The use of unstable surface training (UST) popularity has increased over recent years as a tool for injury prevention and rehabilitation and to improve athletic performance using a variety of equipment such as Swiss Balls, balance discs and wobble boards among other equipment. However, the use of UST can be a controversial topic as proponents claim that it can offer performance enhancement through core stability and functional balance whilst opponents of UST claim it can reduce force output and does not offer any crossover sports performance gains. The aim of this article is to analyse the value of using UST and look at research in relation to its applied use in both general and athletic populations.
UST is used to challenge the nervous system to better recruit stabilising musculature in order to improve local and global stabilisation (1). Our ability to control motion in normal ranges using our core and joints is essential in preventing us from falling over and to perform movements such as walking, running or turning (1). Any movements we perform require reflex actions to protect us and help us to rebalance. UST is used as a training modality to improve balance. Balance can be described as our ability to maintain our body’s centre of gravity within its support base and can be categorised as either static or dynamic (3). Our ability to sustain our body in static equilibrium or within its base of support is referred to as static balance; whereas, our ability to maintain equilibrium during a transition from a dynamic to a static state is referred to as dynamic balance, with the latter being more challenging (3). In order to control the body within its base of support, both static and dynamic balance requires effective integration of vestibular, visual and proprioceptive inputs to produce an efferent response (4).
UST is used for both injury rehabilitation and prevention. In rehab settings, UST is used to improve poor balance and or postural control as these are usually associated with injury or falls in different populations (8). For example, postural sway and a slow response time in muscle stabilisation were associated with ankle instability (8), whilst poor balance increases the likelihood of ankle sprain injury (12). Balancing on an unstable surface causes sudden joint displacement, therefore, the generation of muscle tension is required to resist this displacement which leads to an increase in proprioception response (4).
Wobble boards, for example, are used to improve proprioception and trunk stability as part of the treatment of ankle injury and acute ankle sprains (10). Post an inversion sprain, there is a delayed proprioception response to angular displacement, therefore it is important to retrain the altered afferent neuromuscular pathways proprioception response and help restore normal joint reflex stabilisation (4). The increased proprioception response and activation of key stabilising muscles following the intervention of UST are reasons for its use for rehabilitation and future injury prevention (1). The use of UST for functional ankle stability was shown to have a positive effect in decreasing muscle latency and residual symptoms (8). UST can be used to prevent injury reoccurring, but this may be limited to only those with a previous ankle injury as there is little evidence to support the use of UST in healthy individuals with no history of ankle injury (12).
There is evidence that supports trunk stability training as an effective tool in the treatment of lower back pain, but the relationship between the improvement in lower back pain and spinal stabilisation or core control is not entirely clear (5). However, UST provides an increase in muscle activation at lower loads which makes it a suitable tool for rehabilitation and an increase in co-contraction may also provide increased joint stability despite reducing force production (1). Research looking at the benefits of UST for balance revealed that a 12-month balance training in the elderly population improved static and dynamic balance and resulted in a reduction in fall frequency (7).
UST is also used for athletic performance. UST shows greater trunk activation vs stable surfaces which leads to its increased use in a performance setting. Trunk activation is higher on unstable surfaces and increases with greater instability but this activation is restricted to the trunk muscles (14). Trunk activation and stability are also inherent in traditional free weight exercises (9). Research shows that activity of trunk muscles during squats and deadlifts were equal or higher than trunk-specific exercises on a Swiss ball (9). Therefore, it is important to ask if there is a need to devote specific time to doing these exercises when traditional exercises can be overall more effective with stable surfaces allowing for greater force production (9).
Researchers looking at athletic performance examined drop jump, countermovement jump and sprint time over 40 yards. Results of the study showed that combining a stable surface lower body strength program and a UST program actually attenuated performance (2). Core stability training also appears to be highly task specific, which may be attributed to the fact that many of the exercises performed are in a static state may only transfer to other similar skills (2, 1). Researchers also looked at the effects of 6 weeks Swiss Ball training on core stability and running economy. The results showed an improvement in core stability but there was no change in EMG activity or running economy (13). Research looking at force output shows that there is little evidence to support the use of UST to increase force output vs on stable surfaces (1). In fact, UST causes a reduction in force output despite the increase in muscle activation and EMG activity. The decrease in force output can be attributed to the need to stabilise posture in order to perform the required task (1,6). The decrease in balance associated with UST may force limb musculature to play a greater role in stabilising the joints rather than towards force output (11).
There is a potential use for UST to improve proprioception response following injury and this is especially supported in ankle rehabilitation. There is also evidence that UST can be used to prevent future injuries but evidence mainly supports this in those with previous injuries, therefore, it may not be effective as a prehab tool where previous injuries do not exist. UST may be useful in a rehab setting as it can be used to maintain high levels of activation whilst decreasing stress on the tissue. When it comes to performance, if the aim is to increase force output then instability is not ideal as it causes a decrease in force output. Using free weights on stable surfaces is still recommended to be the more effective method to enhance sports performance.
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