Joint flexibility is a vital measure of physical fitness in humans, especially in terms of determining athletic performance. It’s answerable for protecting the muscle-tendon unit under stressful conditions by resisting external forces for long periods of time and ensuring a wider range of motion (RoM) of the joints. Joint stiffness of the lower limbs can, subsequently, negatively influence body fitness, leading to increased risk of falls and sports injuries. Stiffness of the muscle tissue are thought to influence the stiffness of the joints they’re in touch with. Nevertheless, this association has not been fully explored, especially within the case of calf muscles (triceps surae) and the ankle joint present in the lower limbs in humans.
To this address this data gap, a research team comprising Professor Ryota Akagi from Shibaura Institute of Technology and Dr. Kosuke Hirata from the Faculty of Sport Sciences at Waseda University, each in Japan, studied the age-related association between stiffness in triceps surae and passive stiffness of the ankle joint. Their study was published within the journal Frontiers in Physiology on 05 September 2022. “Understanding this association may help improve joint flexibility, improve athletic performance, reduce the danger of injuries during sports and/or each day living activities, and improve the general quality of life in older people,” say Dr. Akagi and Dr. Hirata, explaining the motivation behind the study.
To realize this, a study population of 40 young (21–24 years) and old (62–83 years) adult males were recruited. The ultrasound shear-wave elastography technique was employed to measure the muscle shear modulus (which is indicative of muscle stiffness) of the muscles comprising the triceps surae, namely the medial [MG], lateral gastrocnemius [LG], and soleus [Sol] muscles. The values were recorded for every subject with their knees fully prolonged on the ankle neutral position (NP) and the 15° dorsiflexed position (DF15) where the ankle is bent towards the body.
The passive stiffness of the ankle joint was estimated from the slope of the curve formed by passive torque-joint angle (resulting from passive/involuntary ankle dorsiflexion) for NP and DF15 after which normalized by the body mass. To evaluate muscular rest during joint stiffness measurement, the electromyographic (EMG) activity for MG, LG, and Sol of the triceps surae was recorded. A statistical evaluation of the info was then performed to determine the link between absolute, normalized ankle joint stiffness, and muscle shear modulus.
The analyses showed that absolute ankle joint stiffness on the DF15 was significantly related to muscle shear modulus in young participants, but not in older participants, whereas on the NP, there was no such association for either group. The normalized ankle joint stiffness at DF15 was also significantly related to muscle shear modulus of all muscles within the triceps surae in each groups, whereas it was only related to MG and LG for each groups on the NP. Explaining the consequence of those findings, Dr. Akagi and Dr. Hirata state, “Our results show that the stiffness of the complete triceps surae, even Sol, which is essentially the most compliant muscle found between the triceps surae, affects passive ankle joint stiffness, especially when the triceps surae is dorsiflexed and normalized by body mass.”
The researchers found that there was no age-related influence on passive joint stiffness. Nevertheless, the muscle shear modulus of the triceps surae was notably higher on the NP within the young group in comparison with the older group. Then again, no significant difference was recorded between these groups at DF15.
These results support the team’s hypothesis that joint stiffness results from a mixture of mechanical resistance of several tissues that cross the ankle joint. The researchers, thus, suggest that manipulating the mechanical properties of the triceps surae through exercises that relieve its stiffness can positively influence ankle joint flexibility. Speaking in regards to the significance of their results, Dr. Akagi concludes, “Our findings could help curate effective exercise programs to enhance joint flexibility of athletes and old people affected by weak joints.”
Source:
Shibaura Institute of Technology
Journal reference:
Hirata, K & Akagi, R., et al. (2022) Contribution of muscle stiffness of the triceps surae to passive ankle joint stiffness in young and older adults. Frontiers in Physiology. doi.org/10.3389/fphys.2022.972755.