Background Anatomical studies and the mechanical property studies showed that there is a strong correlation between Achilles tendon (AT) elasticity and individual gastrocnemius muscle (the medial head of gastrocnemius (MG) and the lateral head of gastrocnemius (LG)) elasticity. Limited ankle dorsiflexion range of motion has been correlated with decreased flexibility of the MG/LG/AT complex. However, no studies have been conducted to examine the exact correlation between the Achilles tendon and the individual muscle of the gastrocnemius. Purposes The purposes of the present study were (1) to evaluate intra- and interoperator reliabilities of elastic property measurements in the gastrocnemius muscle-Achilles tendon complex by using the shear wave elastography (SWE) and (2) to examine the correlation between the regional elastic properties of the AT and the individual muscle of the gastrocnemius. Methods Twenty healthy subjects (mean age: 22.50 (3.02) years) were recruited in this study. The elastic properties of the AT and the individual muscle of the gastrocnemius were quantified using the SWE. Findings The SWE has comparatively high reliability in quantifying the elastic properties of the muscle-tendon range from good to excellent. The intraoperator ICC of the gastrocnemius muscle-Achilles tendon complex was 0.77 to 0.95, while the interoperator ICC was 0.76 to 0.94. The minimal detectable change (MDC) of the muscle was 1.72 kPa, while the AT was 32.90 kPa. A significant correlation was found between the elastic modulus of AT and the elastic modulus of the MG (r = 0.668 and p = 0.001 at the relaxing position and r = 0.481 and p = 0.032 at the neutral position). Conclusions The SWE has the potential to assess localized changes in muscle-tendon elastic properties, provide more intuitive relations between elastic properties of the muscle tendon and function, and evaluate the therapeutic effect of the muscle tendon. A significant correlation between the AT and the MG was found, and it may provide a new treatment idea (targeted to the tight muscle heads) for the clinical setting to treat subjects with AT disorders.

Stiffness is a valuable indicator of the functional capabilities of muscle-tendon-fascia. Twenty healthy subjects participated in this study in which the passive elastic properties of the medial gastrocnemius (MG), lateral gastrocnemius (LG), soleus muscles (SOL), Achilles tendon (AT, at 0 cm, 3 cm and 6 cm proximal to the calcaneus tubercle, corresponding to AT0cm, AT3cm and AT6cm, respectively) and plantar fascia (PF) were quantified when their knee was fully extended or flexed to 90° using shear wave elastography at 25° of dorsiflexion (DF25°), 0° (neutral position) of flexion, and 50° of plantar flexion (PF50°) of the ankle joint. The stiffnesses of the AT, MG, LG, SOL and the fascia with the knee fully extended were significantly higher than those with the knee flexed to 90° (p < 0.05), while the stiffness of the PF showed the opposite relationship (p < 0.05). When the knee was fully extended, the stiffness was higher in the LG than in the MG at PF50° and 0° (p < 0.01), and it was higher in the MG than in the LG at DF25° (p = 0.009). Nevertheless, regardless of the knee angle, the stiffness decreased from AT3cm > AT0cm > AT6cm at PF50° and 0° (p < 0.001), while the stiffness decreased from AT0cm > AT3cm > AT6cm at DF25°. Regardless of the knee and ankle angles, the stiffness of the PF increased in a proximal-to-distal direction (p < 0.001). These insights can be used to gain a more intuitive understanding of the relationships between the elastic properties of the muscle-tendon unit and its function. Achilles tendon (AT) injuries and plantar fasciitis can cause chronic pain and impairment 1. In the clinic, the type of treatment administered depends in part on the region and intensity of pain. For example, eccentric exercises are more effective in the treatment of mid-substance tendinopathy than in the treatment of insertional tendinopathy 1. However, because of the complexity of the anatomy and mechanics of the AT and plantar fascia (PF), it can be challenging to identify the region and severity of the damage. In terms of anatomy, the AT, which is the conjoined tendon of the medial gastrocnemius (MG), the lateral gastrocnemius (LG), and the soleus (SOL), is an important bridge for walking, running and jumping in daily life, and each of the contributing muscles exhibit unique structural features 2,3. The twisted structure of the AT is formed by the MG tendons, LG tendons and SOL tendons. These muscle tendons rotate as they descend but do not run parallel to each other 4. In addition, the superficial layer of the AT is formed by the MG tendons, while the deep layer consists of the LG tendons and SOL tendons 5. Furthermore, the LG is shorter and smaller than the MG, so the MG and LG differ in terms of muscle strength and their contribution to the AT 6. In other words, these regional structural features (including those of the MG, LG, SOL, AT and PF) have great inherent variability, which may affect the position and severity of damage in an individual 6. Therefore, it is necessary to further understand the relati...

The objectives of this study were (1) to investigate the passive stiffness of the medial gastrocnemius (MG) and lateral gastrocnemius (LG) in patients with and without plantar fasciitis (PF), (2) to explore the correlation between gastrocnemius stiffness and plantar fascia thickness (PFT) as well as the intensity of pain in patients with PF, (3) to detect optimal cutoff points for stiffness of the MG and LG for identifying patients with pf. forty patients (mean age = 51.1 years ± 12.9) participated in this study. The elastic properties of the MG and LG were quantified using shear wave elastography ultrasound. The thickness of the plantar fascia was measured by B-mode imaging. the intensity of pain was assessed using a visual analogue scale. The results showed that when the ankle was in the relaxed position, patients with PF had increased passive stiffness in the MG (P < 0.05) but not in the LG. Significant correlations were found between pain and the stiffness of the MG (middle, distal; all P-values < 0.05) and no correlation was observed between pain and pft (P = 0.416). The initial cutoff point for the stiffness of the MG was 29.08 kPa when the ankle was in the relaxed position. The findings from the present study show that an increase in muscle stiffness is not the same in the individual muscles of the gastrocnemius muscle. traditional treatment of the whole gastrocnemius muscle might not be targeted at the tight muscle.

The elastic properties of the Achilles tendon (AT) are altered in local injury or other diseases and in response to changes in mechanical load. Recently, elastography has been used to evaluate variations in tendon elastic properties, mainly among healthy individuals or athletes. Therefore, this study evaluated the biomechanical changes in ATs in individuals with and without plantar fasciitis (PF). The purposes were as follows: (1) to evaluate the passive stiffness of three regions of the AT which defined as 0 (AT0 cm), 3 (AT3 cm), and 6 cm (AT6 cm) above the calcaneal tuberosity in participants with and without PF, (2) to investigate the interplay between the passive stiffness in patients with PF and pain, (3) to detect optimal cut-off points of stiffness of the AT in assessing individuals with chronic PF, and (4) to determine the correlation between the plantar fascia thickness (PFT) and pain. This cross-sectional study included 40 participants (mean age = 51 ± 13 years). When the ankle was in a relaxed position, patients with PF experienced increased passive stiffness in AT0 cm (p = 0.006) and AT3 cm (P = 0.003), but not in the neutral position. Significant correlations were observed between pain and stiffness of AT (AT0 cm r = 0.489, P = 0.029; AT3 cm r = 487, P = 0.030; AT6 cm r = 0.471, P = 0.036), but not in the PFT (P = 0.557). Optimal cut-off stiffness was AT (452 kPa) in the relaxed ankle position. The plantar fascia of patients with PF was significantly thicker than that of the controls (P &lt; 0.001). Findings from the present study demonstrate that tendon stiffness is a good indicator of the clinical situation of patients with PF. Monitoring passive tendon stiffness may provide additional information to assess severity of the condition and guide therapeutic. The treatment programs for PF should also be tailored to the distal AT, as conventional therapy might not be targeted to tight tendons.

The mechanical properties of the deep fascia, particularly their stiffness, strongly affect the development of muscle pathologies (such as compartment syndrome) and the action of the muscles. However, the mechanical characteristics of the deep muscular fascia are still not clearly understood. The present study focuses on examining the reliability of ultrasonic shear wave elastography (USWE) devices in quantifying the shear modulus of the gastrocnemius fascia in healthy individuals, particularly their ability to measure the shear modulus of the deep fascia of the gastrocnemius during ankle dorsiflexion. Twenty-one healthy males (age: 21.48 ± 1.17 years) participated in the study. Using USWE, the shear moduli of the medial gastrocnemius fascia (MGF) and lateral gastrocnemius fascia (LGF) were quantified at different angles during passive lengthening. The two operators took turns measuring each subject’s MGF and LGF over a 1-h period, and operator B took an additional measurement 2 h later. For the intra-operator test, the same subjects were measured again at the same time of day 5 days later. Both the intrarater [intraclass correlation coefficient (ICC) = 0.846–0.965)] and interrater (ICC = 0.877–0.961) reliability values for measuring the shear moduli of the MGF and LGF were rated as excellent; the standard error of the mean (SEM) was 3.49 kPa, and the minimal detectable change (MDC) was 9.68 kPa. Regardless of the ankle angle, the shear moduli of the LGF were significantly greater than that of the MGF (p < 0.001). Significant increases in the shear moduli of both the MGF and the LGF were observed in the neutral position compared to the relaxed position. These results indicate that USWE is a reliable technique to assess the shear modulus of the gastrocnemius fascia and detect its dynamic changes during ankle dorsiflexion. USWE can be used for biomechanical studies and intervention experiments concerning the deep fascia.