Remote Changes of Mechanical Stiffness Following Local Stretching or Contraction: A Systematic Review with Meta-Analysis.

backgroundFascia links the skeletal muscles, creating a body-wide network of myofascial continuity. Experimental studies confirmed the mechanical relevance of this architecture as substantial amounts of force can be transmitted across tissue connections. Against this background, it has been suggested that exercise may not only modify local but also distant tissue properties. This systematic review with meta-analysis evaluated the effects of local tissue lengthening and local muscle contraction on the stiffness of remote structures within the same myofascial chain.

methodsTwo investigators performed a systematic literature search using Web of Science, PubMed, and Google Scholar. We included controlled experimental trials comparing the effects of local tissue lengthening (e.g., gastrocnemius stretching) or tensioning (e.g., gastrocnemius contraction) on non-local tissue properties (e.g., stiffness of the plantar fascia or erector spinae). Study quality and risk of bias were examined by means of a modified Downs and Black checklist. Funnel plots and Egger's tests were used to identify reporting bias. We used robust variance estimation to pool the standardized mean differences between intervention (local stretching or contraction) and control (tissue in neutral, slack position). The GRADE criteria were applied to determine the certainty about the evidence.

resultsA total of 15 studies with mostly high methodological quality (11.3±1.7 points) were identified. Visual inspection of funnel plots and the Egger's test revealed a possible reporting bias for contraction and lengthening. While tissue lengthening enhanced distant tissue stiffness with moderate magnitude (Hedges' g= -0.54, 95%CI -1.03 to -0.05, p=0.04, 12 studies, 42 effect sizes (ES), τ² = 0.42, very low certainty), contraction induced a large non-local stiffness increase (g= -1.25, 95%CI -2.15 to -0.34, p=0.016, 7 studies, 67 ES, τ² = 0.61, moderate certainty).

conclusionBoth muscle contraction and stretch increase non-local stiffness in structurally connected body regions. This finding is of relevance for exercise professionals and therapists aiming to optimize performance or rehabilitation. The high heterogeneity and considerable differences between the individual study results, particularly regarding local lengthening, call for further research.

trial registrationProspective registered in the PROSPERO database (CRD42024615692).