Training on unstable surfaces such as stability balls and balance boards continues to gain popularity. Exercises on unstable surfaces are often promoted to improve balance and challenge core stability more than traditional resistance training using free weights and machines. However, scientific proof that training on unstable surfaces is superior to traditional resistance training performed on stable surfaces, such as a bench, is lacking. Given that most activities of daily living are performed on stable rather than unstable surfaces, it is important to determine whether exercising on unstable surfaces transfers to improvements in activities performed on stable surfaces.
One group of researchers designed a study to answer the following questions:
1. Can you lift more weight on stable surfaces compared to unstable surfaces?
2. Which requires more core stabilization – lifting on a stable or unstable surface?
3. What effect does lifting an unstable load (dumbbells vs a barbell) have on strength and core stabilization?
A study by Kohler and his associates1 measured the amount of resistance that could be lifted during an overhead press using stable vs unstable loads (barbell vs dumbbells) and stable vs unstable surfaces (weight bench vs stability ball). Thirty subjects with at least one year of resistance training experience volunteered to participate in the study. Each subject performed an overhead press under four conditions:
1. Using a barbell seated on a bench (no back support) – stable load, stable surface
2. Using dumbbells seated on a bench (no back support) – unstable load, stable surface
3. Using a barbell seated on a Swiss ball – stable load, unstable surface
4. Using dumbbells seated on a Swiss ball – unstable load, unstable surface
Researchers measured strength for each exercise during a 10 RM (Repetition Maximum) shoulder press exercise. The test measures the amount of resistance that could be lifted 10 times to failure during each exercise condition. This allowed researchers to determine if subjects were able to lift equal amounts of weight when using unstable loads and surfaces. Next researchers measured the activity of the core muscles while subjects performed 3 sets of each exercise.
Subjects lifted the most weight when using a barbell seated on a stable surface and the least when lifting dumbbells (unstable load) on a stability ball (unstable surface). This demonstrates that as the load and/or the surface becomes unstable that the maximum amount of weight lifted decreases. If an individual’s goal is to increase strength, the reduced ability to load an exercise when using unstable loads (dumbbells) or surfaces will limit strength gains.
Muscle activity in the abdominals was higher during exercises performed on stable surfaces. This suggests that the ability to lift more resistance on stable surfaces requires more abdominal musculature. For the back muscles, activity was signficantly higher when lifting stable loads (barbell) on both stable and unstable surfaces. These findings may, however, be specific to the overhead press and may not reflect core muscle activity for other exercises like the bench press or rowing exercises.
TAKE HOME MESSAGE: The results of this study emphasize the need to include some traditional strength training exercises into your exercise program to maintain and improve muscular strength. Although this study did not measure balance or ability to perform activities of daily living, another study by Spennewyn2 reported that training on unstable surfaces can improve balance. Until more research is available regarding the effects of training on unstable surfaces, it is a good idea to incorporate a mix of traditional resistance training, in addition to exercises on unstable surfaces into your exercise program. This is especially important if the goal of the program is to improve muscular strength.
1. Kohler, J.M., Flanagan, S.P., & Whiting, W.C. (2010). Muscle Activation Patterns While Lifting Stable and Unstable Loads on Stable and Unstable Surfaces. Jour Stren & Cond Res, 24(2), 313-321.
2. Spennewyn, K.C. (2008). Strength Outcomes in Fixed Versus Free-Form Resistance Equipment. Jour Stren & Cond Res, 22(1), 75-81.