Biomechanics of Sprinting

Biomechanics of Sprinting
Simon Dietrich
Keiser University
01/16/13

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. Covering the joint actions of the lower portion of the body is just the basics. Physiologically, the body sparks using phosphocreatine (PCr) and adenosine triphosphate (ATP) to trigger the immediate energy system. This system will last about two to three seconds before oxygen and adipose tissue are used to fuel the body with ATP. A sprinter’s skill relies heavily on muscular strength and endurance. According to sprintscience.com “studies have showed that maximal strength, particularly during a half squat, is strongly correlated with sprinting performance” (sprintscience, 2010). This is true for the mid-sprinting process, however, muscular power is what begins the process. The power of the quadriceps and gastrocnemius muscles are what spring a sprinter forward from the starting line. Power exercises such as the vertical jump, depth jump, and loaded jump squats are all very closely correlated to the starting performance of a sprinter (sprintscience, 2010). Muscular endurance is another skill that a sprinter must utilize. When a sprint lasts longer than about 30 seconds the immediate energy system switches to the anaerobic system and then into the aerobic system. Each of these systems require more oxygen for ATP production. Because sprinting is a power sport, the muscles that produce the power must have endurance as well. With higher endurance a sprinter will be able to sustain maximal sprinting velocity for a longer period of time (sprintscience, 2010). So all together this means that if a sprinter has superior muscular strength, power, and endurance then he or she is more likely to be the first one to cross the finish-line. The primary function of the skeletal system while sprinting is in the lower region of the body. The legs are comprised of the femur, the tibia and the fibula. The tibia, or the shin bone, and the fibula share the ankle joint where the foot is attached. The main muscles used to force our lower legs to move are the quadriceps muscles, hamstring muscles, the calf muscles and the anterior tibialis muscle. Together these muscles pull on our skeleton to move our legs and feet to the motion of sprinting. The first group of muscles that were mentioned were the quadriceps muscles. The vastus medialis, vastus lateralis, vastus intermedialis, and the rectus femoris, are the four muscles that make up the quadriceps. The vastus muscles work together to extend the knee and keep it aligned with the rest of the leg, whereas the rectus femoris helps the body to raise it’s knee. All together this makes the quadriceps a very powerful muscle group. On the hind side of the leg, behind the quadriceps, are the hamstring muscles. These muscles, when contracting, flexes the knee and brings the foot behind and up towards the glutes. There are three muscles that make up the hamstrings group. They are the bicep femoris, the semitendinosus, and the semimembranosus. Like the quadriceps the hamstrings are another very powerful muscle group. Also on the backside of the leg, but on the lower portion, are the calf muscles. This includes the gastrocnemius and the soleus muscles. Both of these muscles give the body the ability to force the toes down into the ground or stand on the toes. This is a very essential movement used by sprinters. Without these muscles a sprinter would not have the ability to stay on their toes which in return would decrease their speed. Not only are these muscles essential to sprinters, but also to anyone who likes the ability to walk at all. The last muscle of the lower limbs that was mentioned before is the anterior tibialis. This muscle is very often overlooked. It is the muscle that gives the body the ability to stand on its heels. This motion is called dorsiflextion and it is also an important part in the process of a sprint. Most people do not know, but usually shinsplints are felt when this muscle is weak in comparison to the gastrocnemius. Shinsplints can only reside with treatment of ice and the stretching of the gastrocnemius (Lee, Reid, Elliott, & Lloyd, 2009). Sprinting can easily be classified as an open-loop movement. Both feet of a sprinter leave the ground at some point of his or her stride, and for every stride the sprinter makes. Due to the nature of open-loop movements there are many things that can go wrong resulting in an injured sprinter laying on the track (Davidson, Jones, Andreae, & Sirisena, 2002). Some of the most common injuries that occur during a sprint are strains in the hamstring or quadriceps. These injuries are caused by overuse and over-stretching of the muscles and tendons that attach the muscles to the bones. These injuries can be treated by rest, ice, compression, and elevation (Schache, Kim, Morgan, & Pandy, 2010). Other sprinting injury that can occur are fractures or complete breaks of the femur, tibia, or the fibula. These injuries must be treated medically. The force that is exerted on the runner’s leg is massive, therefore if the leg is too unstable when the force is exerted then it may cause the bone to fracture or break. Joint dislocation and hyperextension is another injury that is often seen in sprinting. This may occur when the force exerted on the sprinter’s leg is so great that it pulls the joint apart. Ice, compression, and elevation are the best treatments for this injury (Schache et al., 2010). To avoid these injuries a sprinter must be trained properly. A sprinter can improve their performance by improving their movement efficiency. Much like a baby learning to walk, a sprinter must repeat their movements over and over again. This is a training necessity for a coach to teach. A baby learns to walk by getting up, falling, learning, then getting up again. The sprinter learns first how to run with proper form. This includes proper form of starting position and the proper form of a stride. A long stride is key for a sprinters speed and endurance, however too long of a stride may cause injury. This is why repetition is essential for a sprinter. When a sprinter practices his or her stride they feel out their limits (Cronin & Hansen, 2006). This same technique of repetition works when practicing a sprint start, or kick off. When a sprinter is in starting position, he or she is bent over, low to the ground, with both hands and both feet on the ground. As the runner gets ready he or she then extends their legs but still staying in a static position. This movement shifts the sprinter’s center of gravity forward. Without the sprinter’s hands holding their body’s weight, he or she would face-plant straight into the ground. Instead the sprinter uses this unbalanced weight to propel him or her forward in a very quick manor. As the gunshot fires to start the race, the sprinter is leaning forward with the majority of his or her body weight being held up by their hands. When the shot is heard, the sprinter lifts his or her hands up and pushes off with their feet, letting their center of gravity steer them forward (Mann & Hagy, 1980). In conclusion a sprinter must be trained very well and conditioned as well as possible. Sprinting is a seemingly simple movement that puts major stress on the body. This stress can cause many different injuries to occur. Learning and understanding the biomechanics of sprinting can help someone avoid injury and improve their performance. Proper training, conditioning, and education on sprinting processes, technique and form are essential when building an elite sprinter and athlete.
References
American Kinesiology Association. (2010). AKA clarifies the definition of kinesiology. Retrieved from http://www.americankinesiology.org/white-papers/white-papers/------aka-clarifies-the-definition-of-kinesiology
Cronin, J., & Hansen, K. (2006). Resisted sprint training for the acceleration phase of sprinting. Strength & Conditioning Journal (Allen Press), 28(4), 42.
Davidson, P. R., Jones, R. D., Andreae, J. H., & Sirisena, H. R. (2002). Simulating closed- and open-loop voluntary movement: A nonlinear conrol-systems approach. IEEE Transactions on Biomedical Engineering, 49(11), 1242-1251.
Lee, M., Reid, S., Elliott, B., & Lloyd, D. (2009). Running biomechanics and lower limb strength associated with prior hamstring injury. Medicine & Science In Sports & Exercise, 41(10), 1942-1951. doi:10.1249/MSS.0b013e3181a55200
Mann, R., & Hagy, J. (1980). Biomechanics of walking, running, and sprinting. The American Journal Of Sports Medicine, 8(5), 345-350.
Medical Dictionary. (2013). Biomechanics. Retrieved from http://medical-dictionary.thefreedictionary.com/biomechanics
The Physics Classroom, (2012-a). Newtons first law of motion. Retrieved from http://www.physicsclassroom.com/class/newtlaws/u2l1a.cfm
The Physics Classroom, (2012-b). Newtons second law of motion. Retrieved from http://www.physicsclassroom.com/class/newtlaws/u2l3a.cfm
The Physics Classroom, (2012-c). Newtons third law of motion. Retrieved from http://www.physicsclassroom.com/class/newtlaws/u2l4a.cfm
Schache, A., Kim, H., Morgan, D., & Pandy, M. (2010). Hamstring muscle forces prior to and immediately following an acute sprinting-related muscle strain injury. Gait & Posture, 32(1), 136-140. doi:10.1016/j.gaitpost.2010.03.006
Sprintscience. (2010). Physiological analysis. Retrieved from http://sprintscience.com/physiology.htm
Ward-Smith, A. (1984). Air resistance and its influence on the biomechanics and energetics of sprinting at sea level and at altitude. Journal Of Biomechanics, 17(5), 339-347.

References: American Kinesiology Association. (2010). AKA clarifies the definition of kinesiology. Retrieved from http://www.americankinesiology.org/white-papers/white-papers/------aka-clarifies-the-definition-of-kinesiology Cronin, J., & Hansen, K Davidson, P. R., Jones, R. D., Andreae, J. H., & Sirisena, H. R. (2002). Simulating closed- and open-loop voluntary movement: A nonlinear conrol-systems approach. IEEE Transactions on Biomedical Engineering, 49(11), 1242-1251. Lee, M., Reid, S., Elliott, B., & Lloyd, D. (2009). Running biomechanics and lower limb strength associated with prior hamstring injury. Medicine & Science In Sports & Exercise, 41(10), 1942-1951. doi:10.1249/MSS.0b013e3181a55200 Mann, R., & Hagy, J Medical Dictionary. (2013). Biomechanics. Retrieved from http://medical-dictionary.thefreedictionary.com/biomechanics The Physics Classroom, (2012-a) The Physics Classroom, (2012-b). Newtons second law of motion. Retrieved from http://www.physicsclassroom.com/class/newtlaws/u2l3a.cfm The Physics Classroom, (2012-c) Schache, A., Kim, H., Morgan, D., & Pandy, M. (2010). Hamstring muscle forces prior to and immediately following an acute sprinting-related muscle strain injury. Gait & Posture, 32(1), 136-140. doi:10.1016/j.gaitpost.2010.03.006 Sprintscience Ward-Smith, A. (1984). Air resistance and its influence on the biomechanics and energetics of sprinting at sea level and at altitude. Journal Of Biomechanics, 17(5), 339-347.