Purpose:
To determine the validity, intra-rater reliability, and inter-rater reliability of an anchored sphygmomanometer for assessing shoulder strength during scaption, lateral rotation, and medial rotation. The hand-held dynamometer (HHD) was used as the standard measurement tool for this purpose.

Methods:
Fifty subjects (23 years old ±3 years) were included in the validity study. Shoulder strength was assessed using an HHD and a sphygmomanometer, both anchored to a fixed ladder by an inextensible belt. Twenty-three subjects (25 years old ±3 years) were included in the reliability study. Two raters assessed strength, each taking two measurements one week apart, using the fixed sphygmomanometer.

Results:
Validity results showed high to very high magnitude correlations, and no differences were found between the sphygmomanometer and the HHD measurements or among trials. Intra-class coefficient of correlation (ICC) showed high reliability between measurement tools and among trials. Intra-rater results showed very high ICC, very high correlation, low coefficient of variation (CV) with adequate standard error of measurement (SEM), and minimal detectable change (MDC). Inter-rater results showed moderate to high ICC, high to very high correlation, acceptable SEM and CV, but not adequate MDC. The anchored sphygmomanometer is a low-cost tool that provides objective measurements. The results obtained from the anchored sphygmomanometer were found to be similar to those obtained from an HHD, which has a valid predictive model.

Conclusions:
The sphygmomanometer is suitable for monitoring shoulder strength during scaption, internal rotation, and external rotation. The anchored sphygmomanometer enables coaches and physical therapists to establish the maximal voluntary isometric contraction and monitor exercise program outcomes at a low cost. However, caution is recommended when interpreting results between raters.