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A Bayesian approach to interpret intervention effectiveness in strength and conditioning Part 1

A meta-analysis to derive context-specific thresholds


  • Paul Swinton
  • Katherine Burgess
  • Andy Hall
  • Leon Greig
  • John Psyllas
  • Rodrigo Aspe
  • Patrick Maughan
  • Andrew Murphy



S&C, Evaluation, Effect size, Bayesian, Specificity


Background Strength and conditioning (S&C) interventions comprising methods such as resistance, sprint and plyometrics are used to enhance athleticism and sports performance. The effectiveness of interventions can be evaluated using effect sizes calculated from physical outcomes and then compared to threshold values. The purpose of this large meta-analysis was to identify threshold values specific to S&C and assess factors that influence effect size distributions.

Methods An online database and hand search of published and unpublished S&C intervention studies from the 1950’s onwards was conducted. Interventions were categorized as the following: resistance, combined, plyometric, ballistic, sprint, isokinetic, concurrent, or agility. Pre- and post-intervention data comprising means and standard deviations were extracted from outcomes categorized as: maximum strength, power, explosiveness, jump, sprint, or agility. Study and participant data including intervention length, gender and training status (untrained, recreationally trained and highly trained) were also extracted. Standardised mean difference effect sizes (SMDpre) were calculated and modelled with 4-level Bayesian hierarchical meta-analysis models using 0.25-, 0.5-, and 0.75-quantiles to determine small, medium, and large threshold values, respectively.

Results Data from 679 studies comprising 8904 effect sizes were included in the analyses. Threshold values obtained across the entire data were: small - 0.12 [95%CrI: 0.11 to 0.14]; medium - 0.43 [95%CrI: 0.42 to 0.45]; and large - 0.78 [95%CrI: 0.77 to 0.80]. Effect size distributions were shown to be shifted to higher values for longer duration interventions comprising maximum strength outcomes, untrained participants, females, and higher specificity coupling between training method and outcomes. Results from analyses were synthesised to provide updated threshold values to interpret effectiveness.

Conclusions The effectiveness of S&C interventions are influenced by a range of factors creating systematic shifts in SMDpre values. It is recommended that researchers and practitioners use the S&C specific threshold values presented instead of Cohen’s generic values, with scope provided for adjustment based on relevant factors.


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