Pectoralis minor muscle elongation and scapulothoracic motion do not differ in individuals with short versus typical resting pectoralis minor muscle length: a cross-sectional study.

BACKGROUND: Individuals with short resting pectoralis minor muscle length have been shown to have aberrant scapulothoracic motion when compared to individuals with long resting pectoralis minor muscle length. However, the degree to which the pectoralis minor muscle can be lengthened and whether or not scapulothoracic motion differs between individuals with short and typical resting pectoralis minor muscle length is unknown. OBJECTIVES: To determine if: (1) pectoralis minor muscle elongation (percent pectoralis minor muscle can be actively and passively lengthened beyond resting length), (2) pectoralis minor muscle percent length change during overhead reaching, and (3) scapulothoracic motion during overhead reaching differ between individuals with short and typical resting pectoralis minor muscle length. DESIGN: Two group comparison. METHODS: Thirty healthy individuals were placed into a short or typical resting pectoralis minor muscle length group. A caliper was used to measure resting pectoralis minor muscle length and pectoralis minor muscle length during active and passive muscle lengthening. An electromagnetic tracking system was used to measure pectoralis minor muscle length change as well as scapular, humeral, and trunk motion during several arm elevation tasks. Pectoralis minor muscle elongation and length change during arm elevation tasks were compared between groups using independent t-tests. Two-factor mixed-model analyses of variance were used to compare scapulothoracic motion at arm elevation angles of 30°, 60°, 90°, and 120°. RESULTS: Pectoralis minor muscle elongation and pectoralis minor muscle length change during arm elevation did not differ between groups. Scapulothoracic motion did not differ between groups across arm elevation tasks. CONCLUSIONS: Although resting pectoralis minor muscle length differed between groups, pectoralis minor muscle lengthening and scapulothoracic motion were similar between participants with short and typical resting pectoralis minor muscle length. Additional studies are needed to better understand the role of pectoralis minor muscle elongation on scapulothoracic motion.

Reliability and validity of active and passive pectoralis minor muscle length measures.

BACKGROUND: Pectoralis minor muscle length is believed to play an important role in shoulder pain and dysfunction. Current clinical procedures for assessing pectoralis minor muscle length may not provide the most useful information for clinical decision making. OBJECTIVE: To establish the reliability and construct validity of a novel technique to measure pectoralis minor muscle length under actively and passively lengthened conditions. DESIGN: Cross-sectional repeated measures. METHODS: Thirty-four healthy adults (age: 23.9, SD=1.6 years; 18 females) participated in this study. Pectoralis minor muscle length was measured on the dominant arm in three length conditions: resting, actively lengthened, and passively lengthened. Based upon availability, two raters, out of a pool of five, used a caliper to measure the distance between the coracoid process and the 4th rib. The average of two pectoralis minor muscle length measures was used for all muscle length conditions and analyses. Intraclass correlation coefficients determined intra-and inter-rater reliability, and measurement error was determined via standard error of measurement and minimal detectable change. Construct validity was assessed by ANOVA to determine differences in muscle length across the three conditions. RESULTS: Our intra- and inter-rater reliability values across all three conditions ranged from 0.84 to 0.92 and from 0.80 to 0.90, respectively. Significant differences (p<0.001) in muscle length were found among all three conditions: rest-active (3.66; SD=1.36cm), rest-passive (4.72, SD=1.41cm), and active-passive (1.06, SD=0.47cm). CONCLUSIONS: The techniques described in this study for measuring pectoralis minor muscle length under resting and actively and passively lengthened conditions have acceptable reliability for clinical decision making.