Instability Training

Hello everyone,

digging through my archives I found this paper that I wrote during my undergrad. I thought I'd share it with you all. If you think it's absolute garbage let me know - I'm fine with that. I wrote this when I was but a wee lad of 20.


Instability exercises as a means of training has become extremely popular in the media. Infomercials attesting the benefits of swiss balls, wobble boards, and other such equipment are common. One may be left to wonder how effective instability training actually is. Many studies show the effectiveness of using swiss balls or other such devices as a training modality, however can one achieve the same benefits from classic weight training? This paper will investigate the use of unstable platforms as a means of training and whether one actually needs to include it in their work out routine.

Personal trainer monitoring a client's movement during a fitball exercise
Behm, Hamlyn, and Young (2007) completed a study in which they compared trunk muscle activation during dynamic weight-training exercises to isometric instability exercises. Electromyograph (EMG) signals were recorded from the lower abdominals, external obliques, upper lumbar erector spinae, and the lower lumbar erector spinae. Subjects were to perform a squat and deadlift at 80% of 1 repetition maximum (RM), a squat and deadlift using lone body weight as resistance, and a side-bridge and superman exercise on a swiss ball. They found that the 80% 1 RM exercises elicited the greatest EMG activity in the lumbar-sacral erector spinae and upper lumbar erector spinae. They also found that no one exercise showed a significant difference in the external oblique and lower abdominal EMG activity. From their findings it was concluded that a moderately high intensity resistance, when performing dynamic exercises, can provide grater muscle activation than similar instability exercises and that it may be unnecessary to include instability exercises to a training program.

Supporting Behm et al. is Cavill et al. (2008). In this study the activation of trunk muscles during stability ball and free weight exercises were compared. Using the same stable exercises as Behm et al. (squat and deadlift) and comparing the muscle activation to three stability ball exercises (quadruped, pelvic thrust, and ball back extension) it was found that there was no significant difference in rectus abdominis and exertnal obliques between either type of exercise. It was also found that EMG activity of the back extensor muscles was greater during deadlifts and squats at all intensities when compared to stability ball exercises. They concluded that exercises performed on the stability ball were of too low an intensity to significantly increase core strength.

In 2005 a study by Marshall and Murphy was done on the difference between core stability exercises performed on and off a swiss ball. In their study eight subjects were to participate in four exercise protocols on a swiss ball and off a swiss ball – upper-body roll out, inclined press-up, contra-lateral single-leg hold, and a quadruped exercise. EMG activity was recorded from the rectus abdominis, exertnal obliques, the transversus abdominus and the internal obljques (TA-IO), and the erector spinae. Their results showed that EMG activity was significantly increased for the rectus abdominis and TA-IO at the top of the press-up when performed on a swiss ball instead of a stable bench. The rectus abdominis showed significantly higher activity when performing a single leg hold and at the top of the press-up on a swiss ball. Finally, the erector spinae showed increased activity with the left arm and right leg raised during the quadruped exercise.

This study somewhat contradicts the Behm and associates study in that it shows greater muscle activation when exercises are performed on a unstable platform. Also, these types of exercises may be more practical than moderately high intensity resistance training since they require a single piece of equipment (swiss ball) and a lowering intensity.

Grenier, McGill, and Vera-Garcia (2000) also found conflicting evidence to the 2007 Behm et al. study. They tested healthy men, with no history of low back pain, performing curl-ups using four different exercises – curl-up on stable bench, curl-up with upper body on swiss ball and feet on floor, curl up with upper body on swiss ball and feet on bench, and curl up with upper body on wobble board. EMG signals were recording from the upper and lower rectus abdominis as well as the external and internal oblique muscle on the left and right side of the body. It was found that curl-ups performed on a stable bench resulted in the lowest EMG activity whereas curl-ups performed with an instability device supporting the upper body resulted in nearly doubled the EMG activity. Results showed the greatest increase in the rectus abdominis muscle (upper and lower).

While the Gernier et al. and the Marshall studies do not compare the use of an instability device to resistance training they do show that muscle activity is greatly increased, especially in the rectus abdominis, and TA-IO when performing exercises with a unstable surface. This is significant because Behm et al. found that no one exercise increased muscle activity in the lower abdominals whereas these studies showed increased activity in the rectus abdominis and TA-IO, which extend into the lower abdominals.

A study in which weight bearing activity, as opposed to callisthenic exercise, showed increased muscle activity during a swiss ball bench press (Marshall, P and Murphy, A., 2006). In this study EMG activity was recording from anterior deltoid, biceps brachii, triceps brachii, pectoralis major, rectus abdominis, and the TA-IO. A dumbbell bench-press was performed on both a stable base and with the upper body supported by a swiss ball. The results showed that muscle activation was greater for all muscles when the exercise was performed on the swiss ball and that activation was also higher during the eccentric phase of the press.

This study is very significant because it compares a weight bearing activity performed on both a stable and unstable supporting surface. Behm et al. compared weight-bearing activity to callisthenic exercise. Since these exercises are inherently different one would expect there to be greater EMG activity in an exercise in which the muscle must produce force to lift a weight. The 2006 Marshall and Murphy study proves that weight training in combination with a unstable supporting surface yield greater muscle activity and therefore will be more beneficial then weight-training or instability training alone.

In choosing a work out routine one must be cognizant of the available exercise modalities available to them and what will best suit their needs. While it is true that resistance training is effective in core strengthening (activation of muscles in the trunk) it is not the only way to target those muscles. It has also been shown that callisthenic exercises performed on an unstable surface can provide greater muscle activation then the same exercise performed on a stable surface (Grenier, McGill, and Vera-Garcia), but not to the same extent as deadlifts or squats performed at a moderately high intensity (Behm D.G., Hamlyn N., and Young W.B.). The most effective protocol appears to be the combination of a weight-bearing exercise and instability ((Marshall, P and Murphy, A.)


Behm, D., Hamlyn, N., & Young, W. (2007). Trunck muscle activation during dynamic weight-training exercises and isometric instability activities. Journal of Strength and Conditioning Research, 21 (4), 1108-1112.

Cavill, M. J., Cormie, P., McBride, J. M., McCaulley, G. O., & Nuzzo, J. L. (2008). Trunk muscle activity during stability ball and free weight exercises. Journal of Strength and Conditioning Research, 22 (1), 95-102.

Grenier, S. G., McGill, S. M., & Vera-Garcia, F. (2000). Abdominal muscle response during curl-ups on both stable and labile surfaces. Physical Therapy, 80 (6), 569.

Marshall, P., & Murphy, B. (2006). Changes in muscle activity and percieved exertion during exercises performed on a swiss ball. Applied Physiology, Nutrition & Metabolism, 32, 376-383.

Marshall, P., & Murphy, B. (2005). Core stability exercises on and off a swiss ball. Arch Physo Med Rehabil, 86, 242-249.

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