Reliability of an ultrasound-motion capture approach to measure the lengthening behavior of the gastrocnemius medialis muscle-tendon unit, muscle belly, and Achilles tendon in vivo during gait.

BACKGROUND

Human muscle-tendon units (MTUs) exhibit significant plasticity and are subject to structural and functional alterations in response to various pathological conditions, such as diseases or disorders. The assessment of these pathological modifications, as well as the evaluation of therapeutic interventions, necessitates the application of robust and scientifically validated examination methodologies. In this study, a simple approach combining two-dimensional (2D) ultrasound and three-dimensional (3D) motion capture was developed and evaluated with regard to the reliability of dynamic length measurements of the gastrocnemius medialis (GM) muscle-tendon unit (MTU), muscle belly, and Achilles tendon.

METHODS

Ten participants were included in the study. To evaluate the reliability of the novel approach, two ultrasound measurement sessions were performed. By combining ultrasound tracking of the myotendinous junction with 3D motion capture, the tissue lengths were assessed during overground walking. The intra-day and inter-day reliability of one examiner was determined using the coefficient of variation, standard error of measurement (SEM), minimal detectable change (MDC95), and intraclass correlation coefficient (ICC).

RESULTS

The ultrasound approach showed excellent intra-day as well as inter-day reliability, with high ICC (≥0.95), small SEM (≤0.72 mm), and good MDC95 (≤2.1 mm) values for all investigated tissues.

CONCLUSION

The proposed ultrasound approach demonstrated reliability in evaluating the GM MTU, GM muscle belly, and Achilles tendon tissue lengthening behavior during overground walking. These findings underscore its potential as an effective tool for examining the impact of training interventions or therapeutic strategies, including surgical procedures and conservative treatments such as stretching exercises and orthotic management.