Unstable surface training (UST), otherwise known as unstable balance training or instability training, has sparked an ongoing debate in the health and fitness community. Some argue it’s a game-changer for improving balance, proprioception, and injury prevention, while others see it as an unnecessary or even detrimental form of training when compared to traditional exercises on stable surfaces.

In this definitive guide, we’ll explore UST from every angle: what it is, how it works, its benefits, limitations, and practical applications for everyone from athletes to older adults.

What Is Unstable Surface Training?

Unstable surface training (UST) involves performing exercises on surfaces that provide instability, such as Bosu balls, Swiss balls, balance boards, foam pads, hedgehogs, and various obstacle course implements. The idea behind it is that by challenging your body’s ability to stabilize, you engage more muscles, especially stabilizer muscles, and improve neuromuscular control. Stabilizer muscles, for the purpose of this article, are considered to be the smaller muscles that stabilize joints and allow proper movement patterns. Prime movers, which we will be discussing a few times, are the larger muscles such as the chest muscles or large leg muscles that facilitate movement throughout your environment.

But does UST live up to the hype? Let’s start by understanding how UST affects your body at a physiological level.

The Physiology Behind Unstable Surface Training

The body’s reaction to unstable surfaces is largely driven by the need to maintain balance. After all we never want to fall down if we can avoid it. When you stand or perform exercises on an unstable surface, your central nervous system (brain and spinal cord) and three bodily balance systems (vision, vestibular, proprioception) work overtime to keep you upright. This involves constant feedback from your muscles, tendons, joints, and ligaments to maintain posture and prevent you from falling.

If you don’t know the three systems of balance yet, I highly encourage you to read this article here for a better global understanding.

Increased Muscle Activation

EMG (electromyography) studies have demonstrated that UST can increase activation of the smaller stabilizer muscles. (1, 2, 3) These include the core muscles (transversus abdominis, multifidus), muscles surrounding the ankle (like the peroneus longus) and knee (vastus medialis). For example, a 2020 study found that half-squats performed on a BOSU resulted in significantly higher activation of the vastus lateralis, vastus medialis, and biceps femoris, compared to a standard half-squat on the floor. (4)

It’s important to note that EMG levels do not directly translate to force output, but rather the amount of neural drive to a muscle. (5) So although the EMG activity in the biceps femoris (a part of the hamstring) is more activated during a half-squat on a BOSU, that does not mean it is generating more force than during a heavy loaded half-squat, only that it is generating more activation compared to a similarly loaded stable half-squat. The amount of load that is being lifted has a significant impact on the amount of muscle that can be gained.

This increase in EMG activation isn’t limited to the lower body. Upper body exercises performed on unstable surfaces, such as push-ups on a stability ball, have shown increased core activation, particularly in the rectus abdominis and obliques. (6) However, this comes with a trade-off in the form of reduced force output of the prime movers (chest and shoulders) compared to standard versions of the exercises such as the floor push-up.

Improved Proprioception

Proprioception is your body’s ability to sense its position and movement in space. (7) It plays a vital role in balance, coordination, and injury prevention. UST enhances proprioceptive feedback because it forces your body to make micro-adjustments in response to the unstable environment in an effort to stay as stable as possible. (8, 9, 10) This can improve coordination, efficiency of sensory reweighting (where the brain is getting its information), and reduce the risk of falls particularly in populations prone to balance issues, such as older adults.

For example, you may have seen the use of a blue foam pad in physical therapy clinics. This is an increasingly popular unstable balance tool for use during rehabilitation. The instability provided by the foam surface encourages engagement of stabilizing muscles, which are often weakened after an injury, while also challenging the body’s sense of proprioception. (11) Being in a controlled environment while using the unstable surface allows patients to practice movements without the risk of falling, excessive strain on the recovering tissues, and simultaneously enhance their balance quicker than on solid ground alone.

Types of Balance Strategies

When it comes to maintaining balance, your body uses several strategies, depending on the challenge posed by the surface or external forces. (12) These strategies include the ankle strategy, hip strategy, and, in extreme cases, the stepping strategy.

1. Ankle Strategy: Used during small perturbations, the ankle muscles make small adjustments to keep the body balanced. This is typically the first line of defense and is most commonly employed when standing on relatively stable surfaces or during minor instability. During normal daily standing, we utilize this strategy to stay relatively still.

2. Hip Strategy: When instability increases, your hips come into play. This strategy involves larger movements at the hip joint to realign the center of mass over the base of support. For example, during exercises like single-leg stands on a balance board, you’re more likely to rely on this strategy as the instability increases. In real life, this may come into play if you are suddenly bumped into by someone while standing talking to your friends.

3. Stepping Strategy: In more extreme instability situations, where the ankle and hip strategies aren't enough, the body may initiate a stepping strategy, where you take a step to regain balance. This type of strategy occurs when you get knocked out of your base of support and begin the process of falling but are able to stop an actual fall.

If you want to learn more about these strategies, including two additional strategies, click here.

Balance Strategy on Unstable Surfaces

UST engages both ankle and hip strategies, influenced by the surface type and balance disruption intensity. (13) Initially, the ankle exerts more effort during significant wobbling, indicating a breakdown of this strategy as the neuromuscular system is relatively untrained in the task. This breakdown and inadequacy of the ankle strategy leads to instability, requiring the hip strategy to pick up the slack for better control. As training progresses, reliance shifts back to the ankle strategy, indicating improved motor control and balance skills. This transition reduces dependence on the hip strategy, enhancing overall stability, proficiency, and decreasing neuromuscular demand.

The Debate on Unstable Surface Training in Sports Performance

UST is a hotly debated topic in sports performance circles. Advocates argue that using tools like Bosu balls, wobble boards, or balance discs improves proprioception, core stability, and neuromuscular control, critical components for injury prevention and athleticism. They believe that conditioning athletes to stay balanced in unstable environments helps them react better to off-balance moments during competition.

However, many performance coaches question whether these benefits translate effectively to real-world sports movements. One key critique is that UST lowers the amount of force an athlete can produce, which is true as we will see further down in this article. For example, squatting on a wobble board significantly reduces the weight an athlete can lift safely, limiting their ability to build the strength and power needed for explosive movements like sprinting or jumping.

Another argument against UST is that it doesn’t accurately replicate the dynamic instability athletes experience in sports. Most coaches follow the SAID Principle (Specific Adaptations to Imposed Demands), or rather if you want to get better at an activity you must do the activity. Coaches often prefer ground-based exercises, like agility drills and plyometric training, that better mimic the demands of competition. Research on UST is also mixed. While the research shows improvements in balance, evidence supporting meaningful improvements in athletic performance remains limited.

Ultimately, UST can still play a role in injury prevention or rehabilitation, but many coaches reserve it for warm-ups or supplemental work. The debate highlights a broader question: Should training prioritize force production and sport-specificity, or emphasize functional balance and stability? For now, most experts agree that UST works best as one tool in a larger, well-rounded training program.

Benefits of Unstable Surface Training

Although controversy surrounds UST, it does have benefits:

1. Improved Balance and Coordination

One of the most widely accepted benefits of UST is its positive impact on balance and coordination. (14, 15, 16) By forcing the body to constantly adapt to changes in the surface, UST enhances proprioception and improves neuromuscular coordination. This can be particularly beneficial for populations at risk of falls, such as older adults or those recovering from injury.

2. Increased Core Stability

Because UST challenges your body’s ability to stay upright, your core muscles are often working overtime. Numerous studies have shown increased EMG activity in the transversus abdominis, multifidus, and obliques during UST. (17) Core stability is essential for everything from maintaining proper posture to preventing lower back pain and enhancing athletic performance.

3. Injury Prevention

UST may help prevent injuries by improving joint stability and general motor control. (18, 19, 20, 21) Studies have shown that unstable surface exercises increase muscle activation around key joints like the knee and ankle. This can be particularly useful for athletes looking to prevent ligamentous injuries, such as ACL tears. Enhanced proprioception, joint stability, and motor control mean that you’re better equipped to handle unexpected movements or unstable environments, reducing the risk of injury.

4. Enhanced Functional Fitness

UST can translate well into real-world functional fitness, as life often presents us with unstable surfaces, whether it’s hiking on uneven terrain, walking on icy sidewalks, maintaining balance while carrying groceries, or engaging in board sports that are relatively less about power and strength (surfing, snowboard, skiing, skateboarding). (22, 23, 24) UST can simulate these real-world conditions more closely than exercises performed on a stable surface. Of course practicing the goal activity is always better than simulating with an unstable surface, as the more specific an exercise is, the more it will improve the goal activity.

Limitations of Unstable Surface Training

While UST offers numerous benefits, it’s important to understand its limitations to avoid overestimating its value:

1. Reduced Force Output

One of the biggest criticisms of UST is that it limits your ability to generate maximal force. (19, 25) For example, a squat performed on a Bosu ball engages more stabilizer muscles but significantly reduces your ability to lift heavy weights. Studies show that UST exercises activate stabilizers at the expense of prime movers, like the glutes and quadriceps. This makes UST suboptimal for building maximal strength and hypertrophy.

2. Lower Transfer to Traditional Strength Training

Research indicates that while UST improves balance and stabilizer activation, it has limited carryover to traditional strength training exercises. (9, 19) If your goal is to improve maximal strength or power (e.g., for lifting heavier in a deadlift or sprinting faster), UST should not replace traditional training methods. Strength gains from unstable surface exercises are often modest compared to those achieved with stable, heavy-load training.

3. Potential Risk of Injury

Performing UST excessively or improperly can lead to injury, particularly in the ankles and knees, as these joints are repeatedly subjected to unusual stress during prolonged training. Additionally, due to the unstable nature of UST, risk of falling is increased. Care should be taken to incorporate appropriate rest periods, avoid overloading your joints in novel positions to quickly, and perform these exercises in a safe manner just like any exercise modality or method.

4. Limited Applicability for Some Populations

For individuals looking to maximize strength, power, speed, or aesthetics UST might not offer significant benefits. (9, 19, 24) Powerlifters, Olympic weightlifters, sprinters, and bodybuilders for example, may not find much value in UST since their performance is based on generating maximal force output on stable surfaces. Additionally, these athletes most often already have a good base of stability and control.

5. Overemphasis on Balance vs. Strength

For individuals who are untrained or focus primarily on balance due to the difficulty of it, there is a risk of overemphasizing balance training at the expense of foundational strength. This is especially problematic when UST replaces foundational exercises like squats, deadlifts, or lunges, which are crucial for overall strength development. Additionally, while balance is key for healthy aging, it must be matched with equal amounts of useable strength. A proper training plan should always be implemented.

Practical Applications: Who Can Benefit from Unstable Surface Training?

1. Older Adults

Older adults who are at a higher risk of falling can greatly benefit from UST. Research has shown that balance training, including UST, can reduce fall risk by improving proprioception, coordination, and relative lower body strength. (9, 16) Exercises like standing on a foam pad while performing simple movements (e.g., leg lifts or arm movements) can help maintain independence and reduce the likelihood of falls.

2. Rehabilitation and Physical Therapy

UST is frequently used in rehabilitation programs, particularly for patients recovering from ankle, knee, or lower back injuries. (9, 19) By improving joint stability and neuromuscular control, UST can help prevent future injuries. A typical rehab protocol might include single-leg balance exercises on a wobble board or Bosu ball to strengthen the muscles around the affected joint and improve the proprioceptive feedback available. This may also be beneficial to simply allow exercise in a low stress way to help de-load an injured area for healing purposes before re-integrating loaded exercises.

3. Athletes in Specific Sports

Athletes in sports that require agility, balance, and quick changes of direction, such as basketball, tennis, soccer, or snowboarding, can benefit from UST. (26) By improving proprioception and neuromuscular control, UST helps athletes react more effectively to unpredictable situations on the field or court. Although, this aspect of their training should be minimal in comparison to weight lifting and sport specific drills.

4. General Population

For the average person, UST can add variety to a workout and provide functional fitness benefits if optimal function and balance is a goal. (19) However, it should complement, rather than replace, traditional strength and conditioning exercises.

Best Practices for Incorporating Unstable Surface Training

To maximize the benefits of UST while minimizing its limitations, follow these best practices:

1. Use UST as a Supplement: Incorporate UST as part of a balanced workout routine, but don’t rely on it as the sole form of training. Combine it with traditional strength training and cardiovascular training for maximum results. Use this form of training as part of a warm-up, active rest, cool-down, or just for a fun variety session.

2. Focus on Form: Proper form is critical during UST. Start with basic exercises and only progress to more complex movements when you can maintain decent form and you have a specific reason for it. Proper form in this context means generally stable and showing no excessive losses of position.

3. Don’t Overdo It: UST should be used sparingly, especially when training for strength or hypertrophy. Incorporate UST into your routine 1-2 times per week, or for a short time during warm-ups or cool downs, depending on your goals and fitness level. Of course, if you enjoy unstable balance training you may do it as much as you’d like.

4. Choose the Right Surface: Different unstable surfaces provide varying levels of challenge. Start with softer, more forgiving surfaces like foam pads, and gradually progress to more unstable surfaces like Bosu balls or wobble boards. Compare this to going up in weight on a exercise, you need to start slow to prevent injury.

Progression in Unstable Surface Training

If you want to incorporate UST into a structured workout program, understanding how to progress is key. Progression should be gradual and based on your current fitness level, goals, and experience with balance training.

Phase 1: Mastering Stability on Stable Surfaces
Before progressing to UST, it’s crucial to first master exercises on stable surfaces. For example, a beginner should be able to squat with decent form on a flat, stable floor before attempting to squat on a balance board or Bosu ball. Proper form ensures that you’re targeting the correct muscles and avoiding compensatory movements that could lead to injury.

Phase 2: Introduce Light Instability
Once you’ve mastered basic movements, you can begin introducing light instability. Start with simple balance exercises, such as single-leg stands or lunges on a foam pad or soft surface. Progressively challenge yourself by using more unstable surfaces like a Bosu ball or wobble board.

Phase 3: Incorporate Instability with Load
As you become more proficient, you can begin to add light weights to your unstable surface exercises. For example, performing a single-leg squat while holding dumbbells on a balance board will further challenge your stability. However, it's important not to overload the movement, as heavy weights on unstable surfaces can compromise form and increase injury risk. It is also important to understand the “why” behind the exercise. For most individuals this type of progression is of little real world use beyond a party-trick.

Phase 4: Advanced Dynamic Movements
In this phase, you can begin incorporating advanced, dynamic movements on unstable surfaces. Plyometric exercises, such as lateral hops onto a Bosu ball, or single-leg deadlifts on a wobble board, can be added for athletes looking to improve sports performance. It’s important to ensure that proper form is maintained throughout these movements, as the risk of injury increases with the complexity of the exercises. Again, there should be a specific intent and reason for this level of UST training. The risk of injury dramatically escalates at this level, and the benefits should be weighed against that.

Final Thoughts: Is Unstable Surface Training Right for You?

Unstable surface training is a valuable tool that can improve balance, proprioception, and muscular stability in the right context. It’s particularly useful for older adults, individuals recovering from injury, and athletes looking to improve agility and coordination in specific sports. However, UST should not be seen as a replacement for traditional strength training, and you should always have a reason for the exercise you are doing. Its limitations in terms of force output and muscle activation make it a suboptimal choice for those whose primary goals are strength, power, hypertrophy, or aesthetics. Additionally, the risk of injury at higher levels of difficulty usually is not worth the reward for the average person.

Make sure to check your programs and ensure that UST is not overutilized, while knowing that some form of UST may be beneficial in the warm-up, cool-downs, or as a break from traditional training. If you're interested in functional fitness, injury prevention, or improving balance and coordination, UST can play an important role in your training regimen. But like any tool in fitness, it’s best used in moderation, in combination with other training modalities, and with specific intention for the most well-rounded results.

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