Sawatsky, A. | Search bioRxiv

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↗

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↗