Raphael Brandon draws on new research to reach his verdict.
In the last 10 years large inflatable plastic balls variously known as Swiss balls, gym balls or stability balls have become de rigueur gym equipment. Ranks of them line the back walls of class studios, a couple always lurk in the abs and stretch area and, increasingly, they are kept in the free weights room. They will also be found in most physiotherapy clinics. But can they justify their popularity in terms of effectiveness? Some recent sports science research goes some way towards helping us resolve the issue of whether Swiss balls are beneficial or simply fashionable.
Fitness trainer Paul J Goodman(1) argues that Swiss ball-based exercises are the key to effective improvements in trunk strength. As actions per-formed on the ball involve greater stimulation of the ‘neuromuscular system’, users develop better balance, coordination and proprioception, Goodman says.
These assertions are not backed up by any research references – rather, they come from Goodman’s experience working with clients using Swiss balls. (The article is in fact a useful reference tool, with many illustrated exercises targeting the trunk muscles.)
Evidence to support the efficacy of Swiss ball exercises comes in a piece of research from a Canadian laboratory. Kathryn Clark and her research team at the School of Health and Human Performance of Dalhousie University compared the electromyographic (EMG) activity of the rectus abdominis muscle during various abdominal exercises(2).
EMG gives an indication (through the level of electrical activity) of the degree of muscle activity going on. High levels of EMG are associated with high forces and a greater number of muscle fibres being recruited.
Clark’s team analysed the curl-up (floor), Swiss ball curl-up, reverse curl, ab roller curl-up, Swiss ball roll-out to bridge and supine leg lowering exercises. The average level of EMG activity for three repetitions of each exercise was calculated as a percentage of each subject’s maximum level of EMG activity (which varies from one subject to another).
The max EMG for the rectus abdominis muscle was determined by the subject performing a maximal voluntary contraction during the ab crunch movement against an immovable resistance provided by a trainer pushing down the shoulders.
The researchers found that the Swiss ball curl-up resulted in the highest EMG score out of all the ab exercises, at about 90% of max EMG. The score was significantly higher; for instance the ab curl on the floor elicited an EMG recording of about 70% of max EMG.
Clark’s findings are supported by those of another Canadian researcher, Stuart McGill. His team also looked at the EMG activity of the Swiss ball ab curl versus the ab curl on the floor. McGill reports(3) that the EMG activity of rectus abdominis and obliques are greater when the ab curl is performed on the Swiss ball.
Thumbs up for the Swiss ball so far.
Another piece of research looked at the Swiss ball from a different angle. David Behm and team, from the Memorial University of Newfound-land, analysed changes in the muscle force and activation of the limbs when an exercise is performed under stable (on a bench) or unstable (on a Swiss ball) conditions(4).
They examined muscle force and EMG of the quadriceps during leg extension and calf during plantar-flexion performed in stable and unstable modes, also noting the EMG of the antagonist (opposite) muscles: the hamstring and dorsiflexors.
This produced some unexpected results. As you might expect the leg extension and plantar-flexion forces were greater where the subject was stable, seated on the bench rather than on the Swiss ball. However, while the quadriceps and calf EMG was lower during the unstable movement, the EMG of the antagonist muscles (hamstring and dorsiflexors) increased.
This suggests that agonist (prime-mover) muscle activity is inhibited during unstable exercise, with in-creased antagonist activity. So Swiss balls are not going to be the best way of developing prime-mover muscle strength.
Behm et al did not measure the effect of the different training surfaces on core muscle EMG, but the likelihood is that it would have increased significantly on the unstable surface, because the instability has the effect of spreading the forces over a greater number of joints and placing more stress on active stabilising muscles, thereby limiting the force directed through the prime movers.
In simple terms, the Swiss ball changes the task from pure leg extension to leg extension while controlling the body. It turns the movement into a stability/proprioception exercise rather than a limb-strengthening exercise.
So this research does not support the use of Swiss ball for strength exercises of the leg muscles. Yet it does indirectly support Swiss ball exercises for use in core stability programmes.
Together, these recent research findings will lend encouragement to devotees of Swiss ball training and the growing number of trainers and therapists who prescribe ball-based exercises most of the time for all muscle groups, in the belief that this will increase core stability and ‘make the exercise more functional’.
I routinely see athletes and gym users performing many exercises on balls, including core strength, a range of dumbbell upper-body exercises such as bench press, and squatting movements. Before we leap in and endorse such an approach, a few questions and observations are in order.
A: To answer this, look not at the theory, but at what happens in practice. Just because a research article suggests an increased core-training effect can be gained does not mean that your average gym user or rehab patient will be able to reap those benefits. This is because it is the quality of the individual’s technique, not the equipment they are using, that overwhelmingly determines how effective the exercise is.
Let’s take the Swiss ball ab curl, which the researchers have proved to have a superior training effect. Most of the times I have seen this exercise performed on a Swiss ball, the exerciser does not have sufficiently good technique to be gaining any significant benefit.
What normally occurs is that the exerciser simply pivots their low back around the curvature of the ball, levers their shoulders up and probably uses their hip flexors to help pull their trunk up. This lever action significantly reduces the load on the abdominals and obliques.
No one has taught them to fix their pelvis using the gluteals, so that the pelvis holds fast as the shoulders curl up off the ball. Unless your patients or clients have this level of technique (which implies that they already have some core strength), they will be better off performing the exercise on the floor.
Swiss ball ‘roll-ups’ – as I call the bad-technique version – are easy and anyone can do many repetitions without any benefit. Swiss ball curl-ups – fixing the pelvis with strict technique – are tough, and sets of 10 reps will be challenging for most people.
Using the Swiss ball, then, is no guarantee of increased training success. Balls change exercises, usually making them more advanced, and superior strength and technique are required to perform the modified exercises effectively. Instructors should always put technique and correct muscle recruitment ahead of any ‘favoured’ piece of equipment.
If a patient or client cannot use the targeted muscle groups effectively or control the unstable surface adequately, then the exercise will not have the desired effect and the instructor should find an alternative. This brings us nicely to the next issue…
A: If Swiss ball curl-ups (with good technique) are very effective at challenging the abdom-inals, McGill’s research alerts us to increased levels of trunk muscle co-contraction, which is associated with increased spinal loading. This is important for anyone involved in rehab work: you will need to balance the aim of effective strengthening and increased stability against the need to avoid stress on the healing structures.
McGill also challenges an-other contemporary instability fashion, for prescribing Swiss balls or air cushions as suitable sitting surfaces in the office (Swiss ball plus frame is sup-posed to replace your office chair). The rationale is to help the individual strengthen their trunk muscles during daily activity and keep their spine mobile through-out the day.
McGill’s research shows that spinal loads are greater on unstable surfaces than sitting on a chair. He would not recommend this for patients.
He states: ‘There is a time and place for labile surfaces’, referring to their use for advanced training only.
A: Exercisers seem to perform traditional strength exercises, often using free weights, on balls in the belief that this will make the actions somehow more ‘functional’ or help them further improve their core stability. Yet as we have seen above, the Behm study found that the specific strength training effect using Swiss balls is reduced as exercise stresses are dissipated throughout the body. The amount of weight lifted in a shoulder press exercise on a Swiss ball is significantly less than on a bench.
Multi-joint, closed-chain exercises using free weights already possess a great deal of ‘functionality’ and have a proven cross-over into athletic performance and injury rehab. The dumbbell bench press, for instance, requi-res coordination of shoulder and elbow and stability from the trunk even when performed on the bench.
When the exercise is transferred to a lying position on the ball, the reality is that the leg muscles are quite active and provide much of the stabilising function to control the moving ball under the spine as the dumbbells are pressed up and down. This is because the legs are the natural anchors when lying on your back on a ball.
Overall, then, I would argue that it is more efficient to lift heavier weights and gain the full strength benefit with traditional (and stable) leg and arm exercises, and then complement them with specific exercises for the trunk muscles which are guaranteed to target the core.
More research is needed to establish the full range of benefits and limitations of using Swiss balls, but in the absence of scientific support, you would do well not to assume that anything done on a ball adds value to your training regime. Some of it may do (if you are already advanced enough in your fitness and technique to cope with it); other exercises will do you little or no good and if you have a low back injury you may be impeding the healing process.
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