View Full Version : Summary and further questions for 'Acceleration following leanmost effecient?'

07-03-2008, 04:38 AM
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