Why Do Your Thighs Burn on a Bicycle?

Your quads and glutes are the primary muscles you use to ride a bike. The "burn" you experience in your thigh muscles when riding a bicycle is related to muscle fatigue. Specifically, this sensation is thought to be caused by a decreased flow of calcium to muscles, which occurs with exhaustive exercise. Building muscular endurance in the quadriceps and other leg muscles can help you resist muscle fatigue when cycling.

The once commonly held belief that the accumulation of lactic acid in muscles causes the burning pain that accompanies muscle fatigue has been largely discredited by physiologists, according to a 2008 ScienceDaily article. According to a study published in the "Journal of Clinical Investigation" in 2008, the burning pain associated with tired muscles — including burning thighs while riding a bike — is likely caused by a calcium deficit in your muscles. The study's lead author, Dr. Andrew R. Marks, says that when muscles become tired from exertion, they start leaking calcium, which weakens contractions and stimulates an enzyme that destroys muscle fibers. Marks and his team found that muscle fibers in mice who ran on a treadmill to exhaustion, and the thigh muscles of cyclists who biked for three hours a day, produced this calcium leak.

Although burning thighs while riding your bike is unpleasant, the muscle damage incurred during muscle fatigue is repaired by the body after a few days of rest, says Marks. Furthermore, riding your bike regularly, even for just a few miles each day, will help improve your muscular endurance, or the length of time it takes your muscles to fatigue during aerobic activity. Riding your bike aerobically on a regular basis will help develop the slow-twitch muscle fibers — the muscle fibers involved in aerobic exercise — in your thighs, which will eventually allow you to bike for longer periods of time before encountering the burning sensation indicative of muscle fatigue.

Strength-building activities can help prevent muscle fatigue in your thighs' fast-twitch fibers — the muscle fibers involved in short, intense bursts of exertion, such as riding your bike up a hill. For example, static holds, or isometric exercises, that target the quads can help build strength useful in delaying muscle fatigue when cycling against resistance. Some static holds that target the quadriceps include the horse pose, the lateral angle pose and variations, the bow pose and the static L-hold. To do the most basic static hold for the quads, the horse pose, simply squat down with feet a little wider than shoulder-length apart as you would when doing a regular squat. Lower until your thighs are parallel with the floor, and then hold the pose for as long as you can.

Although it is normal for muscles to fatigue and "burn" during exhaustive exercise, it is important to stop exercising and rest if you feel any significant pain when cycling or performing other types of exercise. Pushing yourself past your limits can lead to injuries, especially if you are out of shape. Furthermore, if you experience a burning sensation on the skin of your thighs, rather than in your thigh muscles, you may have a skin condition unrelated to muscle fatigue. Burning itchy skin may indicate you have dermatitis caused by an allergic reaction or a chronic skin condition such as eczema, for which you may need to seek medical treatment.