In general, weak correlations between physical activity and screen time have been found.
Age had a moderate association with number of comorbidities (rho =0.44) and weaker associations with physical activity time (rho =−0.33) and BMI (rho =0.22), supporting the inclusion of age as a potential confounding variable.
Two studies on other diseases suggest no or only weak relationships among actual physical activity, patients' capacity, and self-reported physical functioning [ 13, 37].
A possible explanation for the weak relationship is that physical activity is determined by other factors such as self efficacy [ 34], personality, knowledge, beliefs and social support [ 35] and not just physical mobility.
The weak independent association between physical activity and insulin resistance shown in the present study (r = −0.07 to 0.00) is consistent with the reports reviewed by Wareham et al. (3).
The associations become weaker when controlling for physical activity variables and slightly stronger when controlling for body weight related variables.
Sensitivity analyses for longer (≥10 year) and shorter (<10 year) follow-up time showed that studies with longer follow-up time found weaker protective effect of physical activity for cognitive decline, RR 0.89 (0.62 – 1.27), and dementia, RR 0.86 (0.86 – 1.11).
Interestingly, studies that used unspecific measurement instruments for physical activity reported weak or no relationships between physical activity and overweight [ 9, 26, 29].
TUG was a significant, but weak predictor of self-reported physical activity in our TKA cohort.
5 6 Evidence supporting the link between interventions delivered by sports organisations with increases in sport participation or physical activity is weak.
