The safety of different exercises depends largely on proper technique. While performing an exercise incorrectly may be dangerous, some exercises pose dangers to certain groups of people even when performed correctly. Exercises that place your head lower than your heart, for example, may pose risks to people with low blood pressure and other cardiovascular problems.
Increased Intracranial Pressure
Exercise places great oxygen demands on your body's muscles. To meet these needs, your blood pressure and heart rate temporarily increase while exercising to transport a greater amount of oxygen in a short period of time. By placing your head lower than your heart, the combination of this increased blood flow and gravity leads blood to pool in your head. Known as increased intracranial pressure, this pooling may cause your brain to swell. As your skull does not flex, this swelling may lead to headaches, loss of consciousness and brain damage in areas pressed against the skull.
Orthostatic Hypotension
The effects of orthostatic hypotension are familiar to anyone who has ever felt faint or dizzy after quickly standing up. While these transient effects happen infrequently and pass relatively quickly for most people, some conditions, such as chronically low blood pressure, may lead to more severe symptoms. By exercising with your head lower than your heart for an extended period of time, you may increase the likelihood and severity of orthostatic hypotension due to blood pooling in your head. The sudden and severe change in intracranial pressure when standing up after such exercises may lead you to lose consciousness, potentially suffering more severe injuries as a result.
High Blood Pressure
You may suffer more severe effects when exercising with your head below your heart if you have high blood pressure. With increases in blood pressure due to exercise and intracranial pressure due to the relative positions of your head and heart, your elevated resting blood pressure may exacerbate any problems arising from swelling of your brain. This may result in damage to blood vessels in your brain, potentially leading them to burst and hemorrhage.
Eye Disorders
Similar to people who suffer from high blood pressure in general, you may suffer serious side-effects when exercising with your head lower than your heart if you have eye pressure disorders. Glaucoma, for example, is a disorder that causes an increase in resting intraocular pressure, or the pressure in your eye, beyond that which your eye can tolerate. As this increased pressure can cause damage to your optic nerve, potentially leading to blindness, you should avoid exercises that further increase your intraocular pressure, such as yoga poses that place your heart higher than your head. In a study published in the August 2006 issue of "Ophthalmology," a team headed by Mani Baskaran of the Medical and Vision Research Foundation in Chennai, India, noted that such poses may more than double your intraocular pressure.
References
- "My Yoga Online"; High Blood Pressure and Inversions; Kreg Weiss; April 2008
- Medline Plus: Increased Intracranial Pressure
- American Heart Association: Low Blood Pressure
- EMedicine Health: Ocular Hypertension
- Optometry: Glaucoma
- "Ophthalmology"; Intraocular Pressure Changes and Ocular Biometry During Sirsasana (Headstand Posture) in Yoga Practitioners; Mani Baskaran et al.; August 2006
