Perceptions of the Likelihood and Importance of Physical Activity Outcomes at 14 Years Affects Physical Fitness at 17 Years.

Dozens of comparisons were run on one data set with no statistical adjustment, so some of the significant results are likely to be chance findings, and the authors say so themselves. Several comparisons pitted a tiny group against a very large one: 24 boys and 16 girls expected activity to lead to others making fun of them, against roughly 500 who did not. Those results should not be relied on. Questionnaire answers were collapsed from a 7-point scale into two groups for the fitness analyses, so much of the detail in how strongly a teenager felt about something was thrown away. Everyone came from a single Australian cohort born in one region between 1989 and 1992, so the ranking of motivations may not hold for adolescents elsewhere or now. Fitness was estimated from a bicycle test rather than measured directly, and only teenagers who completed everything at both ages were included.

The 14- and 17-year follow-ups were funded by the National Health and Medical Research Council and the Raine Medical Research Foundation. The authors declare no conflicts of interest.

Do not read this as evidence that changing what teenagers believe about exercise will change their fitness. Nothing was manipulated or tested here; the study compared questionnaire answers given at 14 with a bike fitness test at 17, it ran many separate comparisons on the same data without adjusting for that, and the fitness result for girls rested on a single item.