Despite physical education's health enhancing potential, students' activity levels in lessons are low. We evaluated a school-based intervention that involved rope skipping on students' moderate-to-vigorous physical activity (MVPA) in physical education. The intervention was evaluated using a clustered randomized controlled trial in 24 classes (N = 731 students; M = 14.38 years; all from Secondary 2) from 12 Hong Kong schools during September to December 2013. The primary outcome was percentage of lesson time spent in MVPA. Secondary outcomes included students' vigorous activity, counts per minute, perceived autonomy support and motivation for physical education. Accelerometer-based activity measures were taken from a sub-sample of 168 students during lessons 1 to 3 (baseline) and lessons 5 to 7 (treatment phase). Participants self-reported motivation variables at lessons 4 and 8. Teachers allocated to the experimental group included an intervention during treatment phase; those in the control group continued usual practices. The intervention involved a 15-minute rope skipping activity where students completed intervals of skipping with rests in between. Using multilevel modeling, we examined the intervention effects on measured outcomes, and whether effects differed for boys and girls. Overall intervention effects were not found. However, girls in the intervention group spent more time in MVPA (β = 0.25) and had higher counts per minute (β = 0.32) than control group counterparts at treatment phase. Perceived autonomy support and motivation variables were similar across groups. The intervention increased activity levels of girls, but not boys. Implementation of the intervention may reduce differences between boys' and girls' physical education activity levels. Trial registration: ANZCTR: ACTRN12613000968774. Copyright © 2017 Elsevier Inc. All rights reserved.

Background: Schools present venues for physical activity promotion among youth, with physical education (PE) considered the primary vehicle responsible for increasing activity levels. Yet students are not very physically active during typical school PE classes. With the aim to engage Hong Kong students in more moderate-to-vigorous physical activity (MVPA) during PE, a fitness infusion intervention using rope skipping was designed, and its effectiveness will be examined. Rope skipping was chosen because a) it provides moderate-to-high intensity physical activity; b) is inexpensive; c) students find it enjoyable; and d) is feasible in typical environments in Hong Kong, where PE classes are large in size (up to 40 students) and space available for physical activity is usually limited. Methods/Design: A matched-pair cluster randomized controlled trial was designed. Secondary school students from 24 classes (from 12 schools) will be recruited to participate in the trial. Students' baseline MVPA will be measured during school PE. Classes will be matched according to baseline variables and one class from each pair will be randomized into the experimental group. Teachers in the experimental group will be invited to attend a teacher workshop, and will insert a 15-minute rope skipping activity in four consecutive PE lessons. Motivational factors based on self-determination theory will also be measured as secondary outcomes. The effectiveness of the intervention will be evaluated by comparing changes in the proportion of lesson time spent in MVPA from baseline to follow-up across the experimental and control groups. Discussion: Physical activity levels in PE are often very low and there is a need to identify feasible low-cost interventions that can be easily disseminated. If the results of the study suggest the intervention to be effective, it could be implemented to schools throughout Hong Kong and other cities where space is limited.
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