A SYSTEMATIC REVIEW AND META ANALYSIS EXAMINING THE EFFECT OF BENCH PRESS VARIATIONS ON ELECTROMYOGRAPHICAL ACTIVITY: A SYSTEMATIC REVIEW AND META ANALYSIS Ronald L. Snarr, Michael V. Fedewa, and Michael R. Esco Department of Kinesiology, The University of Alabama, Tuscaloosa, AL Abstract Purpose Results The primary aim of this study was to examine the differences in EMG between bench press variations in an attempt to determine the most effective method of motor unit recruitment of the pectoralis major. Electromyography (EMG) is a laboratory technique designed to measure the electrical activity and motor unit recruitment pattern of skeletal muscle. Despite consistent evidence indicating that EMG activity is related to strength of contraction during exercise, conflicting evidence exists regarding EMG activity in a specific muscle during exercise modifications. To date, comprehensive EMG research has mainly focused on the acute and chronic effects of resistance training in regards to alterations in volume, intensity, or periodization models. PURPOSE: The primary aims of this study was to examine the differences in EMG between bench press variations in an attempt to determine the most effective method of motor unit recruitment of the primary movers. METHODS: A systematic review of peer-reviewed articles published before September 16, 2015 was conducted in accordance with the PRISMA guidelines. All studies included in the current analysis were: (1) Published in English, (2) Peer-reviewed, and (3) compared the EMG activity of the pectoralis major from a bench press to a similar exercise modification. Each exercise variation was examined and categorized into one of two groups: (1) mimics traditional movement of bench press; or (2) altered joint pattern and range of motion. Exercise variations that did not restrict movements in a particular plane or changed body position were considered to reproduce the same movements as one would encounter during the bench press. Exercises that were completed standing (i.e., cable press), with the assistance of a uni-planar machine (i.e., Smith machine), or changed movement pattern in the body (i.e., Swissball Bench) were classified as group 2. Data are presented as mean (M), standard deviation (SD), and 95% confidence interval (CI). RESULTS: Data from 119 participants was analyzed (23.42 ± 2.15 years). The cumulative results of 15 effects gathered from 8 studies (1.88 ± 2.47 effects per study) published between 2006 and 2013 indicate that no significant change in EMG activity within the pectoralis major occurs with modification of a flat bench press (mean ES = -0.19 (95% CI: -0.70, 0.33; P = 0.47). Meta regression analysis determined that exercise movement variation independently explained 44.3% of the variation in EMG activity (β = 0.67, P < 0.001), and remained significant after accounting for the variation explained by the number of repetitions performed and exercise intensity (β=-0.16, P=0.40; β=0.13, P=0.48; respectively). Exercises that altered joint pattern and range of motion produced significantly lower EMG activity (ES = -0.94, 95% CI: -1.59, -0.28) when compared to exercises that mimicked the traditional movement of the bench press (ES = 0.91, 95% CI: 0.11, 1.70) (P < 0.001). CONCLUSION: The data indicates that altered joint pattern and range of motion during exercise significantly reduced EMG activity, and explained nearly half of the variation in EMG activity of the pectoralis major during exercise. PRACTICAL IMPLICATIONS: Exercise variations should closely mimic the motions and joint patterns of the bench press in an attempt to maximize muscular activation. Additionally, modifications of the bench press that result in reduced degrees of freedom, changes in joint mechanics, or alterations in body position may reduce the ability of the individual to produce similar activation of the muscle compared to a standard bench press. Methods Figure 3. Forest plot of Hedges’ d effect sizes. The cumulative results of 15 effects gathered from 8 studies (1.88 ± 2.47 effects per study) published between 2006 and 2013 indicate that no significant change in EMG activity within the PM occurs with bench press modification (mean ES = -0.19 (95% CI: -0.70, 0.33; P = 0.47). Meta regression analysis determined that exercise movement variation independently explained 44.3% of the variation in EMG activity (β = 0.67, P < 0.001), and remained significant after accounting for the variation explained by the number of repetitions performed and exercise intensity (β = -0.16, P = 0.40; β = 0.13, P = 0.48; respectively). Exercises that altered joint pattern and range of motion produced significantly lower EMG activity (ES = -0.94, 95% CI: -1.59, -0.28) when compared to exercises that mimicked the traditional movement of the bench press (ES = 0.91, 95% CI: 0.11, 1.70) (P < 0.001). Figure 1. Flowchart of Study Selection. Introduction While many variations exist, anecdotal claims recommend the performance of one technique over another to increase muscular activation and maximum results during resistance training. Traditionally, both the standard bench press and push-up are performed on stable surfaces; however, multiple variations exist including instability training, utilization of barbells, dumbbells, or machines, changes in inclination or declination, differences in hand-grip or width position, or any combination of these. While not all modifications induce differences in muscular recruitment, other variations, such as instability devices have been shown to elicit significantly greater activity of the prime movers. Useful to practitioners, EMG activation levels can often be interpreted as an indicator of exercise intensity. To-date, very few meta-analyses exist on the topic of electromyography; most pertaining to the use of EMG biofeedback in the physical therapy setting. Conclusions & Practical Applications Standard Error Based on the cumulative results from peer-reviewed research publications between 2006 and 2014, a small, non-significant, effect was found for electromyographical differences between the traditional bench press and exercise variations. Modifications of the bench press that result in reduced degrees of freedom, changes in joint mechanics, or alterations in body position may reduce the ability of the individual to produce similar activation of the muscle compared to a standard bench press. Effect Size Figure 2. Funnel plot of ES versus SE. Random effects mean ES for exercise variation on EMG activity.