Warm weather is ahead, which means lots of sweat. Get ready for “head rushes.”

Have you ever stood up quickly from a sitting or squatting position and suddenly experienced a “head rush” or dizziness? Many runners are familiar with the sensation, but not the name of the condition: orthostatic hypotension. Commonly described as lightheadedness when you “stand up too fast,” it is something that many people experience, including non-runners. However, some research indicates that highly fit runners are more susceptible to it, especially when dehydrated. This “head rush” usually prompts people to say “Whoa...all the blood rushed to my head.” Indeed, the sensation is caused by the exact opposite - the blood (and oxygen) goes “out of your head.”

Again, the technical term for this experience is orthostatic hypotension. “Orthostatic” means “standing upright,” and hypotension means “low blood pressure.” It is caused primarily by the pooling of blood in the lower extremities while sitting, squatting, or lying down, followed by a sharp drop in blood pressure when moving into an upright position. This in turn causes a rapid loss of blood supply – and oxygen – to the brain, which causes the sensation of dizziness, tingling, blurred vision, and other disconcerting sensations.

There is no serious risk of injury from orthostatic hypotension, other than potential injuries associated with a fall if you pass out or otherwise lose your balance. While it is important to note that orthostatic hypotension can be a sign of more serious medical conditions, the likelihood of underlying medical problems is low.

Several factors can increase the effects of orthostatic hypotension, including dehydration, low sodium or electrolyte levels, and hypovolemia, which is low blood-plasma volume. A runner who has lost of lot of sweat and electrolytes is going to be dehydrated, have low electrolyte levels, and have blood that is “thicker” than normal due to dehydration – all the right conditions for a serious head rush if that runner sits for a period of time or maybe bends over to tie a shoelace and then suddenly stands up.

The important note for runners is to be prepared for the effects of orthostatic hypotension and to understand the conditions that worsen the situation. Basically, take your time moving from a sitting, kneeling, squatting or prone position into a standing position, especially if you are dehydrated or otherwise physically depleted after a workout. Be prepared to grab onto something nearby if you get dizzy after standing, and take deep breaths to help get some oxygen back to your brain. And stay hydrated during hot months ahead!

Paul Carmona is the Online REVEL Coach who has designed training plans specifically for REVEL downhill courses. He is a 25-time REVEL marathon finisher and has run multiple Boston Qualifiers on every REVEL course that he has run, with his current streak at 23 BQs in a row at REVEL marathons!