Canadian researchers Anderson and Behm have shown that instability training can provide similar muscle activation levels at lower resistance levels compared to training on stable surfaces. Unfortunately, however, unstable surface training also results in a decrease force output of prime movers.
California State University researchers set out to evaluate the electromyographic (EMG) activity of prime movers and core stabilizers during a seated overhead press exercise. 30 healthy, resistance-trained subjects performed an overhead press with dumbbells and barbells while sitting on a stable surface and on an exercise ball. The investigators were interested in looking for differences in EMG levels between the stable load (barbell) and unstable load (dumbbell), on both stable (bench) and unstable surfaces (exercise ball).  Subjects used a 10RM resistance (maximum amount of weight lifted for 10 repetitions) for each of the 4 conditions; thus, each condition had a slightly different absolute load.

As expected, the loads used in each condition decreased with decreasing stability. Most resistance was used with the barbell on the bench (stable load on stable surface), followed by the barbell on the exercise ball (stable on unstable), utilizing 89% of the stable on stable condition. The dumbbell on bench (unstable on stable) utilized 86%, while the dumbbell on the ball (unstable on unstable) used 79% of the stable conditions. The researchers suggested that exercising on unstable surfaces reduces force output approximately 15%.

The upper extremity muscle EMG also decreased as the stability decreased, while the erector spinae muscles had great activation on the exercise ball compared to the stable bench. Interestingly, exercises performed on a stable surface required more abdominal activation, indicating that the abdominals require greater activation with greater loads during an overhead lift.

The authors concluded that exercise balls should not be used during the overhead press exercise when the goal is to increase muscle activation of the arms or abdominals, even with reduced loads. However, performing barbell overhead press on an exercise ball does result in increased activation of the low back muscles.

These results are relatively consistent with other studies that suggest unstable surfaces such as exercise balls should not be used to increase strength of extremities using traditional resistance training exercises. While other studies have shown increased activation of the abdominals with resistance training, these authors did not evaluate the seated overhead press exercise; therefore, preferential activation of certain core muscles may be specific to the exercise performed on the exercise ball.  The Thera-Band exercise ball remains a valuable tool for stabilization training, although its role in core strengthening during traditional resistance exercise remains questionable.

REFERENCE: Kohler JM, Flanagan SP, Whiting WC. Muscle activation patterns while lifting stable and unstable loads on stable and unstable surfaces. J Strength Cond Res. 2010 Feb;24(2):313-21.

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The exercise ball consistently had significantly more rectus activation than the curl-up on the floor. The chart below provides the percent of maximal contraction (MVIC) of each portion of the abdominals during each exercise:

The study also found that the jack knife was the best exercise for lower abdominal activation compared to all other exercises. This may help clinicians choose an exercise that specifically targets one portion of the abdominals over another. However, some researchers suggest that isolating one muscle may not be beneficial for core stabilization, instead focusing on quick and strong activation of all abdominals simultaneously for lumbar stabilization. Therefore, the exercise ball should be considered an unstable surface used to elicit unconscious activation of muscle through the sensorimotor system, rather than a tool to simply increase voluntary muscle activity.

In summary, this study demonstrated significantly more activation of the abdominals using an exercise ball compared to a curl-up performed on the floor. Clinicians may use a Thera-Band® Exercise Ball for selective activation of the abdominal muscles, but should consider it as an unstable surface tool for neuromuscular training as well. 

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Duncan M. Muscle activity of the upper and lower rectus abdominis during exercises performed on and off a Swiss ball. J Bodyw Mov Ther. 2009 Oct;13(4):364-7.

Fall prevention exercise programs

Physical therapist researchers at Cal State University Northridge performed a study to determine the effectiveness of a balance exercise training program on strength, balance, gait, and fall risk in 23 healthy community-dwelling older adults at risk for falls. Subjects were randomly assigned to an exercise group or non-exercising control group. The exercise group performed a small group-based balance program, “A Matter of Balance” for 12 weeks, three times a week in a class setting at the PT department.

According to the authors, the exercises included balance exercises standing on foam surfaces and balance boards, as well as squats with an exercise ball. Interestingly, there was no resistive strengthening component in their description of the exercise program, although the original “A Matter of Balance” program developed at Boston University  did use Thera-Band® resistive bands.

After the training program, the exercise group significantly improved lower extremity strength, improved their balance and functional mobility, and reduced their incidence of falls compared to the control group. The results of this program are promising, but more research is needed on larger sample sizes, as well as a cost-benefit analysis.

Simple balance training devices such as Thera-Band® Stability Trainers, balance boards, and exercise balls can be helpful at reducing falls and improving function in older adults.

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 Beling J, Roller M. Multifactorial intervention with balance training as a core component among fall-prone older adults. J Geriatr Phys Ther. 2009;32(3):125-33.

Core training

Few studies have investigated the effects of core training on functional performance. Athletic training researchers investigated the effects of a shoulder training program with and without core stability exercises. 19 baseball players were randomly assigned to an open and closed-chain exercise program, or the same program with additional core training. 15 healthy age-matched non athletes were used as a quasi-control group. Each subject was tested for throwing accuracy, core stability, and proprioception before and after the 6-week program.

Both groups performed a shoulder training program that included free weights, closed-chain balance board, step-up, and exercise ball exercises, as well as plyometric ball tosses. The core training group also performed stabilization exercises such as the dead bug, sit-up, bridge, wall slides, and sitting on an exercise ball.

After the training program, both groups improved in function, stability and proprioception. The addition of core stability exercises did not result in significantly different outcomes. It’s possible that the core stability program may not have been functionally challenging to the core. Relatively static exercises were used in the core training program, rather than sports specific training.

 Thera-Band® products such as exercise balls, soft weights, and balance boards can be used successfully in a baseball training program to improve throwing accuracy.

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Lust KR, et al. The effects of 6-week training programs on throwing accuracy, proprioception, and core endurance in baseball.J Sport Rehabil. 2009 Aug;18(3):407-26.

Anterior cruciate ligament (ACL) tears

Initially, Dr. Herman published a study concluding that while the protocol was effective at improving strength, the biomechanics of the athletes remained unchanged. He concluded that strengthening alone was not sufficient, and set out to find what needed to be combined with the training program. His subsequent study combined the Thera-Band strengthening protocol with video-assisted feedback, and he compared the combined intervention to a group receiving feedback only. Dr. Herman and his colleagues found that the group receiving both feedback and strengthening improved their biomechanics more than the feedback-only group. The paper won the 2008 O’Donoghue award from the American Orthopedic Society for Sports Medicine, given to the best overall paper that deals with clinical based research or human in-vivo research. While the Thera-Band training protocol combined with video feedback improves lower extremity strength and biomechanics in female athletes, research must determine if the protocol is effective at actually reducing ACL injuries.

Herman DC, et al. 2009. The effects of strength training on the lower extremity biomechanics of female recreational athletes during a stop-jump task. Am J Sports Med. 37(7):1301-1308.

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