Are Plantarflexor Muscle Impairments Present Among Individuals with Achilles Tendinopathy and Do They Change with Exercise? A Systematic Review with Meta-analysis

Abstract

Background Understanding plantarflexor muscle impairments among individuals with Achilles tendinopathy (AT) may help to guide future research and inform clinical management of AT. Therefore, the aim of this review is to evaluate plantarflexor muscle impairments among individuals with AT and whether plantarflexor muscle function changes following resistance training interventions. Methods We searched relevant databases including Cochrane Central Register of Controlled Trials, Ovid (MEDLINE, EMBASE, AMED) and EBSCO (CINAHL Plus and SPORTDiscus) up to September 2020. Studies investigating plantarflexor muscle function were included if they met the following criteria: (1) any study design enabled comparison of plantarflexor muscle function between individuals with and without AT, or the affected and unaffected side of individuals with unilateral AT, and (2) any studies enabled investigation of change in plantarflexion muscle function over time with use of resistance training intervention. We included studies that recruited adults with either insertional or mid-portion AT of any duration. Study selection, quality assessment and data extraction were undertaken independently by two reviewers. Discrepancies were resolved via discussion, or by consulting a third reviewer where necessary. The Joanna Briggs Institute (JBI) critical appraisal tools specific to each study design were used to assess the methodological quality of included studies. Grading the strength of evidence for each outcome was determined according to the quality and number of studies. Results A total of 25 studies (545 participants) met inclusion. Participants’ mean age was 40 ± 7 years old. Six studies were high quality for all domains, while the remaining were susceptible to the risk of bias (e.g. selection criteria, reporting findings). This review identified moderate evidence that individuals with AT have impairment in maximal plantarflexor torque (seven studies including one with a mixed population) on their affected side, compared with the unaffected side. Impairments were modest (9% and 13% [pooled effect divided by mean of the unaffected side scores]) and of uncertain clinical importance. The remaining evidence, primarily among individuals with mid-portion AT, showed conflicting impairments for plantarflexor function (i.e. explosive strength and endurance) between sides. There was limited to very limited evidence for improvement in plantarflexor endurance (7% and 23%) but not power or strength (five studies including one with a mixed population for strength) over time, despite individuals undertaking several weeks of resistance training. Conclusions Plantarflexor impairments appear more common between sides than compared with control groups but given limitations in the literature further exploration of these relationships is needed. Registration PROSPERO Database; number CRD42019100747.

Runners with mid‐portion Achilles tendinopathy have greater triceps surae intracortical inhibition than healthy controls

“…The lack of group difference in plantar flexor isometric peak torque is in line with the result of other studies 27,31 . In contrast, weakness in plantar flexor dynamic peak torque has been widely reported in AT 5,9,12 . Perhaps, as observed in other chronic musculoskeletal disorders, such as chronic hamstring strains, 32 chronic AT presents deficits in dynamic but not in isometric peak torque.…”

“…Muscle weakness has been reported in individuals with AT as reduced maximal concentric and eccentric strength, and endurance. These deficits in muscle strength and endurance are still observed after years of rehabilitation, 6,7 even with improvements in pain and function 5,8,9 . Thus, it is of great clinical relevance to understand the mechanisms underpinning chronic muscle weakness to develop better rehabilitation strategies.…”

Runners with mid-portion Achilles tendinopathy have greater triceps surae intracortical inhibition than healthy controls

“…The copyright holder for this preprint this version posted July 2, 2021. ; https://doi.org/10.1101/2021.06.25.21259561 doi: medRxiv preprint the result of other studies 23,26 . In contrast, weakness in plantar flexor dynamic peak torque has been widely reported in AT 5,9,12 . Perhaps, as observed in other chronic musculoskeletal disorders, such as chronic hamstring strains 27 , chronic AT presents deficits in dynamic but not in isometric peak torque.…”

“…Studies that have adopted the SLHR endurance test 2 or calculated the total work done in dynamometry 5 for endurance measurement have also observed a reduction in endurance capacity compared to the non-symptomatic side and to controls, respectively. Bilateral deficits in unilateral presentations have been widely described in chronic AT 9,12 . These deficits on both symptomatic and non-symptomatic sides, emphasize that the non-symptomatic leg should not be used as comparison for neuromuscular function in AT.…”

“…Muscle weakness has been reported in individuals with AT as reduced maximal concentric and eccentric strength, and endurance. These deficits in muscle strength and endurance are still observed after years of rehabilitation 6,7 , even with improvements in pain and function 5,8,9 . Thus, it is of great clinical relevance to understand the mechanisms underpinning chronic muscle weakness to develop better rehabilitation strategies.…”