Pichet JewmongkonchaiArunothai MuangmaPattama RitruechaiMahidol University. Faculty of Veterinary Science. Department of Clinical Science and Public Health2018-06-112018-06-112018-062016Journal of Applied Animal Science. Vol.9, No.3 (2016), 37-491906-2257https://repository.li.mahidol.ac.th/handle/20.500.14594/15257The longissimus dorsi is the largest back muscle of the horse and has the potential to contribute movement to the horse's back. Damage to the longissimus dorsi is very common to cause back injuries, which is also a major cause of poor performance and gait abnormalities in horses. The muscle indenter is a tool that allows measuring the stiffness of the back muscles. We hypothesized that the longissimus dorsi muscle tone after training would be stiffer than at rest. One sound mare and three gelding Thoroughbred racehorses were used in this study. The muscle tone was measured using a muscle indenter along both sides of the T14, T16, T18 and L2 longissimus dorsi muscle. Blood sample were collected to measure the blood lactate concentration before and after training. Heart rate was measured at rest and at 0, 5, 10, 15 and 20 minutes after training. We found a significant increase in muscle tone after training at T14, T16 and T18. The blood lactate concentration of studied horses significantly increased after training, although the values were still within the normal range. The recovery heart rates for all horses are tended to decrease (< 70 bpm) after 5 minutes of stopping exercise. We confirmed that the longissimus dorsi is a key muscle in horse movement that can be sensitive to relatively small training sessions; that is why this muscle is prone to get injured. Generally, the muscle intender was a successful tool of objectively measuring this muscle tone.engMahidol UniversityHorseThoroughbredlongissimus dorsimuscle indentermuscle toneม้าพันธุ์โทโรเบรทเครื่องวัดแรงตึงแรงตึงของกล้ามเนื้อJournal of Applied Animal ScienceResearch ArticleFaculty of Veterinary Science Mahidol University