We studied the sensitivity of cardiac structures to endurance training. To evaluate variability in adaptation, 20 sedentary subjects and ten pairs of monozygotic twins were submitted to a 20-week endurance training program. Maximal oxygen uptake increased significantly in both groups: 11 mL O2/kg/min-1 or 30% in the sedentary group and 6 mL O2/kg/min-1 or 13% in the monozygotic twins. Statistically significant increases in left ventricular diameter, posterior wall and septal thicknesses, as well as left ventricular end-diastolic volume and left ventricular mass were observed in the sedentary subjects, but not in the monozygotic twins. We could demonstrate that after training, twin pairs differed more from each other than at the start. Concomitantly, within-pair resemblance was greater after training than before. Results indicate that cardiac dimensions are amenable to significant modifications under controlled endurance training conditions and furthermore that the extent and variability of the response of cardiac structures to training are perhaps genotype dependent.
Landry F, Bouchard C, Dumesnil J. Cardiac Dimension Changes With Endurance TrainingIndications of a Genotype Dependency. JAMA. 1985;254(1):77–80. doi:10.1001/jama.1985.03360010083031