Self-reported physical activity is not a valid method for measuring physical activity in 15 year old South African boys and girls

Valid instruments for the assessment of physical activity remains a challenge in field studies. This study determine the level of agreement between objectively measured physical activity by ActiHeart® and the international physical activity questionnaire short form (IPAQ-S) among adolescents attending schools in the Tlokwe Local Municipality, South Africa. A total of 63 boys and 45 girls aged 15 years were participants in PhysicalActivity and Health Longitudinal Study (PHALS). Objective physical activity (PA) was measured by a means of ActiHeart® for seven (7) consecutive days. Subjective physical activity was assessed with self-reported IPAQ-S. Objective PA indicated that 93% of the participants were inactive and only 6% highly active. IPAQ-S showed that 24% were inactive with 57% active. A non-significant correlation (r = 0.11; p = 0.29) between ActiHeart® measure of activity energy expenditure (AEE) and total physical activity (IPAQ-S) was observed. Cohen’s Kappa (k) show poor agreement between the two measurement instruments, κ 0.011, P < 0.005