06/02/2026
𝗢𝗽𝘁𝗶𝗺𝗶𝘇𝗶𝗻𝗴 𝗔𝗰𝗵𝗶𝗹𝗹𝗲𝘀 𝗧𝗲𝗻𝗱𝗼𝗻 𝗥𝗲𝗵𝗮𝗯𝗶𝗹𝗶𝘁𝗮𝘁𝗶𝗼𝗻: 𝗔 𝗗𝗲𝗲𝗽 𝗗𝗶𝘃𝗲 𝗶𝗻𝘁𝗼 𝗟𝗼𝗮𝗱𝗶𝗻𝗴 𝗠𝗲𝗰𝗵𝗮𝗻𝗶𝗰𝘀 𝗮𝗻𝗱 𝗔𝗱𝗮𝗽𝘁𝗮𝘁𝗶𝗼𝗻
◻️ Resistance-based therapeutic exercise is widely recognized as the first-line treatment for Achilles tendinopathy.
◻️ However, despite its prevalence, the specific mechanisms that make exercise effective are still debated, and protocols vary significantly between clinicians.
◻️ A 2022 narrative review by Merry et al., published in the Journal of Clinical Medicine, explores the foundational principles of tendon remodeling and the biomechanics of the Achilles tendon to determine how to optimize therapeutic exercise prescriptions.
◻️ Here is a thorough breakdown of the review’s findings regarding anatomy, remodeling, and clinical parameters for exercise prescription.
𝟭. 𝗧𝗵𝗲 𝗔𝗻𝗮𝘁𝗼𝗺𝘆 𝗼𝗳 𝗟𝗼𝗮𝗱𝗶𝗻𝗴 🦵
◻️ The Achilles tendon is the largest and strongest tendon in the body, capable of withstanding forces of 5 to 7 body weights during running.
◻️ It acts as a spring, storing and returning energy to facilitate movement.
◻️ The tendon connects the triceps surae muscles (soleus, medial gastrocnemius, and lateral gastrocnemius) to the calcaneus.
◻️ A key anatomical feature is that these muscles insert via three distinct "subtendons" that rotate (clockwise on the left, counterclockwise on the right) as they travel distally.
◻️ Because the soleus and gastrocnemii have different force-production capacities and insertion pathways, understanding how force is transmitted through these subtendons is critical for understanding injury and rehabilitation.
𝟮. 𝗣𝗿𝗶𝗻𝗰𝗶𝗽𝗹𝗲𝘀 𝗼𝗳 𝗧𝗲𝗻𝗱𝗼𝗻 𝗥𝗲𝗺𝗼𝗱𝗲𝗹𝗶𝗻𝗴 🔬
◻️ To heal or strengthen a tendon, it must be subjected to mechanical loading that triggers mechanotransduction—the process by which cells convert mechanical signals into biochemical responses.
𝗛𝗲𝗮𝗹𝘁𝗵𝘆 𝗧𝗶𝘀𝘀𝘂𝗲 𝗔𝗱𝗮𝗽𝘁𝗮𝘁𝗶𝗼𝗻
◻️ For healthy tendons, adaptation is driven by strain (deformation).
◻️ The review highlights the following parameters for positive remodeling (increased stiffness and cross-sectional area):
◻️ Load Intensity: High-intensity loading is required. Loads greater than 70% of maximum voluntary contraction (MVC) are typically needed to induce stiffness adaptation.
◻️ Strain: The "sweet spot" for adaptation appears to be strain levels of 4.5–6.5%.
◻️ Duration: Interventions generally need to last around 12 weeks to see structural changes.
𝗣𝗮𝘁𝗵𝗼𝗹𝗼𝗴𝗶𝗰𝗮𝗹 𝗧𝗶𝘀𝘀𝘂𝗲 𝗔𝗱𝗮𝗽𝘁𝗮𝘁𝗶𝗼𝗻
◻️ Tendinopathy results in a tendon that is thicker but less stiff, with a lower modulus (material quality).
◻️ While exercise aims to restore these properties, the review notes that structural improvements (like normalizing collagen structure) do not always correlate with pain reduction.
◻️ Clinical benefits may also stem from neuromuscular changes, such as increased muscle strength or shifts in the length-tension curve of the triceps surae.
𝟯. 𝗕𝗶𝗼𝗺𝗲𝗰𝗵𝗮𝗻𝗶𝗰𝗮𝗹 𝗖𝗼𝗻𝘀𝗶𝗱𝗲𝗿𝗮𝘁𝗶𝗼𝗻𝘀 𝗳𝗼𝗿 𝗘𝘅𝗲𝗿𝗰𝗶𝘀𝗲 𝗣𝗿𝗲𝘀𝗰𝗿𝗶𝗽𝘁𝗶𝗼𝗻 ⚙️
◻️ The review analyzes five distinct parameters that clinicians modify when prescribing exercise for AT.
🟢 𝗔. 𝗠𝘂𝘀𝗰𝗹𝗲 𝗖𝗼𝗻𝘁𝗿𝗮𝗰𝘁𝗶𝗼𝗻 𝗧𝘆𝗽𝗲
◻️ Historically, eccentric (lengthening) exercise was the gold standard.
◻️ However, the review finds that mixed protocols (combining concentric and eccentric phases) and isometric protocols also produce comparable results.
◻️ Key Takeaway: There is insufficient evidence to exclusively prescribe eccentric exercises. Clinicians should focus on patient tolerability and engagement rather than a specific contraction type.
🟢 𝗕. 𝗟𝗼𝗮𝗱 𝗜𝗻𝘁𝗲𝗻𝘀𝗶𝘁𝘆
◻️ This is arguably the most critical factor.
◻️ In healthy individuals, high-magnitude loads (>70% MVC) are necessary to achieve the high strain levels required for adaptation.
◻️ The Challenge: Translating this to injured populations is difficult due to pain and strength deficits.
◻️ Heavy Slow Resistance (HSR): This approach is highlighted as a viable option. It uses heavy loads (up to 6-repetition maximum) and has shown clinical benefits and high patient satisfaction.
◻️ Key Takeaway: Prioritize high-magnitude loading and load progression over time to avoid a rehabilitation plateau.
🟢 𝗖. 𝗟𝗼𝗮𝗱𝗶𝗻𝗴 𝗙𝗿𝗲𝗾𝘂𝗲𝗻𝗰𝘆 𝗮𝗻𝗱 𝗥𝗮𝘁𝗲
◻️ While research in this specific area is limited, high loads combined with low frequencies (e.g., 3 seconds loading/3 seconds relaxation) appear superior for adaptation in healthy tissue.
◻️ Key Takeaway: Most successful AT protocols, such as HSR and Alfredson’s, utilize "slow" loading speeds (e.g., 6 seconds per repetition).
🟢 𝗗. 𝗘𝘅𝗲𝗿𝗰𝗶𝘀𝗲 𝗣𝗼𝘀𝗶𝘁𝗶𝗼𝗻𝗶𝗻𝗴
◻️ The position of the hip, knee, and ankle dictates how much force passes through the Achilles.
◻️ Knee Position: The soleus contributes to plantar flexion regardless of knee angle, but the gastrocnemius is disadvantaged when the knee is flexed. Therefore, performing exercises with the knee extended generally allows for greater force transmission and tendon strain.
◻️ Ankle Position: Maximum dorsiflexion increases force through the tendon.
◻️ Weight-Bearing (WB): WB exercises are preferred not necessarily because of the position itself, but because they facilitate high-magnitude loading by using body weight.
◻️ Caveat: For insertional Achilles tendinopathy, loading in deep dorsiflexion can be irritable and should often be avoided in early rehabilitation.
🟢 𝗘. 𝗘𝘅𝗲𝗿𝗰𝗶𝘀𝗲 𝗦𝗰𝗵𝗲𝗱𝘂𝗹𝗲
◻️ The famous "Alfredson protocol" prescribes a high volume of exercise: 180 repetitions per day (3 sets of 15, twice daily, 7 days a week).
◻️ Key Takeaway: This high volume may not be necessary. A "do-as-tolerated" approach has shown equal improvement to the standard 180-rep protocol.
◻️ A 12-week intervention duration remains the standard recommendation.
𝟰. 𝗖𝗹𝗶𝗻𝗶𝗰𝗮𝗹 𝗥𝗲𝗰𝗼𝗺𝗺𝗲𝗻𝗱𝗮𝘁𝗶𝗼𝗻𝘀 📋
◻️ Prioritize Magnitude: High-magnitude, repeatable loading is likely the most important factor for tendon adaptation. This can be achieved through weight-bearing exercises or non-weight-bearing exercises with added resistance.
◻️ Individualize the Program: There is no single "optimal" protocol. Exercise should be tailored to client tolerability to ensure adherence.
◻️ Use Heavy Loads: Progression toward heavy loads (>70% MVC or heavy slow resistance) is supported by principles of healthy tendon remodeling.
◻️ Simplify Positioning: While knee extension and dorsiflexion theoretically maximize load, achieving high-magnitude loading is more important than the specific posture. Weight-bearing positions are practical and effective.
◻️ Rethink Volume: Excessive repetition volume (like the strict Alfredson protocol) may not be superior to lower-volume, high-intensity approaches that are executed as tolerated.
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⚠️Disclaimer: Sharing a study or a part of it is NOT an endorsement. Please read the original article and evaluate critically.⚠️
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