Achilles Tendon Rehabilitation: Maximize Anabolic Tendon Remodeling

*Significant differences between tasks compared with heel raise. 
#Significant differences between 1) unloaded and loaded heel rise and 2) running at three m/s and five m/s.

Exercise Selection

Exercise training is the most common method to apply mechanical loading to tendons⁽²³⁾. During mechanical loading, the extracellular matrix supplies tensile strength to the tendon⁽²⁴⁾. Tendon cells detect mechanical forces as stimuli that are transduced to biochemical signals, eliciting cellular responses. Further adaptations in tendon tissue to resistance training include changes in tissue thickness, strength, resistance to damage, blood flow, and normalization of the fibrillar morphology^(25-27).

Resistance training includes concentric and eccentric muscle actions against loads (workload) to achieve a specific training outcome⁽²⁸⁾. Targeted tendon loading of adequate magnitude induces positive changes in tendon morphological, material, and mechanical properties^(29,30).

To achieve optimal Achilles tendon exercise outcomes, clinicians must design programs that generate high-magnitude loading through the triceps surae muscle-tendon unit, be tolerable and practical for the athlete, and be repeatable during exercise and assessment.

Once clinicians understand the three principles, they must consider two primary considerations in exercise selection: lower limb joint angles (i.e., ankle, knee, hip) and weight-bearing (WB) versus non-weight-bearing (NWB)⁽³¹⁾. The duration of the program is also an important consideration as 12-week programs at loads of greater than 70% of maximum voluntary contraction (MVC) or strains of 4.5–6.5% deliver the appropriate loading-induced tendon stimulus to initiate mechanotransduction pathways^{(29,30,32-35)}. However, the relationship of tendon force and resulting strain can vary substantially between individuals^(36,37).

Once clinicians select an exercise, they must decide how the athlete must complete it. Incorporating eccentric and concentric movements demonstrates similar results. Although clinicians regard eccentrics as the gold standard for Achilles tendon rehabilitation, these results question the role of muscle contraction type^(38-41).

The lower limb joint angles also remain a contentious area. Still, despite the dorsiflexion restraining effect of knee extension, the force through the Achilles tendon and, subsequently, the Achilles displacement are superior in knee extension. Furthermore, greater ankle dorsiflexion, knee extension, and, indirectly, hip extension may position the body to generate maximal plantar flexor torque, thereby maximally straining the Achilles tendon (see figure 2). Of these lower limb joint angles, ankle angle appears to be the most deterministic of Achilles tendon loading as ankle angle largely dictates the force through the Achilles tendon and tendon elongation^(42,43). Furthermore, clinicians must consider the impact of the knee range on targeting the soleus and gastrocnemius (see figure 3 and 4).

Exercise Intervention Suggestions

Exercise prescription aims to improve muscle and tendon capacity to manage the load. Clinicians must consider the Goldilocks approach when prescribing programs. Too little and there won’t be a sufficient stimulus; too much and the response will be compromised. As the athlete’s load tolerance increases, the exercise resistance will progress. There is value in performing exercises with an extended and flexed knee.

Isometric exercises
During the acute recovery phases, clinicians can introduce isometrics into the rehabilitation program. They may assist with pain relief and prevent physiological decay. Patients can perform them multiple times per day for pain relief. Clinicians can prescribe 30-45-second holds and one to five repetitions. They can progress to ± 70% MVC as pain allows.

Strength exercises
Once athlete’s pain and function have improved, they can progress to eccentric and concentric contractions. Clinicians must be aware of the range of motion when prescribing exercises, as ankle dorsiflexion compresses the tendon (particularly in insertional Achilles tendinopathy)(see figure 5). Clinicians can include slow controlled repetitions (three sec eccentric and three sec concentric). They can progress the resistance and adjust the intensity utilizing pain as an indicator (no more than 3-4/10 pain while performing exercise). Furthermore, athletes can use the 24-48 hour pain/stiffness score to guide exercise progression/reduction.

Effective Achilles tendon rehabilitation hinges on understanding biomechanics and optimizing exercise selection. Clinicians should aim for high-magnitude loading within the anabolic strain range (5–6%) to promote optimal tendon remodeling without causing damage. Considerations like joint angles, weight-bearing, and program duration are vital, and a Goldilocks approach to exercise prescription ensures a balanced stimulus-response. Incorporating isometric exercises in acute phases and progressing to eccentric and concentric contractions as pain improves provides a comprehensive strategy for managing Achilles tendon injuries.

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