Mediated Effects of Perceived Competence on Youth Physical Activity and Sedentary Behavior

PURPOSE

This study evaluates whether physical activity (PA) and sedentary behavior (SB) are influenced by a common mediating relationship.

METHOD

A total of 1,552 participants in 3rd to 12th grade completed an online survey that included assessments of PA at school (PAS), PA at home (PAH), and SB as well as a battery of psychosocial variables (i.e., attraction to PA and perceived competence).

RESULTS

Perceived competence had a direct positive effect on PA and a negative effect on SB. These associations were consistently (but partially) mediated by attraction to PA; however, the indirect effect (IE) of perceived competence was stronger for PAH (IE = .27, p < .05) than for PAS (IE = .07, p < .05), or SB (IE = .13, p < .05).

CONCLUSIONS

This study revealed some direct effects and IEs of perceived competence on PAS, PAH, and SB through attraction to PA as the mediator. PA and SB may be influenced by some common underlying psychosocial mediators.

Calibration of the biotrainer pro activity monitor in children

The unique physical and movement characteristics of children necessitate the development of accelerometer equations and cut points that are population specific. The purpose of this study is to develop an ecologically valid cut point for the Biotrainer Pro monitor that reflects a threshold for moderate-intensity physical activity in elementary school children. A sample of 30 children (ages 8-12) wore a Biotrainer monitor while completing a series of 7 movement tasks (calibration phase) and while participating in an organized group activity (cross-validation phase). Videotapes from each session were processed using a computerized direct-observation technique to provide a criterion measure of physical activity. Analyses involved the use of mixed-model regression and receiver operator characteristic (ROC) curves. The results indicated that a cut point of 4 counts/min provides the optimal balance between the related needs for sensitivity (accurately detecting activity) and specificity (limiting misclassification of activity as inactivity). Results with the cross-validation data demonstrated that this value yielded the best overall kappa (.58) and a high classification agreement (84%) for activity determination. The specificity of 93% demonstrates that the proposed cut point can accurately detect activity; however, the lower sensitivity value of 61% suggests that some minutes of activity might be incorrectly classified as inactivity. The cut point of 4 counts/min provides an ecologically valid cut point to capture physical activity in children using the Biotrainer Pro activity monitor.