how do you know that muscle contractions or such make it highly nonlinear such that there is a "perfect" power level ? a lower power/voltage/current might be more dangerous then a higher one then a lower then low one .
the human body is amazing complex. i.e. perhaps it shunts particular combinations of voltage/current the current across nonvital organs etc. probobly has to do with 5 billion other factors like hormone levels, muscle tone, hydration, age, gender, etc