@David - well strictly
work = Energy / time
so it's the work to move a 'tonne of stuff' in a set amount of time that you are thinking of, while the Energy involved is a different question
although I acknowledge that I said 'work' done riding a bicycle when strictly it was Energy I was referring to;
so say you call 1 – strong – human power = 0.5 horsepower ~= 375 watts, that's 375 J/s, would allow acceleration of 100kg at a tad less than 3 ms^-2, deceleration similarly.
conversion back to F=ma gives F=300N, similar to the weight of a 30kg load at normal gravity, so sounds right in a 'constant load' scenario, although human peak power reaches closer to 1kW => 4+ ms^-2 for that 100kg load in say a <10% duty cycle. As Andus says, that could be a surprise when sent Tesco style – NASA Breakfasts are high protein :-)
compare a cricket fast bowler who bowls a 150g ball at 150km/h, kinetic energy of 130J, baseball pitcher 105mph, kinetic energy 163J; the difference being that the amount of time for acceleration is an important limiting factor