Review Questions Jan 27 1 How long have the biomechanics of sport been studied a For centuries thousands of years Ancient greeks were aware 2 What are the two main aspects of sports that biomechanics can of it explain and optimize a Maximize performance minimize injury potential 3 What are two examples of how biomechanics research and development has brought about real change in sports a Equipment Clapskate Hinge 1980s by Gerit Jan van Ingen Scenau b Technique Somersault long jumping 1970s by Tom Ecker Jan 29 1 What structures lubricate the joints What is this helpful for a Cartilage and the sac of fluid called the synovial fluid Keeps the coefficient of friction down and cushions during impact b Primarily the cartilage Synovial fluid and menisci Keeps movement smooth 2 What is the key difference between muscles and ligaments a Muscles are active can move ligaments are passive brought along by the muscles b Active control versus passive movement of the ligament 3 How do you calculate angular joint and segment kinematics from a Get marker positions and use those positions to move into full b Computational Measure the linear positions of the joint centers and use geometry to figure out the joint angles linear marker data data Jan 31 1 What is kinetics a The cause of motion b The underline causes of the movement 2 When is momentum conserved When is energy conserved a When the net force is zero Energy is always conserved b Conserved when the net force is acting on the center linear The moment of the center of mass angular Energy is always conserved 3 What is inverse dynamics What does it do Do I know how to calculate joint forces and moments using it a A method of taking motion and calculating joint kinetics from it b Inverse dynamics is the process of measuring forces outside the body and calculate what is happening inside the body Measure the movement of the body and forces outside the body Feb 3 1 What is the relationship between walking running gait mechanics and speed a Speed is a walking metabolic cost that needs to be minimized Trying to walk at a slower or faster the metabolic cost is higher With running the metabolic cost is the same The natural gait mechanics is the lowest metabolic cost b There are two variables Metabolic rate speed calories are used and metabolic cost calories per mile Walking is minimized at a comfortable speed more of a u shape running is much less low peaked Stride length and frequency effects it 2 What biomechnical features distinguish running from walking What are the fundamental models for each gait mode a The presence of a flight phase with running while wlaking does not have one The antiphase and inphase difference b The pattern of when the feet are on the ground Walking has a double support phase running has an airborne phase The patterns of mechanical energy at the center of mass Antiphase for walking pendulum inphase for running springy leg Feb 5 1 Running speed is the product of what two stride parameters a Stride length and stride frequency 2 How can many runners improve their economy a Taking slightly shorter slightly quicker steps Improve metabolic rate b Reduce stride length by just a few percent Shorter quicker steps can reduce the metabolic cost of running Decrease metabolic cost by increasing stride length 3 What is a long Achilles tendon short Achilles tendon moment arm good for fibers shortened a Force velocity relationship economical relationship Keeps the b Long Achilles tendons with short Achilles tendon arms produce a lot of power The long Achilles allows the fibers to remain mostly isometric Short Achilles moment arm makes it move quicker because if it doesn t need to move that much the velocity is high Feb 7 1 What are the two leading theories for the biomechanical limit to maximum sprinting speed What mechanical property of muscle do they both implicate a The two theories are the time to generate force stance phrase and time to position the foot swing phase b Time to generate force hypothesis Time to swing phase the leg hypothesis The stance phase one says that as we are generating gate forces the faster we run the less time that our foot is touching the ground and we have to generate force quicker to step quicker The swing phase one says that our hamstring muscles have to swing the leg faster and faster to go faster 2 Which feature of the force velocity relationship has the strongest effect on sprinting speed What physiologyical property of muscle does this feature relate to a The muscle fibers are most important It relates to the speed that they fire Fast twitch vs slow twitch fibers b The shape of the force velocity curve depends on muscle fiber type Slow twitch fast twitch 3 Why are short Achilles tendon moment arms good for sprinting a Shorter Achilles have slower fiber velocities operate on stronger powerful regions of the muscles force velocity curve and tendon action is critical b They are good in sprinting because the shorter the moment arm is the closer you are to the joint center so you can produce a lot more force and power Keeps plantarflexion muscles closer Feb 10 1 What type of motion laws of physics are at play when a jumper leaves the ground a Projectile motion b When we leave the ground our motion is predetermined Only gravity is still acting on us The body is a projectile Projectile motion 2 What information do you need to predict peak jump height How do you measure and calculate this information a You only need the vertical velocity of the center of mass Calculate by using the vertical ground reaction force period when the feet are on the ground Use a force platform that will show a graph force relative to jumpers body weight Be able to label four different parts of the graph Basically what part is which on the graph Movement initiation bottom part of body movement zero downard take off and landing Calculating take off velocity is the integral below the curve from start until take off Force times time divided by mass gives take off velocity b Take off velocity and flight time if flight time projection Use a force platform and then the equation flight time too if you need it 3 Which method for predicting peak jump height is more accurate Why a Method 1 is more accurate Do not use flight time because it depends on how you land Method 1 does not make any assumptions The assumption that the flight time is split half evenly is not a good assumption b Half the time is spent going up and half is going down Flight