Are you seeing more people train on balls while working out in the gym? Training with unstable surfaces such as Thera-Band® exercise balls, stability trainers, and balance boards do promote activation of core muscles. The “core” can be defined as the axial skeletal and its muscular and fascial attachments, including the pelvic and shoulder girdle.
Canadian researchers David Behm PhD and colleagues published a comprehensive review on the use of instability to train the core. Research has shown that exercises performed on unstable surfaces produce higher levels of muscle activation in both the core and extremity muscles compared to stable surfaces. However, force and power outputs are decreased while exercising on unstable surfaces, sometimes up to 70%. Interestingly, increasing levels of core muscle activation can also be achieved with free weight exercises such as squats and Olympic lifts without added instability.
In their article, the authors made several recommendations for both athletes and non-athletic conditioning based on their review of the literature. Dr. Behm et al. noted that athletes should emphasize “higher-intensity ground-based lifts” (such as Olympic lifts, squats and deadlifts) while including resistance exercises with unstable devices, as well as unilateral exercises that provide “transverse stress to the core musculature.” Furthermore, they stated that “unstable exercises should not be used when hypertrophy, absolute strength, or power is the primary training goal.”
Similar recommendations were made for the general population, noting the benefits of both free weight and instability training on promoting spinal stability. It’s important to remember to decrease resistance loads on exercises performed on unstable surfaces.
During rehabilitation, unstable surfaces can be effective at improving muscle reaction time and co-contractions that protect joints. In addition, resistance training on unstable may provide localized muscle endurance training, beneficial for the high proportion of Type I “aerobic, slow-twitch” muscle fibers found in core muscles. Dr. Behm and colleagues recommend core endurance training exercises generally be performed at higher repetitions (greater than 15 per set), while athletes requiring more strength and power perform less than 6 repetitions per set. The authors further noted that unstable surfaces can provide musculoskeletal health benefits such as decreased injury risk and increased spinal stabilization as opposed to using free weights.
In summary, unstable exercise devices such as Thera-Band Exercise Balls and Stability Trainers should be included as part of a well-rounded conditioning program for athletes and non-athletes, but not for increasing primary strength and power. In addition, resistance exercises performed on an unstable surface should be performed at a reduced intensity level because of the reduction in force output.
Behm DG, et al. The use of instability to train the core musculature. Appl Physiol Nutr Metab. 2010 Feb;35(1):91-108.
Behm DG, et al. Canadian Society for Exercise Physiology position stand: The use of instability to train the core in athletic and nonathletic conditioning. Appl Physiol Nutr Metab. 2010 Feb;35(1):109-12.