Reliability, Responsiveness, and Criterion Validity of the Kiio Sensor, a New Tool for Assessment of Muscle Function

Musculoskeletal injuries are a leading cause of disability in both the general population and military, and the ability to effectively quantify musculoskeletal function remains problematic. The aim of the current study is to investigate the reliability, responsiveness, and criterion validity of the kiio Sensor for measurement of muscle strength, a key aspect of comprehensive functional assessment. Forty-four (24 male, 20 female) physically active civilian adults (mean [SD] = 21.2 [1.5] years of age) with no history of upper extremity injuries in the last year and no current complaints of pain, weakness, or functional limitation completed two sessions of maximum shoulder external rotation contractions. The forces were measured with a kiio Sensor and isokinetic dynamometer. The devices showed strong correlation (r = 0.89) and no significant mean difference (0.3 ± 3.3 lb, p = 0.47). Intrasession reliability for both devices was analyzed using intraclass correlation coefficients (ICC_3,1 = 0.96 [95% confidence interval = 0.93-0.98)], with the kiio Sensor having slightly less standard error and trial-to-trial variability. The kiio Sensor 7-day reliability was ICC_3,3 = 0.97 (95% confidence interval = 0.94-0.98). The kiio Sensor demonstrates excellent reliability, responsiveness, and validity compared with a gold standard isokinetic dynamometer. Several key attributes contributing to this technology's military relevance are discussed.