Mixed
Instability resistance training using devices like physioballs or wobble boards is not recommended as the primary exercise for hypertrophy, absolute strength, or power in trained athletes, as ground-based free-weight exercises produce greater core muscle activation and force output.
If your goal is to build muscle or get stronger, prioritize stable, ground-based free-weight exercises like squats, deadlifts, and overhead presses. Use unstable devices (like Swiss balls or balance boards) only for rehabilitation, warm-ups, or as supplementary exercises for balance, not as your main strength builders.
While unstable devices have been shown to be effective in decreasing the incidence of low back pain and increasing the sensory efficiency of soft tissues, they are not recommended as the primary exercises for hypertrophy, absolute strength, or power, especially in trained athletes. For athletes, ground-based free-weight exercises with moderate levels of instability should form the foundation of exercises to train the core musculature.
Why this rating
Based on a comprehensive review of multiple studies comparing activation levels and force output, though it is a review rather than a single primary trial.
Source
The use of instability to train the core musculature
David G. Behm et al. · Applied Physiology Nutrition and Metabolism · 2010
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