and exercise selection. Due to the high proportion of slow-twitch fibers, the soleus benefits from high-volume and high-frequency training. It also responds well to high-load strength training, given its substantial force output potential.
Here’s a sample soleus strengthening program:
Exercise: Seated and/or bent-knee calf raises (single or double leg)
Frequency: 2-4 sessions per week
Volume/Intensity: 3-4 sets of 15-20 repetitions with a load that induces appropriate fatigue
When trained with proper frequency, intensity, and technique, the soleus can significantly impact running performance. Strengthening the soleus can enhance running speed and endurance while reducing the risk of common running injuries, such as Achilles tendinopathy.
Whether you’re new to running, preparing for your first endurance event, or a seasoned runner looking to improve your performance, don’t overlook the importance of including soleus-focused exercises in your strength training regimen!
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