title: Effects of intensity and duration of exercise on muscular responses to training of thoroughbred racehorses.
abstract: This study examined the effects of the intensity and duration of exercise on the nature and magnitude of training adaptations in muscle of adolescent (2-3 yr old) racehorses. Six thoroughbreds that had been pretrained for 2 mo performed six consecutive conditioning programs of varying lactate-guided intensities [velocities eliciting blood lactate concentrations of 2.5 mmol/l (v2.5) and 4 mmol/l (v4), respectively] and durations (5, 15, 25 min). Pre- and posttraining gluteus muscle biopsies were analyzed for myosin heavy chain content, fiber-type composition, fiber size, capillarization, and fiber histochemical oxidative and glycolytic capabilities. Although training adaptations were similar in nature, they varied greatly in magnitude among the different training protocols. Overall, the use of v4 as the exercise intensity for 25 min elicited the most consistent training adaptations in muscle, whereas the minimal training stimulus that evoked any significant change was identified with exercises of 15 min at v2.5. Within this range, muscular adaptations showed significant trends to be proportional to the exercise load of specific training programs. Taken together, these data suggest that muscular adaptations to training in horses occur on a continuum that is based on the exercise intensity and duration of training. The practical implications of this study are that exercises for 15 to 25 min/day at velocities between v2.5 and v4 can improve in the short term (3 wk) the muscular stamina in thoroughbreds. However, exercises of 5-15 min at v4 are necessary to enhance muscular features related to strength (hypertrophy).
authors.affiliation: Laboratory of Muscular Biopathology, Dept. of Comparative Anatomy and Pathological Anatomy, University of Cordoba, 14014 Cordoba, Spain. an1lorij@uco.es
authors.forename: José-Luis L
authors.initials: JL
authors.lastname: Rivero
authors.forename: Antonio
authors.initials: A
authors.lastname: Ruz
authors.forename: Silvia
authors.initials: S
authors.lastname: Martí-Korff
authors.forename: José-Carlos
authors.initials: JC
authors.lastname: Estepa
authors.forename: Escolástico
authors.initials: E
authors.lastname: Aguilera-Tejero
authors.forename: Jutta
authors.initials: J
authors.lastname: Werkman
authors.forename: Mathias
authors.initials: M
authors.lastname: Sobotta
authors.forename: Arno
authors.initials: A
authors.lastname: Lindner
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D002196:Capillaries / Q000502:physiology; D048429:Cell Size; D005993:Glycerolphosphate Dehydrogenase / Q000378:metabolism; D006019:Glycolysis; D006736:Horses / Q000502:physiology*; D019344:Lactic Acid / Q000097:blood; D018485:Muscle Fibers, Skeletal / Q000502:physiology; D018482:Muscle, Skeletal / Q000098:blood supply / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D018995:Myosin Heavy Chains / Q000378:metabolism; D018919:Neovascularization, Physiologic; D010084:Oxidation-Reduction; D010805:Physical Conditioning, Animal / Q000379:methods*; D010807:Physical Endurance / Q000502:physiology*; D011897:Random Allocation; D013385:Succinate Dehydrogenase / Q000378:metabolism; D013997:Time Factors
chemical_list: D019344:Lactic Acid; D005993:Glycerolphosphate Dehydrogenase; D013385:Succinate Dehydrogenase; D018995:Myosin Heavy Chains