Jones pioneered the principles of high-intensity training in the late 1960s. He emphasized the need to maintain perfectly strict form, move the weights in a slow and controlled manner, work the muscles to complete failure (positive and negative), and avoid overtraining. Casey Viator saw fantastic results training under the direction of Jones, and Mentzer became very interested in this training philosophy. Eventually, however, Mentzer concluded that even Jones was not completely applying his own principles, so Mentzer began investigating a more full application of them. He began training clients in a near-experimental manner, evaluating the perfect number of repetitions, exercises, and days of rest to achieve maximum benefits.