Muscle fiber types in horses refer to the classification of muscle fibers based on their metabolic and contractile properties. These fibers are categorized into different types, primarily type I (slow-twitch) and type II (fast-twitch), with type II further subdivided into type IIa and type IIb. Type I fibers are known for their endurance capabilities and rely on aerobic metabolism, whereas type II fibers are associated with strength and speed, utilizing anaerobic pathways. The distribution and proportion of these muscle fiber types can vary significantly among horse breeds and individuals, influencing their performance in various equestrian disciplines. This page compiles peer-reviewed research studies and scholarly articles that investigate the characteristics, distribution, and functional implications of muscle fiber types in equine physiology and performance.
Lindholm A, Piehl K.LINDHOLM, ARNE and KARIN PIEHL: Acta vet. scand. 1974, , 287–309. — Measurements of metabolites, electrolytes, water, RNA and protein concentrations, the activity of certain muscle enzymes (SDH and PFK) and muscle fibre composition were made on biopsy specimens from the gluteus medius muscle of 68 standardbred horses, ½ to 8 years old. The muscle fibres were classified in 3 major categories, slow twitch (ST), fast twitch and high oxidative (FTH) and fast twitch (FT) fibres. The percentage of FTH fibres was higher after the age of 4 years, averaging 54 %. ST fibres comprised 24 % and this...
Li X, Meng C, Xue Y, Shen Z, Ren W, Zeng Y, Meng J.Skeletal muscle is the largest organ system in mammals. To investigate the differences in energy metabolism across various skeletal muscles in Yili horses, this study examined muscle fiber type distributions through immunohistochemical staining of muscles, including the splenius, triceps brachii, longissimus dorsi, and gluteus medius. The splenius and gluteus medius muscles, which exhibited the greatest differences in the proportion of slow-twitch fiber area, were selected for further comparison of differential metabolites and transcriptomic expression profiles between slow-twitch and fast-twi...
Valberg SJ, Williams ZJ, Ames EG, Mickelson JR, Nout-Lomas YS, Landolt G, Sanz M, Gardner K.Equine myotonic dystrophy (eMD) is a rare neuromuscular disorder of undetermined origin marked by muscle hypertrophy and stiffness, dystrophic muscle histopathology, and myotonic discharges. In humans, myotonic dystrophy (DM) arises from trinucleotide repeat expansions in dystrophia myotonica protein kinase (DMPK) (DM1) or tetranucleotide expansions in cellular nucleic acid-binding protein (CNBP) (DM2), which disrupt mRNA processing and induce embryonic splicing patterns across multiple genes. In 6 eMD Quarter Horse types, (2-36 months-of-age) and 8 control Quarter Horses we determined: (1) fi...
Aleman M.Muscle disease has various clinical manifestations that range from exertional and non-exertional rhabdomyolysis, fasciculations, weakness, rigidity, stiffness, gait abnormalities, poor performance, and alterations in muscle mass and tone. Neurogenic disorders and non-neurogenic disorders such as primary muscle disease can cause muscle atrophy and changes in muscle tone. Myotonic disorders can have a genetic (eg, inherited channelopathies) or acquired (eg, electrolyte derangements) origin. Normal muscle enzyme activities do not rule out a myopathic disorder as the underlying cause of muscle atr...
Ding W, Gong W, Bou T, Shi L, Lin Y, Shi X, Li Z, Wu H, Dugarjaviin M, Bai D.Speed is not only the primary objective of racehorse breeding but also a crucial indicator for evaluating racehorse performance. This study investigates a newly developed racehorse breed in China. Through whole-genome resequencing, we selected 60 offspring obtained from the crossbreeding of Thoroughbred horses and Xilingol horses for this study. This breed is tentatively named "Grassland-Thoroughbred", and the samples were divided into two groups based on racing ability: 30 racehorses and 30 non-racehorses. Based on whole-genome sequencing data, the study achieved an average sequencing depth o...
Firshman AM, Valberg SJ.Type 1 Polysaccharide Storage Myopathy (PSSM1) is an autosomal dominant glycogen storage disorder affecting more than 20 breeds of horses that can present with a variety of signs, including exertional rhabdomyolysis (ER). It is diagnosed by genetic testing or muscle biopsies containing muscle fibers with abnormal amylase-resistant polysaccharide. Type 2 PSSM has recently been subdivided. PSSM2-ER is a glycogen storage disorder identified in Quarter Horses that causes ER and is diagnosed by muscle biopsy as its genetic basis is unknown. Both PSSM1 and PSSM2-ER respond well to a low nonstructura...
