• Individual differences;
  • Heart rate;
  • Oxygen consumption;
  • Additional heart rate;
  • Response consistency;
  • Twin studies;
  • Behavior genetics


This program of experiments examined heart rate responses to mental arithmetic and a video game. Attention first focused on their metabolic relevance. Comparison with heart rate/oxygen consumption regression equations generated from isotonic exercise data revealed that the heart rate increases of certain individuals were considerably in excess of those necessitated by contemporary metabolic demand. Both temporal and intertask consistency of reaction were explored, and supportive evidence was obtained. The relationship between laboratory and real-world reactions was investigated, and preliminary evidence found suggesting that in-laboratory responses are indicative of responses to more naturalistic stressors. Finally, twin studies examining the genetic and environmental determinants of individual differences in heart rate change during the tasks revealed a substantial genetic component for these responses.