Useful tools or personal trainer's toys.
In the late period of 1990, unstable surface training (UST) became the mainstream, with resistance balls, semi-circular balance balls BOSU and small flat inflatable cushions all over the floor of each gym. Over the years, these tools have become notorious. Fitness athletes and bodybuilders often look down on this training method and avoid training on these tools, because it won't make you bigger and stronger. At the same time, many personal trainers are betting on these new tools, and begin to let novices or people with poor physical fitness do only the core training of resistance ball and do nothing else. Finally, they gave this kind of training a bad reputation for functional training.
Resistance ball started with physical therapy.
UST was originally applied to clinical rehabilitation, such as physical therapy, especially to solve ankle problems. After ankle sprain, many patients develop functional ankle instability. Basically, the fibula (the muscle on the outside of the calf) triggers slowly, which makes you less protected from "re-sprain".
Fortunately, the study pointed out that UST (improving perceptual function) can be added to solve this problem, so that the central nervous system can receive better feedback and improve the transmission of action information. As physiotherapists successfully used UST to solve functional ankle instability, they finally began to apply this method to others. At that time, most studies were poorly designed: previous injury history was not considered, there was no simple control group or the research time was too short. There are some favorable results, but there are also some contradictory results.
The problem of unstable surface training
UST ignores the principle of particularity of training. Almost all athletes exercise on a stable surface, and instability is further applied to the power chain. In the competition, the feet are on the stable ground, while the trunk and arms are unstable. This is why unstable plane training may be more useful in training the core and upper limbs. This means that when training, the body is sitting or lying on the ball, but when training for lower limb instability, it is necessary to be more specific and carry out various trainings on a stable plane. Considering the particularity of sports, most of them occur at high speed, and at the same time, they involve contraction and extension cycle (SSC) to a great extent. However, unstable surface training will prolong the pause between centrifugation and centripetal motion in SSC, so the force generated immediately after centrifugal preloading will be quite small. It's like jumping on the beach, because any stored elastic energy will be lost, so you can't generate enough force.
Of course, unstable surface training may be beneficial to athletes with injury history or related proprioception disorders, but the bigger problem is that unstable surface training will damage the SSC function of healthy athletes. "Slow training is slow", and unstable face training will force you to train slowly.