In a study published by researchers at Appalachian State University, it was shown that the squat and the deadlift produced more activity in the trunk muscles (abdominals, obliques, and lower back) than three stability ball exercises specifically targeting the same muscles. It was concluded that the stability ball exercises (quadruped, pelvic thrust, and ball back extension) did not provide enough stimulus for either increased strength or hypertrophy therefore questioning their role in a sports conditioning program. Squats and deadlifts, however, were found to provide the necessary stimulus for hypertrophy of the back extensors.
Another study published by Eastern Illinois University demonstrated the lack of advantage of recruitment of the trunk muscles when performing the back squat, deadlift, overhead press, and curls both on and off a BOSU trainer. These lifts were performed at 50% and 75% of 1RM.
Researchers at Charles Stuart University in New South Wales, Australia demonstrated that the utilization of unstable surfaces engages assistor muscles to the detriment of the prime movers and actually decreases the athlete’s overall power. This means that the athlete’s body is working so hard to balance that the large muscle groups begin to not work as effectively. Therefore, using unstable surfaces to train in season would actually be detrimental to the power athlete.
Finally, a review written by Dr. JM Williamson from Eastern Illinois University tries to make sense of when it may be appropriate to use stability training in a sport specific setting. He concludes that for the athlete, balance training has its place in the off-season. The stability ball, with light resistance, can be used to maintain core endurance in the post-season period. In the off-season, balance boards or unstable surfaces such as the BOSU paired with plyometrics can be a good tool for developing propreoception, the ability to sense where one’s body is in regard to one’s surroundings. However, in the pre-season training period, training on a stable surface is the best method for building substantial strength and power in the trunk and extremities.
The practical applications from the study for fitness professionals is that stability ball training is simply not necessary to have a strong core if you have a barbell. As noted in the introduction, stability training was developed and used primarily by physical therapists in a rehabilitation setting. For someone who is very weak from illness or injury and/or deconditioned, balance training can serve to activate the deep trunk musculature and small assistor muscles that are necessary for simple things like maintaining upright posture and developing core endurance. However, for someone who is already fit and foundationally strong, squats and deadlifts are much better for building a strong midsection all around. For safety purposes, proper form is of the utmost importance with these lifts so if you are not sure of your technique, please be sure to work with a qualified coach or trainer.
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Journal of Human Kinetics. 2018 Jun; 62: 43–53.