Original articleAn unstable support surface does not increase scapulothoracic stabilizing muscle activity during push up and push up plus exercises
Introduction
An unstable surface is often used during rehabilitation exercises in an attempt to increase muscle activation in stabilizing muscles as well as increasing the proprioceptive balance demands on a patient. Numerous authors have shown increases in muscle activity for specific trunk and leg muscles when an unstable surface is incorporated into squatting movements (Anderson and Behm, 2005), bridging exercises (Marshall and Murphy, 2005; Lehman et al., 2005a, Lehman et al., 2005b) and during traditional upper body strength exercises (Behm et al., 2005; Lehman et al., 2005a, Lehman et al., 2005b). These same experiments have also shown that not all muscles respond with increases in muscle activity. Recently, Drake et al. (2006) found that the average peak trunk muscle activity either decreased or did not change during trunk extension exercises performed on a Swiss ball compared with a mat. To date little work has investigated the influence of a Swiss ball on the muscles of the shoulder during push up exercises. Lehman et al. (2006) documented increases in the EMG of the triceps muscles when the hands were on a Swiss ball during a push up exercise compared with a push up performed on a stable surface; however, no change EMG amplitude between conditions was evident in the pectoralis major muscle. To date no studies have documented the influence of a Swiss ball on scapulothoracic and glenohumeral stabilizing musculature (upper and lower trapezius, serratus anterior, biceps brachii) during push up exercises and common push up exercise variations (push up plus). Considering the popular usage of Swiss balls in rehabilitation and resistance training and the current lack of information on the response of the scapulothoracic musculature to these exercises, this study was initiated to address this current deficit in our knowledge regarding neuromuscular function. Determining the influence of the Swiss ball on scapulothoracic muscle activity may aid in advocating certain exercises for the rehabilitation and training of the scapulothoracic musculature. The objective of this study is to determine if the addition of a Swiss ball to push up exercises influence mean scapulothoracic muscle activation levels.
Section snippets
Patient characteristics
Ten male participants (height (cm) 174.7±12.9, mass (kg) 83.3±10.9, age 26.3±1.1) were recruited from the undergraduate population of the research institution. Participants were excluded if they had recent shoulder or neck pain/injury (within 1 year). Participants were required to read and sign an information and informed consent form prior to the study approved by the institution's Research Ethics Board.
Study protocol
The surface myoelectric activity of the upper trapezius, lower trapezius, serratus anterior
EMG analysis
Both MVC and exercise task myoelectric data were processed in an identical manner. Using EMG analysis software (EMGWorks, Delsys, Boston, MA), the myoelectrical signal had the bias removed (removed mean from the raw signal), then, a moving average technique (mean absolute value—window of 300 data points and an overlap of 150 data points) was used to smooth the data thus providing a linear envelope of EMG activity. Using the electrical markings left by the foot switch trigger at the start and
Results
Table 1 depicts the mean and standard deviation for the group average activity during each exercise and for each muscle. A post hoc power analysis (using an average standard deviation of differences between pairs to be 3.1 (range: 0.32–6.89)) which assumed a biologically meaningful difference between pairs to be 3–5% of MVC revealed that a sample size of 10 had estimated statistical power at 80% to detect a difference of 2.75% MVC or more.
There was no statistically significant difference in
Discussion
The addition of a Swiss ball to the push up and push up plus exercises did not influence the muscle activity of the selected shoulder stabilizing muscles despite anecdotal claims by therapists and exercise specialists suggesting that a Swiss ball results in the greater recruitment of the “stabilizing” muscles around joints. While differences in muscle activity were seen across exercises there was no difference in any muscle when the only difference between the exercises was the replacement of
Conclusion
The addition of a Swiss ball to push up variations does not result in an increase in select scapulothoracic or glenohumeral muscles.
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