Core Stability Exercises On and Off a Swiss Ball Paul W. Marshall, PG Dip Sci, Bernadette A. Murphy, PhD ABSTRACT. Marshall PW, Murphy BA. Core stability ex- ercises on and off a Swiss ball. Arch Phys Med Rehabil 2005; 86:242-9. Objectives: To assess lumbopelvic muscle activity during different core stability exercises on and off a Swiss ball. Design: Prospective comparison study. Setting: Research laboratory. Participants: Eight healthy volunteers from a university population. Intervention: Subjects performed 4 exercises on and off a Swiss ball: inclined press-up, upper body roll-out, single-leg hold, and quadruped exercise. Main Outcome Measures: Surface electromyography from selected lumbopelvic muscles, normalized to maximum volun- tary isometric contraction, and median frequency analysis of electromyography power spectrum. Visual analog scale for perception of task difficulty. Results: There was a significant increase in the activation of the rectus abdominus with performance of the single-leg hold and at the top of the press-up on the Swiss ball. This led to changes in the relation between the activation levels of the lumbopelvic muscles measured. Conclusions: Although there was evidence to suggest that the Swiss ball provides a training stimulus for the rectus abdominus, the relevance of this change to core stability train- ing requires further research because the focus of stabilization training is on minimizing rectus abdominus activity. Further support has also been provided about the quality of the quad- ruped exercise for core stability. Key Words: Abdominal muscles; Electromyography; Exer- cise; Rehabilitation. © 2005 by American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation T HE SWISS BALL (or gym ball) is widely reported in the recreational training environment to be a training device for core stability exercises. 1 However, there is little scientific evidence to support its use. 2,3 It is also not clear whether performing an exercise on a Swiss ball has greater benefit than performing the same exercise on a stable surface. The term core stability is a generic description for the training of the abdominal and lumbopelvic region. To define core stability, the combination of a global and local stability system has been used. The global stability system refers to the larger, superficial muscles around the abdominal and lumbar region, such as the rectus abdominus, paraspinals, and external obliques. 4,5 These muscles are the prime movers for trunk or hip flexion, extension, and rotation. Local stability refers to the deep, intrinsic muscles of the abdominal wall, such as the transverse abdominus and multifidus. These muscles are asso- ciated with the segmental stability of the lumbar spine during gross whole body movements and where postural adjustments are required. 4,6-8 The validity of both the concept of core stability and the optimal training protocols for core stability requires inves- tigation. For example, an exercise such as abdominal hollowing (eg, the drawing-in technique) attempts to emphasize local over global stability. 9,10 For long-term core stability exercise pro- grams, this type of exercise neglects the synergistic relation between the muscles of the global and local stability systems. For any movement task that involves the trunk region, it would be wrong to believe that only 1 specific muscle system is actively involved. It is known that 1 muscle cannot be identified as being more important for lumbar stability than another. 11 A more appropriate approach to core stability train- ing is to find exercises that incorporate the synergistic relation between the global and local stability systems, but still elicit a satisfactory training effect. Our purpose in this study was to compare the activation patterns of muscles associated with the global and local stabil- ity systems during different core stability tasks on and off a Swiss ball. The exercises did not involve prime movement tasks for the trunk region but permitted us to investigate the synergistic relation between muscles when the overall stability of the lumbopelvic region is challenged by the weight force of the body segments. The hypotheses of this study were (1) the exercises performed on the Swiss ball would have greater levels of muscle activation compared with the stable surface, and (2) the synergistic relationship between the ventrolateral abdominals and erector spinae expressed relative to the activity of the rectus abdominus would not be influenced by the exer- cise surface. METHODS Participants Eight healthy subjects (4 men, 4 women) from our university volunteered for this study. The mean anthropometric charac- teristics  standard deviation (SD) of the men were age, 23.52.65y; height, 1.85.04m; and weight, 81.53.42kg; for the women, they were age, 23.52.65y; height, 1.64.07m; and weight, 61.52.89kg. No subject was experiencing pain in his/her body when tested, and no subject had experienced a significant episode of low back pain (LBP) within the last 5 years. Informed written consent was received from the subjects before their participation. This study was approved by the Auckland Human Subjects Research Ethics Committee. Data Recording All testing was performed in the somatosensory physiology laboratory at the University of Auckland. Skin impedance to the electric signal was reduced to below 5k by (1) shaving excess body hair if necessary, (2) gently abrading the skin with fine grade sandpaper, and (3) wiping the skin with isopropyl alcohol swabs. If the measured impedance was greater than From the Department of Sport and Exercise Science, University of Auckland, Auckland, New Zealand. No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the authors(s) or upon any organization with which the author(s) is/are associated. Reprint requests to Paul Marshall, Dept of Sport and Exercise Science, University of Auckland, Tamaki Campus, Private Bag 92019, Auckland, New Zealand, e-mail: p.marshall@auckland.ac.nz. 0003-9993/05/8602-8830$30.00/0 doi:10.1016/j.apmr.2004.05.004 242 Arch Phys Med Rehabil Vol 86, February 2005