What Causes Leg Fatigue While Running?

Runner athlete running on seaside
Incorrect posture or worn-out shoes could contribute to leg fatigue. (Image: lzf/iStock/Getty Images)

Running can be an exhilarating workout: filling your lungs with fresh air, pumping your legs along the terrain and allowing feel-good endorphins to course through your body. However, your runner’s high might be offset by legs that feel tired, painful or weak. If you’re experiencing leg fatigue while running, you could be pushing yourself too hard, running too long or wearing inappropriate footwear.

Ambiguity of Fatigue

Part of the challenge in addressing causes for leg fatigue lies in the ambiguity of the experience, according to Exercise is Medicine.org. Fatigue might be accompanied by cramping, pain, aches or weakness. If you’re experiencing intermittent leg fatigue while you’re running, try noting the conditions when it occurs. This can help you isolate the problem; for example, perhaps you experience leg fatigue while running sprint intervals or only after very long distances. You could become more tired when running on sandy trails compared to synthetic tracks, according to Kean University. Not being properly hydrated could also make you feel more tired.

Genetics and Lactate Levels

Your endurance level is partly genetic, according to IDEA Fit. Some individuals can run longer distances because their bodies’ lactate levels remain relatively stable during exercise. Lactate levels relate to your body’s composition of mitochondria with regard to size, shape and enzyme levels. When mitochondria levels increase, respiration improves and your endurance levels boost. If your body doesn’t have a genetic composition resembling those of high-performance athletes, fatigue could set in earlier and your legs will feel tired.

Running Strategies

You might experience leg fatigue because of incorrect posture or technique while running. Running in a straight line and at a constant speed tends to be more efficient compared with running erratically or at various speeds, according to Kean University. Slick running shoes, or shoes that don’t have adequate tread, could negatively impact your ability to strike the ground efficiently, resulting in lost momentum and creating the potential for fatigue. Lowering your center of gravity while running could increase your balance and power, making it easier to run without becoming fatigued.

More Serious Complications

If you experience persistent leg fatigue while running that doesn’t seem to be associated with appropriate gear or overtraining, something more serious could be occurring, according to Exercise is Medicine.org. Muscular issues, circulation issues or spinal issues could be contributing to fatigue. Vein issues, for example, are often accompanied by a heavy feeling in your legs. Experiencing weakness or pain in your hip, thigh or buttock might indicate spinal problems. If chronic leg fatigue while running seems to be a problem, consult with your doctor.

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