Myocardial Adaptations to Competitive Swim Training

Abstract

Swim training is performed in the prone or supine position and obligates water immersion, factors that may augment cardiac volume loading more than other endurance sports. At present, prospective data defining the cardiac responses to swim training are lacking. We therefore studied myocardial adaptations among competitive swimmers to establish a causal relationship between swim training and left ventricular (LV) remodeling. Collegiate swimmers were studied before and after a 90-d period of training intensification. Transthoracic echocardiography was used to examine LV structural and functional adaptations under resting conditions and during an acute LV afterload challenge generated by isometric handgrip testing (IHGT). A sedentary control population was identically studied with IHGT. In response to a discrete period of swim training intensification, athletes (n = 17, 47% female, 19 ± 0.4 yr old) experienced eccentric LV remodeling, characterized by proportionally more chamber dilation than wall thickening, with attendant enhancements of resting LV systolic (LV twist) and diastolic (early and late phase tissue velocities) function. Compared with baseline and controls, athletes posttraining demonstrated greater systolic twist impairment during IHGT. However, training-induced LV dilation coupled with gains in diastolic function offsets this acquired systolic susceptibility to acute afterload, resulting in the relative preservation of stroke volume during IHGT. Swim training, a sport characterized by unique cardiac loading conditions, stimulates eccentric LV remodeling with the concomitant augmentation of systolic twist and diastolic relaxation. This volume-mediated cardiac remodeling appears to result in greater systolic susceptibility to acute afterload challenge. Further work is required to establish how training-induced changes in function translate to human performance and whether these are accompanied by physiologic trade-offs with relevance to common forms of heart disease.