Physical Therapy and UST
Balance training (also referred to as neuromuscular training or proprioceptive training) is prescribed by physical therapists to help patients recover from or prevent lower extremity injuries. Balance training is used to increase body awareness/control and increase the strength of muscles in the lower extremities.
A review by You-jou Hung (2) concluded that balance training might benefit individuals with an unstable ankle; however it is unlikely to prevent injuries caused by fast and large perturbations such as landing on an unstable surface with a single limb. In addition, the JOSPT Clinical Practice Guidelines for Ankle Ligament Sprain (3) give therapeutic exercise and activities, such as single leg balance and using unstable surfaces, a level C evidence (weak evidence).
Another population where the UST may be used in physical therapy is with the elderly and those at an increased risk of falls. A study by Martinez-Amat et al. (3) looked at the effect of a 12-week proprioceptive training program on postural stability, gait, balance, and fall prevention in adults older than 65 years. The results of the training program, which used the BOSU ball and Swiss ball, indicated that unstable surface training is effective in improving postural stability, static, and dynamic balance. It could also lead to an improvement in gait and balance capacity and may decrease the risk of falling in adults aged 65 years and older.
Weight Lifting and UST
Unstable surface training may serve a purpose in physical therapy, but what about in a healthy, athletic population?
There are several research articles comparing the use of an unstable surface (i.e. BOSU ball) versus stable ground when performing exercise. A study by Willardson et al. (4) investigated core muscle activation when using a BOSU ball versus stable ground and found that there was no advantage to using a BOSU ball for the squat, deadlift, overhead press, or curling exercises. With that being said, it was recommended that these exercises be performed on a stable surface without the fear of losing the potential core muscle training benefits. An article by Li et al (5) using electromyography comparing squatting on a reebok core board and stable ground found similar results to the Willardson study. No significant difference was found in the EMG readings of lower extremity muscles during stable and unstable exercises. An increase in muscle activation was found when weight load was increased, regardless of surface.
So far the evidence has stated that UST does not lead to an increase in muscle activation compared to a stable surface, but rather an increase in load correlates to an increase in muscle activation. A study by Drinkwater et al. (6) analyzed the effects of using a BOSU ball during the squat found adverse effects. What the researchers found was that as the weight increased while performing the squat on a BOSU ball, the participant’s kinematics and technique (or squat form) decreased. In other words, when trying to progressively overload a muscle on a BOSU ball by increasing the load, the form decreases leading to compensations and a higher risk of injury.
A study published in the Journal of Strength and Conditioning Research looked at the use of unstable surface training on athletic performance in elite athletes. After the 10-weeks of training, it was found that the control group (stable training group) showed improvements in jumping peak power, while the unstable surface training group did not show significant improvements. Both groups saw an improvement in 40-yard sprint, 10-yard sprint and agility test times, however the stable training group saw larger improvements. The study concluded that using an unstable surface reduces possible performance improvements in healthy, trained athletes. (7)
So maybe your purpose is to increase core strength and stability. This is not to say that every lower extremity exercise using UST does not increase core activation; however several studies using common functional exercises have shown no benefit to using an unstable surface for core activation. Another aspect to consider is that you are sacrificing strength and power while using an unstable surface. Here is an example:
In the second scenario the weightlifter sacrificed overloading their musculoskeletal system by adding in another factor, the unstable surface, thus causing them to focus more on their form and neuromuscular system. If the weightlifter performed the squats on the BOSU ball with the same weight as before, they would create an unsafe environment. They would compensate, correct form would be lost, and an increased risk of injury would result.
Overall unstable surface training may serve a purpose if implemented in the correct manor, however it is too often used with no real purpose. Remember to always have a purpose for all of your exercises and be able to answer “why” you chose that specific one!
1) Hung Y. “Neuromuscular control and rehabilitation of the unstable ankle.” World J Orthop. 2015 June 18;6(5):434-438.
2) Martin R, Davenport T, Paulseth S, Wukich D, Godges J. “Ankle stability and movement coordination impairments: ankle ligament sprains.” J Orthop Sports Phys Ther. 2013;43(9):A1-A40.
3) Martinex-Amat A, Hita-Contreras F, Lomas-Vega R, Caballero-Martinez I, Alvarez PJ, Martinez-Lopez E. “Effects of 12-week proprioception training program on postural stability, gait, and balance in older adults: a controlled clinical trial.” J Strength Cond Res. 2013 Aug;27(8):2180-8.
4) Willardson JM, Fontana FE, Bressel E. “Effect of surface stability on core muscle activity for dynamic resistance exercises” Int J Sports Physiol Perform. 2009 Mar;4(1):97-109.
5) Li Y, Cao C, Chen X. “Similar Electromyographic Activities of Lower Limbs Between Squatting on a Reebok Core Board and Ground.” J Strength Cond Res. 2013 May;27(5):1349-1353
6) Drinkwater EJ, Pritchett EJ, Behm DG. “Effect of instability and resistance on unintentional squat-lifting kinetics.” Int J Sports Physiol Perform. 2007 Dec;2(4):400-13.
7) Cressey E, West C, Tiberio D, Kramer W, Maresh C. “The effects of ten weeks of lower-body unstable surface training on markers of athletic performance.” JOSPT. 2007 May;21(2).