HEBESTREIT, H., W. SCHRANK, L. SCHROD, H.-M. STRAßBURG, and S. KRIEMLER. Head Size and Motor Performance in Children Born Prematurely. Med. Sci. Sports Exerc., Vol. 35, No. 6, pp. 914–922, 2003.
Purpose: The objective of this study was to determine the relationship between head circumference (HC) and motor performance in 6- to 12-yr-old children born prematurely (PRE: birthweight ≤ 1500 g, gestational age ≤ 32 wk) and in children born at term (CON).
Methods: Thirty-three PRE and 21 CON without an apparent neurological deficit participated in this study. HC was measured on the day of testing and was rated as small HC (SHC, HC more than 1 SD below the 50th percentile of reference data) or as normal HC (NHC). Subjects were examined by an experienced neuropediatrician, and whole-body coordination was assessed by the Körper-Koordinationstest für Kinder (KTK). Peak exercise performance was determined by a Wingate test and an incremental cycling test to volitional fatigue. Net oxygen cost of cycling was measured during four different tasks lasting 5–7 min each. Subjects pedaled at an intensity corresponding to 30% and 60% of peak oxygen uptake (V̇O2peak) at a cadence of 36 and 76 rpm, respectively.
Results: Prematures with SHC showed no statistically significant difference in their neurological examination and whole-body coordination compared with prematures with NHC. Wingate test performance and V̇O2peak relative to body mass were similar among SHC, NHC, and CON. In SHC, but not in NHC and CON, net oxygen cost of cycling increased significantly (P < 0.05) when cadence was increased from 36 to 76 rpm.
Conclusion: At the age of 6–12 yr, SHC have a higher oxygen cost of cycling in exercise tasks requiring high velocity, which might be explained—at least in part—by an impaired neural control of intra- and intermuscular coordination.
With the increase in survival of children born prematurely (PRE), quality of life issues become more relevant. Although more than 90% of children with a birth weight ≤ 1500 g and/or a gestational age ≤ 32 wk do not show a severe disability at school age, as many as 40% are estimated to be unable to become fully independent adults (34). In general, mild developmental abnormalities, behavioral and learning disorders are commonly reported in these children (18,22).
In PRE, a small head circumference is associated with a reduced IQ and higher incidence of neurologic impairment (8,17). Based on the association between head size and brain weight and brain volume in children and adolescents (4,6), a small head circumference in PRE may indicate brain atrophy (8). Indeed, cerebellar atrophy has been demonstrated in PRE using magnetic resonance imaging (MRI) (18). Furthermore, studies employing MRI showed abnormalities of ventricles, white matter, and corpus callosum in these children (18,32).
Compared with children born at term, some apparently unimpaired PRE may show deficits in equilibrium, reaction time, and body coordination (see 9 for review). Furthermore, it has been shown that PRE may perform inferior to children born at term in exercise tasks requiring a high power output and/or a high speed of motion, such as a standing high jump, a Wingate anaerobic test, or an unloaded cycling task to determine maximal cadence (7,16,31). These findings suggest that motor control might be impaired after premature birth even in the absence of overt neurological complications. In line with the hypothesis of an impaired motor control in PRE, it was shown that preterm, small-for-gestational-age children (SGA) had a higher oxygen uptake during running than controls born at term (2). Interestingly, SGA born prematurely have an increased risk for a subnormal head growth (25).
Measurements of oxygen uptake during defined exercise tasks have been used to study motor control in a variety of tasks and populations (3,14,20,33), and it has been established that an increased oxygen uptake during running and cycling is common in individuals with poor motor coordination (14,33). In cerebral palsy, excess oxygen requirement for a given task has been linked to an increased co-contraction of antagonistic muscle groups (33).
We hypothesized that PRE in general, but especially PRE with a small head circumference, would be at risk for an impaired performance in various exercise tasks. We expected that low performance in these children would be most evident during tests in which neuromotor control rather than involved muscle mass is limiting such as the measurement of oxygen cost of cycling at submaximal levels with a high cadence.
The objective of the present study was to assess the association of head size at the time of testing with motor performance in children born prematurely. In addition to maximal exercise capacity in short- and medium-term exercise tasks, we intended to evaluate whole-body coordination and the oxygen cost of cycling at submaximal levels and different cadences.