Acceleration Revisited

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  • Carl Valle
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    Carl Valle on #17208

    Daniel Andrews did a nice job of looking at velocity and change in acceleration with his graphs. I didn’t get the use of the Jerk, since the units of time and distance were nothing close to the time and distance with 60m of sprinting. After thinking about biological limits and commonalities, things are less murky. Everyone is talking about the first 10yards in combine prep (40y mark provided by

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    Daniel Andrews on #104044

    Carl:

    Jerk is the rate of change in acceleration. In any movement, Jerk must peak before acceleration peaks, and acceleration must peak before velocity peaks. This alone should satisfy the requirement of being able to break up a sprint start into 3 distinct phases all of which signify changes in Jerk in peak Jerk, valley Jerk, and Zero Jerk and the hysteresis of the movement pattern with relation to velocity, acceleration, and jerk.

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    star61 on #104054

    Jerk is of no value in analyzing sprints. Very few professions use jerk, outside of rollercoaster design and a few others.

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    Daniel Andrews on #104067

    why do rollercoaster designers use jerk? Oh yes, so the design of the coaster doesn’t exceed normal human limits with regards to acceleration! Has anyone tried to evaluate sprints using jerk? NO! Sometimes we have to step outside of the box to find useful information. Given a chart on Jerk we can deduce what is actually going on with regards to acceleration and velocity. If we took that chart and corresponded distance in the race and kinematics of the stride pattern you will find surprising results.

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    Daniel Andrews on #104073

    I just wanted to add something on why I believe Jerk is important.

    To be a fast sprinter for 60m or 100m races you need to have a high initial impulse and a slow rate of decay in changes in acceleration. That high initial impulse is the exit from the blocks, obviously my graphic has some flaws, primarily the lag in description on the graph, you could cut off the first 10m of the graph and come to the same conclusion understanding velocity (m/s) = 0, acceleration (m/s^2) = 0, and jerk (m/s^3) = 0 as the starting point. Secondly, you must understand jerk is a change in rate of acceleration. To support Carl’s point about the first 10 yards, while important in my opinion, it doesn’t take precedence over slowing jerk in developing 40 yard dash speed. Why? Well it’s theoretically possible to achieve maximum velocity within 10 yards or meters and even with a blazing fast 10 yard time you lose about 3s of time to develop a higher velocity if the change if you are no longer accelerating for a 40 yard race. So what does the rate of decay in acceleration tell us about a sprinter? It gives us information indirectly about leg stiffness! Thus you will see these characteristics in the kinematics of the sprinter as the velocity increases with distance. Coupling impulse and jerk together should give a coach the information to build a better training plan for a given sprinter.

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    star61 on #104103

    why do rollercoaster designers use jerk? Oh yes, so the design of the coaster doesn’t exceed normal human limits with regards to acceleration! Has anyone tried to evaluate sprints using jerk? NO! Sometimes we have to step outside of the box to find useful information. Given a chart on Jerk we can deduce what is actually going on with regards to acceleration and velocity. If we took that chart and corresponded distance in the race and kinematics of the stride pattern you will find surprising results.

    Sprinting does not involve rapid changes in acceleration anywhere near that could be experienced on a roller coaster. And while I agree that one needs to step outside the box occasionally, it must always be kept in mind that our ability to acquire, analyze and interpret data far, far exceeds our ability to integrate such knowledge into a useful form of training. While the velocity curve is useful for examining things like the athletes rate of acceleration, point max velocity is reached, magnitude of max velocity itself, and late stage speed endurance,I don’t think the nuances of any specific athlete’s acceleration curve is used to any great extent in formulating a training program. The jerk curve is exponentially more complex, so I just don’t see how information derived from it might be integrated into training.

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    JeremyRichmond on #104107

    [quote author="Daniel Andrews" date="1292552319"]why do rollercoaster designers use jerk? Oh yes, so the design of the coaster doesn’t exceed normal human limits with regards to acceleration! Has anyone tried to evaluate sprints using jerk? NO! Sometimes we have to step outside of the box to find useful information. Given a chart on Jerk we can deduce what is actually going on with regards to acceleration and velocity. If we took that chart and corresponded distance in the race and kinematics of the stride pattern you will find surprising results.

    Sprinting does not involve rapid changes in acceleration anywhere near that could be experienced on a roller coaster. And while I agree that one needs to step outside the box occasionally, it must always be kept in mind that our ability to acquire, analyze and interpret data far, far exceeds our ability to integrate such knowledge into a useful form of training. While the velocity curve is useful for examining things like the athletes rate of acceleration, point max velocity is reached, magnitude of max velocity itself, and late stage speed endurance,I don’t think the nuances of any specific athlete’s acceleration curve is used to any great extent in formulating a training program. The jerk curve is exponentially more complex, so I just don’t see how information derived from it might be integrated into training.[/quote]
    On the contrary, acceleration from each individual leg would probably differ a lot. The coach could probably use jerk as a guide to smooth out the early phase of acceleration by adjusting step lengths which could be related to force, force production time and likely influenced by peripheral factors such as too much effort, or velocity and force-time specific strength imbalances between each leg. Jerk would be a good guide as to the conservation of energy with the more efficient use of energy benefiting the length of the acceleration phase.

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    Daniel Andrews on #104108

    Sprinting involves accelerations greater than the acceleration due to gravity. Each step in a sprint race represents drastic changes in accelerations on ground contact. The 42+ steps in a 100m race are greater than the number of turns and drops in most rollercoaster rides. How about the High Hurdles races? Is jerk so complicated it cannot be linked to leg stiffness and the rate of decay in acceleration as one approaches max velocity? The simple answer is NO!

    Your argument of since the acceleration curve isn’t used that the jerk curve shouldn’t be used doesn’t hold water. I think some things should be looked at. Especially the acceleration curve over time which is representative of jerk and the jerk curve over time which is representative of the derivative of jerk. we could probably go one more derivative curve and find some meaning. Just because we don’t, doesn’t mean we shouldn’t when it costs us nothing if we have the data capable to glean the information.

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    star61 on #104115

    Sprinting involves accelerations greater than the acceleration due to gravity. Each step in a sprint race represents drastic changes in accelerations on ground contact. The 42+ steps in a 100m race are greater than the number of turns and drops in most roller coaster rides. How about the High Hurdles races? Is jerk so complicated it cannot be linked to leg stiffness and the rate of decay in acceleration as one approaches max velocity? The simple answer is NO!

    The accelerations changes on a roller coaster, which are both positive and negative, could easilty exceed those that a human can tolerate. Nothing even remotely close to that is achieved in a sprint, unless the athlete hits a concrete barrier.

    The rate of acceleration decay is not just a factor of leg stiffness, far from it. Secondly, you can see the rate of decay simply by looking at the acceleration curve. Has anyone developed novel training schemes based on the deceleration curve? If we don’t know how to do that, why are we already looking at jerk?

    Leg stiffness can be related to power output and possibly velocity and maximum acceleration, which is one thing, but relating leg stiffness to acceleration over time in a manner than is anything more than a curiousity is doubtful. I see absolutely no trainable information that could be deduced from relating leg stiffness to jerk.

    Your argument of since the acceleration curve isn’t used that the jerk curve shouldn’t be used doesn’t hold water. I think some things should be looked at. Especially the acceleration curve over time which is representative of jerk and the jerk curve over time which is representative of the derivative of jerk. we could probably go one more derivative curve and find some meaning. Just because we don’t, doesn’t mean we shouldn’t when it costs us nothing if we have the data capable to glean the information.

    If you can’t relate a variable to another variable, how can you relate a variable to the derivative of that variable? And even if you could, how does this help you train an athlete? For science, it may prove interesting. For athletes and trainers, I just don’t see it.

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