Biomechanics of Sprinting
Biomechanics of Sprinting
When adrenalin is pumping and someone is gunning for the finish line there is no thought on controlling their legs. Their legs just go. Most people don't think twice about what all goes into the process of making the lower limbs move or how precise each muscle contraction must be to stay up on a runner's toes. Understanding kinesiology will help with understanding the biomechanics that explain the functioning of the body, and explains how exactly our body can sprint.
The American Kinesiology Association (AKA) defines kinesiology as “the academic discipline which involves the study of physical activity and its impact on health, society, and quality of life” (American Kinesiology Association, 2010). Biomechanics defined by the Medical Dictionary is “the study of the mechanics of a living body, especially of the forces exerted by muscles and gravity on the skeletal structure” (Medical Dictionary, 2013). Together these fields of study cover the forces that act upon the body during physical activity.
Sprinting highly qualifies as physical activity, therefore there are biomechanical and kinesiological aspects that are behind this vigorous act on the body. Sprinting is an essential activity and skill that is a key element in a wide smorgasbord of sports. Some of the more popular sports include football, baseball, soccer, and track that all require a great deal of sprinting. It could be a quick sprint to first base, a short sprint to finish a play in soccer, a long sprint towards the end zone protecting a football, or even a sprint to be the first to cross the finish-line in track. Each of these acts put a lot of stress on the body and it's up to the biomechanics of the lower limbs to work precisely in order to handle the stress.
Sprinting and running in the biomechanical world is actually a very common movement that is studied because of the variety of sports and activities that rely on it (Mann & Hagy, 1980). The main forces that act upon the body when sprinting are gravity and wind resistance. All three of Newton's laws of motion are a part of sprinting. Newton's first law of motion is the law of inertia. According to this law an object in motion will stay in motion until an outside force acts upon that object (The Physics Classroom, 2012-a). Inertia allows the sprinter to keep momentum. However, wind resistance and gravity slows the sprinter down. If all forces that are acting upon the sprinter are balanced, (which would be impossible on earth), he or she could keep momentum or inertia.
Newton's second law of motion is the law of acceleration. Acceleration can change an objects speed, direction, or both. This is the net force, or unbalanced forces that change the speed and direction (The Physics Classroom, 2012-b). For a sprinter, acceleration can come from the wind acting as tail-wind. It could also be a slight reduction in gravity by sprinting in higher altitude (Ward-Smith, 1984).
The third and final law is Newton's law of action and reaction. This law simply states that for every action there is an equal and opposite reaction (The Physics Classroom, 2012-c). The sprinter pushes their feet into the ground, therefore the ground is pushing the sprinter back, with an equal amount of force, propelling him or her forward.
All three of Newton's laws play key roles in a runner's sprint. However, there is a lot more that goes into it. The main joint actions of a sprinter's lower limbs are in the sagittal plane. When looking at the full body, there is movement in the transverse plane. The twisting motion of the torso is in the transverse plane. Movement in the sagittal plane include hip flexion and extension, knee flexion and extension, dorsi-flexion, and plantar-flexion of the foot (Lee, Reid, Elliott, & Lloyd, 2009). These seven essential movements are what propel an athlete down a track or across a field.
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