Musculoskeletal disorders of the shoulder are extremely common, with 1 in 3 people experiencing shoulder pain at some stage of their lives . Shoulder pathology is the third most common musculoskeletal condition treated in primary care and up to 2% of the population consult with their General Practitioner annually because of pain and dysfunction in this region [2–5]. Of concern, shoulder pathology is associated with substantial dysfunction and morbidity , with 54% of sufferers reporting on-going symptoms after 3 years .
In the absence of a specific or identifiable cause of symptoms, poor upper body posture, colloquially referred to as a 'forward head posture', 'slouched posture', 'poking chin posture', or 'rounded shoulder posture' has been cited as a potential etiological factor in the pathogenesis and perpetuation of many clinical syndromes involving the shoulder. Beliefs relating to posture have permeated into clinical practice and are frequently used to explain to patients the basis for pathology and the rational for rehabilitation. An example of this is provided by Gray and Grimsby  (p138):
"In a person with good postural alignment, elevation of the arm is free to proceed through a full 160° to 180° of motion without impingement of soft tissues in the subacromial space. In the patient with the classic forward head, rounded shoulders, and increased thoracic kyphosis, the scapula rotates forward and downward, depressing the acromial process and changing the direction of the glenoid fossa. Now as the patient attempts to elevate the arm, the supraspinatus tendon and/or the subdeltoid bursa may become impinged against the anterior portion of the acromion process. Repeat motions of this nature may accelerate overuse injuries or cumulative trauma disorders and lead to early changes consistent with tendinitis and/or bursitis".
These theories are appealing and the suggestion that once a postural abnormality is identified, restoration to an ideal 'normal' posture will lead to a reduction in symptoms and improvement in function. In the specific example given above  the rationale is that an improvement in shoulder posture will lead to a reduction of the impingement process, reduced irritation on the rotator cuff tendons and a lessening in symptoms. Within the physical therapy, osteopathic and medical literature there is considerable reference to faulty posture and muscle imbalance and its relationship with shoulder pathology and symptoms. In addition to this, clinical assessment and rehabilitation procedures have been proposed to identify and treat postural abnormalities [9–17].
One muscle that is frequently implicated in shoulder and upper quadrant pathology is the pectoralis minor and a shortening of this muscle has been associated with a forward head posture [9–11, 16, 18, 19].
It has been argued that due to its attachment on the coracoid process a shortening of pectoralis minor will lead to the anterior tilting of the scapula [11, 16, 20]. Sahrmann  has described a number of clinical syndromes that are associated with a shortening of pectoralis minor. These include; thoracic outlet syndrome, scapular winging and tilting syndrome, scapular abduction syndrome, scapular depression syndrome and scapular downward rotation syndrome. To identify a postural shortening of pectoralis minor in association with these and other upper quadrant syndromes a test of the muscles length has been proposed. Sahrmann  (p211 [Figure 5–30] and p338–340) has described that when the pectoralis minor muscle is of normal length the distance between the treatment table and posterior aspect of the acromion (patient supine, arms by side, elbows flexed) should not exceed 2.54 cm (1 inch). A distance greater than this would suggest a muscle imbalance had occurred and the muscle had shortened. Identifying a muscle imbalance involving a short pectoralis minor is then used within the context of the clinical reasoning process to inform and direct the clinician as regards appropriate therapeutic intervention.
Although posture and muscle imbalance is commonly implicated as part of the pathological process the evidence available to support these theories is limited, with research studies reporting equivocal findings [21–27]. In addition to this, the concept of correcting posture and its associated muscle imbalance through stretching and strengthening programs [16, 28] has been widely accepted. However, there is no definitive evidence that an ideal posture exists , or that deviations from an ideal norm are associated with compromised function and disability [12, 22, 23, 30]. As clinical practice is frequently based on the assessment of posture and muscle imbalance it is important that fundamental questions concerning these issues are addressed.
To be of value, clinical tests must be reliable and have acceptable diagnostic accuracy. In part, the findings of clinical tests and measurements are used by clinicians to inform the clinical reasoning process. To have meaning these tests must be reliable. Sim and Wright  have defined reliability in three categories; equivalence, stability and internal consistency. Internal consistency relates to the homogeneity of a multi-item instrument. Equivalence relates to the consistency of measurements, for a given entity, when used by two or more investigators. Stability relates to the consistency of an instrument when used to measure the same entity on repeated occasions. Equivalence and stability are sometimes respectively referred to as reproducibility and repeatability [31, 32]. Stability (repeatability) is usually determined for a single investigator and is generally referred to as intra-rater reliability and is sometimes referred to as test-retest reliability . Most clinical tests have two possible outcomes. A positive test implies the condition is present and a negative result implies the condition is not present. This may be expressed by the sensitivity and specificity values for a test. An additional method of describing the diagnostic value of a test includes the positive and negative likelihood ratios. Likelihood ratios provide numerical information concerning the likelihood that a test result or finding would be present in a patient with the disorder or condition in comparison to the likelihood that the same finding or result would be expected in a patient without the condition or disorder . In addition, likelihood ratios provide a robust determination of the usefulness of a clinical test as they incorporate both the sensitivity and specificity together in one analysis and do not treat them as separate entities.
To determine the diagnostic accuracy of a test the clinical measurements are compared to a 'gold standard' reference test. At present there is no gold standard reference test for the measurement of pectoralis minor length. Sahrmann  (p211) has stated that the shoulders tilt anteriorly because of a shortness of pectoralis minor and that the lateral border of the spine (posterior aspect of the acromion) should be no more than 2.54 (2.6) cm from the treatment table when the subject is in supine. For the purposes of this investigation and to attempt to establish a relationship between pectoralis minor length and symptoms a negative pectoralis minor length test was defined as a table to posterior acromion measurement of less than or equal to 2.6 cm, and a positive test as being a measurement greater then 2.6 cm.
A review of the medical data bases (MEDLINE, CINAHL, AMED, PEDro, EMBASE) and a manual literature search; using the search terms; pectoralis minor, length, length test, posture, forward head posture, scapular position, scapula, shoulder, diagnosis, and reliability failed to identify any English language publication that has investigated the reliability of the pectoralis minor length test in subjects with and without shoulder symptoms and the diagnostic accuracy of the test in subjects with shoulder symptoms.
Therefore the aims of this investigation were to determine the;
(i) intra-rater reliability of the pectoralis minor length test in subjects without symptoms
(ii) intra-rater reliability of the pectoralis minor length test in subjects with symptoms, and
(iii) diagnostic accuracy of this clinical test of pectoralis minor length against the 'gold standard' recommendation of normal range being no greater than 2.6 cm above the table.