This paper reviews specific examples of how energy expenditure during submaximal exercise is affected by mechanical and muscular factors. Structural biomechanical variables are discussed as a possible reason for economy differences between individuals. The practical question, "Can economy of performing a certain task be modified?" is posed. Examples of how the manipulation of a particular movement pattern results in an energetic minimum (optimal phenomena) are presented. The physiological mechanisms for these phenomena are summarized. The influence of positive vs negative work and storage of elastic energy in relation to the topic of economy and muscular efficiency is considered. The effects of athletic equipment such as footwear, track surfaces, and bicycle components on economy and muscular efficiency are presented. The prospects for improving athletic performance by improving economy are evaluated, and recommendations for future directions are made.