As the name implies, instability training involves training on an unstable surface, most often using a piece of equipment such as a Bosu ball or a Swiss ball. According to research published in the Sports Health journal, instability training is frequently used for performance enhancement, rehabilitation, and overall musculoskeletal health.The idea is to strengthen the core and trunk muscles and, in some cases, to prepare athletes to train on unstable surfaces such as sand.
Instability exercises may be body-weight in nature—like standing on a wobble board to improve your balance—or can involve resistance. In both cases, you can look forward to stronger abs, obliques, and lower back.
But what does the science say? One study found that exercises performed under unstable conditions increased trunk muscle activation by an average of 47.3%. A stronger core will help you in the long term during exercises like the squat, deadlift, and bench press, but pairing instability training with strength training will reduce your ability to produce max force and can lead to injury—from literally falling off a tottering platform to tweaking a muscle while trying to balance.
In the study noted above, performing leg extensions while seated on a physioball resulted in a 70.5% drop in force compared with performing the same exercise on a stable bench. And quadriceps activation diminished 40.3%.
So, if power output is your goal, stable ground is s