During which phase of resistance training is stroke volume significantly increased?

The correct answer is that stroke volume is significantly increased during the eccentric phase of resistance training. The eccentric phase refers to the portion of an exercise where a muscle lengthens under tension, often described as the lowering or releasing phase of an exercise (for example, lowering a dumbbell during a bicep curl). During this phase, muscles are still actively generating force, and there is an increase in venous return to the heart as muscles lengthen and compress veins. This venous return enhances the filling of the heart, subsequently leading to a higher stroke volume—the amount of blood ejected by the heart with each contraction.

In contrast, during the concentric phase, which involves muscular shortening and lifting, the heart is working to pump blood under higher resistance, which may not necessarily focus on maximizing stroke volume to the same extent. The isometric phase, where the muscle contracts without changing length, does not effectively promote increased venous return or contribute in a similar manner to stroke volume. In the resting phase, the cardiovascular demands are at their lowest, and there would be no significant increase in stroke volume due to muscular activity.