Immediate and long-term effects of mechanical loading on Achilles tendon volume: A systematic review and meta-analysis

Abstract

Introduction: The Achilles tendon may experience transient changes in dimensions related to fluid flow under load. The extent to which fluid flow involves redistribution within or flow out of the tendon is not known and could be determined by investigating volume changes. This study aimed to synthesize data on immediate and long-term effects of mechanical loading on tendon volume among people with a healthy AT and midportion Achilles tendinopathy (MAT). A secondary aim was to synthesise data from the included studies investigating parallel change in cross-sectional area and length. Methods: The review was reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) and was registered with the International Prospective Register of Systematic Reviews (PROSPERO; reference CRD42020146733). Two reviewers performed an independent literature search for studies examining the effect of load on AT volume among healthy people or people with MAT. Systematic electronic search was performed in MEDLINE, EMBASE, CINAHL, AMED, and Scopus from inception until May 2020. Standardized mean differences (SMDs) were calculated for intervention-induced changes from baseline for all outcomes. Methodological quality was assessed using modified version of Newcastle Ottawa Scale (NOS). Twelve studies were included in meta-analysis. Results: For healthy AT, there were negligible to small changes in volume following cross-country running (_0.33 [95% CI = -1.11 to 0.45] (P = 0.41)) and isometric exercise (0.01[95% CI = -0.54 to 0.55] (P = 0.98)) and a large increase at the short-term with 12-week isometric protocol (0.88 [95% CI = -0.10 to1.86] (P = 0.08)). For MAT, there was an immediate large reduction in volume with isometric exercise (-1.24 [95% CI = -1.93 to -0.55] (P = 0.0004)), small increase with eccentric exercise (0.41 [95% CI = -0.18 to 1.01] (P = 0.18)) and small reduction at the short-term with long-term interventions (-0.46 [95% CI = -0.87 to -0.05] (P = 0.03)). Discussion: The current study suggests that healthy AT may have distinct volume adaptation compared to MAT in response to different loading interventions. The healthy AT seems to remain isovolumetric in response to acute interventions, regardless of reductions in CSA as a result of fluid redistribution. In contrast, pathological tendons may display a significant reduction in volume in response to acute and long-term interventions. Conflict of interest disclosure: The authors declare that they have no competing interests.