Associations of Fat Mass and Fat-Free Mass with Physical Fitness in 4-Year-Old Children: Results from the MINISTOP Trial

Abstract

Physical fitness is a powerful marker of health in youth. Studies in adolescents and adults suggest that higher fat mass is related to worse physical fitness. However, there is limited knowledge whether fat mass and fat-free mass are associated with physical fitness already in preschoolers. Baseline data from the MINISTOP (Mobile-based INtervention Intended to STop Obesity in Preschoolers) trial was utilized for this cross-sectional analysis. Body composition was assessed using air-displacement plethysmography. Fat mass index [fat mass (kg)/height2 (m)] and fat-free mass index [fat-free mass (kg)/height2 (m)] were used to provide height-adjusted measures of body composition. Physical fitness was measured using the PREFIT (FITness testing in PREschool children) battery, which assesses cardiorespiratory fitness, upper-body and lower-body muscular strength as well as motor fitness. In total, this study included 303 children (168 boys and 135 girls), who were on average 4.48 ± 0.15 years old. Higher fat mass index was associated with worse cardiorespiratory fitness (standardized β = −0.17, p = 0.002), lower-body muscular strength (β = −0.17, p = 0.003) and motor fitness (β = −0.21, p < 0.001) in regression analyses adjusted for age, sex and mutually adjusted for fat-mass index and fat-free mass index. Conversely, higher fat-free mass index was associated with better cardiorespiratory fitness (β = 0.18, p = 0.002), upper-body muscular strength (β = 0.39, p < 0.001), lower-body muscular strength (β = 0.22, p < 0.001) and motor fitness (β = 0.17, p = 0.004). Thus, fat mass and fat-free mass in preschoolers appear to have joint but opposite associations with physical fitness, an important marker for current and future health.

Physical fitness in preschoolers according to body composition

“…It could be assumed that overweight children avoid strenuous weight-bearing physical activities like running and prefer light physical activities. Overweight children had expectedly better results in handgrip strength, which is also reported in previous studies in preschoolers [6,15]. In the present study both higher BMI and FM weakened the results of weight-bearing physical fitness tests.…”

“…It is not surprising that overweight children had significantly higher BMI values in our study. However, it is important to emphasize that BMI reflects both the FM and the FFM in the body, which may have different associations with physical fitness [6]. This opinion could explain the negative association between FFM and results of 20m shuttle run and 4x10m shuttle run in present study.…”

“…Accordingly, the assessment of physical fitness in children is relevant from a public health point of view. Existent evidence refers primarily adolescents with few information about fitness and health in 6-7-years old preschoolers [6]. There is no reason to believe that fitness is less important in preschoolers than in older children [3].…”

Physical fitness reference standards for preschool children: The PREFIT project

“…As a result, heavier children usually perform worse than their counterparts with lower body mass. In line with this, Henriksson et al 32 confirmed that a better performance on weightbearing tests in preschool children was associated with a lower fat mass index. The researchers concluded that the more favourable body composition you have, the fitter you are.…”

Associations between Daily Step Counts and Physical Fitness in Preschool Children

“…Physical fitness assessments were performed according to the validated PREFIT battery [2], a s evidenced by previous publications [13,35,36]. The details of each testing item were described as below:…”