Training duration rather than intensity was the strongest predictor of cardiac remodeling, potentially highlighting a shift in how exercise should be quantified from subjective intensity estimates to objective duration recording, according to a study published January 7 in the EHJ.

During the longitudinal study, 69 young (16-23 years) and 82 middle-aged (45-70 years) male endurance athletes recruited from the Pro@Heart and Master@Heart studies wore a heart rate monitor on their chest over three months to ≥80% of their training sessions. Training duration, session count and intensity were recorded, as well as cardiac dimensions, including indexed left/right ventricular volumes, ejection fraction and left ventricular mass.

Results showed that while both training duration (r>0.33; p<0.05) and intensity as measured by Edwards training impulse (r>0.29; p<0.05) correlated for cardiac dimensions, duration always outperformed intensity. Furthermore, when intensity was classified into five heart rate zones, time spent in Zones 1 and 2 correlated more with cardiac dimensions than the high-intensity zones.

Additionally, compared with the older athletes, younger athletes trained more (169 hours vs. 78 hours) and exhibited larger cardiac volumes. With a partial least squares analysis, study authors Christophe Dausin, MS, et al., identified training duration in Zones 1, 2 and 3 and age as key determinants of cardiac remodeling.

"Categorization of exercise intensity according to chart-based estimation of [metabolic equivalent of tasks] had limited utility in this population as most exercise would be interpreted as high intensity," write the authors. "These findings highlight how direct quantification of exercise intensity and duration can provide new insights into cardiac remodeling assessments."