No abstract

Objective: Examine the repeatability of ultrasound imaging for capturing cross sectional area (CSA), tendon length and elongation of the distal biceps brachii (dBB) tendon at rest and during submaximal elbow flexion contractions. The secondary purpose was to assess the influence of these architectural measures on tendon mechanics of stress and strain. Methods: Within a testing session and between two days CSA, tendon length and elongation of the dBB were captured with ultrasound. Measures were compared within a session and between days. Pearson's correlations were performed to determine the intra-class correlation coefficients. Bland and Altman plots were used to identify the agreement between measures as well as the bias in measurements. Paired T-test were performed to ensure the calculated variables did not differ between days. Results: Resting tendon CSA was repeatable and strongly correlated (r = 0.98) within a session and between days; however, modest differences were observed in resting tendon length between days (∼1.8 mm) although values were correlated (r = 0.98). During submaximal contractions of 10%-80% maximal tendon elongation (r = 0.83) and CSA (r = 0.98) were also repeatable. From the measures of elongation and CSA, the calculated values of tendon strain (r = 0.97) and stress (r = 0.96) were also repeatable. Conclusions: Elongation and CSA of the dBB tendon captured with ultrasound are repeatable between testing sessions. From these measures tendon mechanics can be calculated to define the tendon's role in upper limb tasks, long-term adaptation and diagnostics.

Although plantar flexion force steadiness (FS) is reduced in persons with Parkinson’s disease (PD), the underlying causes are unknown. The aim of this exploratory design study was to ascertain the influence of maximal voluntary contraction (MVC) force and gastrocnemius-Achilles muscle-tendon unit behaviour on FS in persons with PD. Nine persons with PD and nine age- and sex-matched non-PD controls (~70 years, 6 females per group) performed plantar flexion MVCs and sub-maximal tracking tasks at 5, 10, 25, 50 and 75% MVC. Achilles tendon elongation and medial gastrocnemius fascicle lengths were recorded via ultrasound during contraction. FS was quantified using the coefficient of variation (CV) of force. Contributions of MVC and tendon mechanics to FS were determined using multiple regression analyses. Persons with PD were 35% weaker during MVC (p = 0.04) and had 97% greater CV (p = 0.01) with 47% less fascicle shortening (p = 0.004) and 38% less tendon elongation (p = 0.002) than controls. Reduced strength was a direct contributor to lower FS in PD (ß = 0.631), and an indirect factor through limiting optimal muscle-tendon unit interaction. Interestingly, our findings indicate an uncoupling between fascicle shortening and tendon elongation in persons with PD. To better understand limitations in FS and muscle-tendon unit behavior, it is imperative to identify the origins of MVC decrements in persons with PD.