Malek MH, Nalbone DP, Berger DE, et al. Importance of health science education for personal fitness trainers. J Strength Cond Res. 2002 Feb;16(1):19-24.
A survey of 115 health fitness professionals revealed that a bachelor's degree in the field of exercise science and possession of American College of Sports Medicine or the National Strength and Conditioning Association certifications as opposed to other certifications were strong predictors of a personal trainer's knowledge, whereas years of experience was not related to knowledge.
Mazzetti SA, Kraemer WJ, Volek JS, et al. The influence of direct supervision of resistance training on strength performance. Med Sci Sports Exerc. 2000 Jun;32(6):1175-84.
Twenty moderately trained men were randomly assigned to either the supervised group or unsupervised group who performed identical resistance training programs using free-weight and variable-resistance machine exercises. The study showed the directly supervised men demonstrated a greater rate of training load increase and magnitude which resulted in greater maximal strength gains compared with unsupervised training group.