Transient responses in cardiac function below, at, and above anaerobic threshold

Area of Science:

• Cardiovascular Physiology
• Exercise Science
• Sports Medicine

Background:

• Understanding exercise-induced cardiac adaptations is crucial for assessing fitness levels.
• Differences in cardiac function between trained and untrained individuals are well-documented at rest, but require further elucidation during dynamic exercise.

Purpose of the Study:

• To investigate exercise-induced alterations in cardiac function, specifically stroke volume (SV) and stroke index (SI), during graded cycling in trained versus untrained young men.
• To compare cardiac performance metrics at submaximal and maximal exercise intensities between the two groups.

Main Methods:

• 13 trained and 13 untrained young men underwent graded cycling exercise.
• Cardiac function parameters, including stroke volume (SV) and stroke index (SI), were measured using impedance cardiography.
• Measurements were taken at rest, during submaximal exercise, and at maximal exercise intensities.

Main Results:

• Trained individuals demonstrated consistently greater SV and SI at rest and during both submaximal and maximal exercise compared to untrained individuals.
• Training-induced bradycardia was observed in the trained group at rest and during submaximal exercise.
• Even when matched for heart rate and left ventricular ejection time, trained individuals maintained higher SV and SI.
• Untrained individuals showed a relative decrease in SV above the anaerobic threshold, potentially due to impaired diastolic filling and/or systolic emptying.

Conclusions:

• Trained individuals possess superior stroke volume and stroke index during exercise, reflecting enhanced cardiac efficiency.
• Differences in cardiac filling and contractility likely contribute to the observed variations in SV between trained and untrained subjects during exercise.
• These findings highlight the significant impact of endurance training on cardiac performance during physical exertion.