Can my muscles get strong faster than my tendons can cope?
Plausibly: muscle adapts faster than tendon, and adolescent jumpers showed raised tendon strain. That the gap causes injury is the authors' hypothesis, not shown (B+).
Mersmann, Bohm and Arampatzis explore the hypothesis that an imbalanced adaptation of muscle and tendon contributes to tendinopathy in youth sport. Tendons transmit muscle force to bone, so a gain in muscle force that the tendon's stiffness does not match raises the strain on the tendon at a given activation.
The review argues that the two tissues differ in their time course of adaptation and in the stimuli that drive it.
Tendon has a lower cell content, blood supply and metabolism than muscle, the half-life of its collagen is estimated to be almost tenfold that of actin and myosin, and its core is barely renewed after adolescence (REF-1356); muscle morphology can change within 3 to 4 weeks of heavy training and neural adaptation raises strength before that, while no comparably fast tendon changes are reported.
In two 3-month interventions strength rose 1-2 months before tendon stiffness changed. Plyometric loading seems a stronger stimulus for muscle than for tendon, and during growth rising sex hormones might widen the gap.
In the authors' own studies of elite adolescent volleyball athletes, patellar tendon cross-section lagged behind adults' with similar muscle, and over a year in 3-month steps the athletes showed larger swings in strength and both higher and more fluctuating tendon strain during maximal contractions than non-athlete controls (12 athletes, 8 controls).
The case for an injury link is circumstantial: cyclic loading at higher strain shortens tendon life in cadaver tests, tendinopathy is common in jumping sports and rises through adolescence, and soft-tissue injuries rise when loads are raised quickly.
The authors call this "a solid theoretical background for the hypothesis" and state plainly that the association of such imbalances with tendon overuse injury, and the preventive value of tendon training, "has not been established thus far".
They propose a tendon programme (85-90% of maximal isometric voluntary contraction, 3 s of high strain per contraction, five sets of four, 2 min between sets, three times a week for at least 12 weeks; about 15 min of exercises in the regular training schedule).
Our reading: this is the clearest statement of the "clocks out of step" idea that PHYS-38 calls a cause of overuse injury, from the field's leading tendon-adaptation group; it supports the mechanism's plausibility and the different time courses, not a measured link to injury, and systematic reviews of running injuries find only conflicting (REF-1367) or very limited (REF-565) evidence of a link with quick load rises.
Protocol
Key Results
Muscle vs tendon adaptation (the authors' synthesis of cited studies):
| Point | What the review says | Basis cited |
|---|---|---|
| Tissue renewal | tendon collagen half-life almost tenfold that of actin and myosin; adult tendon core barely renewed (bomb-pulse 14C) | Lundholm 1981, Thorpe 2010, Heinemeier 2013 (REF-1356) |
| Speed of change | muscle morphology and architecture can change after 3 to 4 weeks of heavy resistance training; no reports of comparably rapid tendon changes | Seynnes 2007, DeFreitas 2011 |
| Order of change | in two 3-month interventions (patellar and Achilles tendon) a marked strength gain preceded significant changes in tendon stiffness by 1-2 months; tendon cross-section did not change | Kubo 2010, 2012 |
| Contrary data | an 8-week study found no change in Achilles strain at maximal contraction (uniform adaptation), though single strain values ranged from 8.6 to 13.5% between sessions | Urlando & Hawkins 2007 |
| Stimulus | plyometric loading seems a more potent stimulus for muscle than for tendon; tendon needs high strain magnitude held for about 3 s, contraction type does not seem to matter | authors' and others' training studies |
| Adolescent athletes (own data) | adolescents had a patellar-tendon cross-section deficit vs adult athletes with similar muscle, hence higher tendon stress and strain; over 1 year athletes had larger strength swings and higher, more fluctuating tendon strain than controls | Mersmann 2014, 2016, 2017a, b |
Link to injury (as the review frames it):
| Line of argument | Type of evidence | The authors' own qualifier |
|---|---|---|
| Higher strain shortens tendon life under cyclic loading | cadaver Achilles tendons (Wren 2003) | "suggests" |
| Raised strain in tendinopathy patients | some in vivo studies; others found none | "might be a methodological issue" |
| Soft-tissue injury rises with rapid load increases | epidemiology (Gabbett 2016) | "could also have different origins" |
| Tendinopathy common in jumping sports, rising with age in youth | epidemiology, meta-analysis (Simpson 2016) | "could well be related" |
| Overall | — | "There certainly is a need to provide more direct support"; the association with overuse injury "has not been established thus far" |
Proposed prevention programme (authors' recommendation, from adult data): 85-90% of maximal isometric voluntary contraction; five sets of four contractions, 3 s contraction and 3 s relaxation, 2 min between sets; three times a week for at least 12 weeks; about 15 min of exercises in the regular training schedule; isometric at about 60° knee flexion (patellar tendon) or about 10° dorsiflexion with the knee extended (Achilles), or slow dynamic movements (about 6 s) through the high-force range.
Mechanisms
Practical Application
Limitations
How this entry was checked and changed
an authoritative narrative review from the leading group on human tendon adaptation (Humboldt University Berlin; the same authors as the meta-analysis REF-517); no systematic method. The level is for its synthesis of muscle and tendon adaptation; the injury link it is cited for is a hypothesis it states but does not test