I was foam rolling the other day and wondered if it mattered
whether or not you had both legs on the roller at once when rolling out you
quads. Logically it makes sense that you are doubling the weight and doubling
the area on which that force is acting. But this can also be thought of in
terms of pressure, or force/surface area. Because putting a second leg under
the foam roller while the force remains the same (as body weight and gravity
are not changing) changes the surface area, the total amount of pressure felt
is less.

Here is an example with rough estimates:

Surface area of one leg (the amount of thigh that would be of
the roller) about 20 cm

^{2}or 0.002m^{2}
Force of thigh on roller: The thigh is estimated to be 12%
of body weight in females (10.5% in males). We will assume the person weighs
130 pounds. 130 x 0.12 = 15.6 pounds or 0.45 kg

P= F/A = (0.45kg)(9.8 m/s

^{2})/0.002m^{2}
= 2205 Pa

Both legs:

P =
2(.45kg)(9.8 m/s

^{2})/(0.002m^{2})2
= 2205 Pa

Through these calculations, you can see that the same amount
of pressure is felt regardless of having one or both legs on the roller.

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