Under most favourable conditions, human physical effort can be 30 per cent efficient, turning 30 per cent of the energy consumed into mechanical work and the remaining 70 per cent into heat. Heat is not the only form in which energy is wasted. Unproductive static or dynamic effort is equally important. Hence, the highest level of efficiency is possible only by converting as much as possible of the mechanical effort into a useful form, with little or none of it being dissipated in holding or supporting things. The greater the proportion of mechanical energy to go into