118 Can we reasonably recommend strength training twice weekly for the general adult population aged 18-64 years to secure optimal body functionality?

TL;DR

This study evaluates the scientific basis for recommending strength training twice weekly for adults aged 18-64 to improve body functionality.

Contribution

The study critically assesses the quality of evidence supporting the revised Danish strength training recommendations for general adults.

Findings

Only 25 out of 879 studies met criteria for quality assessment, with many scoring low on quality.

Most studies focused on adults with functional limitations, not the general population.

The evidence does not clearly support recommending twice-weekly strength training for all adults aged 18-64.

Abstract

The objective of the study was to conduct a quality assessment of the scientific literature underlying the Danish Health Authorities (DHA) revised recommendations on physical activity (PA), with focus on the new advice on strength training twice a week to secure optimal body functionality in the adult population aged 18-64 years.

The study was a scoping review. Reviews conducted by the World Health Organization (WHO), the American and Canadian Health Authorities, and evidence referenced in earlier reports from DHA were included for initial review, as DHA refer to these as base for their PA-guideline revision. Studies included in the reviews were title- and abstract screened to assess whether they investigated PA and/or strength training in a population of adults aged 18-64 years. Studies identified through this screening, were furthermore full text screened, and finally included in a quality assessment, if they investigated a strength training intervention in relation to a measure of body functionality. The quality assessment was inspired by STROBE and the Jadad Scale (for observational studies and RCTs respectively) and extended with an assessment of the study’s research goal compliance (causal or predictive) to evaluate the study’s ability to detect eventual effects of the intervention on body functionality.

A total of 25 out of 879 studies identified in the reviews were selected for quality assessment. Great variations in quality were identified, and many studies (13 out of 25) did not achieve 2/3 of potential quality points. The studies generally support strength training as an effective intervention on body functionality. However, 15 of the 16 RCTs investigated a study population with functional limitations, e.g. populations with musculoskeletal disorders, and most studies were based on a study population in the higher end of the age spectrum 18-64 years.

The literature does not clearly support a recommendation on strength training twice weekly for the general adult population to secure optimal body functionality.

The formulation of PA-guidelines should be based on evidence that 1) aims to draw causal conclusions on the effect of the recommended intervention and 2) investigates a population comparable to the target audience.

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