Physical activity intensity, sedentary behavior, body composition and physical fitness in 4-year-old children: results from the ministop trial

BACKGROUND: Existing knowledge on associations of physical activity (PA) and sedentary behavior (SB) with body composition and physical fitness in preschoolers is limited. OBJECTIVE: To examine associations of PA and SB with body composition and physical fitness in healthy Swedish 4-year-old children. METHODS: We utilized baseline data collected in 2014 for the population-based MINISTOP trial (n = 307). Light-intensity PA (LPA), moderate-intensity PA (MPA), vigorous-intensity PA (VPA), moderate-to-vigorous PA (MVPA) and SB were measured using accelerometry (ActiGraph-wGT3x-BT). Body composition was measured using air-displacement plethysmography, and physical fitness (that is, cardiorespiratory fitness, lower and upper body muscular strength and motor fitness) was measured using the PREFIT fitness test battery. Multiple linear regression models adjusted for relevant confounders, and in addition, isotemporal substitution models were applied. RESULTS: Greater MVPA was associated with lower fat mass percent (%FM, P = 0.015), and greater VPA and MVPA were associated with higher fat-free mass index (FFMI, P = 0.002 and P = 0.011). In addition, greater VPA and MVPA were associated with higher scores for all physical fitness tests (P = 0.042 to P<0.001). The results for MVPA were primarily due to VPA. SB was associated with weaker handgrip strength (P = 0.031) when PA was not adjusted, but after adjusting also for VPA, the significant association disappeared (P = 0.25). Substituting 5 min per day of SB, LPA or MPA with 5 min per day of VPA was associated with higher FFMI and better scores for cardiorespiratory fitness and motor fitness. Correspondingly, substituting 5 min per day of VPA with SB or LPA was associated with weaker performance for lower muscular strength. CONCLUSIONS: Time spent on VPA was associated with higher FFMI and better physical fitness. The results suggest that promoting VPA may be important to improve childhood body composition and physical fitness already at an early age.