Swelling of the fingers while running could be simply the result of increased blood flow to your digits, but if swelling in your body is extreme, painful or sustained, you may want to check with your doctor. Edema, swelling caused by excess fluid in your body's tissues, could be indicative of a much more serious condition, including heart failure, kidney disease, liver problems from cirrhosis and more.
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Blood Movement and Finger Swelling
When you run, your body actively engages nearly every organ in your body to support the increase in muscle action, blood flow and respiration. Your body is a highly coordinated machine, and the hundreds of physiological changes a good run initiates work to dissipate heat and distribute more oxygen. This can cause your hands to swell with excess blood, as your body distributes blood to your skin and blood vessels in your extremities. It's perfectly normal and a good indicator that your body is undergoing healthy processes.
Your blood contains cells that move oxygen and essential nutrients to your muscles, as well as a fluid component composed primarily of water. Blood usually stays in your blood vessels when you're at rest, but exercise can cause blood to enter the soft tissues of your body, including your fingers. This movement aids the body's effort to maintain a constant core temperature; as you run, your body heats up, and blood moves from your blood vessels to the softer tissues in your fingers and skin to dissipate excess heat. You may notice your fingers swelling more often on particularly hot days, since your body is working extra hard to keep you cool.
Inactive Hands Draw Blood Flow
Generally, your hands are pretty inactive during a run. Good running form means keeping your arms at a 90-degree angle with your hands and wrists relaxed, positioning that makes them an ideal place for your body to move a bit of extra blood for heat dissipation. The soft tissues of your fingers allow heat to dissipate quickly. Since your fingers contain no muscles and are inactive when running, there's no heat generation there during a run. Keep your hands relaxed to promote the natural function of your core temperature regulation, and don't worry if your fingers swell slightly from this increase in fluid.
Sodium Loss and Finger Swelling
While some finger swelling is normal during a run, an overhydrated individual can experience a very different type of swelling called hyponatremia. Hyponatremia occurs when the sodium level in your blood dips below normal levels, which can happen if you're diluting your sodium levels by overhydrating or if you’re not taking in enough electrolytes to offset the salt you're losing through your sweat. Hyponatremia's symptoms include the swelling of cells throughout the body as they fill with excess water, and it is commonly diagnosed by swelling in your fingers, hands and feet. Closely monitoring your water intake and replacing lost electrolytes through a sports drink, salty food or an electrolyte supplement will keep hyponatremia at bay.
Unusual Swelling in the Body
While some finger swelling is normal, you should always pay attention to your body and consult a doctor if something feels uncomfortable or painful. Your fingers can swell for a number of other reasons than normal blood movement. Edema is a swelling of the hands, feet or ankles caused by kidney failure, liver cirrhosis, heart failure or sunburn. If hand swelling persists after you're done exercising, it's time to consult your doctor to determine if you're at risk of a serious condition.