Absorb and Recoil: The Stance Phase of Running.

November 9, 2009 | by Dr. Jess

Some of you have heard me talk about how running is mostly about the body's ability to control and store elastic energy like a rubberband only to have it let go and recoil to propel the body up and forward. Today, I'd like to take this opportunity to briefly blog about the stance phase of running. The stance phase is the period between foot contact and push off. Simply, it is the entire period of time the single foot is on the ground. Conversely, the swing phase is the entire period of time the foot is not in contact with the ground. Float phase is a very brief moment where BOTH feet are not in contact with the ground. Let's focus on the stance phase since this is the moment that the greatest risk of injury occurs due to joints being loaded and muscles and tendons attempting to control these forces. The stance phase can be divided into two sub-phases. The first one being between initial contact where the foot first hits the ground and then midstance where the ankle, knee, and hip are at maximum flexion. This is called the "absorption" or "breaking" phase. This is an important phase for sports medicine practitioners to evaluate since the knee, and ankle have to flex and the foot has to roll in (pronate) in order to absorb the impact. The muscles have to go through an eccentric contraction (muscles is elongating while contracting) to control the flexion and pronation. Here is the important part: At this time, the muscles, connective tissue, and tendons are storing elastic energy (during the eccentric contraction). We equate this to pulling or stretching a rubberband or pushing down on a spring. The second subphase occurs between midstance and toe-off where the foot starts to leave the ground. We call this the "propulsion" phase. Now, the hip, knee, and ankle extend to propel the body up and forward. The body mostly achieves this by using up all the stored energy during the absorption phase. We equate this to unloading or letting go of the rubberband or spring- recoiling back to it's original resting length. The most important point to take away from this is that the calf, quadriceps, hamstring, and gluteal activity is LESS in the propulsion phase than the absorption phase since the propulsion phase occurs mostly from stored elastic energy. They are more active in the absorption phase due to their eccentric contraction to control joint positions while creating stiffness in the legs to allow the tendons to lengthen and then recoil. To avoid injury, I suggest strengthening the eccentric contraction of muscles to assist in absorbing impact and storing more elastic energy. The more energy stored, the greater the propulsion. Some of you have heard me talk about how running is mostly about the body's ability to control and store elastic energy like a rubberband only to have it let go and recoil to propel the body up and forward. Today, I'd like to take this opportunity to briefly blog about the stance phase of running. The stance phase is the period between foot contact and push off. Simply, it is the entire period of time the single foot is on the ground. Conversely, the swing phase is the entire period of time the foot is not in contact with the ground. Float phase is a very brief moment where BOTH feet are not in contact with the ground. Let's focus on the stance phase since this is the moment that the greatest risk of injury occurs due to joints being loaded and muscles and tendons attempting to control these forces. The stance phase can be divided into two sub-phases. The first one being between initial contact where the foot first hits the ground and then midstance where the ankle, knee, and hip are at maximum flexion. This is called the "absorption" or "breaking" phase. This is an important phase for sports medicine practitioners to evaluate since the knee, and ankle have to flex and the foot has to roll in (pronate) in order to absorb the impact. The muscles have to go through an eccentric contraction (muscles is elongating while contracting) to control the flexion and pronation. Here is the important part: At this time, the muscles, connective tissue, and tendons are storing elastic energy (during the eccentric contraction). We equate this to pulling or stretching a rubberband or pushing down on a spring. The second subphase occurs between midstance and toe-off where the foot starts to leave the ground. We call this the "propulsion" phase. Now, the hip, knee, and ankle extend to propel the body up and forward. The body mostly achieves this by using up all the stored energy during the absorption phase. We equate this to unloading or letting go of the rubberband or spring- recoiling back to it's original resting length. The most important point to take away from this is that the calf, quadriceps, hamstring, and gluteal activity is LESS in the propulsion phase than the absorption phase since the propulsion phase occurs mostly from stored elastic energy. They are more active in the absorption phase due to their eccentric contraction to control joint positions while creating stiffness in the legs to allow the tendons to lengthen and then recoil. To avoid injury, I suggest strengthening the eccentric contraction of muscles to assist in absorbing impact and storing more elastic energy. The more energy stored, the greater the propulsion.
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