Cardiac remodeling in response to 1 year of intensive endurance training.
Level 4 - case-series / case-control
Prospective single-arm pre-post interventional study without a concurrent non-training control group.
PubMed 25281664 · doi:10.1161/CIRCULATIONAHA.114.010775
What was done
Twelve previously sedentary healthy individuals (aged 29±6 years; 7 men, 5 women) completed a 12-month progressive, intensive endurance training program targeting marathon completion. Cardiac magnetic resonance imaging was conducted at baseline and at 3, 6, 9, and 12 months to measure left and right ventricular mass and volumes. Maximal oxygen uptake (VO2 max) and cardiac output (via acetylene rebreathing) were measured at the same intervals. Invasive pulmonary artery catheterization with volume manipulation (lower body negative pressure and saline infusion) was performed pre- and post-intervention to construct Starling and pressure-volume curves.
What was found
Over 12 months, VO2 max increased significantly from 40.3±1.6 to 48.7±2.5 mL/kg/min (P < 0.00001), accompanied by increases in maximal stroke volume and cardiac output. Both left and right ventricular mass increased progressively to magnitudes observed in elite endurance athletes. However, structural adaptation differed between chambers: right ventricular volume increased progressively from training onset (eccentric remodeling), whereas left ventricular volume remained unchanged until 6 months (initial concentric remodeling before later dilation restored baseline mass-to-volume ratios). Cardiac compliance and Starling curves approached, but did not match, values seen in elite athletes.
Why it matters
This study demonstrates that intense endurance training alone can drive substantial athletic cardiac remodeling in previously sedentary adults without requiring genetic predisposition. It reveals an unexpected temporal divergence in chamber adaptation, with the right ventricle undergoing early eccentric remodeling while the left ventricle initially undergoes concentric hypertrophy before dilating.
Limits
The study is constrained by a very small sample size (n=12) and the lack of a parallel, non-exercising control group to rule out time-dependent confounding. Findings in young, healthy adults (average age 29) cannot be generalized to older populations or individuals with pre-existing cardiovascular conditions. Additionally, one year of training remained insufficient to replicate the full cardiac compliance profile of lifelong elite athletes.
Cited by
- supports Exercise training increases cardiac size by 15% to 20%, and there is a 75% difference in cardiac muscle mass between elite runners and patients with spinal cord injuries.
- supports Intensive endurance training of sedentary young adults in their 30s preparing for a marathon or 100-mile bike ride induces significant cardiac remodeling and fitness gains, but does not achieve the heart size observed in elite competitive endurance athletes.