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Seung Ho Chang, Kyungun Kim, Jihyun Lee and Sukho Lee

Background: Children and youths from low-income families and certain ethnic minority groups show high levels of risk and vulnerability to physical inactivity. The aim of this review was to examine the effectiveness of interventions to increase physical activity (PA) in children and youths from low-income and ethnic minority (LIEM) families. Methods: Eight databases were systematically searched for PA interventions for LIEM children and youths. Twenty-six studies were included in the analyses. Effect sizes (ESs) were calculated using a random-effects model. The ESs were computed using Hedges g with 95% confidence interval. Results: There were small to medium effects of interventions on PA in LIEM children and youth (Q = 1499.193, df = 30, P < .05; I 2 = 97.999). Analyses on the moderator variables showed that ES for participants aged 9–12 years (ES = 0.542, P = .01); intervention length less than 13 weeks (ES = 0.561, P = .01); specialists as the intervention agent (ES = 0.680, P < .05); interventions without technology (ES = 0.363, P = .02); and interventions with a behavioral modification component (ES = 0.336, P = .03) were significantly different from zero. Conclusion: PA intervention can be an effective strategy to increase PA for LIEM children and youths.

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Hyun Chul Jung, Myong Won Seo, Sukho Lee, Sung Woo Jung and Jong Kook Song

We investigated the effects of vitamin D3 supplementation on physical performance during winter training in vitamin D insufficient taekwondo athletes. Thirty-five collegiate male and female taekwondo athletes, aged 19–22 years with low serum 25(OH)D concentration (28.8 ± 1.10 nmol/L), were randomly assigned to a vitamin D group (n = 20) or a placebo group (n = 15). Subjects received either a vitamin D3 capsule (5,000 IU/day) or a placebo during 4 weeks of winter training. Blood samples were collected for analyzing serum 25(OH)D concentration. Physical performance tests included Wingate anaerobic test, isokinetic muscle strength and endurance, a countermovement jump test, sit-ups, agility test, and 20-m pacer. Serum 25(OH)D concentrations increased significantly in the vitamin D group (96.0 ± 3.77 nmol/L) after 4 weeks of supplementation, but no changes were found in the placebo group (F = 242.44, p = .000). There were significant interaction effects for anaerobic peak power (F = 7.49, p = .010) and isokinetic knee extension at 180 deg/s (F = 6.08, p = .019). Changes in serum 25(OH)D concentration were positively associated with changes in peak power and isokinetic knee extension at 180 deg/s. However, no significant interaction effects were observed in other performance variables. This study suggests that 4 weeks of vitamin D supplementation elevates serum 25(OH)D concentration to sufficient levels. Correcting vitamin D insufficiency improves some but not all aspects of performance. Thus, efficacy of vitamin D supplementation to enhance performance remains unclear.