The Swiss ball is an unstable training device used to increase the difficulty of various bodyweight and traditional free-weight resistance exercises (3). An English physiotherapist by the name of Mary Quinton is cited as having first started to use Swiss balls with children who had cerebral palsy in 1958 (33). A Swiss therapist then introduced the idea of using these balls to Dr. Susanne Klein Vogelbach, who started using them with her physiotherapy students and clients with orthopedic problems. Dr. Vogelbach later published a book detailing the Swiss ball exercises she developed over her years in clinical and teaching practice (23). Recently, research has investigated the use of Swiss balls during exercise using electromyography to quantify the activity of the various muscle groups involved. Some of the greatest interest in the use of Swiss balls is in the application during body-weight exercises that involve no added external resistance. This is widely accepted as being one of the defining modes for a type of training known as “core stability” exercise. The description of a “core stability” exercise relates to how a movement, usually involving bodyweight only for resistance, provides a training stimulus for the trunk musculature. Although evidence exists regarding the use of the Swiss ball for increasing trunk muscle activity during core stability exercises compared with stable surface movements (27,42), these are commonly static or simple tasks that do not use the ability of the ball to roll (17). Moreover, evidence suggesting that Swiss ball exercises are less effective than conventional resistance exercises for trunk muscle activity only use basic movements such as the quadruped, pelvic thrust, and back extension movements for comparison (32). There is no evidence examining some of the more difficult Swiss ball exercises that are observed in the recreational gymnasium environment. Therefore, we are unsure whether these more complex movements that take advantage of the Swiss ball's design and material properties elicit muscle activity greater than that which has been reported for conventional resistance exercises such as the deadlift or squat.
When surface electromyographic (EMG) recordings are rectified and smoothed, the amplitude has been shown to be positively and linearly related to isometric force output (1,9,14, 25). It has been suggested that EMG activity in excess of 60% of a maximal voluntary isometric contraction (MVIC) is required for strength training, with endurance benefits resulting from exercise intensities below 25% (2,5,43). The highest recorded trunk muscle EMG levels for Swiss ball exercises we currently have information on are generally of a moderate intensity. Abdominal activity of approximately 50% has been measured for Swiss ball curl-ups (42) and for bilateral isometric leg holding (28). Activity of the back extensors while using a Swiss ball ranges between 19.5 and 45.5% (15,32). These intensities may be appropriate for eliciting a strength training effect in novice individuals (37) and possibly an endurance effect if more repetitions are performed by advanced individuals (12). In contrast to the Swiss ball research we are currently aware of, trunk muscle activity during conventional resistance exercises have been shown to be appreciably greater.
Recent evidence has found that resistance exercises performed with moderate intensities (ca. 50% of a 1 repetition maximum) elicit greater trunk muscle activity than performing basic Swiss ball exercises (32). Other research investigating variations of the deadlift technique with moderate load (12 repetition maximum) reported trunk and leg muscle activity in excess of 60% MVIC (18). Although this research clearly suggests that moderately loaded resistance exercises elicit trunk and lower body muscle activity greater than that elicited in the current body of Swiss ball research, advanced Swiss ball exercises have not currently been evaluated.
Therefore, the purpose of this study was to measure normalized muscle activity using surface EMG from abdominal, lumbar, and upper and lower body musculature during supposedly more difficult Swiss ball exercises. This will allow comparison of these exercises to what has been previously measured in the literature for Swiss ball exercises, and comparison to muscle activity levels reported for conventional resistance exercises. The hypothesis of this study is that all of the advanced Swiss ball exercises measured will elicit trunk muscle activity in excess of 60% MVIC and that exercises involving an upper or lower body focus will also elicit muscle activity in those regions commensurate with a strength training effect.
Experimental Approach to the Problem
A within-subject cross-sectional experiment was performed to examine normalized muscle activity using surface EMG during several advanced Swiss ball exercises. No comparison to a stable surface was performed because these exercises could only be performed using a Swiss ball. Subjects participated in 2 sessions. The first was a familiarization session where the subjects were trained in how to perform the specific exercises by an experienced practitioner. Subjects were not provided with a Swiss ball to continue practicing these exercises, and all individuals were asked to refrain from attempting these movements in their personal training sessions. One week later, subjects attended the testing session where 3 repetitions of each exercise were performed while surface EMG was continuously recorded. Before testing, MVICs were performed for each muscle to normalize the measured activity during testing. The order of exercises was randomized among subjects.
A power calculation was performed using the results of a previous study for the difference in triceps EMG between the Swiss ball and a stable surface for a push-up exercise because this most closely resembles one of the starting positions used in this study (28). The calculation of the sample size was carried out with α = 0.05 (5% chance of type I error), 1 − β = 0.80 (power 80%), and a calculated effect size of δ = 1.41. This provided a sample size of n = 14 for this study.
Fourteen healthy, recreationally active subjects volunteered to participate in this study after providing informed written consent (7 men and 7 women, aged 24.1 ± 1.7 years; height 1.74 ± 0.08 m; and weight 72.9 ± 13.1 kg). The University Human Participants Ethics Committee approved all procedures used in this investigation. All subjects had been performing regular physical activity on at least 3 days per week for the last 3 months including both aerobic and resistance training modalities. Although some of these subjects had experience using a Swiss ball for exercise, no subject reported regular training on a Swiss ball or familiarity with any of the exercises tested in this study. No subject reported current or recent participation in a competitive, organized sports competition. Subjects reported that they were not taking performance-enhancing stimulants at the time of testing and had no musculoskeletal injuries or disorders. Subjects were instructed to refrain from any resistance or anaerobic exercise and were required to maintain normal dietary habits in the 24 hours before the testing session. Subjects were required to present to testing in a 2-hour postprandial state.
Electromyographic Measurement and Analysis
After careful skin preparation using disposable razors to remove excess hair, fine sandpaper, and isopropyl alcohol swabs to reduce electrode impedance to below 5 kΩ (measured using a digital multimeter), pairs of Red Dot silver/silver-chloride electrodes (3M, St. Paul, MN, USA) with a 3-cm center-to-center distance were applied to the following muscles on the right hand side of the body only, aligned in a parallel arrangement to the muscle fibers. Rectus abdominis (RA), internal obliques (IO), erector spinae (ES), pectoralis major (PM)-clavicular placement, anterior deltoid (AD), lateral head of triceps brachii (TB), vastus lateralis (VL), and biceps femoris (BF) (13). If the measured impedance was above 5 kΩ, the electrodes were removed, and preparation procedures were performed again. The most common sites that involved additional preparation were the abdominal sites in the male subjects owing to not removing sufficient hair in the first preparation. Crosstalk is an issue to address in surface EMG recordings. To minimize crosstalk, each pair of electrodes was placed according to previous recommendations for ideal anatomical placement (13) to ensure that electrodes were well within the borders of the target muscles. This included measurements to relevant bony landmarks and other prominences to maintain consistency of placement among subjects. The IO site that was inferior and medial to the anterior superior iliac spine has previously been validated for anatomical placement (26).
Electromyographic signals were recorded using a Grass Instruments data acquisition board (Grass-Telefactors, West Warwick, RI, USA; common mode rejection ratio of 90 dB at 60 Hz; input impedance 100 MΩ, −6-dB band pass roll off at 10 and 1,000 Hz) at 2,000 Hz with 16-bit analog to digital conversion into a Pentium IV computer. Data collection and analysis was conducted using LabVIEW (National Instruments Corporation, Austin, TX, USA). All collected signals were subsequently band pass filtered (between 10 and 500 Hz), then rectified and smoothed by using a root mean square (RMS) calculation with a 50-millisecond sliding window (19). The basis of the data analysis from the RMS signal was identification of the greatest average 1-second RMS from each muscle signal collected during each exercise task. This was normalized to the MVIC measured for each muscle before testing.
Procedures used for the MVIC for each muscle have previously been presented (22,28). After familiarization with the technique required, 2 MVICs were performed for each muscle with at least 2 minutes of rest between trials (14). The greatest RMS calculated from either trial was used as the MVIC for the muscle. The MVIC procedures cannot be expected to only elicit activity from the muscle of interest. However, each movement was a prime movement for the target muscle, performed at the midpoint of its length to obtain the greatest amount of recruitment for normalization of exercise intensities.
Six different exercises were studied (Figure 1). However, because the starting point for the Praying Mantis exercise represents a position commonly used for exercise, this was also measured to provide muscle activity recorded in a static hold position as a representation for the type of exercises previously reported in the literature. Therefore, 7 different exercises were analyzed. The same solid surface was used beneath the Swiss ball for all tests. This was a laboratory nonslip surface that allowed the ball to roll but did not slip and potentially be unsafe for testing. For the bridge and hold and crunch exercises, a training mat was used to beneath the participant only. Three trials were collected for each exercise with a 1-minute break between each trial. The normalized RMS for the 3 collected trials was averaged for each subject to provide the muscle activity for each site for each exercise. For all exercises, either a 55- or 65-cm diameter Swiss ball was used depending on the height of each subject. The ball was chosen based on whether an individual could lie prone with their abdomen on the ball with their hands on the ground directly underneath the shoulders and their spine in a relatively neutral position.
Prone Hold and Praying Mantis
The prone hold position was a 4-second isometric contraction performed with the individual supporting themselves on the Swiss ball with their forearms flat on the surface, and their shoulders flexed to 90°. The Praying Mantis exercise was performed separately to the isometric contractions but using the hold as a starting position. For the Praying Mantis exercise, the subject was required to rotate the ball 360° clockwise, then 360° anticlockwise by moving the shoulder girdle only (although adjustments in whole body posture occurred these were not the focus of initiating ball movement). The movement was instructed to be performed at a natural, self-selected speed. The ball was maintained underneath the subject throughout the movement. The position of the hands (linked via fingers) was used to indicate the 0° starting point for the movement, and this was used to guide the individual's eyes for the degree of rotation. One trial represented the full rotation in each direction.
Single Leg Squat
The ball was placed so that the lowest point of contact was just superior to the ES electrodes (L5-S1 location). Individuals were required to slowly lower themselves to 90° of knee flexion, pause for 1 second, then stand back up. The duration of individual trials never exceeded 4 seconds. The contralateral thigh was required to be flexed to 90°, and the shank left free although no ground contact was allowed. Foot position was marked on the floor to ensure consistency between trials. Foot position was based on the individual being able to reach 90° of knee flexion at the bottom of the squat with 90° of hip flexion. Three trials were collected for the right and left leg squats. The greatest activity was always measured for the right leg squat.
Hold and Crunch
Individuals were required to lie on the floor with their legs flexed to 90° and their shoulders flexed to be placed on the floor behind them. The Swiss ball was then placed between their ankle joints. Recording commenced once the ball was placed. The individual was required to hold the ball in place for 1 second, then crunch up with a controlled movement while maintaining full elbow extension but extending their shoulders to take the ball out from between their legs, then slowly return to the starting position with the ball in their hands and legs flexed to 90°. This was one repetition.
Individuals were required to kneel on the floor with the ball directly in front of them and their hands placed on the ball. They were instructed to push the ball away from themselves as far as possible while maintaining contact with the surface. This involves lowering the trunk toward the ground and flexing the shoulder until. The initial movement involved alternating hands pushing the ball out, until both hands were required for the final push to attain the fully extended bridge (pivoting from the knees to allow maximal extension of the body), which was maintained for 1-second. The hands were maintained on the superior aspect of the ball to ensure the subject was able to return to the starting position by extending the shoulder downwards into the surface. This was one trial. No trial exceeded 5 seconds in duration.
Each individual was required to assume a full “roll-out” position with the ventral aspect to the feet only in full contact with the ball and the ankle plantarflexed, with the hands placed on the ground directly beneath the shoulders. The individual was required to extend the hip only. The distance of hip extension was based on limiting any torso rotation (usually pivoting about the leg still on the ball) to aid greater hip displacement. This ensured that only a hip movement was tested. The hip movement was at a self-selected cadence. At the limit of extension each individual attained, an isometric contraction was maintained for 2 seconds, and then the leg was lowered back onto the ball. This was one trial. No trial exceeded 4 seconds in duration. Three repetitions were performed for the right and left legs.
Each individual was required to lie supine on the ball with the thoracic spine supported by the surface and their hands linked by the fingers and placed on the xiphoid notch. This movement involved rotation of the whole body to induce rotation of the ball. To move the ball left, the right side of the trunk is initially rotated into the ball, maintaining a relatively rigid segment. The right leg is then required to be moved in line with the trunk, and then the whole body is rotated into a prone position with the right leg moving underneath the supporting left leg. From this position, the individual was required to rotate back to the starting position by initiating movement of the right side of the body again into the ball. Each trial consisted of moving from supine to prone to supine, then repeating for the opposite side of the body (move the ball right-left side of body initiates movement into the ball). Trials were approximately 6 seconds in duration.
The Statistical Package for the Social Sciences (SPSS Inc, v16.1, Chicago, IL, USA) was used for analysis. Descriptive statistics were calculated for all exercises for each muscle. A one-way analysis of variance (ANOVA) was used to identify differences between exercises for each muscle. Gender was entered as a covariate in the analysis. If the main effect of the ANOVA was significant, repeated contrast statistics and pairwise comparisons were used to identify where the differences were. The level of significance for all data was p ≤ 0.05. Unless otherwise stated, all data are presented as mean ± SD.
Gender was not a significant covariate in the analysis of normalized EMG levels. The average normalized EMG levels for each muscle during the exercise tasks are presented in Tables 1-3.
Abdominal Muscle Activity
Rectus abdominis activity was greatest during the Swiss ball bridge (Table 1; p ≤ 0.01). This was identified at the terminal point of the bridge. The praying mantis, hold and crunch, and roll exercises were not different from each other but had greater activity than the remaining exercises (p ≤ 0.05). Prone holds were different from hip extensions (p ≤ 0.05), which were different from the single leg squats (p ≤ 0.001) that had the lowest RA activity (2.1 ± 2.5%) of all exercises.
Internal oblique activity was greatest during the Swiss ball roll exercise (p ≤ 0.001). Swiss ball bridging, praying mantis, and hip extension IO activity were not different but were greater than the remaining exercises (p ≤ 0.05).
Erector spinae activity was greatest during the Swiss ball roll exercise (p ≤ 0.001). Activities during hip extensions and single leg squats were not different but were significantly greater than the remaining exercises (p ≤ 0.05).
Upper Body Muscle Activity
Pectoralis major activity was greatest during Swiss ball roll, praying mantis, and bridge exercises (Table 2; p ≤ 0.001). Activity during hip extensions was different from the remaining exercises only (p ≤ 0.001).
Anterior deltoid activity was greatest during Swiss ball roll and hip extension exercises (p ≤ 0.001). Activity during the praying mantis was different from the remaining exercises only (p ≤ 0.001).
Triceps brachii activity was greatest during the Swiss ball roll exercise (p ≤ 0.001). Activity during praying mantis and bridge exercises was different from the remaining exercises (p ≤ 0.001). Activity during hip extensions and the prone hold was greater than during the hold and crunch and single leg squat (p ≤ 0.001).
Lower Body Muscle Activity
Vastus lateralis and BF activities were greatest during the Swiss ball roll (Table 3; p ≤ 0.001). The high level of activity is associated with the right leg being the primary support point with a stable contact when the left side of the body is being rotated. For VL, activity during the hip extension, praying mantis, and single leg squat was greater than during the remaining exercises only (p ≤ 0.001).
For BF, activity during hip extension was greater than during the remaining exercises (p ≤ 0.001). This activity was measured in the test leg that was held in isometric extension. Biceps femoris activity during the praying mantis was different from the remaining exercises (p ≤ 0.01).
This study has measured the activity of upper body, abdominal and lower body muscles during several more advanced Swiss ball exercises. It is important to note that no falls or injuries were sustained during testing despite the difficult nature of the exercises. This is probably owing to the use of a familiarization session before testing. The speed roll exercise was an especially difficult exercise to learn and perform owing to the combined rotation of the body and ball. It is important to note that these were recreationally active participants who had a good level of physical fitness and strength. Owing to the complicated nature of these exercises, caution should be taken when prescribing these movements for the untrained population.
A further consideration for the results of this study is that the EMG for each exercise was analyzed from the greatest 1-second average activity during each trial. This may have been during dynamic or isometric contractions for the different exercises. This activity was then normalized to MVICs, as is the standard procedure used in all studies examining muscle activity during core stability exercises (6,7,14-17,21,27,28,42). This may have introduced an overestimation of the activity of some exercises where significant concentric actions are involved. It is expected that the greatest EMG will be measured during the concentric phase compared with isometric or eccentric actions (14). Some exercises, such as the praying mantis and roll, cannot incorporate a focused isometric component. It is important to note that some of the highest EMG levels measured in this study (VL during the roll and RA during the bridge) were measured during relatively isometric contractions. Despite the possibility that relative activity levels are overestimated, we believe that the measured patterns of activity accurately represent the difficulty of each exercise.
Another consideration, which is normal for any EMG study, is the considerably large SDs of the data. This suggests that in the prescription of these exercises, some individuals may find that they are more or less difficult than the average activity indicated here. Finally, core stability of the spine is a complex issue defined as combining the musculature, the passive skeletal structures, and the central nervous system as the control unit (34,35). This study presents the acute muscle activity levels in an isolated session only. Therefore, individuals should not assume what the effects of performing the type of exercise measured in this study may be on maladaptive core muscle recruitment patterns, or strength and endurance characteristics, until appropriate training studies are performed.
We have found limited support for our experimental hypotheses that all the advanced Swiss ball exercises tested here would elicit muscle activity levels commensurate with recommendations for a strength training effect. The majority of exercises studied do not differ appreciably to the intensity levels described for Swiss ball exercises in previous literature, which are of a low to moderate level. Furthermore, there was little evidence presented in this study to suggest that advanced Swiss ball exercises can elicit greater trunk, upper body, or lower body muscle activity levels than moderately loaded conventional resistance exercises such as the bench press, squat, and deadlift (11,18,20,32). The Swiss ball roll movement clearly stands out as a significantly difficult exercise with potential to elicit strength training effects. Activity levels of 83.6 ± 44.2% for VL and 72.5 ± 33.4% for TB indicate that this exercise is at an appropriate intensity for these muscles, which may elicit strength effects in advanced trainers (36,37). The highest recorded erector spinae activity (54.3 ± 28.7%) was also measured during the roll exercise. Remaining upper, lower, and abdominal muscle activity during the roll exercise ranged from 30 to 55%. This indicates that for most individuals, a higher number of repetitions of the Swiss ball roll exercise might be able to elicit endurance adaptations (12), whereas for some untrained individuals, this exercise may be appropriate as a strength training stimulus for multiple muscles. Resistance exercises stressing multiple muscle groups have been shown to elicit the greatest acute metabolic response (8,38,41). Increased metabolic demand is an important factor for the adaptations in muscle associated with strength and endurance. Therefore, the Swiss ball roll appears to be the most likely exercise from the current study to apply and investigate in clinical and research contexts for significant muscular adaptation.
It is surprising given the widespread advocacy of Swiss ball exercises as providing a significant abdominal stimulus that apart from the bridge none of these advanced exercises had levels of activity where one could reasonably justify prescribing them for a trunk or “core” strengthening program. The Swiss ball bridge had RA activity at an approximate level for strength training in untrained individuals and possibly some more advanced trainers (61.3 ± 28.5%). The results from this study are commensurate with those of previous research, which is yet to identify any Swiss ball exercise as being able to elicit trunk muscle activity in the range of a strength training stimulus (15,17,24,27,28,32). Although there are probably more difficult Swiss ball exercises that could be performed to elicit higher trunk muscle activity levels, the complexity of the movements begins to make this exercise modality unfeasible for the majority of individuals, especially when greater trunk muscle activity levels can be achieved using relatively basic, moderately loaded resistance exercises such as the squat and deadlift. Support for basic resistance exercise movements eliciting high levels of trunk muscle activity has also been provided with recent evidence showing that maximal isometric shoulder movements, such as bilateral shoulder extension, elicit trunk muscle activity levels greater than performing maximal isolated trunk exertions (40). The Swiss ball roll, although obviously providing the highest overall muscle activity for the body, was the most complicated movement to teach. Although no acute accidents happened during testing, the likelihood of an incident occurring with the use of an unstable Swiss ball during complex whole-body exercises, or an injury from prolonged exposure to this type of difficult movement, cannot be discounted. This raises the issue for the practicality of prescribing Swiss ball exercises, when the majority of research is providing a case against its use as a beneficial training surface.
Recent intervention studies have not found significant positive evidence to recommend use of the Swiss ball over other modalities of exercise. Stanton recently found that a 6-week Swiss ball training program did not significantly improve running fitness, economy, or posture, compared with previous research the author cited using conventional resistance training, which positively influences these variables (39). A study that randomized individuals with chronic low back pain to either supervised Swiss ball exercise or an unsupervised control exercise advice group (no Swiss ball exercise) found no difference between interventions for changes in primary disability and pain outcome measures at the long-term follow-up (30,31). Other research has investigated the Swiss ball as a support surface during resistance exercises and shown little practical use. Some research has found reductions in maximal isometric force output using a Swiss ball as a support surface (4,10), whereas other research has found no changes in prime mover muscle activity during the bench press (20,29). In conclusion, this study has provided little evidence to support the hypothesis that advanced Swiss ball exercises can elicit muscle activity commensurate with recommendations for strength training.
This is the first study we know of to measure muscle activity during more advanced Swiss ball exercises that are observed in the recreational training environment. If the goal of strength and conditioning coaches is to increase the strength of the upper body, lower body, or trunk musculature, it seems that advanced Swiss ball exercises will be no more beneficial than moderately loaded resistance exercises. Moreover, the only Swiss ball exercise to achieve a high level of muscle activity was the most complicated movement to perform. When compared with relatively basic to teach and perform resistance exercises such as shoulder extensions, squats, and deadlifts, the use of a Swiss ball seems redundant. Additionally, the benefit of conventional resistance training is that increasing the external load will increase the activity of muscle groups of interest, while allowing for periodization and progression of the training dose over time, whereas a Swiss ball based program appears to require more complex and difficult movements for ongoing progression. Advanced Swiss ball exercises should be considered a novelty movement that could be introduced in small amounts to alleviate staleness with long-term training. Coaches should be advised to learn, and then prescribe, large conventional multijoint exercises for the greater benefits they provide rather than use complicated circus like movements on a Swiss ball. It must be considered that the practical difficulty and potential risks involved with performing an advanced Swiss ball exercise, such as the roll in this study, or standing on a Swiss ball with weights as observed in some recreational trainers, probably outweigh any benefits.
The authors have no professional relationships with any company or manufacturer who may benefit from the results of the current study. The results of the current study do not constitute endorsement of the product used by the authors or the National Strength & Conditioning Association.
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