Beyond the Rep Count: Is a 1.5x Bodyweight Seated Calf Raise the Missing Link in Runner Injury Prevention?

Introduction

As physical therapists, we routinely manage running-related injuries, with Achilles tendinopathy consistently ranking among the most common and frustrating diagnoses. While we diligently assess gait, flexibility, and proximal control, are we giving sufficient attention to the raw capacity of the workhorse beneath the gastrocnemius – the soleus? Emerging clinical benchmarks suggest a specific strength target for the seated calf raise may offer valuable insights into a runner's resilience and risk profile. This post explores the critical role of the soleus, its link to tendinopathy, and the clinical utility of aiming for a bilateral seated calf raise strength of 1.5 times bodyweight (BW).

The Unsung Hero: Why the Soleus Demands Our Attention

While the gastrocnemius provides explosive power, the soleus is the tireless endurance muscle crucial for running. Its unique advantages include:

• Massive Load Absorption: During running, the soleus manages incredibly high loads, estimated at 6.5-8 times body weight with each stride (Komi, 1992; Fukashiro et al., 1995).

• Postural Control & Fatigue Resistance: Its predominantly slow-twitch fiber composition allows it to provide sustained postural control and resist fatigue during long-duration activities like distance running.

• Achilles Tendon Regulation: It plays a primary role in controlling tibial advancement over the foot and modulating load transmission through the Achilles tendon.

Connecting Soleus Capacity and Tendinopathy Risk

Insufficient soleus strength or endurance capacity has significant implications, particularly for Achilles tendon health. When the soleus fatigues or lacks the requisite strength to manage running loads:

• Increased Tendon Strain: Load that the muscle cannot attenuate may be excessively transferred to the Achilles tendon, increasing strain and potentially leading to micro-damage over time (Malliaras et al., 2015).

• Altered Biomechanics: Compensatory strategies may arise, potentially altering foot and ankle mechanics in ways that further stress the tendon or other structures.

• Reduced Shock Absorption: Diminished capacity compromises the lower limb's ability to absorb ground reaction forces effectively.

Research has demonstrated links between deficits in plantarflexor strength and endurance (including soleus function) and the presence of Achilles tendinopathy (O'Neill et al., 2019; Willy & Meira, 2016).

Quantifying Strength: The Seated Calf Raise Benchmark

While the traditional single-leg standing calf raise test (aiming for >25-30 reps) provides valuable information about gastrocnemius/soleus endurance and function, it may not adequately capture peak soleus strength.

The seated calf raise, by flexing the knee (~90 degrees), preferentially isolates the soleus. This makes it an ideal exercise for assessing and targeting this crucial muscle. A strong clinical guideline is emerging:

• Target: Aim for runners to achieve a bilateral seated calf raise (e.g., estimated 1RM or heavy 3-5 rep sets) approaching 1.5 times their body weight.

Why 1.5x BW? This figure isn't (yet) derived from large-scale RCTs establishing it as a definitive injury cut-off. Rather, it's a clinical benchmark reflecting the known high demands placed on the soleus during running. Achieving this level suggests a robust capacity to handle repetitive loading, potentially offering a buffer against fatigue-related strain and injury. It aligns with the principles of heavy slow resistance training often found effective in tendinopathy rehab (Beyer et al., 2015).

Clinical Application for Physical Therapists

Integrating this benchmark into practice can enhance runner management:

1. Assessment: Use the seated calf raise (bilaterally, with proper form emphasizing full range of motion) to gauge soleus capacity relative to body weight. Document the load achieved for a specific rep range (e.g., 5RM) and compare it to the 1.5x BW guideline.

2. Rehabilitation Target: For runners recovering from Achilles tendinopathy or other lower leg injuries, progressively building towards this 1.5x BW goal can be a key criterion for load tolerance and return-to-running readiness.

3. Injury Prevention Screening: In asymptomatic runners, assessing seated calf raise strength can identify potential deficits before they contribute to injury, allowing for targeted preventative strengthening.

4. Patient Education: Explaining the role of the soleus and providing a tangible strength goal can improve patient understanding and adherence to strengthening programs.

Important Considerations

• Guideline, Not Gospel: This is a clinical benchmark, not an absolute guarantee against injury. Individual needs vary.

• Quality Over Quantity: Emphasize proper form, full range of motion (especially the stretch at the bottom), and controlled tempo.

• Holistic Approach: Soleus strength is one piece of the puzzle. Continue assessing and addressing kinetic chain factors, gait mechanics, training load management, and plyometric capacity.

• Equipment Variation: Be mindful that leverage and resistance can vary between different seated calf raise machines.

Conclusion

The soleus muscle is fundamental to a runner's ability to tolerate load and resist injury, particularly Achilles tendinopathy. While traditional endurance tests are useful, evaluating and enhancing peak soleus strength via the seated calf raise provides critical insights. Targeting a bilateral seated calf raise capacity of approximately 1.5 times body weight offers a valuable, clinically relevant benchmark for physical therapists aiming to build more resilient runners and effectively rehabilitate lower leg injuries. Let's ensure we aren't underestimating—or under-loading—this vital muscle.

References 

Beyer, R., Kongsgaard, M., Hougs Kjær, B., Øhlenschlæger, T., Kjær, M., & Magnusson, S. P. (2015). Heavy slow resistance¹ versus eccentric training in patients with chronic Achilles tendinopathy: A randomized controlled trial. The American Journal of Sports Medicine, 43(7), 1704–1711. https://doi.org/10.1177/0363546515584760

Fukashiro, S., Komi, P. V., Järvinen, M., & Miyashita, M. (1995). In vivo achilles tendon loading during jumping in humans. European Journal of Applied Physiology and Occupational Physiology, 71(5), 453–458. https://doi.org/10.1007/BF00238589

Komi, P. V. (1992). Stretch-shortening cycle. In P. V. Komi (Ed.), Strength and power in sport (pp. 169–179). Blackwell Scientific Publications.

Malliaras, P., Barton, C. J., Reeves, N. D., & Langberg, H. (2013). Achilles² and patellar tendinopathy loading programmes: A systematic review combining clinical and mechanical findings. British Journal of Sports Medicine, 47(6), 377–389. https://doi.org/10.1136/bjsports-2012-091985 (Note: While about loading programs, discusses principles relevant to strength deficits)

O'Neill, S., Barry, S., & Watson, P. (2019). Plantarflexor strength and endurance deficits associated with mid-portion Achilles tendinopathy: The role of the soleus. Physical Therapy in Sport, 37, 69–76. https://doi.org/10.1016/j.ptsp.2019.03.002

Willy, R. W., & Meira, E. P. (2016). Current concepts³ in biomechanical interventions for patellofemoral pain. International Journal of Sports Physical Therapy, 11(6), 877–890. (Note: Discusses general principles of load management and strength deficits often relevant across lower limb issues)

Eliminate the 0-5 scale and get objective with your strength and power testing with the Activforce 2