The mechanical function of the tibialis posterior muscle and its tendon during locomotion

The tibialis posterior (TP) muscle is believed to provide mediolateral stability of the subtalar joint during the stance phase of walking as it actively lengthens to resist pronation at foot contact and then actively shortens later in stance to contribute to supination. Because of its anatomical structure of short muscle fibres and long series elastic tissue, we hypothesised that TP would be a strong candidate for energy storage and return. We investigated the potential elastic function of the TP muscle and tendon through simultaneous measurements of muscle fascicle length (ultrasound), muscle tendon unit length (musculoskeletal modelling) and muscle activation (intramuscular electromyography). In early stance, TP fascicles actively shortened as the entire muscle-tendon unit lengthened, resulting in the absorption of energy through stretch of the series elastic tissue. Energy stored in the tendinous tissue from early stance was maintained during mid-stance, although a small amount of energy may have been absorbed via minimal shortening in the series elastic elements and lengthening of TP fascicles. A significant amount of shortening occurred in both the fascicles and muscle-tendon unit in late stance, as the activation of TP decreased and power was generated. The majority of the shortening was attributable to shortening of the tendinous tissue. We conclude that the tendinous tissue of TP serves two primary functions during walking: 1) to buffer the stretch of its fascicles during early stance and 2) to enhance the efficiency of the TP through absorption and return of elastic strain energy

Foot structure is significantly associated to subtalar joint kinetics and mechanical energetics

Introduction/aim: Foot structure has been implicated as a risk factor of numerous overuse injuries, however, the mechanism linking foot structure and the development of soft-tissue overuse injuries are not well understood. The aim of this study was to identify factors that could predict foot function during walking

The Reliability of Foot and Ankle Bone and Joint Kinematics Measured With Biplanar Videoradiography and Manual Scientific Rotoscoping

The intricate motion of the small bones of the feet are critical for its diverse function. Accurately measuring the 3-dimensional (3D) motion of these bones has attracted much attention over the years and until recently, was limited to invasive techniques or quantification of functional segments using multi-segment foot models. Biplanar videoradiography and model-based scientific rotoscoping offers an exciting alternative that allows us to focus on the intricate motion of individual bones in the foot. However, scientific rotoscoping, the process of rotating and translating a 3D bone model so that it aligns with the captured x-ray images, is either semi- or completely manual and it is unknown how much human error affects tracking results. Thus, the aim of this study was to quantify the inter- and intra-operator reliability of manually rotoscoping in vivo bone motion of the tibia, talus, and calcaneus during running. Three-dimensional CT bone volumes and high-speed biplanar videoradiography images of the foot were acquired on six participants. The six-degree-of-freedom motions of the tibia, talus, and calcaneus were determined using a manual markerless registration algorithm. Two operators performed the tracking, and additionally, the first operator re-tracked all bones, to test for intra-operator effects. Mean RMS errors were 1.86 mm and 1.90° for intra-operator comparisons and 2.30 mm and 2.60° for inter-operator comparisons across all bones and planes. The moderate to strong similarity values indicate that tracking bones and joint kinematics between sessions and operators is reliable for running. These errors are likely acceptable for defining gross joint angles. However, this magnitude of error may limit the capacity to perform advanced analyses of joint interactions, particularly those that require precise (sub-millimeter) estimates of bone position and orientation. Optimizing the view and image quality of the biplanar videoradiography system as well as the automated tracking algorithms for rotoscoping bones in the foot are required to reduce these errors and the time burden associated with the manual processing

Tibialis anterior muscle-tendon unit and fascicle behaviour during human walking

Muscle and ankle mechanic

The immediate effect of foot orthoses on subtalar joint mechanics and energetics

Foot orthoses maybe used in the management of musculoskeletal disorders related to abnormal subtalar joint (STJ) pronation. However, the precise mechanical benefits of foot orthoses for preventing injuries associated with the STJ are not well understood. The aim of this study was to investigate the immediate effect of foot orthoses on the energy absorption requirements of the STJ and subsequently tibialis posterior (TP) muscle function.Eighteen asymptomatic subjects with a pes planus foot posture were prescribed custom-made foot orthoses made from a plaster cast impression. Participants walked at preferred and fast velocities barefoot, with athletic footwear and with athletic footwear plus orthoses, as three-dimensional motion capture, force data and intramuscular electromyography of the TP muscle were simultaneously collected. Statistical parametric mapping was used to identify time periods across the stride cycle during which footwear with foot orthoses significantly differed to barefoot and footwear only.During early stance, footwear alone and footwear with orthoses significantly reduced TP muscle activation (1 - 12 %), supination moments (3 - 21 %) and energy absorption (5 - 12 %) at the STJ, but had no effect on STJ pronation displacement.The changes in TP muscle activation and STJ energy absorption were primarily attributed to footwear as the addition of foot orthoses provided little additional effect. We speculate that these results are most likely a result of the compliant material properties of footwear. These results suggest that athletic footwear may be sufficient to absorb energy in the frontal plane and potentially reducing any benefit associated with the addition of foot orthoses

Tibialis anterior tendinous tissue plays a key role in energy absorption during human walking

The elastic tendinous tissues of distal lower limb muscles can improve the economy of walking and running, amplify the power generated by a muscle as well as absorb energy. This paper explores the behaviour of the tibialis anterior (TA) muscle and its tendinous tissue during gait, as it absorbs energy during contact and controls foot position during swing. Simultaneous measurements of ultrasound, surface electromyography and 3-dimensional motion capture with musculoskeletal modelling from twelve healthy participants were recorded as they walked at preferred and fast walking speeds. We quantified the length changes and velocities of the TA muscle-tendon unit and its fascicles across the stride at each speed. Fascicle length changes and velocities were relatively consistent across speeds, although the magnitude of fascicle length change differed between the deep and superficial regions. At contact, when the TA is actively generating force, the fascicles remained relatively isometric as the MTU actively lengthened, presumably stretching the TA tendinous tissue and absorbing energy. This potentially protects the muscle fibres from damage during weight acceptance and allows energy to be returned to the system later in the stride. During early swing the fascicles and MTU both actively shortened to dorsiflex the foot, clearing the toes from the ground; although, at the fast walking velocity the majority of the shortening occurred through tendinous tissue recoil, highlighting its role in accelerating ankle dorsi-flexion to power rapid foot clearance in swing

Flip-flops do not alter the neuromuscular function of the gastrocnemius muscle and tendon during walking in children

Introduction/Aim: Flip-flops are a popular choice of footwear for children. However, their inherent design provides minimal support to the foot and ankle and has been suggested to increase the work performed by muscle and tendon structures, potentially predisposing them to injury. Therefore, the aim of this study was to compare the length change behaviour of the medial gastrocnemius (MG) muscle fascicles and muscle tendon unit (MTU) and their mechanical function at the ankle and subtalar joints in children during walking with and without flip-flop. Methods: Eight healthy children walked barefoot and with flip-flops whilst 3D gait analysis and simultaneous B-mode ultrasound images of the MG fascicles during level walking were collected. Joint kinematics, kinetics and MTU lengths were analysed using musculoskeletal modelling and fascicle lengths using a semi-automated tracking algorithm. Results: The muscles and tendons across the ankle absorbed greater amounts of power during barefoot walking compared to flip-flop walking. The muscle activations of the lateral gastrocnemius, soleus and tibialis anterior remained invariant across the conditions as did the activation, and fascicle length change behaviour of the medial gastrocnemius. In the barefoot condition, there was a trend of greater MTU lengthening, to potentially absorb greater amounts of power, although no differences in shortening was observed during late stance. Conclusion: Walking with flip-flops does not increase the mechanical work performed by the MG muscle at the ankle and subtalar joints, suggesting that flip-flops do not increase the stresses and strains of the Achilles tendon and hence its predisposition to strain induced injury. Instead, our results suggest that flip-flops, act as a compliant surface and absorb energy during contact and hence the strain experienced by the Achilles tendon