Background: The present article systematically reviews recent literature on the in vivo adaptation of asymptomatic\nhuman tendons following increased chronic mechanical loading, and meta-analyzes the loading conditions,\nintervention outcomes, as well as methodological aspects.\nMethods: The search was performed in the databases PubMed, Web of Knowledge, and Scopus as well as in the\nreference lists of the eligible articles. A study was included if it conducted (a) a longitudinal exercise intervention\n(?8 weeks) on (b) healthy humans (18 to 50 years), (c) investigating the effects on mechanical (i.e., stiffness),\nmaterial (i.e., Youngâ��s modulus) and/or morphological properties (i.e., cross-sectional area (CSA)) of tendons in vivo,\nand was reported (d) in English language. Weighted average effect sizes (SMD, random-effects) and heterogeneity\n(Q and I2 statistics) of the intervention-induced changes of tendon stiffness, Youngâ��s modulus, and CSA were\ncalculated. A subgroup analysis was conducted regarding the applied loading intensity, muscle contraction type,\nand intervention duration. Further, the methodological study quality and the risk of bias were assessed.\nResults: The review process yielded 27 studies with 37 separate interventions on either the Achilles or patellar\ntendon (264 participants). SMD was 0.70 (confidence interval: 0.51, 0.88) for tendon stiffness (N=37), 0.69 (0.36, 1.03)\nfor Youngâ��s modulus (N=17), and 0.24 (0.07, 0.42) for CSA (N=33), with significant overall intervention effects\n(p<0.05). The heterogeneity analysis (stiffness: I2=30%; Youngâ��s modulus: I2=57%; CSA: I2=21%) indicated that\ndifferences in the loading conditions may affect the adaptive responses. The subgroup analysis confirmed that\nstiffness adaptation significantly (p<0.05) depends on loading intensity (I2=0%), but not on muscle contraction type.\nAlthough not significantly different, SMD was higher for interventions with longer duration (?12 weeks). The\naverage score of 71�±9% in methodological quality assessment indicated an appropriate quality of most studies.\nConclusions: The present meta-analysis provides elaborate statistical evidence that tendons are highly responsive\nto diverse loading regimens. However, the data strongly suggests that loading magnitude in particular plays a key\nrole for tendon adaptation in contrast to muscle contraction type. Furthermore, intervention-induced changes in\ntendon stiffness seem to be more attributed to adaptations of the material rather than morphological properties.
Loading....