Biology subjects

Ross, S. A.

Publications and source records attributed to Ross, S. A..

6 recordsLinked to original sources

bioRxiv2026

Sarcomere length, fascicle length, and serial sarcomere number are preserved in paretic hindlimb muscles following chronic stroke in rats despite persistent motor impairment

Stroke causes motor impairments that are commonly attributed to altered neural control, but chronic changes in neural activation and muscle use may also influence skeletal muscle structure. This study examined whether chronic stroke alters sarcomere length and dispersion, fascicle length, or serial sarcomere number in adult skeletal muscle. Twenty-four female Sprague-Dawley rats underwent photothrombotic stroke or sham surgery. Limb-specific motor impairment was assessed longitudinally using a beam traversal task. At 4.5 months post-surgery, the lateral gastrocnemius and extensor digitorum longus muscles were harvested from paretic and non-paretic limbs. We measured fascicle length directly from isolated fascicle bundles and quantified sarcomere length and dispersion using laser diffraction. Stroke animals exhibited persistent impairment of the paretic limb during beam traversal with elevated misstep rates. Despite this persistent motor impairment, sarcomere length and dispersion did not differ between stroke and sham animals or between limbs. Fascicle length and serial sarcomere number were greater in stroke than sham animals, but these differences were not limb-specific and were therefore unlikely to reflect stroke-related changes. Fascicle length, sarcomere length and dispersion, and serial sarcomere number differed between the lateral gastrocnemius and extensor digitorum longus, consistent with differences in architecture or relative length at the selected joint angles. These findings indicate that persistent neural impairment following adult-onset stroke does not necessarily result in substantial changes in sarcomere length or sarcomeres in series. Instead, sarcomere changes may depend on additional factors, including the timing of neural injury relative to growth and the mechanical environment experienced by the muscle.

physiology↗

bioRxiv2026

Force sharing between plantarflexor muscles in sheep during treadmill gait

Muscle force sharing during locomotion is influenced by the mechanical demands of movement and the contractile properties of synergistic muscles. In cats, plantarflexor muscles exhibit distinct functional specialization, with the slow-fibred soleus maintaining relatively constant force across conditions while faster muscles such as the plantaris and gastrocnemius increase force production with increasing locomotor demand. However, it remains unclear whether similar force-sharing patterns occur in larger animals with different musculoskeletal designs. Therefore, the purpose of this study was to examine force sharing between the superficial digital flexor (SDF) and medial gastrocnemius (MG) muscles during treadmill locomotion in sheep. Tendon buckle force transducers were surgically implanted on the SDF and MG tendons of seven sheep, and in vivo muscle forces were recorded during walking and trotting across different speeds and inclines. Both muscles increased force with increasing speed and incline; however, speed had a substantially greater effect than incline. The SDF consistently produced greater absolute force than the MG across all conditions, whereas the MG exhibited slightly larger relative increases in force with increasing speed. Time to peak force decreased with increasing speed in both muscles, although the SDF reached peak force later in stance than the MG across conditions. In contrast to the distinct specialization observed in cats, neither muscle displayed a relatively condition-independent, soleus-like force contribution. These findings suggest that force sharing in sheep is more distributed across synergistic muscles and may reflect the influence of musculoskeletal design, tendon compliance, and mixed fibre-type composition on muscle function in larger species.

bioengineering↗

bioRxiv2026

The muscle coordination required for efficient locomotion scales with body size

AO_SCPLOWBSTRACTC_SCPLOWMuscle efficiency decreases with increasing size, largely due to a relative decrease in its mechanical output. Muscle mechanical output depends on its activation, strain, and strain rate and thus varies between different muscles within a limb during locomotion. Distinct muscle coordination patterns are required for efficient cycling, and so we would expect that the coordination patterns for efficient cycling or indeed locomotion would change across animal sizes. We tested whether muscle coordination would change with muscle size using data derived from human cycling: this paradigm allowed for controlled changes in both crank torque and cadence, allowing the multifactorial problem of muscle power output to be decomposed. We used kinematic and pedal data from 12 cyclists undergoing steady pedalling at cadences from 80 to 140 r.p.m. and generated musculoskeletal simulations of their movements. We introduced novel multisegment muscle models in the simulation that incorporated the internal muscle mass and thus accounted for the scaling effects of muscle tissue inertia. We solved the simulations for the muscle activity that was required to minimise the metabolic cost during cycling for each condition. The masses of the muscle models were scaled across five orders of magnitude. The predicted muscle activations were classified by Principal Component analysis to identify whether the coordination of muscle activity was modulated across models with different sized muscles. Analysis of variance revealed significant changes in coordination at the large-scale factors. This study shows how the coordination of muscle activity during locomotion will likely change across a range of body sizes due to the non-linear effects of the inertial mass within the muscle tissues.

bioengineering↗

bioRxiv2026

The effects of muscle fibre type distribution on gait biomechanics: A predictive simulation study

Muscle fibre type distribution influences both metabolic and contractile properties of muscles and its influence on gait biomechanics is difficult to investigate \textit{in vivo}. This study aimed to predict the influence of muscle fibre type distribution on the metabolic cost and biomechanics of simulated gait. A muscle model that independently represented slow and fast twitch fibres was implemented in a predictive musculoskeletal simulation framework and used to investigate how cost of transport, stride length, stride frequency, and mechanical work performed by slow and fast twitch fibres were influenced by fibre type distribution across locomotion speeds (1.0 - 4.5 m {middle dot} s-1). Cost of transport decreased as proportion of slow twitch fibres increased, while stride length and frequency were minimally affected by fibre type distribution during walking. During running, cost of transport decreased and increased with increasing proportions of slow twitch fibres above and below a threshold speed, respectively. Stride frequency decreased and stride length increased with increasing proportions of slow twitch fibres above this speed. These shifts in spatiotemporal characteristics may allow key muscles to operate close to their peak mechanical efficiency. In conclusion, fibre type distribution may influence both the energetics and biomechanics of gait in a locomotion speed dependent manner.

bioengineering↗

bioRxiv2024

A Surgical Technique for Individual Control of the Muscles of the Rabbit Lower Hind-limb.

Little is known regarding the precise muscle, bone, and joint actions resulting from individual and simultaneous muscle activation(s) of the lower limb. An in situ experimental approach is described herein to control the muscles of the rabbit lower hind-limb, including the medial and lateral gastrocnemius, soleus, plantaris, and tibialis anterior. The muscles were stimulated using nerve-cuff electrodes placed around the innervating nerves of each muscle. Animals were fixed in a stereotactic frame with the ankle angle free to rotate in the sagittal plane to quantify the behaviour of the lower hind-limb muscles. To demonstrate the efficacy of the experimental technique, isometric plantarflexion torque was measured at a 90 {degrees} ankle joint angle at a stimulation frequency of 100, 60, and 30 Hz. Individual muscle torque and the torque produced during simultaneous activation of all plantarflexor muscles are presented for four animals. These results demonstrate that the experimental approach was reliable, with insignificant variation in torque between repeated contractions. The experimental approach described herein provides the potential for measuring a diverse array of muscle properties which is important to improve our understanding of musculoskeletal biomechanics. HighlightsO_LIA reliable surgical technique was developed for isolated activation of the plantarflexor muscles and the tibialis anterior in the rabbit. Joint torque data are presented for four rabbits at a single joint angle and three stimulation frequencies. C_LI

biophysics↗

bioRxiv2021

The contributions of extracellular matrix and sarcomere properties to passive muscle stiffness in cerebral palsy

Cerebral palsy results from an upper motor neuron lesion and has significant effects on skeletal muscle stiffness throughout the body. The increased stiffness that occurs is partly a result of changes in the microstructural components of muscle. In particular, alterations in extracellular matrix, sarcomere length, fibre diameter, and fat content have been reported; however, experimental studies have shown wide variability in the degree to which each component is altered. Many studies have reported alterations in the extracellular matrix, while others have reported no changes. A consistent finding throughout the literature is increased sarcomere length in cerebral palsy muscle. Often more than one component is altered, making it difficult to determine the individual effects on stiffness. The purpose of this study is to use a modeling approach to isolate individual effects of microstructural alterations that typically occur during cerebral palsy on whole muscle behavior; in particular, the extracellular matrix volume fraction, stiffness, and sarcomere length. These microstructural effects can be captured using a three dimensional model of muscle. We found that the extracellular matrix volume fraction has a larger effect on stiffness compared to sarcomere length, even when coupled with decreased extracellular matrix stiffness. Additionally, the effects of sarcomere length in passive stiffness are mitigated by the increased extracellular matrix volume fraction. Using this model, we can achieve a better understanding of the possible combinations of microstructural changes that can occur during cerebral palsy. Developing these insights into diseased muscle tissue will help to direct future clinical and experimental procedures.

physiology↗