Content-based theories of motivation may best uti lize the meta-theory of work motivation. Process-based theories may benefit most from adopting Locke and Latham's goal-setting approaches and measures. Decision-making theories should utilize the measurement approach operationalized by Ilgen et al. Sustained effort theories should utilize similar approaches to those used in numerous studies of intrinsic motivation, but the measurement of which is typically observational or attitudinal. This paper explored the implications of the four approaches to studying motivation on the newly estab ished model of mental energy. The approach taken for examining motivation informs the measurement of mental energy. Specific recommendations for each approach were developed and provided. As a result of these efforts, it will now be possible to diagnose, measure, and experimentally test for changes in human motivation, which is one of the three major components of mental energy.