Located deep in the front of the hip and connecting the leg, pelvis, and abdomen, the hip flexors— surprise, surprise— flex the hip. But despite being some of the most powerful muscles in our bodies (with a clearly important role), it’s easy to neglect our poor hip flexors— often without even knowing it. It turns out just working at a desk all day (guilty!) can really weaken hip flexors since they tend to shorten up while in a seated position. This tightness disrupts good posture and is a common cause of lower back pain. Weakened hip flexors can also increase the risk of foot, ankle, and knee injuries (especially among runners) Hip muscle weakness and overuse injuries in recreational runners. Niemuth, P.E., Johnson, R.J., Myers, M.J., et al. Rocky Mountain University of Health Professions, Provo, VT. Clinical Journal of Sport Medicine, 2005 Jan; 15 (1): 14-21.. So be sure to get up, stand up every hour or so! And giving the hip flexors some extra attention is not just about injury prevention. Adding power to workouts, working toward greater flexibility, and getting speedier while running is also, as they say, all in the hips The effect of walking speed on muscle function and mechanical energetics. Neptune, R.R., Sasaki, K., and Kautz, S.A. Department of Mechanical Engineering, The University of Texas, Austin, TX. Gait & Posture, 2008 Jul; 28 (1): 135-43..
When a muscle contracts, it shortens. Take the biceps for example. Without getting too technical, the biceps are attached at the forearm and shoulder. When your biceps contract, they shorten and bring those two points closer together. When you rest, the muscle returns to its normal length, and the two points move farther away. Constantly contracting your biceps over a long period of time would cause them to get shorter, even at rest.
Movement at the ankle is controlled by two joints. The ankle or talocrural joint is formed from the tibia and fibula of the lower leg and talus of the foot. Functionally, it acts as a hinge, allowing dorsiflexion (pulling the foot upwards towards the lower leg) and plantarflexion (pulling the foot downwards away from the lower leg). Eversion (tilting of the sole of the foot away from the midline) and inversion (tilting of the sole of the foot inwards towards the midline) is controlled by the subtalar joint formed between the talus and calcaneus bones of the foot.

The rectus femoris is one of the four quadriceps muscles -- the quadriceps are the major muscle group of the front of the upper leg. The rectus femoris attaches to the anterior inferior -- the part toward the feet -- portion of the iliac crest and runs to the base of the patella, also known as the knee. The femoral nerve supplies the rectus femoris with nerves. This is the only muscle that crosses the hip joint, which enables it to work as a hip flexor and a knee extender muscle.
There’s much more happening behind the scenes when the hip flexes! Learning the attachments of the 11 hip flexor muscles is the best way to begin getting a handle on what’s happening when personal training clients complain of tight hip flexors or seem to have referred back pain from an imbalance in the muscles. You’re then able to design and suggest stretches and exercises that are specific to the issue at hand when you understand the form and function of these muscles. Here’s a few thoughts for you when doing that…
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