Running uphill might feel challenging and leave you out of breath. But do not be fooled -- running down the backside of that hill also works your body. After running downhill, you might feel an onset soreness in your legs because you are activating your muscles differently, placing a new demand on your body. Consult your doctor if your leg soreness persists or worsens.

Muscles Worked

Running downhill engages your muscles differently than uphill training. As you run downhill, your body should fall more forward. This type of hinging works the glutes and hamstrings. If you lean back when running downhill, you can put too much pressure on the lower back and hip flexors. You should focus less on your quadriceps as you go downhill and work more from your glutes and hamstrings to control your legs so there is less pressure on the knees.

Eccentric Movement

British athletics coach Brian Mackenzie explains on his website that running downhill is an eccentric movement, one which runners are not often used to. Eccentric movements focus on slowing down the elongation of the muscle process, challenging the muscles. This type of movement provides a braking mechanism for the muscles. For example, as you run downhill, you must brake with your legs to keep your body in control of your movements. Holding your body in a more controlled fashion and slowing down your stride can cause more soreness to develop in the legs. Eccentric contractions are also the explanation for DOMS; or delayed onset muscle soreness, which manifests hours, or even days after a run.

Stay In Control

Improving your form when running downhill reduces your risk for injury and might even help with leg soreness. It is important to keep your upper body relaxed and lean forward so your body remains as close as possible to perpendicular to the hill. Increase your leg turnover as you gain speed so you are not fighting gravity down. Resisting your hill can lead to onset muscle soreness lasting up to five days.

Stretch It Out

Dynamic stretching before your run is crucial to helping reduce your muscle soreness. Dynamic stretching involves stretching while moving, with stretches like leg swings, lateral lunges and even walking lunges. Stretch statically after your run to elongate the muscles, holding each stretch for about a minute. Perform runner's stretches like standing quadriceps stretches, forward folds and a calf stretch.