Measuring up: Is frequency enough for assessing adherence to muscle-strengthening guidelines?

Abstract Aim The World Health Organization (WHO) advises engaging in muscle-strengthening activities (MSAs) involving all major muscle groups on at least two days per week and at moderate or greater intensity. MSAs guideline adherence is oftentimes inferred based only on the frequency of MSAs, though. Thus, we aimed to explore the differences in MSAs guideline adherence depending on a frequency-only vs. comprehensive operationalization. Methods In a sports psychological, cross-sectional online survey, we included a questionnaire that assessed whether participants engaged in MSAs and whether they performed them according to the WHO guideline on at least two days per week, at moderate or greater intensity, and involving all major muscle groups. A convenience sample was recruited via advertisements online and offline (e.g., in fitness centers). Results Data were available for 235 (after exclusions) adults, who were mostly young and middle-aged, well-educated, and physically active. 71.1% of participants reported performing MSAs. 55.7% of participants reported performing MSAs on at least two days per week, whereas only 26.8% met all three components of the WHO guideline on MSAs. Not training all major muscle groups was a major barrier to MSAs guideline adherence. Conclusion Our results indicate the importance of considering all components of the WHO guideline on MSAs (frequency, intensity, involved muscle groups) for inferring guideline adherence, as a frequency-only operationalization may overestimate MSAs guideline adherence substantially.