By the end of a long run, you might find your shoes feel tight and your feet are swollen and sore. You’re suffering from peripheral edema, and although it sounds scary, it’s likely not serious. Many people retain fluid in their feet due to overuse of venous insufficiency.
If your foot swelling is accompanied by pain or other alarming symptoms, however, contact your doctor immediately to be sure it’s not a kidney or thyroid disorder, or any other condition that needs medical attention.
If you’ve just completed an extra long training run for a marathon, for example, and aren’t used to the distance, it could cause your feet to swell. A long run, meaning several hours on your feet, can naturally cause blood and fluids to pool so your feet swell.
And, if you're not accustomed to running, doing too much, too soon can make your feet swell -- as well as make you sore and tired. When you start running, keep your miles to a maximum of about three miles per run just three times per week. Gradually increase your mileage by about 10 percent the next week -- so instead of 9 miles, do about 10 miles. As your body becomes accustomed to the impact, you can add more miles and additional running days.
Not Enough Electrolytes
Consider your hydration and electrolyte status during your run. If you took in little in the way of fluid or salts (from sports drinks or electrolyte tabs), your swollen feet could be due to low sodium levels in the blood. This is likely the cause if you have swelling elsewhere in your body, such as your fingers and hands as well as in your feet.
Drinking a lot of fluids to the point of overload during a long run can also make your feet swell. A study of ultra-marathoners published in the Journal of International Sports Nutrition in 2012 showed that the more fluids an athlete consumed, the greater the volume of his foot at the end of the race. Faster runners who took in less fluids experienced less swelling in the feet and thus had less risk of edema.
Perfect hydration levels are truly unique to the individual athlete. However, Lisa S. Bliss, MD, noted in an article published in Ultrarunning Magazine in 2013 that an athlete can safely tolerate fluid loss that results in about a 2 percent loss of weight and still perform well. Greater dehydration levels will likely affect performance and possibly lead to nausea and vomiting.
But, if your total body weight increases during a run, it's usually a sign of overhydration. You may be at risk of edema and hyponatremia — when your body has too much water and not enough sodium. Consume something that's salty — preferably not with a lot of water — such as bouillon cubes dissolved in a scant amount of water or pretzels if you become waterlogged.
Veins return blood to the heart, but the valves that prevent the blood from flowing the wrong way can sometimes become leaky or clogged. If your swollen feet are accompanied by visible ropey or puffy veins, you may have venous insufficiency. Varicose and spider veins are tell-tale signs.
If your swollen feet hurt, consult your doctor for possible treatment such as sclerotherapy or a phlebectomy. Sclerotherapy involves injecting a solution into your veins that causes them to collapse; phlebectomy is a minimally invasive surgical removal of the swollen veins.
Other Potential Causes
Swollen feet are also more likely if you're pregnant or running in hot conditions. Certain medications and hormonal changes may also be to blame. If you twisted your ankle or bruised your foot while running, the swelling might accompany the injury. See a doctor if it hurts to put weight on your foot or if the swelling continues for several days after your run.
How to Reduce Swelling
You may find compression socks help keep the blood flowing during your run and discourage the fluid build-up caused by faulty veins. Find them at sporting goods stores.
Propping your feet up above your heart after your run can also help reduce swelling. Try Legs-Up-the-Wall pose from yoga, in which you lie on your back on the floor with your butt against a blank wall. Stretch your legs up the wall for 5 minutes or longer.
Avoid diuretics to relieve swelling. Although they can help reduce fluid retention, the pills can dehydrate you for future runs.
Read More: Dehydration While Running