1. Activation of Serratus Anterior
during Horizontal Abduction
Park KM, Cynn HS, Yi CH, Kwon OY. Effect of isometric
horizontal abduction on pectoralis major and
serratus anterior EMG activity during three exercises
in subjects with scapular winging. J Electromyogr
Kinesiol. 2013 Apr;23(2):462-8.

2. Why
A high ratio of the upper trapezius to serratus anterior was proposed as a contributing factor
in abnormal scapular motion (Ludewig and Cook, 2000 and Sharmann, 2001).
Also, other previous investigators have reported that the pectoralis major can be activated
simultaneously with the serratus anterior during active scapular exercises (Decker et al., 1999,
Hiengkaew et al., 2003, Hintermeister et al., 1998 and Kim et al., 2010).
Greater activation of the pectoralis major compared with the serratus anterior can be
observed in subjects with scapular winging during the plus phase of the push-up plus (Kim et
al., 2010). It is possible that the pectoralis major may compensate for a weak serratus anterior
because the pectoralis major may act as a synergist (Decker et al., 1999, Hiengkaew et al.,
2003 and Hintermeister et al., 1998).
BUT, the excessive pectoralis major activation may lead to glenohumeral and scapulothoracic
pathologies such as shoulder anterior joint translations or decreased compression forces on
the glenoid (Konrad et al., 2006, Labriola et al., 2005 and McMahon et al., 2003).
No previous studies have investigated a strategy to increase activation of the serratus
anterior and decrease activation of the pectoralis major for subjects with scapular winging.

3. The Exercises
Ending position of three
exercises with and without
IHA (A: forward flexion, B:
scaption, C: wall push-up
plus, 1: without IHA, 2: with
IHA; IHA: isometric
horizontal abduction).

4. Results – pec major activation
Fig. 2 Comparison of PM EMG activity during the serratus anterior activation exercises with
and without IHA (PM: pectoralis major, IHA: isometric horizontal abduction). p < 0.008,
significant simple effect.

5. Results – serratus anterior activation
Comparison of SA EMG activity during the SA activation exercises with and
without IHA (SA: serratus anterior, IHA: isometric horizontal abduction). p>
0.05, significant difference.

6. Results – PM/SA ratio
Comparison of the PM/SA EMG activity ratio during the SA activation exercises with and
without IHA (PM: pectoralis major, SA: serratus anterior, IHA: isometric horizontal
abduction). **p < 0.008. significant simple effect.

7. Clinical Implications
These results showed that adding isometric horizontal abduction using Thera-
Band significantly decreased pectoralis major activity during forward flexion and
wall push-up plus, significantly increased serratus anterior activity, and
significantly decreased the pectoralis major/serratus anterior EMG activity ratio
during forward flexion and wall push-up plus.
Therefore, isometric horizontal abduction using Thera-Band can be
implemented as an effective method for inducing greater serratus anterior
activation while preventing excessive pectoralis major activation during three
exercises.