The results of the current validity analysis suggest a strong relationship between PST and IR.
The mean angle of IR and PST rounded to the nearest degree was 81° and 80° respectively with a statistically significant
r 0.88. Conversely, there was no correlation between ER and PST (r 0.07). Our results were consistent with previous studies that documented a positive association between PST and decreased internal rotation.
Tyler et al reported a good correlation between PST and IR using the sidelying PST measurement method among baseball pitchers and reported r 0.61.
An inverse correlation was reported based upon their use of a linear measurement whereas a loss of internal rotation correlated with a greater distance measured from the medial epicondyle to the plinth.
Laudner et al reported a good correlation between IR and PST (r 0.72) among baseball pitchers. Lin and Yang compared PST to both IR and ER in a symptomatic cohort and reported a moderate to good relationship for IR (r 0.69),
whereas ER had little or no relationship (r 0.25).
Hung et al described measurements of muscle stiffness using a myotonometer in response to IR and ER among participants with clinically reduced ROM and identified increased stiffness (change in passive tension per unit change in length) of the posterior musculature in response to IR lending support to the possible contribution of contractile tissue to PST.
In regards to measurement error and change scores the MDC has not previously been reported for PST tests documented in the literature, thus, clinicians and researchers previously interpreting change may have relied on individual decisions that did not take into account variability and error.
The MDC90 values reported in this investigation indicate that a change greater than or equal to 9° is required over treatment sessions or in research trials to be 90% certain that the change is not due to subject variability or measurement error.
The MDC as reported in this investigation is the smallest amount of change that can be considered above the threshold of error, however, one must not make the assumption that this change has reached the threshold of clinically meaningful improvement.
When interpreting change scores it should be recognized that the MDC is not the same as the minimum clinically important difference (MCID).
The MCID is the amount of change that is clinically meaningful and is typically associated with an external criterion that indicates when meaningful change has occurred.
The authors of this manuscript did not calculate the MCID, thus it is uncertain as to the degree of change that would be
considered clinically meaningful.