Research Summary

Academy Title:Andersen2010
Research Article: Muscle activation and perceived loading during rehabilitation exercises: comparison of dumbbells and elastic resistance
The debate of elastic resistance versus isotonic resistance

Elastic resistance is commonly used in rehabilitation exercises, and has been shown to increase strength and function in over 100 randomized controlled trials (www.thera-bandacademy.com). Even with this amount of clinical evidence, elastic resistance is sometimes criticized because of the difficulty in quantifying intensity. Despite the fact that force elongation charts are available to quantify elastic resistance intensity, it is sometimes difficult to use these clinically. Because of this limitation, few studies have compared elastic and isotonic resistance directly because of the intensity-dosing issue.

Quantifying EMG and RPE of elastic and isotonic resistance

Researchers in Denmark compared elastic and isotonic dumbbell resistances for muscle activation and perceived exertion levels. Healthy females performed 3 different exercises with standard dumbbells ranging from 2 to 7.5 kg, and Thera-Band elastic tubing (red, green, blue, black and silver). The researchers developed a chart comparing isotonic and Thera-Band elastic resistance stretched 125 to 150%.

Red 2 kg
Green 3 kg
Blue 4 kg
Black 5 kg
Silver 7.5 kg

Each subject randomly performed 3 exercises with both types of resistance: standing lateral raise, shoulder external rotation at 0° of abduction, and seated wrist extension. The elastic tubing was stretched 125-150% during each exercise. Electromyographic (EMG) activity of neck, shoulder and forearm muscles was assessed during each exercise along with perceived loading using a Borg CR10 scale for rating of perceived exertion (RPE).

The investigators found no significant difference in muscle activation between isotonic and elastic resistance, noting increasing levels of muscle activation with increasing levels of resistance. Interestingly, the researchers noted approximately a 10% increase in EMG activity between resistance levels in both conditions. In addition, the researchers found that perceived exertion was correlated with resistance level and EMG with both types of resistance. This means that clinicians might be able to use RPE to dose resistance at approximate EMG levels; however, this relationship needs to be validated in patient populations as well.

Elastics and isotonics exhibit similar biomechanics

These results are not surprising in light of the biomechanical and clinical data suggesting that elastic resistance is similar to isotonic resistance. Both types of resistance produce similar ‘bell-shaped’ strength curves (Hughes et al. 1999). Recently, researchers in Spain reported that elastic and isotonic resistance produce the same increases in strength and muscle mass (Colado et al. 2008). They also found that the OMNI RPE scale can be used effectively to dose elastic resistance exercise; therefore it seems that both the Borg CR10 and OMNI scales can be used effectively with Thera-Band elastic resistance.

Lead researcher Lars Andersen PhD and his colleagues concluded, “Comparable levels of muscle activation were obtained during resistance exercises with dumbbells and elastic tubing, indicating that therapists can choose either type in clinical practice.”

REFERENCE: Andersen LL, Andersen C, Mortensen OS, Poulsen OM, Bjornlund IBT, Zebis MK. Muscle activation and perceived loading during rehabilitation exercises: comparison of dumbbells and elastic resistance. Physical Therapy. Published online February 4, 2010.

Disclaimer: The Thera-Band Academy provided elastic tubing for this study and did not provide monetary funding.

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