Alterations in neuromuscular control are thought to contribute to shoulder impingement. Specifically, this alteration in muscle timing is perpetuated by a muscular imbalance between the muscles which stabilize the shoulder and assist in overhead motion.
Recently, rehabilitation focusing on improving the muscular imbalance demonstrates better results than purely strengthening.
Unfortunately, the reliability of testing neuromuscular control is limited. The ability to detect change within a session is necessary to determine whether the change in measures of scapular neuromuscular control improve over time.
“The purpose of this study is to characterize the reproducibility of scapular muscle activity during a resisted bilateral overhead lifting task, determine the stability of these measures over time, and establish the absolute error with the standard error of the measure (SEM) and minimal detectable change (MDC).”
What was done
Sixteen volunteers without shoulder pain were recruited. These volunteers underwent two testing sessions of 10 repetitions of bilateral humeral elevation holding either 3 or 5-pound weights. The amount of weight corresponded with the weight of the volunteer. The volunteers raised their arms with thumbs facing upwards and elbow extended. At each session, 16-channel electromyography (EMG) was used to record muscle activity. The EMG electrodes were placed over the upper and lower portion of the trapezius, serratus anterior and anterior deltoid muscles.
The intraclass correlation coefficient (ICC) for the absolute mean scapular and anterior deltoid muscle activity during both phases of elevation was very good, 0.95 – 0.99. Intra- session MDC values were between 42 and 219 millivolts (mV) in all muscles. Inter-session reliability of absolute mean EMG activity during both phases of the lifting task in the serratus anterior was very good, 0.89 – 0.90, good for the upper trapezius (0.70) and lower trapezius (0.62 – 0.74), and good to very good for the anterior deltoid (0.78 – 0.85).
To track improvement, using reliable methods are essential. This study suggests surface EMG is reproducible. The small MDC indicates approximately a 3% or 46 mV change indicates true changes.
Improving scapular control and muscle timing is essential for any shoulder rehabilitation program. Unfortunately, surface EMG is not currently common in a rehabilitation setting, making this study difficult to transfer to rehabilitation specialist and swim teams.
- Seitz AL, Uhl TL.Reliability and minimal detectable change in scapulothoracic
neuromuscular activity. J Electromyogr Kinesiol. 2012 Jun 8. [Epub ahead of print]