Modification, by tractive loading, of the energy cost of walking in sheep, cattle and man.

1. A study was made in sheep and cattle walking on a treadmill, of the alteration to the energy expenditure that was caused by voluntarily exerted tension in the tether between animal and treadmill. 2. An additional experiment was carried out to investigate in human subjects walking on a treadmill, the alteration to the energy expenditure as a result of positive and negative tractive loads applied at waist level through a rope parallel to the plane of the treadmill. 3. Alterations to the net energy expenditure when walking were generally similar in the three species and varied with speed and gradient up to a maximum value of approximately 0.04 J per metre walked per gram of tension or negative load.