Inconsistent Effects of Experience on Running Biomechanics May be Influenced by Study Heterogeneity and Classification Criteria: a Systematic Review and Proposal of a Revised Taxonomy.

Background: Less-experienced runners are proposed to sustain more running related injuries (RRIs) than more-experienced runners because of differences in their gait biomechanics. However, the effects of running experience on biomechanics remain inconclusive. The objective of this systematic review was to examine the evidence concerning the influence of experience on running biomechanics and summarize the criteria used to classify running experience. A classification procedure for running experience was proposed based on the results.

Methods: Five common databases were searched for relevant articles following PRISMA guidelines (PROSPERO_ID CRD42022296734) and the PICO framework. Peer-reviewed research reporting a statistical effect of running experience on running gait biomechanics in adults (18-65 years) were included. Exclusion criteria were: subjects with current pathologies or symptomatic injuries; reporting running only barefoot, in minimalist shoes, during sprinting, or incline/decline running; classified experience only through performance-related measures; or did not specify running experience group definition. Risk of bias was assessed with the Downs and Black checklist. Extracted data were organized in tables and synthesized descriptively due to study heterogeneity.

Results: Twenty-eight studies with 916 total subjects were included. Although most studies found significance in their comparisons, no studies comparing similar gait variables found the same statistical result. Some variables compared between experience levels were examined in only one study. Experience classification criteria were inconsistent between studies; cut-offs for more-experienced ranged between 2 and 10 years and/or 15-50 km/week and cut-offs for less-experienced ranged between 0.5 and 3 years and/or 0-20 km/week. Meta-analysis was not possible due to heterogeneity among the included studies.

Conclusion: Effects of experience on running mechanics were inconsistent in the current literature. The lack of consistent findings may be due to the heterogeneous criteria used to classify runners into experience groups and the inconsistency of the variables investigated. Replication studies, heterogeneous study design, and longitudinal studies are needed to determine if or how running biomechanics change as runners gain experience. Heterogeneous study designs must begin with standard experience classification criteria for the effect of experience on running biomechanics to be identified. We propose an updated taxonomy to classify runners into groups considering three facets: exposure, performance, and intention.

Trial registration: PROSPERO ID CRD42022296734. Registered 28 September 2022-Retrospectively registered, https://www.chictr.org.cn/bin/project/edit?pid=149714 .