Shoulder rehabilitation often includes Thera-Band® exercises. One popular exercise is the “PNF” diagonal shoulder exercise from the Proprioceptive Neuromuscular Facilitation concept. The PNF diagonal exercise includes tri-planar motion of the shoulder against resistance; the resistance provided can be manual, dumbbell, or elastic band resistance. Few researchers have investigated the EMG activation levels of shoulder muscles during PNF diagonal exercises.
Researchers at the University of Cincinnati in Ohio assessed the activation of scapular muscles in 21 healthy subjects. The subjects performed 4 diagonal patterns (D1 Flexion, D1 Extension, D2 Flexion, and D2 Extension) with both a 3 pound dumbbell and a blue Thera-Band resistance band. For the band exercises, the subjects were seated using a length of band equal to the distance between the floor and their greater trochanter as measured when the subject was standing.
The results showed that both Thera-Band and dumbbell exercises provide similar levels of EMG activity, which is consistent with findings of other researchers who compared EMG levels during isotonic and elastic resistance (Andersen et al. 2010). The serratus anterior, an important scapular stabilizer, remained moderately active in each exercise with no significant difference between exercises (42.5 to 50% of maximal).
When evaluating an exercise for suitability in rehabilitation, it’s important to consider not only the absolute activation but the activation relative to other muscles including agonists and antagonists. The trapezius is prone to muscle imbalance. The upper portion is prone to tightness and the lower portion is prone to weakness according to Janda. Shoulder patients, particularly those with impingement, often exhibit scapular muscle imbalance.
The D2 Flexion pattern had the highest activation levels for the middle and lower trapezius compared to the other patterns; the D1 and D2 flexion patterns also had more upper trapezius activation than their extension movement counterparts. While the Thera-Band resisted D2 Flexion exercise produced higher levels of middle and lower trapezius activation compared to dumbbell resistance, the Thera-Band resistance also produced higher levels of upper trapezius activation compared to the dumbbell.
|Upper Trap||Middle Trap||Lower Trap|
|D2 Flexion Dumbbell||39.6% MVIC||18.4||23.7|
|D2 Flexion Thera-Band||68.5||45.3||44.9|
In contrast to D2 Flexion, the D2 Extension exercise with Thera-Band had the lowest levels of upper trapezius activation. It also had the most desirable ratio of upper to lower trapezius activation (0.9), meaning the lower trapezius was activated at a higher level than the upper trapezius.
As with other surface EMG studies on healthy subjects, these results should be used with caution in patient populations. The authors chose blue Thera-Band resistance, which may not be appropriate in early stages of rehabilitation. It would have been valuable for the authors to report on the eccentric phase of the exercise, or during different phases of the exercise due to the large arc of motion.
The authors concluded that the D2 Flexion pattern with either dumbbell or Thera-Band resistance provides the greatest activation of scapular muscles, and the D2 Extension pattern with Thera-Band provided the best ratio of upper and lower trapezius activation.
REFERENCE: Witt D, Talbott N, Kotowski S. Electromyographic activity of scapular muscles during diagonal patterns using elastic resistance and free weights. Int J Sports Phys Ther. 2011 Dec;6(4):322-32.