In the past I have noticed my hip flexors becoming sore after long runs or weeks with higher distance. This pain in my hip has occurred after multiple long training runs in close succession. After some research I found an interesting article about something called...
The Power Stroke in Running
When I first started my search into hip flexor pain, I came across an article by a Dr. Osborne from Ohio. It discusses something I have never read about in all of my research into running. The column starts off by stating that the leg on the ground has little to do with actually moving the body forward. The author says that the pulling action of the swing phase leg off the ground is the primary forward driving force in running. Now through my training with Newton Running as a certified Natural Running Coach they discussed preventing pushing off with your calf, mainly to prevent fatigue. However they stated nothing about the swing phase as forward propulsion. As with so many natural/barefoot/minimalist running form philosophies out there, they focus on the forward lean as providing forward movement.
Dr. Osborne says that the grounded foot is used as a lever to generate thrust, propelling the body forward. So, if a runner wishes to run faster, he or she must strengthen and condition the swing phase muscles, which include your hip flexors, your psoas major, psoas minor, illiacus, and the inner thigh muscles. If you were to stand up and simply lift a leg up off the ground and bring the knee to your chest, you are engaging your swing phase muscles.
Here is a good example of the swing phase, taken from AthleticQuickness.com
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| Beginning of swing phase |
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| Middle of swing phase |
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| End of swing phase |
The author says that when fatigue occurs one factor is that the leg in the air is the one to slow and the hip flexors and inner thigh muscles are fatiguing.
Another aspect of speed is stride length, which is the distance traveled during the swing phase. When an athlete gets faster they are traveling farther during each stride. An elite marathoner may take 180 steps per minute, same as me. However they are traveling much farther during each stride. You can have the highest VO2 max in the state, but if your stride length is short and your swing phase muscles are weak, improvements will be minimal.
A Dr. Nancy Hamilton from the University of Northern Iowa has done extensive research looking at how the run gain changes with age. She found was that the runners in the 35-39 age group had a similar cadence to those in the 90 year old age group, however there was a 40% reduction in stride length in the 90 year old athletes compared to the 35 year old runners! This goes along with other research looking at walking and running. As people age their cadence stays fairly constant, however distance covered during each step decreases.
Hamilton found as the athlete's age increased, patterns showed up. One was that runners were spending more time in the stance phase with a foot on the ground. The longer you are touching the ground, the more speed you lose.
Another factor she identified was the older runners had less range of motion in the hips and knees. Those 35 and 90 year old athletes we mentioned a couple paragraphs up, the knee flexion was 33% less in the oldest athletes compared to the 35 year old ones.
Lets try to picture what this means. If you have less knee flexion you are keeping your leg straighter during the swing phase, rather than bring your foot up closer to your butt. This means you are making your foot longer and heavier than it should be during this swinging motion. This is a less than desirable situation since longer and heavier levers are more difficult to move. Think of swinging a baseball bat. If you were to put a weight at the end of it, it would take you much more effort to initiate the swing. However, move that weight right to where your hands are gripping the bat, and it takes much less effort to initiate the swing, and it works in a similar way during the swing phase of the run gait. Look at the photos of the runner above, his right knee is not terribly flexed, which lowers the leg, which requires more energy to swing forward.
To strengthen these muscles of the power stroke during the swing phase, which is the motion of using your hip flexors to propel that trailing leg forward to pivot, there are many ways to improve. What I have begun to do is to steal some of Desi's ankle weights and put both of them on my foot. Next I simply stand up straight and bring my knee up and down for as many reps as I can to failure.
Hill repeats are also stated as the best way to strengthen your power stroke muscles. Of course the author also mentions practicing running faster is an excellent way to strengthen these muscles. Currently I am living in the Black Hills where I regularly climb over 200 feet per mile during a run, and go as high as 350 feet per mile average during a single run. I do not do a lot of speed work, but I am hoping to get a bit of strength training in during the winter and along with the hills in the area hopefully I prevent any further pain from developing in my hip flexors.
To preserve your stride length as you age, the biggest factors may be quad flexibility and glute strength. Another factor may be training your muscles to relax when their agonist is activated. That means, if you are in your power strike and your knee is moving up and forward, you want your glutes and hamstrings to be as relaxed as possible.
To lengthen your stride, do not reach out with your forward moving leg, but instead lengthen your stride from the back with a strong buttock muscle push off and flexible quads. If the quadriceps remain tight they will resist backward movement of the leg. Minimalist/Barefoot run form coaches such as Newton Natural Running, Chi Running, and Pose Running all generally recommend to minimize the push off, as it costs energy. Yes, it does require more energy to push off with the leg muscles, but it also propels you forward! I believe the key is not an excessive push off, but still use it a bit when running at a speed that dictates the need. If you want to conserve extra energy, such as during an ultra marathon, I would recommend minimizing the push off a bit more. If I were to participate in a 5k, you would find me pushing off quite a bit more. It is all about balance!
