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Summary and further questions for 'Acceleration following leanmost effecient?'

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  • Summary and further questions for 'Acceleration following leanmost effecient?'

    Thanks for the replies. Listed at the bottom is a summary.

    My interest in this topic is for efficient and fast Badminton movement. The
    requirements for Badminton are exceptionally fast accelerations and
    decelerations and changes of direction, that are chained together into a
    series of flowing movements (move to play a shot, recover to base position,

    In discussions with a colleague the concept of 'balance' seems to be very
    relevant in determining speed and/or effeciency (which is also important to
    conserve energy when maximum speed is not needed). By balance we are
    suggesting that upper body angle is an important factor. In the original
    post I called this lean and assumed that it was to do with balancing torques
    around the COM due to ground reaction forces, and torques due to gravity.

    Intuitively this looks like it works. For example, to execute a lift shot
    near the net a player should lean forward and accelerate to the net then
    straighten up and even lean back slightly to help deceleration and the
    return backwards (to a base position) after playing the shot. Failure to
    lean backwards can mean that the player does not stop their momvement in
    time and oversteps. This wastes time in getting to the next shot and, in
    Badminton, time is in short supply.

    I used the phrase 'effecient' originally because, as an experiment, I can
    lean my upper body forward and still accelerate backwards or forwards.
    However, I feel as though the body is needing to compensate in a way that is
    less effecient/fast than if a lean my upper body in the direction of desired
    accleration. I appreciate that this is not necessarily a correct use of
    lean since what I probably describing is an alteration of my leg angles to
    enable the COM to still be between the feet.

    Furthermore, the relative positioning of a lead foot in the initial push off
    seems important. If the 'weight' is behind the foot I feel (and presume)
    that the foot acts as a sort of brake. If over the foot then the effect is
    neutral, and if past then the foot can aid acceleration as well as the trail
    foot (a sort of double foot push off).

    Another important function of balancing is to not to fall over of course
    and, in some shots where deep lunging occurs, this can mean turning the
    trailing foot to provide a larger base. However, I see this is a slightly
    separate issue than what is being talked above.

    I'm trying to look for a Biomechanically correct conceptual model for this
    intuitive understanding of balance and how it relates to movement in

    In the summary there's a reference to a paper by Romanov and Fletcher. I've
    only read the abstract but it looks very interesting and views gravity as
    the main motive force (if I've read that right).

    Summary of responses (excluding those who requested):

    Bill Rose: I hadn't thought of it as "most efficient". One must lean to
    keep the center of force over the feet. If you didn't, you'd fall over
    backward, which is not efficient. So you're right: it's more efficient to
    lean into an acceleration. (We lean into turns and lean back while
    decelerating, for same reason.)

    Brian Schulz: Right, but beyond just being efficient, to some extent these
    leans are essential. If you don't "lean into" acceleration you can't apply
    the force to the ground and remain dynamically stable. For example, if you
    were to suddenly flex your hips without some kind of anticipatory postural
    adjustment (i.e. a slight posterior movement of your pelvis) you'd fall
    forwards onto your face.

    Melissa Daly: I was under the impression that sprinters leaned forward
    during the acceleration phase to maintain better position in terms of
    creating force. The sprinter then stands more upright to maximize turnover
    speed and stride length (it is harder to get good push off if your legs are
    behind you). Many less experienced sprinters stay leaned over further into
    the run and it actually makes them more prone to falling over. As far as
    jumping is concerned I know that jumpers rotate their arms and legs in the
    air to counteract the forward rotation acting on their center of mass after
    they leave the ground. This knowledge is from years of participating in and
    coaching track, not from my research.

    Ted Andresen: This is a good question. You are correct. In order to
    accelerate a mass the applied force must push it in that direction. After
    the body has reaches it's intended velocity, it is no longer necessary to
    apply a force in that direction. It might be helpful to think of the legs
    in the starting blocks as a set of compressed coiled springs. At the start,
    the runner expands his of her spring-like legs and accelerates their center
    of mass upward and horizontally forward. In about 3 to 5 meters they have
    finished accelerating their CM vertically and horizontally. They have
    reached a constant horizontal speed and there is no need to accelerate the
    CM horizontally. From that point forward there is little need to lean
    forward, since the runner has reached their maximum horizontal velocity.
    Then the runner runs upright with the legs providing the vertical force
    required to repeatedly launch the runner into the air with each step. You
    might find this diagram helpful.

    Marcus Dunn: Some would argue that 'leaning' is the motive element in
    running. Have a look at Romanov and Fletcher's 2007 paper (Sports
    Biomechanics, 6 (3), 434-452) - it's a somewhat different perspective to
    running mechanics.

    Thanks, Joe

    Joe Wright