During resistance exercise, which phase is associated with the greatest increase in cardiac output?

During resistance exercise, which phase is associated with the greatest increase in cardiac output?

• A. Concentric phase
• B. Eccentric phase
• C. Isometric hold
• D. Rest after the set

Answer: (B)

During resistance exercise, cardiac output rises because both heart rate and the amount of blood returning to the heart respond to muscle activity. In the eccentric phase, the muscle lengthens under load, which causes less intramuscular compression of blood vessels than during the lifting (concentric) phase. This allows greater venous return to the heart, increasing end-diastolic volume and thus boosting stroke volume. With the sympathetic drive from exercise, heart rate also remains elevated, so the combination yields a larger cardiac output than in the other phases. In the concentric phase, more vascular compression reduces venous return and limits stroke volume, even though heart rate is up. Isometric holds dramatically raise intramuscular pressure and afterload, which can hamper venous return and limit the rise in cardiac output. Resting does not elevate these responses. So the phase with the greatest increase in cardiac output is the eccentric phase.

During resistance exercise, cardiac output rises because both heart rate and the amount of blood returning to the heart respond to muscle activity. In the eccentric phase, the muscle lengthens under load, which causes less intramuscular compression of blood vessels than during the lifting (concentric) phase. This allows greater venous return to the heart, increasing end-diastolic volume and thus boosting stroke volume. With the sympathetic drive from exercise, heart rate also remains elevated, so the combination yields a larger cardiac output than in the other phases. In the concentric phase, more vascular compression reduces venous return and limits stroke volume, even though heart rate is up. Isometric holds dramatically raise intramuscular pressure and afterload, which can hamper venous return and limit the rise in cardiac output. Resting does not elevate these responses. So the phase with the greatest increase in cardiac output is the eccentric phase.