Ringing in the new year is an exciting time for resolutions, recalibrations, and research. As people all over the world welcome the opportunity to commit to new goals, strengthen their resolve, and further progress in their lives, scientists continue to break new ground with emerging discoveries. The ‘New Year, New Me’ mindset can help kickstart a period of personal growth, and recent research indicates that new animal models can do the same for science. The following publication review covers a fascinating collection of muscle physiology studies in a range of different animal models – from brown bears and cunner fish, to golden retrievers.
Featured image (photo of bear by Andras Stefuca on Pexels with figures adapted from ©De Napoli et al (2025), licensed under CC BY 4.0) depicting the maximal isometric tension produced from skinned fibers taken from individual bears, and bears divided by season. The bottom left graph shows representative traces of force redevelopment (kTR) after a 10% length shortening in a fiber from a winter biopsy compared to a summer biopsy. On its right is the average kTR for individual animals. All data related to summer samples are reported in orange/red color, while those related to winter are in light blue/blue.
Reduced ATP turnover during hibernation in relaxed skeletal muscle
Hibernation has long captivated muscle physiologists, especially in large mammals such as brown bears, who remarkably experience minimal muscle wasting. In contrast, muscle disuse in humans often leads to a significant reduction in muscle mass and function in a mere matter of days. While a drastic reduction in metabolism is known to contribute to tissue sparing during hibernation, De Napoli et al (2025) sought to determine whether the molecular motor of skeletal muscle, known as the myosin protein, has reduced ATPase activity in hibernating bears.
Biopsies were collected from the vastus lateralis muscle of free-ranging brown bears, around 2-3 years of age. For skinned fibers, bundles of the muscle were stored in a skinning solution, dissected, clipped with aluminum T-clips at each end, and mounted on Aurora Scientific’s 802D: Permeabilized Fiber Apparatus. Protein extraction and analysis were conducted through SDS-PAGE and western blotting, while mantATP chasing and ATPase activity assays were used to investigate biochemical properties.
Both the ATPase assay and mantATP chasing approach showed that myosin in single muscle fibers taken from hibernating bears consumes less ATP. In fact, the ATPase activity in relaxed skinned fibers of hibernating muscle is 28% lower than in samples taken from the same bears in the summer. Moreover, single fiber proteomics analysis revealed significant remodeling of the proteome, despite no major loss in fiber size and function. Winter muscles have altered and reduced mitochondrial proteins, and winter fiber show lower MYLK2 kinase content and activity. Viewed in combination, these findings highlight a new energy saving mechanism with compelling implications for future muscle wasting studies.
Kinetic comparisons of jaw opening, jaw closing and locomotor muscles
The cunner fish, found in the coastal Northwest Atlantic, curiously overwinters in the same habitat it occupies year-round. While this may seem fishy in contrast to species such as the striped bass, which migrate south from coastal New England during the winter, thermal compensation is known to occur in the primary locomotor muscle in response to changing temperature. Despite our knowledge of this phenomenon, the specific kinetics and contraction dynamics of fish feeding musculature, especially in response to changes in temperature, remain unknown. To uncover these details, Moran et al (2025) compared jaw opening (sternhyoideus), jaw closing (adductor mandibulae) and locomotor (abductor superficialis) muscles in the cunner fish.
Once these muscles were removed and dissected, they were carefully trimmed and attached to Aurora Scientific’s 800A/805A: in-vitro Muscle Apparatus, which housed the 300C-LR dual-mode muscle lever. Twitch and tetanic contraction were performed with the time to maximum force, time to half relaxation, and absolute maximum force measured in 7°C, 15°C and 22°C. Importantly, these temperatures were selected to mimic the thermal conditions experienced in the wild.
The muscle contraction kinetics across the three muscle types and temperatures were found to be markedly similar, despite a few notable differences. Mainly, the locomotor muscle was slower to contract and relax, and produced more power than the other muscles at 8 Hz and 15°C. In contrast, the jaw closing muscle generated more force than the other muscles when tested at 22°C. Given our understanding of thermal compensation in the cunner fish, it’s possible that more pronounced differences could be observed upon a longer acclimatization period, forming the framework for future studies. Nonetheless, these results expand our understanding of muscle performance in ectothermic vertebrates and provide important considerations for the impact of climate change on fish species.
Bone measurements interact with phenotypic measures in canine Duchenne muscular dystrophy
Duchenne muscular dystrophy (DMD) is a debilitating X-linked recessive disease, roughly affecting 1 in 5000 boys. Caused by genetic mutations in the DMD gene, patients lack the dystrophin structural protein, which leads to detrimental muscle degeneration and impaired bone health. The golden retriever muscular dystrophy (GRMD) dog develops a similar progressive disease, but bone morphology has been critically understudied in the canine model, especially in conjunction with muscle function. To address this, Schneider et al (2025) doggedly committed to uncovering these characteristics in GRMD dogs.
Computed tomography measurements were performed in affected, carrier, and healthy dogs across various ages and gender groups, accompanied by femur length measurements as well as cortical measurements. Muscle strength was studied using Aurora Scientific’s 890A Large Animal Test Apparatus which enabled percutaneous stimulation of fibular and tibial nerves, as well as twitch and tetanic torque readouts. Eccentric contractions were performed by conducting tetanic stimulation of the fibular nerve, flexing the muscles for 800 milliseconds, and extending the foot pedal during the final 200 milliseconds.
Bone and joint measures, such as femoral length (FL) and cortical thickness (CorT), were found to be significantly correlated with maximum hip joint angle flexion. In addition, GRMD dogs had a significantly greater normalized FL compared to carriers, as well as a thinner minimum CorT than healthy dogs. Muscle attenuation (density) also differed across the groups, with the lowest values in GRMD dogs, intermediate phenotypes in carriers, and the highest values in healthy dogs. Taken together, these findings illustrate bone alterations in GRMD dogs and encourage further bone health studies in these canine models.
Conclusions
As we venture into the new year with promising resolutions, 2025 marks a fresh opportunity for personal growth and scientific advancement. These hot-off-the-press publications by De Napoli et al (2025), Moran et al (2025), and Schneider et al (2025) highlight how studying physiological processes across various species drives our understanding of muscle mechanics and disease progression. From the bear necessities of hibernation, fishy feeding musculature kinetics, and bone-afide dystrophic phenotypes of GRMD dogs, these recent studies model a strong start for the new year.
