This article is for any lower extremity amputee or their friends or family members who are interested in learning more about running legs and the related issues that are unique to them. Even able-bodied athletes may be interested in learning more about their disabled counterparts.First and foremost, the most important point to keep in mind is that running on a prosthesis is not the same as running with two abled-body legs. There are a number of different considerations with various levels of relevance, which are organized below. Some of these points will bear further consideration as the individual application may vary by athlete, but this article should provide a broad overview of common issues faced by amputee runners. If at any time the reader is interested in more specific details or recommendations on how to incorporate the points into their own training program, please contact us at Complete Human Performance.
Types of running feet
One of the first considerations for an amputee who is new to running, is deciding which running foot would serve their purpose best. This is based primarily on what distance the athlete is planning to engage in most. The majority of people are familiar with Oscar Pistorius’ “blades” which are designed and manufactured by Ossur and are also known as the Cheetah foot. Otto bock (Ossur’s competitor out of Germany) also manufacturers two sprint feet called the Sprinter and the C-Sprint.
These particular prosthetic feet are designed for sprinting short distances at the track- from the 100m to the 800m. The sprinting feet are actually so specialized that there is one that is specifically designed for the 100m and 200m and another one for the 400m and 800m. Both of these feet are very stiff because of the high force produced with each stride when sprinting and are designed to retain energy for a short period of time and release it very quickly as the prosthetic foot pushes off of the ground. The energy is actually stored in the blade itself (primarily the curved part of the blade) until it is released.
This is in contrast to Ossur’s flex-run foot, which I have dubbed the Impala (to contrast with the Cheetah), which is designed for long distance running such as a 5k or longer. The foot has a large curve making it look more like a “C” than a “J” which is more effective at storing and releasing energy over time, which is imperative during a longer distance event since the pace is much slower than a sprint as is the amount of force produced during each foot strike.
For the vast majority of runners the flex-run (or one of Freedom Innovation’s feet called the Nitro or the Catapult) will do the trick. At $20,000 a pop (more for legs with a knee component), most amputees will choose the foot with more versatility. And as the feet become more specialized, it will be a fine balance between versatility and specificity.
Freedom Innovations’ Catapult foot. Look what you can do with it!
Liner issues The next thing to think about is the type of suspension to be used- the suspension system is what holds the prosthesis on to the residual limb. There are a countless number of different types out there (we won’t get into details of how to choose which suspension system to use here) but, since many involve a silicone liner that makes contact with the skin, we will discuss some relevant issues here. The silicone liners have many advantages like good suspension and protection for the stump, however they are not perfect.
One of the primary issues is sweating, especially in hot/humid conditions or during vigorous exercise, that can disrupt the seal and compromise the suspension of the leg. There are a few things you can do if you’re plagued with this issue. First, you can take the leg off and dry the skin and the liner with a towel, though this often disruptive, especially during a competition or training. An alternative is to spray or rub an antiperspirant onto your skin (available through your prosthestist or over-the-counter) and let it dry before putting on your leg. Remember, your stump may react differently to different agents, so try a few different products if the first one you try doesn’t work. Also, your skin may be sensitive to the chemicals used in these products so if you develop itching, burning, or redness rinse the product off right away.
Lastly, some people actually wear a thin, 1 ply sock under their liner to absorb perspiration. If you want to give this a try then keep in mind that the sock should be shorter than the liner so that the liner can make contact with the skin and make a seal at the top. A combination of the above-mentioned recommendations can also be used for maximum effect, especially if you tend to sweat a lot.
Addressing weaknesses and differences in biomechanicsFor anyone with differences between one side of their body and the other, any repetitive motion like running, cycling or swimming will exacerbate the imbalance and if not closely monitored, can lead to an overuse injury. This is true for an amputation of any limb, upper or lower extremity, but also applies in cases of differing limb length or strength, lasting effects of surgeries, or previous injuries that never healed properly. The biomechanical differences below are directed towards lower extremity amputees while running, but can be applied to any individual affected by a similar biomechanical disadvantage.
Weak hip flexors and adductors can lead to “toe whip”, where the distal portion of the foot actually flicks slightly as the foot is brought through a cycle of rotation, as well as an inward rotation of the foot during running. A “toe whip” leads to wasted energy throughout the running cycle and is typically a sign of weak hip adductors. The inward rotation of the toe is also a telltale sign of weak hip flexors and adductors, but more importantly, leads to an inefficient stride since the toe is being loaded on the outer most edge rather than at the forefront of the prosthetic blade. Luckily this can be easily fixed with exercises to strengthen the hip flexors and adductors and with proper alignment.
For an athlete who either does not have an ankle at all or has an ankle injury or just poor ankle mobility, the hip and knee will be put under a great deal more stress during running, especially when faced with uneven or cambered surfaces. Given the nature of the ankle joint, it can typically rotate such that the rest of the body is not affected by these changes in ground surface. However, when it’s no longer capable of such rotation, the knee and/or hip will suddenly be required to take over this job. One of the most important preventative measures is to isolate the quadriceps of the affected limb to strengthen the muscle and its attachments to the lower leg, which will help to stabilize the knee and prevent twisting or stretching of the knee’s ligaments. For athlete’s without a knee, primarily above-knee amputees, the primary focus should be on balance and recovering their stride in situations when the knee might buckle through balancing drills as well as glute and quadriceps isolation.
Lastly, many amputees suffer from a purposeful “limb length discrepancy”. This is because most running legs are fit so that they are actually about 2 inches higher when standing than when running. This means that when an amputee stands still with both legs straight the hip on the amputated side will be about 2 inches higher than on the sound side. This is because, when running, the weight of the body will actually compress the foot, in order to load the foot with energy. Imagine putting a weight on top of a spring; the spring will compress when the weight is placed on it. As you lift the weight off the spring, it will recoil and release the energy that was put into it. That’s how a running leg works- the individual’s body weight is the weight and the running leg is the spring. This means that when the prosthesis is in contact with the ground and under the body weight of the runner, it will be compressed to the height of the other leg so that the stride appears even. However, as the runner finishes the stride cycle and shifts their body weight to the other leg, the running leg will “spring” back to the length it was when standing (as we said earlier, about 2 inches longer). Initially this height difference is compensated for by raising the hip up on the prosthetic side in order for the toe of the running blade to clear the ground. However, as the runner begins to fatigue he/she will no longer compensate with the hip, causing the toe to catch on the ground as he/she tries to pull the leg under his/her body. This can be disastrous, leading to falls and injuries that could easily be prevented by properly strengthening the muscles of the hip joint so that they don’t tire as quickly.
Protecting the sound limbFor anyone with a single lower extremity amputation, it’s easy to focus on the amputated side. You take special care to make sure your prosthesis fits well and you may go to great lengths to keep the skin healthy and the stump in good shape. You may even work with a physical therapist (or have in the past) to correct imbalances or strengthen muscles surrounding the joints. All this and you may neglect the leg that is actually taking the brunt of the load when it comes to walking, standing, running or cycling. Though you may consciously or subconsciously try to distribute your weight evenly between both legs during day to day activities or during exercise, your stronger leg (likely your sound side) will still be called upon to carry the load. It’s inevitable. So, knowing this, it’s important to protect this leg by strengthening ligament and tendon attachments and addressing injuries as they arise. Overuse injuries are particularly common and include, but are not limited to, shin splints, Achilles tendonitis, Morton’s neuroma, ileotibial (IT) band pain, Osgoodschlater’s, and stress fractures. If you begin to experience pain in your foot, knee, shin, heel, don’t ignore it.
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