Abstract:
BACKGROUND : The pectoralis minor (PM) muscle is commonly regarded as a contributor to
abnormal scapula positioning. Subsequently, the muscle length of the scapular stabilising
muscles may be affected, as these muscles assume a lengthened position, which over time
causes weakness. There are inconsistencies regarding PM muscle length values because of the
different techniques and positions used when the length of the PM muscle is measured.
OBJECTIVE : To determine the PM muscle length in participants aged 18−24 using a Vernier®
caliper and expressed as pectoralis minor index (PMI), with the scapula in three different
positions.
METHOD : The PM muscle length of 144 participants was measured with a Vernier® caliper
(intraclass correlation coefficient 0.83−0.87). Measurements were made with the scapula in the
resting position, in an active and a passive posterior tilt position.
RESULTS : Significant differences were observed in PMI between the resting scapula position
– 10.04 (confidence interval, CI 9.93–10.14) and active posterior tilt – 10.19 (CI 10.09–10.30)
(p < 0.001); the resting position – 10.04 (CI 9.93–10.14) and passive posterior tilt – 10.77
(10.66–10.87) (p < 0.001) and active – 10.19 (CI 10.09–10.30) and passive posterior tilt 10.77
(10.66–10.87) (p < 0.001). The dominant side had lower PMI values than the non-dominant
side.
CONCLUSION : The significant differences between the active and posterior tilt positions
suggested that optimal muscle length of PM was affected by the inner range strength of the
lower fibres of Trapezius.
CLINICAL IMPLICATIONS : It is important that in clinical practice not only the length of PM in
scapular misalignment but also the strength of the antagonistic muscles is considered.
