Longitudinal Changes in Heart Rate-Corrected Measures of Exercise Performance in Children

Abstract

Interpretation of change in exercise performance over time in children with repaired congenital heart disease is often hampered by poor effort that limits the maximum heart rate; this is often difficult to distinguish from chronotropic impairment, a common finding in these children. In an attempt to address this limitation, we sought to examine measures of exercise performance that are corrected for heart rate in healthy children and to determine if these change with somatic growth. We studied two serial graded exercise tests in 24 healthy children at an interval of >3 years. Paired comparisons revealed that maximum oxygen pulse (O₂ pulse), O₂ pulse at ventilatory anaerobic threshold, O₂ pulse at a heart rate of 140 beats per minute, and slope of the VO₂–heart rate relationship all increased with age. However, when indexed to somatic growth, there was no change in the mean values of these parameters over time. We conclude that O₂ pulse and slope of the VO₂–heart rate relationship during exercise increase in proportion to somatic growth in children so that optimal oxygen delivery to the exercising muscles is ensured. This study provides the “normative” response of exercise parameters to growth, against which responses of children with repaired congenital heart disease may be compared.