In order to challenge the stability of an athlete in training, degrees of freedom are usually increased using destabilizing material, e.g. using free weights instead of guided machines or by modifying the lift base through destabilizing surfaces and / or incorporating a vibratory stimulus as a conditioner.
Proponents of instability in resistance training have suggested that unstable equipment might improve coordination, proprioception, balance and muscle activation to a greater extent than conventional training.
On the other hand, several researchers have argued that using unstable equipment leads to the muscles involved prioritizing stability over force production. In particular, they have argued that using unstable equipment decreases dynamic strength, force output, rate of force development (RFD) and jump height compared to using stable conditions. For this reason, they consider that instability in resistance training provides a substantially lower stimulus for strength-training adaptions compared to traditional approaches.
However, the latest research questions this reasoning and demonstrates that training with unstable equipment actually improves force production, muscle properties such as muscle thickness, and neuromuscular adaptations, similar to training with lower stability requirements. In addition, the research argues that this training can lead to greater improvements in jump height. We recommend reading the interesting article by Saeterbakken published in the prestigious journal PLOSONE entitled “The short- and long-term effects of resistance training with different stability requirements“.
Marín PJ, Hazell TJ. (2014). Effects of whole-body vibration with an unstable surface on muscle activation. J Musculoskelet Neuronal Interact. 14(2):213-9.
Saeterbakken, AH. Olsen, A. Behm, DG. Bardstu, HB. Andersen, V. (2019) The short- and long-term effects of resistance training with different stability requirements. PLoS ONE 14(4): e0214302. https://doi.org/10.1371/journal. pone.0214302
Sobhani S, Sinaei E, Motealleh A, Hooshyar F, Kashkooli NS, Yoosefinejad AK. (2018). Combined effects of whole body vibration and unstable shoes on balance measures in older adults: A randomized clinical trial. Archives of Gerontology and Geriatrics 78: 30–37.