Despite growing emphasis on the benefits of physical activity for promoting mental health, inclusion of muscle-strengthening (MS) (e.g., body-weight exercises, resistance machines) activities is limited. Notably, few studies collectively assess MS behavioural frequency, duration, and intensity. To address the gap, the current study examined associations between frequency (days), intensity (rating of perceived exertion in relation to repetitions in reserve [RPE/RIR]), and duration (minutes per typical session) of MS activities on anxiety, depression, and mental well-being.
A cross-sectional study of 601 participants (Mean age = 30.92 years [SD = 12.70]; 57.7 % female) across Ireland was conducted. Participants completed a self-report questionnaire containing MS instruments previously used, or adapted from valid and reliable measures (i.e., International Physical Activity Questionnaire IPAQ, RPE/RIR), alongside, the Generalized Anxiety Disorder-7 (GAD-7), Patient Health Questionnaire-8 (PHQ-8) and the Mental Health Continuum- Short Form (MHC-SF). A multivariate regression model was tested in MPLUS, using dummy coding for MS frequency in relation to no activity (i.e., 0-days) non-adherence (i.e., 1-day), adherence (i.e., 2-days) and enhanced adherence (i.e., ≥3 days) to the MS public health guidelines, with the mental health variables representing the dependent variables. Intensity and duration were specified in the model as continuous variables; gender and age were included as statistical controls.
Three or more days engaged in MS activities was associated with fewer anxiety (β = -0.12, p < .05) and depression (β = -0.14, p < .01) symptoms. Increased intensity had a negative association with anxiety (β = -0.10, p < .05) and depression (β = -0.15, p < .001). Unexpectedly, adherence to the MS guidelines (2-days) did not predict any of the mental health outcomes, whereas 1-day of MS activity was associated with fewer depression symptoms (β = -0.11). No effects were observed for mental well-being, and MS duration exerted a null effect across all mental health outcomes.
Higher frequency and intensity of MS activities may protect against anxiety and depression symptoms. Doing some MS activities (at least 1-day) is likely more beneficial than none for depression. Evidence-based, MS interventions may help curb mental illness rates, and future longitudinal, intervention-based research could consider inclusion of MS frequency, intensity and duration variables to enhance efforts to identify at-risk groups and trends within physical activity and mental illness surveillance.

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