Key result
A physical activity intervention increased absolute intensity gradient (+0.5 SD) in participants with low baseline relative intensity, but decreased it (-0.5 SD) in those with high relative intensity.
Why the study?
It was unknown whether quantifying both absolute and relative intensity of accelerometer-assessed physical activity can inform physical activity interventions.
Does baseline relative intensity of physical activity predict the response to a physical activity intervention in patients after cardiac events?
RCT (n=239)
Does baseline relative intensity of physical activity predict the response to a physical activity intervention in patients after cardiac events?
Patients with lower relative intensity of physical activity at baseline are more likely to increase their absolute physical activity intensity in response to an intervention, suggesting a role for personalized physical activity prescriptions.
Baseline relative intensity predicts differential PA intervention response post-cardiac events; supports personalized prescriptions and extends heterogeneity evidence.
OBJECTIVES: To determine whether quantifying both the absolute and relative intensity of accelerometer-assessed physical activity (PA) can inform PA interventions. We hypothesised that individuals whose free-living PA is at a low relative intensity are more likely to increase PA in response to an intervention, as they have spare physical capacity. METHOD: We conducted a secondary data analysis of a 12-month randomised controlled trial, Physical Activity after Cardiac EventS, which was designed to increase PA but showed no improvement. Participants (N=239, 86% male; age 66.4 (9.7); control N=126, intervention N=113) wore accelerometers for 7 days and performed the incremental shuttle walk test (ISWT) at baseline and 12 months. PA intensity was expressed in absolute terms (intensity gradient) and relative to acceleration at maximal physical capacity (predicted from an individual's maximal ISWT walking speed). PA outcomes were volume and absolute intensity gradient. RESULTS: At baseline, ISWT performance was positively correlated with PA volume (r=0.50, p<0.001) and absolute intensity (r=0.50, p<0.001), but negatively correlated with relative intensity (r=-0.13, p=0.025). Relative intensity of PA at baseline moderated the change in absolute intensity (p=0.017), but not volume, of PA postintervention. Low relative intensity at baseline was associated with increased absolute intensity gradient (+0.5 SD), while high relative intensity at baseline was associated with decreased absolute intensity gradient (-0.5 SD). CONCLUSION: Those with low relative intensity of PA were more likely to increase their absolute PA intensity gradient in response to an intervention. Quantifying absolute and relative PA intensity of PA could improve enables personalisation of interventions.
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Rowlands et al. (2023) conducted an RCT in Cardiac events (n=239). Physical activity intervention vs. Control was evaluated on Change in absolute intensity and volume of physical activity postintervention (p=0.017). A physical activity intervention increased absolute intensity gradient (+0.5 SD) in participants with low baseline relative intensity, but decreased it (-0.5 SD) in those with high relative intensity.
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