What is the clinical evidence from this study?

Study design: Other. Population: Healthy, recreationally active males (n=22). Intervention: Sprint interval training (SIT) vs. Pre-training baseline. Primary outcome: Submaximal exercise cardiac output to oxygen consumption relationship (Q-VO2) in lower cardiac responders (p=0.02).

What does this research mean for the field?

Four weeks of sprint interval training increases the submaximal cardiac output to oxygen consumption relationship via increased stroke volume in young healthy males with a low initial cardiac response, though this does not improve exercising muscle oxygenation. Novelty: ClaimNovelty.INCREMENTAL. Consensus alignment: ConsensusAlignment.CHALLENGES_CONSENSUS.

January 23, 2019Open Access

Submaximal exercise cardiac output is increased by 4 weeks of sprint interval training in young healthy males with low initial Q-VO2: Importance of cardiac response phenotype

Key Result

Four weeks of sprint interval training increased the submaximal cardiac output to oxygen consumption relationship from 3.8 to 4.7 (P=0.02) in young healthy males with a low initial cardiac response.

Structured PICO

Does 4 weeks of sprint interval training improve the submaximal cardiac output to oxygen consumption relationship in healthy young males?

Population

22 healthy, recreationally active males (< 3 hours/week of structured exercise), mean age 21 ± 2 yrs, with no history of smoking, cardiovascular disease or hypertension.

Intervention

4-week Sprint Interval Training (SIT) consisting of 8, 20-second sprints at 170% of the work rate at VO2 peak on a stationary cycle ergometer, 4 times per week, separated by 10 seconds of active recovery.

Comparator

Pre-training baseline (within-subject comparison) and post-hoc comparison between lower and higher cardiac responders.

Outcome

Relationship between cardiac output and oxygen consumption (Q-VO2) during progressive exercise tests.surrogate

Sprint interval training improves submaximal cardiac output via increased stroke volume specifically in individuals with a low initial cardiac output-to-oxygen consumption relationship.

Main Result

Absolute Event Rate: 4.7% vs 3.8%

p-value: p=0.02

Limitations

Small sample size with only male participants
Potential for underestimation of cardiac output using the inert gas rebreathe method due to soluble gas recirculation
Lack of a non-exercising control group
Lack of direct imaging or invasive studies to confirm mechanisms of reduced sympathetic vasoconstriction

Abstract

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 (Formula: see text-Formula: see text) is unaffected by training as submaximal Formula: see text is unchanged. We recently identified substantial inter-individual variation in the exercise Formula: see text-Formula: see text 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 Formula: see text-Formula: see text given an individual's specific Formula: see text-Formula: see text 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 Formula: see text peak) study with progressive exercise tests (PET) until exhaustion. Cardiac output (Formula: see text L/min; inert gas rebreathe, Finometer Modelflow™), oxygen consumption (Formula: see text 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 Formula: see text (Formula: see text) and lower Formula: see text (Formula: see text) responders were identified post hoc (n = 8/group). SIT increased the Formula: see text-Formula: see text post-training in Formula: see text (3.8±0.2 vs. 4.7±0.2; P = 0.02) while Formula: see text was unaffected (5.8±0.1 vs. 5.3±0.6; P = 0.5). Formula: see text was elevated beyond 80 watts in Formula: see text due to a greater increase in SV (all P0.1). In contrast to Formula: see text, Formula: see text responders are capable of improving submaximal Formula: see text-Formula: see text in response to SIT via increased SV. However, the increased submaximal exercise Formula: see text does not benefit exercising muscle oxygenation.

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