Being able to lift your knee when you’re running has a significant impact on your running speed. It's also important for reducing the risk of injury. The muscle group that’s responsible for picking up your knee when running is the hip flexors, which include the iliopsoas, sartorius, rectus femoris, tensor fasciae latae and pectineus muscles. Weakness in the hip flexors can limit your ability to lift your knee. In addition, tightness in your hip-extending muscles, which include your glutes and hamstrings, could prevent you from lifting your leg.
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Hip Flexor Weakness
If your hip flexor muscles are weak, they’ll be unable to lift your knee and leg up in front of you as you run. The upward knee movement is important for producing a more powerful leg drive that can propel you forward when running. According to certified strength and conditioning specialist Kevin O’Neill, in an article for the Athletic Performance Academy, the stronger your hip flexors, the faster you’ll be able to run. In addition, because the hip flexors act as breaks to the hamstrings, they help reduce the risk of injury. In Dr. Paul E. Niemuth’s study, published in 2005 in the "Clinical Journal of Sports Medicine," injured recreational runners had significantly weaker hip flexors than noninjured runners.
Developing Hip Flexor Strength
Improve the strength of your hip flexors by incorporating strengthening exercises into your regimen two to three days per week. Hanging knee raises, straight-leg situps and lying leg raises are effective at targeting the hip flexors. To perform hanging knee raises, hang from an overhead bar with your legs straight toward the floor. Lift your knees, bringing them up toward your chest, and then control them as you lower them back down. To perform straight-leg situps, lie on the floor with your legs straight and spread out into a v-shape. Lift your torso up off the floor until you’re sitting up straight, and then lower your torso back to the floor. To perform lying leg raises, lie on your back on the floor with your legs straight. Keeping the knee extended, lift one leg up until it’s pointed vertically. Lower it to the floor and then switch legs. Complete two sets of 12 reps of each exercise.
Glute and Hamstring Tightness
Tightness in your glutes and hamstrings can restrict the range of motion in your hips and prevent you from being able to lift your leg and knee. The glutes at your buttocks, and the hamstrings, which run down the backside of your thighs, are responsible extending your hips, or driving your legs backward. They have a tendency to become tight because of their heavy involvement in running, and also due to long hours typically spent sitting during day jobs and school work.
Improving Glute and Hamstring Flexibility
To see significant flexibility improvements in your glutes and hamstrings, perform dynamic stretches prior to your runs and incorporate static stretches after your runs. Dynamic stretching involves elongating the muscles while still moving and they’re effective at warming up your muscles prior to activity. High knee jogs, walking straight-leg kicks and high-knee skips will warm up the hip flexors while simultaneously stretching the glutes and hamstrings. Static stretching involves getting into a position where the muscles are elongated and holding that position for 30 seconds. Both the lying knee-to-chest stretch and the hamstring stretch hit the glutes and hamstrings. To perform lying knee-to-chest, lie on your back with your legs straight. Bring one knee toward your chest. Grip your thigh to pull it into your chest to feel the stretch. After you’re finished, switch legs. To perform the hamstring stretch, sit on the floor with your legs extended. Bend forward at the waist and reach toward your toes. Complete each stretch two to three times.