Calf muscle strain injuries (CMSI)

Understanding the Prevalence

Calf muscle strain injuries (CMSIs) are a frequent concern among runners, ranking as the third most common running-related injury after hamstring strains and Achilles tendinopathy. Recent data indicates that soleus muscle strains occur at a rate of 0.1 per athlete per year, with an average recovery time of approximately 25 days, surpassing the 18.8-day average for hamstring strains .

Risk Factors and Recurrence

The likelihood of CMSI recurrence is notably high, especially within the first eight weeks following the initial injury. Approximately 90% of recurrent cases involve the soleus muscle. Factors contributing to increased risk include advancing age and a history of previous calf injuries. Notably, runners over 30 years old may experience a gradual decline in plantar flexor strength, losing about 1% per year, culminating in a 30% reduction by age 60.

Age-Related Biomechanical Changes

As runners age, several biomechanical alterations can predispose them to CMSIs:

• Decreased Step Length: A 13% reduction in step length is observed between ages 20 and 60, increasing to 20% by age 80.

• Reduced Ankle Power: Concentric ankle power during running can diminish by up to 47.9% from ages 20 to 80.

• Increased Tendon Compliance: Older runners often exhibit more compliant Achilles tendons, leading to greater eccentric elongation of the plantarflexor muscles .

Functional Anatomy Insights

The calf comprises two primary muscles: the gastrocnemius and the soleus. The soleus, rich in slow-twitch fibers, plays a pivotal role in endurance running and is responsible for a significant portion of propulsion and vertical support during running. Anatomically, the soleus contains three intramuscular tendinous structures—the medial and lateral aponeuroses and a central tendon—that function as rigid struts to enhance muscle origin and force transmission .

Clinical Implications

Given the high recurrence rates and the impact of age-related changes, it's crucial for runners and clinicians to:

• Implement Strength Training: Focus on exercises that enhance plantar flexor strength, particularly targeting the soleus.

• Monitor Training Loads: Gradually increase training intensity and volume to prevent overloading the calf muscles.

• Incorporate Flexibility and Mobility Work: Maintain optimal muscle-tendon unit flexibility to accommodate the demands of running.

By understanding the underlying factors contributing to CMSIs and adopting proactive measures, runners can mitigate the risk of injury and promote longevity in their running endeavours.