Mechanical, Material and Morphological Adaptations of Healthy Lower Limb Tendons to Mechanical Loading: A Systematic Review and Meta-Analysis.
Level 1 - systematic review of randomized trials
Systematic review and meta-analysis of 61 interventional studies
PubMed 35657492 · doi:10.1007/s40279-022-01695-y
What was done
A systematic review and random-effects meta-analysis was conducted across five databases (PubMed, Scopus, CINAHL, SPORTDiscus, EMBASE) to evaluate healthy lower limb tendon adaptations to mechanical loading. Researchers assessed changes in tendon stiffness, modulus, and cross-sectional area (CSA), and used meta-regression to determine the primary drivers of stiffness changes as well as the influence of training type, loading parameters (strain, duration, volume, contraction mode), and age.
What was found
Across 61 articles (763 total participants; 33 Achilles tendon, 24 patellar tendon studies), mechanical loading produced moderate increases in tendon stiffness (SMD 0.74; 95% CI 0.62–0.86), large increases in modulus (SMD 0.82; 95% CI 0.58–1.07), and small increases in CSA (SMD 0.22; 95% CI 0.12–0.33). Meta-regression identified modulus as the main moderator of increased stiffness. Resistance training induced greater modulus increases (SMD 0.90; 95% CI 0.65–1.15) than other exercise types. High-strain resistance protocols produced significantly greater increases in modulus (SMD 0.82; 95% CI 0.44–1.20; p = 0.009) and stiffness (SMD 1.04; 95% CI 0.65–1.43; p = 0.007) than low-strain protocols. Adaptations in stiffness and modulus were larger in adult participants than in other age groups.
Why it matters
This review clarifies that tendon mechanical adaptation in response to training is primarily driven by material remodeling (increased modulus) rather than hypertrophy (CSA), demonstrating that high tendon strain during resistance exercise is the critical stimulus for maximizing tendon stiffness.
Limits
The average sample size per included study was small (averaging approximately 12.5 participants per study across 61 articles). The majority of evidence was limited to healthy Achilles and patellar tendons subjected to resistance training, limiting direct generalizability to other lower or upper limb tendons, pathological tendons, or non-resistance exercise modalities. Long-term retention of adaptations was not reported in the abstract.
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