Flexibility of equine bioenergetics and muscle plasticity in response to different types of training: An integrative approach, questioning existing paradigms

Abstract

Equine bioenergetics have predominantly been studied focusing on glycogen and fatty acids. Combining omics with conventional techniques allows for an integrative approach to broadly explore and identify important biomolecules. Friesian horses were aquatrained (n = 5) or dry treadmill trained (n = 7) (8 weeks) and monitored for: evolution of muscle diameter in response to aquatraining and dry treadmill training, fiber type composition and fiber cross-sectional area of the M. pectoralis, M. vastus lateralis and M. semitendinosus and untargeted metabolomics of the M. pectoralis and M. vastus lateralis in response to dry treadmill training. Aquatraining was superior to dry treadmill training to increase muscle diameter in the hindquarters, with maximum effect after 4 weeks. After dry treadmill training, the M. pectoralis showed increased muscle diameter, more type I fibers, decreased fiber mean cross sectional area, and an upregulated oxidative metabolic profile: increased β-oxidation (key metabolites: decreased long chain fatty acids and increased long chain acylcarnitines), TCA activity (intermediates including succinyl-carnitine and 2-methylcitrate), amino acid metabolism (glutamine, aromatic amino acids, serine, urea cycle metabolites such as proline, arginine and ornithine) and xenobiotic metabolism (especially p-cresol glucuronide). The M. vastus lateralis expanded its fast twitch profile, with decreased muscle diameter, type I fibers and an upregulation of glycolytic and pentose phosphate pathway activity, and increased branched-chain and aromatic amino acid metabolism (cis-urocanate, carnosine, homocarnosine, tyrosine, tryptophan, p-cresol-glucuronide, serine, methionine, cysteine, proline and ornithine). Trained Friesians showed increased collagen and elastin turn-over. Results show that branched-chain amino acids, aromatic amino acids and microbiome-derived xenobiotics need further study in horses. They feed the TCA cycle at steps further downstream from acetyl CoA and most likely, they are oxidized in type IIA fibers, the predominant fiber type of the horse. These study results underline the importance of reviewing existing paradigms on equine bioenergetics.

Comparison of Shifts in Skeletal Muscle Plasticity Parameters in Horses in Three Different Muscles, in Answer to 8 Weeks of Harness Training

“…In a follow-up study, they reported a decrease in mean CSA in the m. vastus lateralis, to be associated with an increased oxidative and decreased glycolytic capacity (61). A smaller mean CSA in response to training is thought to be associated with a reduced glycogen storage capacity (18), and occurrence of muscle hyperplasia (muscle growth), as previously shown in Friesian horses subjected to aquatraining and dry treadmill training (73).…”

“…In a follow-up study, they reported a decrease in mean CSA in the m. vastus lateralis, to be associated with an increased oxidative and decreased glycolytic capacity ( 61 ). A smaller mean CSA in response to training is thought to be associated with a reduced glycogen storage capacity ( 18 ), and occurrence of muscle hyperplasia (muscle growth), as previously shown in Friesian horses subjected to aquatraining and dry treadmill training ( 73 ). In that study, it was shown that these morphological changes also coincide with an increased capacity to process alternative fuels such as branched-chain amino acids, aromatic amino acids, and gut microbiome-derived xenobiotics, which can more easily reach the muscular metabolic machinery, because of a smaller fiber type specific CSA.…”

“…The observed training-induced changes in the current study suggest that the muscular machinery models itself toward an optimal smaller individual muscle fiber structure to receive and process fuels that can be swiftly delivered by the circulatory system and do not require a major transformation of the mitochondrial machinery. In a previous training study, we have shown that branched-chain amino acids, aromatic amino acids, and gut microbiome-related xenobiotics function as important fuels ( 73 ). These metabolites also showed remarkable changes in other previous training studies, however, without receiving further attention ( 40 , 101 – 103 ).…”

Development of an equine muscle condition score

“…Moreover, human studies have shown that muscle mass is an important factor in relation to outcome of disease and recovery (Wolfe, 2006). It is well‐known in both humans and animals that muscle mass is influenced by several factors including training (De Meeûs D'Argenteuil et al, 2021; Stubbs et al, 2011), age, and disease (Banse et al, 2021; Fielding et al, 2011; Freeman, 2012; Stubbs et al, 2010; Valberg, 2018). For all these reasons, it is important that veterinarians, horse owners, trainers and other people involved in horse management and training are able to evaluate muscle mass in horses to optimise performance, animal welfare and prevent disease.…”

Previous Exercise on a Water Treadmill at Different Depths Affects the Accelerometric Pattern Recorded on a Track in Horses

“…Exercise in water is being increasingly used in sport horses, either for the rehabilitation of musculoskeletal injuries or within a training program as non-specific training exercises [ 1 , 2 , 3 , 4 ]. Despite many clinicians and trainers recommending its use, there are few scientific studies that describe the longitudinal kinematic and kinetic changes through rehabilitation programs for specific musculoskeletal injuries.…”