The 2015 edition of the Women’s FIFA World Cup was both exciting and historic. The U.S. Women’s National Team earned their 3rd World Cup since its 1991 inception, and #10 Midfielder Carli Lloyd propelled herself into the stratosphere of sports mythology as the new face of women’s soccer.
Like any physical therapist, I analyze movement, efficient movement, and how to restore movement. The 2015 World Cup was no exception. It was a patriotic opportunity to once again assess biomechanics. In the afterglow of the cup and Lloyd’s fantastic scoring, I’ve been inspired to discuss a common soccer injury: hip flexor tendinopathy. This is an uncomfortable and painful injury associated with the tendinous insertion of a hip flexor muscle, experienced while kicking a ball.
Incidence of Hip Flexor Tendinopathy as a Soccer Injury
Injuries in sport can be broken up into two categories: traumatic and overuse. Traumatic injuries typically occur in a single moment and would include sprains, breaks, or ruptures. Overuse injuries, on the other hand, occur over time. They are defined as repetitive tasks, forceful exertions, or awkward positions leading to injury. They are often the byproducts of poor training.
Nearly 30 percent of all soccer injuries fall into the category of overuse, including hip flexor tendonopathies. Overuse injuries among soccer competitors occur at and incidence rate of 2.9 per 1000 Athletic Exposure Hours. In short, this means 30 percent of all soccer injuries can be avoided if your body is properly prepared.
In order to understand a mechanism of injury, we have to analyze movement … efficient movement, that is. So take a moment and look at #10, her foot, knee, hip, and trunk.
Anatomy of a Soccer Kick
Lets briefly analyze the kick. The kick can be broken down into six phases (some will argue five):
1. The approach
2. Plant-foot forces
3. Swing-limb loading
4. Hip flexion and knee extension
5. Foot contact
The most important phase of the kick is the plant foot-force. This is the action of the non-kicking foot being planted into the ground. It creates a phenomenon what is referred to by kinesiologists as ground reaction force (GRF). Not only does the plant foot phase dictate ball direction, it provides stabilization and generates power into the swing-limb loading phase. Ultimately this force generation is harnessed through the foot contact phase, producing the kick.
No different than a shortstop digging a grounder or a long jumper propelling into takeoff, the power of a kick is generated at the hip on the planted side. As one plants their non-kicking foot, the gluteus maximus is loaded while the gluteus medius/core stabilize. Similar to a stretched rubber band, the gluteus maximus creates a powerful hip extension force driving the hip forward with a loaded kick leg.
Again, take a look at #10 and examine her right leg. Her foot is planting into the ground generating stabilization through the foot, knee, hip and then the core to load the gluteus maximus. The right leg is providing the force generation for high-energy hip drive, where a high quality kick is the desired outcome.
The Onset of a Soccer Injury
Injuries occur where there are energy leaks. Energy leaks transpire when there is poor stabilization of the hip (glute medius/core) or weak hip extension (gluteus maximus). The hip flexor tendinopathies are simply a casualty of energy leaks. This muscle group, which guides the kicking leg through the phase of follow through, is the direct beneficiary of powerful glutes. If you have energy leaks, over time the compensatory demands of the hip flexor become too great and the tendon breaks down, no different than a fraying rope. The hip flexor takes on the extra work when the glutes are unable, slowly wearing away tendinous fiber. Essentially, the kicking leg’s force capacity is at the mercy of the gluteus maximus, gluteus medius, and core.
Soccer Injury Prevention
Aside from a robust strength-training program, a healthy dosage of the following four exercises and foam rolling can go a long way with hip flexor injury prevention. If you are not comfortable performing them or are unable to feel your glutes activate, I highly recommend seeking out a qualified trainer or health care practitioner. And remember, next time you kick a ball, plant your foot, fire your glutes and bend it like Carli.