The Pros and Cons of Training on Unstable Surfaces
Training on unstable surfaces owes most of its development to rehabilitation where it originated. There are many unstable training surfaces including physioballs, foam pads, inflated rubber disks, and Bosu’s . These surfaces are used on the training floors of most gyms. The idea behind unstable training is that inconsistent motion stimulates sensory apparatus in the muscles and joints leading to increased sensory input and increased muscle activation. In addition these movements cause muscles on both sides of the joint to co-contract. Co-contraction occurs to some extent during virtually all movement. When we significantly increase co-contraction the result is increased joint stability.
Increased co-contractions from unstable training can be very useful in the treatment of ankle instability and lumbar spine injury. The fitness industry has adopted the concepts of unstable training from rehabilitation. However, when we use a concept developed for rehabilitation we need to carefully evaluate how and when to use this approach in a healthy or athletic populations.
For example many trainers have clients perform shoulder presses while sitting on a physioball or standing on Bosu to increase core muscle activation. However, this does not produce the desired result. Studies show that doing shoulder presses on an unstable surface do NOT increase core muscle activation versus the same exercise done on a stable bench.
The reason for this result is that balanced vertical forces in alignment with the spine do not increase core muscle activity — regardless of instability of the surface the exercise is performed on! However the use of asymmetrical loading, like doing a one sided shoulder press, does increase core activation, but this is not increased further by being on an unstable surface.
Horizontal limb movements also increase core activation, but there is not a lot of evidence that adding an unstable surface increases this benefit.
When it comes to lumbar stabilization, research shows that exercises done on balls in a horizontal position (face up or face down) do increase core muscle activity. So exercises like crunches, bridges, push-ups and push-ups on an unstable surface will result in increased core activation.
When it comes to absolute force production performing exercises such as bench press or squats on an unstable surface significantly decreases force production and do not assist in the development of absolute strength. So when training for increased strength performing exercises on stable surfaces is a better choice. This same thing is true when working on increasing sprinting speed because training on a highly unstable surface increases ground contact time and force production which inhibits acceleration. However, doing specific drills on a firm surface that provides slight rebound as PART of a sprint program can produce benefits.
The other consideration when using unstable surfaces like a Bosu is that lifting mechanics are significantly altered, and researchers have suggested that training on highly unstable surfaces can actually increase the risk of knee injuries in certain populations! This is not to mention the risk of injuries from hopping, jumping, and leaping on and off of unstable surfaces.
So the question is: What role should unstable training play in developing programming for apparently healthy and athletic populations who are not injured? Research suggests that a combination of unstable and stable training will provide the best results. This brings up two more questions:
Which should come first stable or unstable?
What level of instability should be used with each particular person?
The answer to the first question is dictated by the rules of proper progression. The three primary phases of stabilization training include:
- “Static” Stabilization (foundational)
- “Dynamic” Stabilization (strength/endurance)
- “Ultra-Dynamic” Stabilization (power)
Within each phase:
- Start with bilateral strength development in stable environments because it is safer and will increase strength more.
- Next progress to stable single limb challenges
- Then progress towards hopping and jumping skills in a stable environment
- Then apply that new strength and power to tasks involving postural control on unstable surfaces.
When it comes to how much instability to use with each person the answer will depend on the goal of the exercise and the ability of the individual. So ideally you will use different levels of instability according to the goal of the exercise and the ability of the individual!