Author and graduation date: Kerri M. KRUSINSKI, May, 2001

Committee members: Peter Francis (Chair), Patricia Patterson, Robert S. Pozos

Thesis title: EMG Activity of Four Muscles during an Overhead Press using both Free Weights and Resistance Machines

This paper examines the popular belief that resistance training while using free weight equipment is superior to that while using resistance machine equipment for a popular exercise.

Twenty subjects performed four conditions of the overhead press exercise while EMG activity was recorded by surface electrodes from the deltoid, triceps brachii, rectus abdominis, and pectoralis major. Subjects performed 16 repetitions of each condition, including the standing barbell overhead press, standing Icarian Smith machine overhead press, seated barbell overhead press with a backrest, and the seated Icarian shoulder press machine with a backrest.

Data were analyzed to compare mean muscular activity of repetitions 1-15 for each condition of the overhead press Next, the muscular activity of repetitions I 1-15 was normalized to repetitions 1-5 to observe physiological fatigue for the deltoid and triceps and substitution that occurred for the rectus abdominis and the pectoralis major. Eight, one-way repeated measure analysis of variance (ANOVA) were performed to determine significant differences across overhead press conditions (alpha = .05).

The deltoid and pectoralis major did not express a significant difference when mean muscle activity was compared from the four conditions. The rectus abdominis was significantly more active when subjects performed the standing Smith machine overhead press, than the other three conditions. The triceps was significantly more active when subjects performed the overhead press on the seated shoulder press machine with a backrest, than the other three conditions. Physiological fatigue of the deltoid was not significantly different during any of the conditions. For the triceps, the fatigue related to the exercise: condition was significantly less when subjects performed the seated shoulder press machine with a backrest, than any of the other conditions. The rectus abdominis was substituted significantly more when subjects performed the standing Smith machine overhead press, than the other three conditions. The amount that the pectoralis major was substituted was not significantly different when subjects performed the standing barbell and the standing Smith machine overhead press exercises, it was significantly less during the seated barbell overhead press, and was significantly greater during the shoulder press machine overhead press.

There were significant differences that occurred for muscle activity and substitution across the overhead press conditions, but each did not consistently support the superiority of training with either free weight or resistance machine equipment. It could not be concluded from this investigation whether resistance machines or free weights are the most beneficial for the user. At this time, it would appear that the wide held belief that free weights are superior to machines must be questioned.

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