Cardiovascular response to prescribed detraining among recreational athletes

Exercise-induced cardiac remodeling (EICR) and the attendant myocardial adaptations characteristic of the athlete's heart may regress during periods of exercise reduction or abstinence. The time course and mechanisms underlying this reverse remodeling, specifically the impact of concomitant plasma volume (PV) contraction on cardiac chamber size, remain incompletely understood. We therefore studied recreational runners (n=21, aged 34 {plus minus} 7 years; 48% male) who completed an 18-week training program (~7 h.w ) culminating in the 2016 Boston Marathon after which total exercise exposure was confined to 1 hour) for 8 weeks. Cardiac structure and function, exercise capacity, and PV were assessed at peak fitness (10-14 days before) and at 4- and 8-weeks post marathon. Mixed linear modeling adjusting for age, sex, VO and marathon finish time was used to compare data across time points. Physiologic detraining was evidenced by serial reductions in treadmill performance. Two distinct phases of myocardial remodeling and hematologic adaptation were observed. After 4 weeks of detraining, there were significant reductions in PV (Δ -6.0%, P