How Your Body is Connected - Biomechanics 101

After learning he had a malignant tumor, Terry Fox set out to run across Canada to raise awareness and money for cancer research. This journey would be daunting for any 21 year-old, cancer or no cancer, but Terry Fox’s feat was remarkable because of his right leg. He was left an amputee, using a below the knee prosthetic, after surgeons removed his malignant tumor. Terry wanted to prove the impossible could be possible.

His path across Canada was more remarkable given that his movements were restricted and literally, painstaking with each step. His will and determination played a large role in understanding the biomechanics of running for those with and without amputations. Biomechanics describes the application of mechanical principles for living organisms. Unlike the study of mechanical engineering or architecture, biomechanics only pertains to living structures due to the unique properties inherit to them. Along with Terry Fox’s efforts to raise cancer awareness, biomechanists have a better understanding of how the human body propels, strains, and struggles with daily motion.

Terry’s body could be interpreted as a system of machines that reacted to mechanical forces. These mechanics can be divided into two types: static and dynamic. Although “static” implies stasis or lack of motion, the term actually involves all the forces acting upon the body equally, thus equal balance and counterbalance creates a steady equilibrium. Dynamic refers to the acceleration caused by an unequal weight of forces. Every stride he took with his prosthetic required a dynamic acceleration of forces to lift his knees and legs. But as he hit the ground with his shoes, the ground reacted with a counterbalancing force near equal to his acceleration, providing him with proprioceptive balance and return energy for the next stride.

As Terry took his strides, each cycle was defined as his gait. Terry oscillated between swing and stance phases. As his left shoe hit the ground, it entered the stage called “heel strike” and his foot would begin to turn in and flatten (pronate). His foot would act as a shock absorber at this stage. As his entire left foot contacted the ground, he would enter “midstance”, and his body shifted directly atop his foot. Lastly, heel lift occurred at the end of this phase and his foot rolled outward (supinate), acting as a rigid lever arm. His right leg prosthetic could not replicate adequately these patterns of motion and obviously caused him pain and strife with every step, thus making his efforts more inspiring for others.

Terry Fox’s “Marathon of Hope” through Canada is similar to someone studying biomechanics. To scientifically analyze the mechanics of human motion is a daunting task, as the demand has increased for more qualitative and quantitative analysis of data points. However, the basics to understanding biomechanics, much like Terry Fox’s story, involve taking only a small uncomfortable step forward and finding the strength to persevere.

Author
Dr. Wenjay Sung

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