physics concept

f=ma is the same as f=(mv-mu)/t
f=(mv-mu/t) = m (v-u)/t

where
(v-u)/t = a

So they are the same thing, just different way of writing it.

For jumping, I'd look at it as a vertical projectile motion:
http://www.physics-formulas.com/Projectile_Motion.html
y = (ut sin A) - ½ gt²

y = max height before you come down
u = initial velocity
t = time from jumping to landing
A = angle of jump
g = gravity acceleration

So you can find out your initial velocity, then calculate how long it takes to accelerate from 0 velocity to your initial velocity, and work out your jump force.

For landing calculation, you can get final velocity with this formula v = (u sin A) - gt, then calculate landing deceleration. One you have the acceleration/deceleration, you can apply F=ma.

Another way to look at jump situation is to calculate potential energy change of the jump: PE = mg (h2 - h1) where h2 - h1 is the height change during the jump.

Both "F" in the equations "F=ma" and "F=(mv-mu)/t" means "NET Force".
Consider F=(mv-mu)/t,
F=m(v-u)/t
F=ma
So, both equations are same but different presentation.