From the Guidelines
Squatting increases both preload and afterload to the heart. When a person squats, there is compression of the veins in the lower extremities, which increases venous return to the heart, thereby increasing preload (the volume of blood in the ventricles before contraction) 1. Simultaneously, squatting causes increased peripheral vascular resistance due to compression of arterial vessels in the legs, which increases afterload (the pressure against which the heart must pump). This hemodynamic response makes squatting a useful maneuver for patients with certain cardiac conditions. For example, in hypertrophic cardiomyopathy, increased preload can help open the obstructed outflow tract, while in aortic stenosis, the increased afterload can help maintain forward blood flow. The physiological basis for these changes involves both mechanical compression of blood vessels and reflex autonomic responses that affect vascular tone and cardiac output.
Some key points to consider:
- The increase in preload and afterload is temporary and reverses when standing resumes 1.
- Squatting has been shown to be beneficial in certain cardiac conditions, such as hypertrophic cardiomyopathy and aortic stenosis, by increasing preload and afterload 1.
- The use of physical countermeasures, such as squatting, can help reduce the risk of syncope and improve cardiovascular parameters 1.
- It is essential to consider the individual patient's condition and medical history before recommending squatting as a therapeutic maneuver.
In terms of the evidence, a recent study published in 2024 found that physical countermeasures, including squatting, can help reduce the risk of syncope and improve cardiovascular parameters 1. Another study published in 2011 discussed the concept of cardiac hypertrophy and its relationship to increased preload and afterload, highlighting the importance of considering the individual patient's condition and medical history 1. However, the most recent and highest quality study, published in 2024, provides the strongest evidence for the benefits of squatting in certain cardiac conditions 1.
From the Research
Effects of Squatting on Preload and Afterload
- Squatting produces a prompt increase in cardiac output and arterial blood pressure, which is accompanied by an immediate decrease in heart rate and forearm vascular resistance 2.
- The rise in cardiac output and blood pressure during squatting is attributed to augmented venous return from compression of leg veins 2.
- Squatting also leads to a decrease in peripheral resistance, which is most likely mediated by arterial baroreflexes activated by the acute rise in arterial blood pressure 2.
- The increase in cardiac output during squatting is due to an increase in stroke volume, which is a result of increased preload 2.
- Preload is increased during squatting due to the compression of leg veins, which increases venous return to the heart 2, 3.
- Afterload is decreased during squatting due to a decrease in peripheral resistance, which is mediated by arterial baroreflexes 2.
Hemodynamic Responses to Squatting
- Both normal individuals and heart transplant recipients exhibit similar increases in stroke volume index and mean arterial pressure during squatting 2.
- Heart rate decreases in normal individuals during squatting, but is unchanged or minimally increased in heart transplant recipients 2.
- Forearm vascular resistance is decreased in normal individuals during squatting, but only minimally and not significantly in heart transplant recipients 2.
- The hemodynamic responses to squatting are similar in normal individuals and heart transplant recipients, suggesting that cardiac denervation does not alter the responses to squatting 2.