Effects of endurance exercise training on left ventricular structure in healthy adults: a systematic review and meta-analysis

To determine the impact of endurance training (ET) interventions on left ventricular (LV) chamber size, wall thickness, and mass in healthy adults. Electronic databases including CINAHL, MEDLINE, PsycINFO, SPORTDiscus, Cochrane library, and EBM Reviews were searched up to 4 January 2022. Criteria for inclusion were healthy females and/or males (>18 years), ET intervention for ≥2 weeks, and studies reporting pre- and post-training LV structural parameters. A random-effects meta-analysis with heterogeneity, publication bias, and sensitivity analysis was used to determine the effects of ET on LV mass (LVM) and diastolic measures of interventricular septum thickness (IVSd), posterior wall thickness (PWTd), and LV diameter (LVDd). Meta-regression was performed on mediating factors (age, sex, training protocols) to assess their effects on LV structure. Eighty-two studies met inclusion criteria (n = 1908; 19-82 years, 33% female). There was a significant increase in LVM, PWTd, IVSd, and LVDd following ET [standardized mean difference (SMD) = 0.444, 95% confidence interval (CI): 0.361, 0.527; P < 0.001; SMD = 0.234, 95% CI: 0.159, 0.309; P < 0.001; SMD = 0.237, 95% CI: 0.159, 0.316; P < 0.001; SMD = 0.249, 95% CI:0.173, 0.324; P < 0.001, respectively]. Trained status, training type, and age were the only mediating factors for change in LVM, where previously trained, mixed-type training, young (18-35 years), and middle-aged (36-55 years) individuals had the greatest change compared with untrained, interval-type training, and older individuals (>55 years). A significant increase in wall thickness was observed in males, with a similar augmentation of LVDd in males and females. Trained individuals elicited an increase in all LV structures and ET involving mixed-type training and rowing and swimming modalities conferred the greatest increase in PWTd and LVDd. Left ventricular structure is significantly increased following ET. Males, young and trained individuals, and ET interventions involving mixed training regimes elicit the greatest changes in LV structure.