Being dizzy or lightheaded while hiking, running, or biking can mean that something serious is at play--a cardiac problem--or it could be due to something as simple as dehydration or being out of shape. How do you tell the difference?
Typically, the dizziness related to the more common conditions is going to be limiting your ability to keep going--your body is going to want you to slow down, and the symptoms should improve as you decrease exertion.
The fact that your body gives you that time to slow down, that warning (or "prodrome" in medical terms), suggests a less serious cause of lightheadedness (near syncope), or passing out (syncope).
Timing is critical: The 2024 HRS Expert Consensus Statement and the ACC/AHA syncope guidelines both emphasize that syncope occurring after cessation of exercise with a typical vasovagal prodrome is almost always benign. In a cohort of 7,568 athletes, all episodes of post-exertional syncope had typical features of neurally mediated fainting with a prodrome and were not related to cardiac disease. In contrast, the absence of prodrome — particularly an acute "face plant" during exertion without warning — is listed as a high-risk feature for cardiac syncope.
So, that "face plant," or feelings of lightheadedness with chest pain or palpations are worrisome, but let's say that none of that is pertinent. You and your friends are just out on a trail and someone is feeling dizzy or lightheaded.
What could be going on?
- Heat exhaustion
- Dehydration
- Hypoglycemia
- Hyponatremia
- Hyperventilation
I've written about heat related illnesses a couple of times, so I'm sure you're well versed on this already. Feel free to refresh your memory though.
Skipping down to hyperventilation; I hadn't really talked about this much before but this is something that can happen with intense exertion. The effects of hyperventilation are pretty interesting, and one could go WAY down the rabbit hole to learn about how carbon dioxide levels in the blood stimulate our drive to breathe, and how the acid/base levels in our blood effect how certain electrolytes are bound to proteins or freely circulating. We don't need to go that deep now, but just know that one effect of hyperventilation is that the blood vessels to the brain constrict causing dizziness and confusion. This can also lead to less circulating calcium which will cause a "pins and needles" feelings in the hands and around the mouth. With controlled breathing, that will all resolve.
So that leaves us with dehydration, hypoglycemia, and hyponatremia, which I discuss together in our classes because they can be prevented all at once.
Before I go any further, I do need to clarify that I have very different philosophies on hydration as it pertains to day to day life versus with exertion.
I agree with Adam Conover and I think that we have been fooled into thinking that we need to constantly to be drinking water. How else would Yeti sell a nearly $50 travel mug?
I trust Dr. Glaucomflecken and I trust my kidneys. If my kidneys tell me to drink, I'll drink. That strategy seems to apply to exercise less than 60-90 minutes as well:
When drinking to thirst is sufficient: A comprehensive review by Kenefick (2018) and a meta-analysis by Goulet (2012) found that for exercise lasting <1 hour to 90 minutes, in cooler conditions, or at lower intensity, drinking to thirst is adequate and actually maximizes endurance performance.
BUT, for longer efforts, higher intensity, or on hotter days, drink up.
How much, and what should you drink you ask?
I'm not even going to try to give specific recommendations for anyone who is trying to develop a fueling or hydration strategy to optimize peak performance or ultra-endurance. If that's you, look elsewhere. Maybe you *could* measure your sweat and calculate an exact re-hydration strategy, but FFS, why? Unless a gold medal is on the line, it doesn't need to be that complicated.
Just keep sipping, and keep ingesting some glucose and some electrolytes. If you keep sipping some Gatorade or Powerade or Vitamin Water or whatever you should be good. Drink more if you're sweating more, drink less if you're feeling full. It's really that simple.
Every sports drink manufacturer will tell you why their formulation is best, and there may be some science behind their claims, but most people in most situations are not going to notice a difference. It's like the people who spend extra money or an aerodynamic bike but never go above 20mph or people who spend extra money on ultralight hiking gear and never go out for more than an hour.
The 2007 study, Exercise and Fluid Replacement, published by the American College of Sports Medicine has guidelines that suggests that sports drinks should offer "6–8% carbohydrate, 110–165 mg sodium per 8 oz" and most drinks hit that target. Some have less carbohydrates (if you're going to also be supplementing with gels or something). Some have more or less sodium, and many have different amounts of potassium, calcium, and magnesium, but for MOST people, the specific amounts don't matter, just have some.
The only caveat that I will add is that there is a limit to the amount of carbs that your body can process and taking in too much can lead to some GI issues. Sadly, 12 chocolate chip cookies in the middle of a ride are NOT going to help you get to the top of a climb any faster. I've tried.
The ACSM guidelines emphasize that carbohydrate concentration should not exceed 8%, as higher concentrations slow gastric emptying. The greatest rates of carbohydrate delivery are achieved with a mixture of sugars (glucose, sucrose, fructose, maltodextrin) rather than a single sugar source. For events >1 hour, a conventional 6–8% sports drink consumed at 0.5–1 L/hour provides 30–80 g/h of carbohydrate, meeting the recommended range.
The bottom line is that you can spend a lot of money on sports drinks, or grab something at the local Cumberland Farms. Just drink what you've got and keep the tank topped off and that will keep your lack of electrolytes, carbohydrates, or fluids from being a limiting factor on the trail.
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