Abstract
Objective: M-mode ultrasound imaging (US) reflects the motion of connective tissue within muscles. The objectives of this study were to evaluate inter-rater and intra-rater reliability of soleus muscle measurements between examiners with different levels of US experience in asymptomatic subjects and to investigate the level of soleus muscle isometric activity in two positions (knee extended and knee flexed at 30°). Methods: Thirty volunteers without a history of ankle pain were evaluated with US examinations of the soleus muscle. Each muscle was scanned independently by two evaluators. Muscle at rest thickness, maximal isometric contraction thickness, time and velocity measures were detailed and blinded to the other examiner. Results: Intra- and inter-rater reliability at rest, in maximal isometric contraction thickness, contraction time and contraction velocity measures for both positions (extended and flexed knee) were reported from good to excellent for all outcome measurements. The position with the knee extended reported a statistically significant increase in thickness after motion showing 1.33 ± 0.27 mm for measurements at rest thickness with knee extended versus 1.50 ± 0.29 mm for measurements at end thickness with the knee in flexed position (p = 0.001), as well as 1.31 ± 0.23 mm for rest thickness with the knee in flexed position measurements with respect to 1.34 ± 0.24 mm for maximal isometric contraction thickness with extended knee measurements (p = 0.058). Conclusions: This study found that intra- and inter-examiner reliability of M-mode ultrasound imaging of the soleus muscle was excellent in asymptomatic subjects and the soleus muscle activity was different between the position with the knee extended and the position with the knee flexed.
Highlights
The triceps surae is the key muscle for the plantar flexor movement of the ankle [1]
The objectives of this study were to investigate the level of soleus muscle isometric activity in two positions: at knee extended and knee flexed at 30◦ by M-mode ultrasound imaging (US), measuring the change of muscle thickness and, secondly, to analyze the intra- and inter-examiner reliability of M-mode imaging of soleus muscle thickness in healthy subjects, measured by an experienced or novice examiner
There were significant changes in the thickness, contraction time and contraction velocity after the muscle contraction in the maximal ankle dorsiflexion. These changes were due to the position with the knee extended reporting a statistically significant increase in thickness after the motion, showing 1.33 ± 0.27 mm for measurements at rest thickness with the knee extended versus 1.50 ± 0.29 mm for measurements at end thickness with the knee in the flexed position (p = 0.001), as well as 1.31 ± 0.23 mm for rest thickness with the knee in the flexed position measurements with respect to 1.34 ± 0.24 mm for maximal isometric contraction thickness with extended knee measurements (p = 0.058)
Summary
The triceps surae is the key muscle for the plantar flexor movement of the ankle [1]. The position of the knee may drastically influence the force production of these muscles due to the length–tension relationship of each one [5]. In this line, the literature is controversial; for example, Pereira et al [6] and Segnorine et al [7] found that, under measurements with the knee flexed at 90◦ , the gastrocnemius muscles were under-activated, increasing the role of the soleus muscle. Hali et al [9] showed that gastrocnemius activation was inhibited during plantar flexion contractions in a flexed position compared to an extended knee joint position, this knee joint position change did not affect the soleus excitability, and Hëbert-Losier et al [10] indicated that the muscle changes in gastrocnemii and soleus activities due to the different knee positions might not be enough to significantly influence clinical outcome measures or muscle-specific benefits
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