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This Article Full Text Free Full Text (PDF) Free All Versions of this Article: 102/5/1871    most recent 01093.2006v1 Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Rivero, J.-L. L. Articles by Lindner, A. Search for Related Content PubMed PubMed Citation Articles by Rivero, J.-L. L. Articles by Lindner, A.

Effects of intensity and duration of exercise on muscular responses to training of thoroughbred racehorses

¹Laboratory of Muscular Biopathology, Department of Comparative Anatomy and Pathological Anatomy, and ²Department of Animal Medicine and Surgery, Faculty of Veterinary Sciences, University of Cordoba, Campus Rabanales, Edificio de Sanidad Animal, Cordoba, Spain; and ³Arbeitsgruppe Pferd, Juelich, Germany

Submitted 29 September 2006 ; accepted in final form 18 January 2007

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).

skeletal muscle fibers; myosin heavy chain; muscle fiber types; blood lactate; equine muscle physiology