If your leg has a mass of 2kg, 1.1×10^10 J of kinetic energy would require your leg to be moving at about 150 100 km/second not faster than the speed of light.
TLDR: Their math is shit.
Besides, if you really needed those kinds of speed, you’d obviously have to calculate with relativistic formulas. Energy is asymptotical at the speed of light.
100 km/sec is not relativistic and even if it were, at no point would that object need to or could exceed the speed of light. Its a fundamental limit that cant be broken.
Setting aside the correctness in OP for the moment, what’s being said here is that you don’t actually need to break lightspeed. The foot would have to be moving asymptomaticly close to lightspeed, but not passing it. OP used an equasion that works classically, but we’re in territory where that model breaks down.
But if the math doesn’t work out that way, anyway, then whatever, classical equasions are fine.
Pretty sure you’re generating twice as much energy as needed, the required speed is only about 106km/s
