Our “Amputee Running Series” aims to provide you with a practical guide to help you begin running with your prosthesis. This sixth installment will help you understand what happens to your body when running with a prosthesis. For the previous articles on amputee running, head to Part 1, Part 2, Part 3, Part 4—AK and BK, and Part 5.
Although it is easier to leave this technical biomechanics stuff for your prosthetist to understand and interpret, taking the time to understand the broad concepts of amputee running biomechanics can help you become more efficient and less injury-prone. Running injuries are rarely sudden; they develop over time from strain and stress. Even if you are not a runner but engage in other adaptive sports that rely on speed and agility, you can gain something from reading this article.
To better understand the complexity of running with a prosthetic leg, we will start by dissecting the different broad stages or phases of the running cycle—stance and swing phase.
Stance phase begins when your foot makes contact with the ground and ends when your toe leaves the ground. Understanding the stance phase of running can help you prevent many running injuries. Many experts highlight the stance phase as a critical aspect of performance. This is because your leg or prosthesis bears up to four times your body weight during this running phase.
The stance phase can be further broken down into two additional phases—the absorption phase and the propulsion phase. Absorption during stance refers to all of the moments when your foot contacts the ground and decelerates your body. Essentially these are the points between when your foot first touches the ground to mid-stride. Then the moment from mid-stride to just before your toe leaves the ground is called the propulsion phase.
Absorption (Deceleration) Phase
The name "absorption phase" explains what is going on in the body: as the heel strikes the ground, the lower limb acts as a shock absorber as well as an energy absorber for the body. Thereby reducing the considerable ground forces passing through the limb, which can be up to four times greater than body weight. Your prosthetic leg will take this energy and use it later in the propulsion phase, which will be discussed later in this article.
Determining the ideal initial foot strike on your sound side is highly contested in the running community when discussing injury prevention. As a runner, you are in either of these two categories—you land more on the heel and subsequently stress your knee, or you are more of a forefoot striker and overload your ankle. If you average a few miles a month, we suggest having your running gait evaluated by a professional to determine whether you should change your foot strike pattern. Össur has prosthetic running clinics all over the US; you should check out their running schedule.
If you are beginning to learn how to run with a prosthesis, more than likely, your running form will lack sufficient knee flexion in comparison to veteran amputee runners. This is not a big issue and can be solved through proper training, strengthening both legs, and adequate stretching.
Above-knee amputee prosthetic users typically land on a fully extended prosthetic knee. Leaning backward before your foot comes in contact with the ground ensures your prosthetic knee will remain in an extended position.
Propulsion (Acceleration) Phase
The acceleration phase or propulsion cycle refers to the moment when your limb is in mid-cycle to the point at which your leg completely leaves the ground and begins to swing. At this point, the forward propulsion of your body comes from swinging your other leg; the stored energy in your prosthetic running feet, which mimics the "elastic energy" normally generated by the Achilles and tendons of the foot; and last, swinging your arms.
The arm swing is difficult to master initially; however, this is crucial in the propulsion phase. The upper body and arms in novice prosthetic runners are usually in a guarded posture and only after training begin to swing naturally and relax.
Upper Body and Arm Mechanics
The upper and lower body work in sync during a run. There should always be a balance achieved between your arms and legs working in direct opposition. While your leg is in the absorption stage, your arm is producing a propulsion moment. Bringing your right arm forward opposes any forward force of your left leg, and so on. Mastering the arm swing is often tricky when learning how to run with your prosthetic leg.
Running as efficiently as possible with your running leg entails that your shoulders need to initiate and drive the arm swing. Focusing your elbows down will prevent your shoulders from coming up and limiting their range of motion.
When learning how to run with a prosthetic leg, start slow. As your knowledge of proper form and biomechanics builds, slowly implement changes to your running form and focus on one improvement at a time.How long have you been running? What tips can you share with the rest of the community?