The association of birth weight and infant growth with physical fitness at 8-9 years of age--the ABCD study.

BACKGROUND: Low birth weight and accelerated infant growth are independently associated with childhood obesity. We hypothesized that birth weight and infant growth are associated with physical fitness in childhood, and thereby could act as a link in the developmental origins of obesity. In addition, we assessed whether these associations were mediated by fat-free mass (FFM), moderate-to-vigorous physical activity (MVPA) or sedentary behavior (SB).

METHODS: We assessed physical fitness in 194 children of Dutch ethnicity aged 8.6 (±0.35) years from the ABCD cohort. Aerobic fitness was assessed using the 20-meter multistage shuttle run test (20-m MSRT), and neuromuscular fitness using the standing broad jump (SBJ) test and hand grip strength test. MVPA and SB were measured by accelerometry, and FFM by bioelectrical impedance analysis. Low birth weight was defined as below the 10th percentile and accelerated infant growth as an s.d. score weight gain of >0.67 between birth and 12 months.

RESULTS: Children with low birth weight and subsequent accelerated infant growth attained a lower 20-m MSRT score than the remainder of the cohort, adjusted for multiple confounders (P<0.01). Birth weight and infant growth were both independently positively associated with hand grip strength, but not after adjusting for current height and body mass index. There was no association of birth weight or infant growth with SBJ. FFM mediated >75% of the association of birth weight and infant growth with hand grip strength, but FFM, MVPA and SB did not mediate the associations with 20-m MSRT.

CONCLUSIONS: Our results indicate that low birth weight and accelerated infant growth might negatively affect childhood aerobic and neuromuscular fitness. Differences in FFM largely explain the developmental origins of neuromuscular fitness. Consequently impaired fitness may constitute a link between low birth weight, accelerated infant growth and obesity. Hence, optimization of fitness in these children may affect their obesity and cardiovascular disease risk.