The use of ultrasound to study muscle-tendon function in human posture and locomotion

Analysis of human movement has traditionally relied on measures such as kinematics, kinetics and electromyography. These measures provide valuable information about movement performance and make it possible to draw inferences about muscle and tendon function. Musculoskeletal models are also used frequently to examine the relationship between joint kinematics and muscle-tendon behaviour, and have provided important insights into both healthy and clinical gait. However, muscles interact with compliant tendons during movement, which complicates interpretation of muscle and tendon function based on external measures such as joint kinematics. Accordingly, methods have been developed that enable muscle and tendinous tissues to be imaged in real-time. Ultrasound is among the most popular methods used for this purpose, and has been applied extensively to the study of in vivo muscle and tendon function in a range of human populations and movement contexts. There is a growing body of literature that proposes different measures of muscle and/or tendon function, and these results need to be discussed in light of the technical differences between the measurement techniques. In this review we first outline the various uses of ultrasound to examine human muscle and tendon function, and then summarise ultrasound-based research specifically during locomotion and postural conditions. We then describe some of the many technical issues associated with this method. Methods of data analysis are introduced, including novel automated techniques that improve the efficiency of the analysis process. Finally, possible future directions in musculoskeletal ultrasound research are discussed.