Several sets of data illustrating dissociation of metabolic and muscular work rates are presented. During response acquisition, the rate of energy expenditure declines although work rates remain constant and goal achievement increases. When higher response costs are demanded for goal achievement, work rates increase whereas energy expenditure remains constant. Decreases in outcome probability also give rise to increases in motor intensity and work rate but do not influence the rate of energy expenditure. It is proposed that behaviourally-related variations in metabolic rate are influenced by environmental uncertainty (“what to do”), whereas variations in the intensity of motor output are influenced by response uncertainty (“how to do it”). The processes of response selection which provide the means by which response uncertainty is resolved, activate motor channels for the expression of energy mobilized by the prevailing state of environmental uncertainty.