Bren Foster can kick up to 60.7974 m/s.
Human leg is 10% of body weight.
Assuming an average American weight of 88 kg. Why not, since Composite Human is the perfect combination of the human being, and athletes usually do weigh that much due to muscles.
So the leg would be 8.8 kilograms.
8.8*60.7974^2*0.5 = 16 264 Joules (actually 16 263.8 something) Joules, Wall level
Heaviest person in the world, according to Wikipedia, weighs 635 kg. Or a whopping 63.5 kilogram leg.
63.5*60.7974^2*0.5 = 117 358 Joules (actually a bit more), still Wall level