Inter-Rater and Intra-Rater Reliability of Handheld Dynamometry for Hip External Rotation in Seated versus Side-Lying

The purpose of this study is to compare the reliability of manual muscle testing (MMT) for hip external rotation (ER) in the side-lying (SL) and seated positions. The SL position aligns hip ER testing with current clinical practice and may allow greater contribution from the piriformis during strength assessment in physical therapy. Hip external rotator strength of 18 subjects was measured using a handheld dynamometer (HHD) placed 3 cm above the medial malleolus in both seated and SL positions. Tibial and femoral lengths were recorded to calculate torque for each position. Inter- and intra-rater reliability were assessed using intraclass correlation coefficients (ICC). Across all three examiners, intra-rater reliability was consistently higher in the SL position, ranging from poor to excellent (ICC = 0.229 [95% CI ?0.072, 0.503], 0.811 [0.594, 0.909], 0.942 [0.889, 0.970]) compared to the seated position (ICC = 0.187 [?0.101, 0.463], 0.555 [0.271, 0.747], 0.739 [0.387, 0.881]). Inter-rater reliability was poor in both positions (seated ICC = 0.240 [0.006, 0.563]; SL ICC = 0.234 [0.003, 0.551]). These findings suggest that testing hip ER strength in the SL position poses similar reliability to assessment in the seated position. While inter-rater reliability was determined to be poor for both testing positions, some examiners were found to have increased intra-rater reliability in the SL position. The SL position aligns resistance against gravity, improves objective strength measurement, enhances isolation of the external rotators, increases contribution from all ER muscles, and reduces hip flexor compensation seen in seated testing. Reliable assessment of these muscles is important for injury prevention and rehabilitation, so the SL position can be considered an equally reliable way to assess hip ER strength clinically.