28 Mitochondrial adaptations to submaximal exercise training in the gluteus medius and triceps brachii of young equine athletes

Abstract

s / Journal of Equine Veterinary Science 35 (2015) 392e397 395 but the use of electrolyte pastes in races was less common (31%). Analyzing the data set using logistic regression, there was a trend (P 1⁄4 0.10) for metabolic failure to increase 0.66 for each increasing level of alfalfa feeding (0 1⁄4 none, 1 1⁄4 occasional, 2 1⁄4 regular, 3 1⁄4 daily). OR for metabolic failure reduced by 0.10 for each additional ride > 90 km the rider had entered in the last 2 years (P < 0.05). Highest current level of competition and total distance completed over 90 km also approached significance for reducing the risk of metabolic failure. Electrolyte use is common among endurance riders competing at all levels in the UK. In this small survey, experience of horse and rider appeared to have a greater influence on the risk of metabolic failure than electrolyte use or nutrition per se. 28 Mitochondrial adaptations to submaximal exercise training in the gluteus medius and triceps brachii of young equine athletes S.H. White*, L.K. Warren, C. Li, and S. Wohlgemuth University of Florida, Gainesville, FL, USA Exercise training has been shown to enhance mitochondrial biogenesis and efficiency in human and rodent models. We hypothesized that lowto moderate-intensity exercise training would result in similar mitochondrial improvements in skeletal muscle of young horses, and that responses would be muscle dependent. Quarter Horse long-yearlings (mean ± SE, 21 ± 0.2 mo, 410 ± 9 kg) were randomly assigned to either: submaximal exercise training (TR; n 1⁄4 18) comprised of walk-trot-canter exercise in a round-pen or while being ridden 30e45min/d, 3 d/wk; or no controlled exercise (UT; n 1⁄4 6). UT horses were grouphoused on 16-ha pastures, whereas housing for TR horses was split between pasture and stall (~6 h/d). Biopsies were taken from the gluteus medius of all horses (n 1⁄4 24) and from the triceps brachii of a randomly selected subset of TR (n 1⁄4 6) and all UT (n 1⁄4 6) before (wk 0) and after 9 wk of training. Muscle was assessed for activities of cytochrome c oxidase (CCO) and citrate synthase (CS) as indicators of mitochondrial function and number, respectively. Additionally, saponin-permeabilized muscle fibers were analyzed for mitochondrial function via high-resolution respirometry, and data were normalized to mitochondrial number in the sample (CS activity). Data were analyzed using a mixed-model ANOVA. The triceps had greater CS activity (P < 0.0001) and lower CCO activity (P < 0.0001) than the gluteus in all horses; however, enzyme activities were unaffected by time or training. An overall effect of time across both muscle groups and training levels was observed, whereby electron transport system capacity (ETSC) increased (P 1⁄4 0.02), and state 3 respiration (P 1⁄4 0.06) and the respiratory control ratio (P 1⁄4 0.06) tended to increase during the 9-wk observation period. Leak respiration (P 1⁄4 0.01) and state 3 with both complex I and II substrates (GMS; P1⁄4 0.007) were higher across bothmuscle groups in TR compared with UT horses. The gluteus in TR horses appeared to be most greatly affected, as demonstrated by an increase in state 3 with complex I substrates (P 1⁄4 0.04), state 3 GMS (P 1⁄4 0.005), ETSC (P 1⁄4 0.04), and the phosphorylation system control ratio with complex I substrates (P 1⁄4 0.01) from wk 0 to 9. As both young untrained and trained horses exhibited improvements in mitochondrial adaptations over time, these changes could reflect alterations in mitochondria due to growth. Nevertheless, submaximal exercise training appeared to further enhance mitochondrial efficiency in the gluteus medius of young horses.