Submaximal exercise cardiac output is increased by 4 weeks of sprint interval training in young healthy males with low initial <i>Q̇</i>-<i>V̇</i>O₂: Importance of cardiac response phenotype

Cardiovascular adaptations to exercise, particularly at the individual level, remain poorly understood. Previous group level research suggests the relationship between cardiac output and oxygen consumption (-) is unaffected by training as submaximal is unchanged. We recently identified substantial inter-individual variation in the exercise - relationship that was correlated to stroke volume (SV) as opposed to arterial oxygen content. Therefore we explored the effects of sprint interval training (SIT) on modulating - given an individual’s specific - relationship. 22 (21±2 yrs) healthy, recreationally active males participated in a 4-week SIT (8, 20 second sprints; 4x/week, 170% of the work rate at peak) study with progressive exercise tests (PET) until exhaustion. Cardiac output ( L/min; inert gas rebreathe, Finometer Modelflow™), oxygen consumption ( L/min; breath-by-breath pulmonary gas exchange), quadriceps oxygenation (near infrared spectroscopy) and exercise tolerance (6–20; Borg Scale RPE) were measured throughout PET both before and after training. Data are mean Δ from bsl±SD. Higher () and lower () responders were identified post hoc (n = 8/group). SIT increased the - post-training in (3.8±0.2 vs. 4.7±0.2; P = 0.02) while was unaffected (5.8±0.1 vs. 5.3±0.6; P = 0.5). was elevated beyond 80 watts in due to a greater increase in SV (all P0.1). In contrast to , responders are capable of improving submaximal - in response to SIT via increased SV. However, the increased submaximal exercise does not benefit exercising muscle oxygenation.