Sprinters: To Drag or not Toe Drag

That is the question, should sprinters toe drag or should they not.

“This friction is almost insignificant…”

Answering this question is not about opinion, who does it or who does not. To answer the question we have to go to basic physics and kinematics and calculate what effects will the toe drag have on the athletes speed, power or energy use.

In theory, by reducing the total amount of weight beared by your propelling leg, you should be able to use more energy to propel yourself forward instead of just keeping you from dropping down. This might give you an advantage at the expense of some friction that would slow down your foot while trying to drive forward. My hypothesis would be though, that this friction is almost insignificant when compared to the reduction of weight bearing on the other foot. Allowing you to propel yourself forward with ‘less’ weight on your body.
To calculate the exact force produced by friction on the foot I used a simple: F*u = F where F is equal to vertical force on the ground and u is equal to the kinetic friction coeficient. Unfortunately, every athlete would apply a different amount of force on the floor which means that we have to test various forces to see if we find any pattern on whether it is beneficial or not. The table below compares the amount of force applied to the ground vs how much horizontal force is then subtracted from the total forward movement.

Here is what I got:

 Weight (kg)Friction coefficient (Rubber / Concrete)Horizontal Force (Applied)Weight bearing (N)Angle of force (degrees)Total force applied (N)Percentage Change of effort
00.6462.1735.857.9868.8
0.20.6463.2733.857.7867.80.12%
0.40.6464.4731.857.6866.70.24%
0.60.6465.6729.957.5865.70.36%
0.80.6466.8727.957.3864.70.47%
4.20.6486.8694.555.0848.12.38%
4.40.6487.9692.654.8847.22.49%
4.60.6489.1690.654.7846.32.59%
4.80.6490.3688.754.6845.42.70%
50.6491.5686.754.4844.52.80%
Horizontal force taken from world record performances of Maurice Green1997

Notes: 1.) I chose using Rubber and Concrete as the kinetic friction coefficient which is maybe the closest to rubber against shoe materials. 2.) The horizontal forces used are taken from Jeremy Richmon’s “Newtonian model of an elite sprinter: How much force do athletes need to produce to be world class” (2008)

The data results shows that the more weight that is relieved on the non-propelling leg the more efficient the push of the athlete. This is because the friction coeficient is not higher than 1, meaning the vertical force difference is higher than the horizontal force by friction. Then, the total force that the athlete has to apply to the ground is actually reduced thanks to the relief of weight bearing on the propelling leg.
When it comes to energy expenditure, we go into a bit more complicated ground to predict whether it is more energy efficient to toe drag or not.

In my personal experience, this is definitely the feeling that you get when you toe trag. You feel your body is lighter and you can achieve lower angles of propulsion.

On my next post I will analyse the theoretical energy expenditure of this technique. Having an instant of force improvement shown above, This might shine more light on the decision whether it should be better or not to toe drag when sprinting on the first 2 steps.

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