Answer:
Push-ups. Let M1 be the mass of the body and M2 be the mass of weights. Assume that M1 must be heavier than M2. Since M1 is heavier, M1 requires more force, and therefore work to be applied, let F1=M1*g. To bring our body back up, we need a force bigger or equal (if already in motion) to F1.
Let F2 = M2*g
Since F1 has to be bigger than F2 due to mass, we can build an equation for energy. Let X be a displacement, which is equal in both situations. Constructing a change of energy equation we can see that work done to lift the body is greater:
W1=F1*x
W2=F2*x
Where W1 is the work of the hands-on body, and W2 is the work of lifting weights. W1 has to be larger than W2. Since more work in W1, more muscle will be needed to complete a repetition, but only assuming that M1 > M2.
