Why Your Heart Rate Increases At T1 Transitions

Why Your Heart Rate Increases At T1 Transitions

HUNTINGTON BEACH. When triathletes exit the water at the finish of the swim leg in the T1 transition, there is almost always a corresponding spike in their heart rate.

Why is this?

When triathletes shift from one posture to another (e.g., from the horizontal position while swimming to the vertical position while running or dolphining out of the water), the blood in their heart and lungs naturally tend to move towards their legs due to the influence of gravity.

As the blood moves towards their lower limbs, the veins in their legs expand and venous pooling occurs.

When in the vertical position, the parts of the body in higher positions than the heart experience a drop in arterial blood pressure. Conversely, parts of the body below the heart experience an increase in blood pressure. When the average adult stands up, there is typically a rise in venous blood pressure in the lower limbs to 90 mmHg. When the veins in the lower limbs expand and pooling occurs, the rate of venous return (i.e., blood flow back to the heart) correspondingly decreases. As a result, the heart’s stroke volume decreases, creating a transient drop in blood pressure.

As the blood pressure falls to compensate for this change, the sympathetic nervous system kicks into action and the heart rate naturally increases along with the vascular resistance. Consequently, blood pressure recovers and a balance is maintained as your heart pounds heavily and quickly.

In order to help adapt to these changes from the swimming position to the running (or walking) position, deck-ups are a great way to help triathletes improve and become accustomed to this sudden heart spike.

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