Outline of the Completed Research

Sports Science

The effects of speed and incline (up and down) on the treadmill to the muscle activities.(2009-2010) 　The effects of speed (1.2-1.5 m/s and 1.7 m/s) and incline (from -6 to +6 %) was evaluated by the integral electromyogram (iEMG) in the fore and hind limbs during walking on the treadmill. There was not a significant change in iEMG due to increasing speed. Therefore, the object of the hand walking (less than 1.7 m/s) should be traditional use for the warm up and cool down before and after training. On the other hand, iEMG during walking down an incline did not increase and decrease in the fore and hind limb, respectively. It was suggested that uphill walking should be combined with downhill exercise to train muscles. Study on the biomechanics of racehorses: Construction of a system for measuring the force applied to tendons and ligaments when running (2005-2008) 　Two devices were created in this study. One was a device for measuring the partial center of gravity and moment of inertia of the shins, pasterns and hooves of a horseﾕs limbs, while the other was a device for measuring the force applied to the pastern ligament from the fetlock angle. Meanwhile, a method of calculating the force applied to the superficial digital flexor tendon from the ground reaction force measured via motion analysis and a force plate was established. Finally, a system for measuring the force applied to the superficial digital flexor tendon of a horse running on a treadmill was constructed by calibrating an AIFP (arthroscopically implantable force probe) sensor implanted inside the tendon. When this system was used to calculate the force applied to the superficial digital flexor tendon of a horse, it became clear that a force of around 4,000N is applied when walking, about 6,500N when trotting, and about 8,000N when cantering at 9m/s. Study on the contraction and relaxation functions of Thoroughbred skeletal muscles (2006-2008) (Commissioned research conducted by Yamaguchi University) 　To ascertain the physiological status of skeletal muscles after temporal high intensity exercise, an attempt was made to estimate the volume of glycogen, the quantification of sarcoplasmic reticulum ﾐCa2+ﾐATPase activity and the generation of free radicals by type of muscle fiber. As a result, a significant decrease in glycogen volumes was recognized in all muscle fiber types after exercise, followed by recovery after one day. On estimating the generation of free radicals using electron paramagnetic resonance, there was a significant increase after exercise and no recovery even after one day. However, no increase in the generation of free radicals immediately after exercise was observed after treadmill running training had been accumulated for 18 weeks. The generation of free radicals immediately after exercise showed a negative correlation with Type IIA fibers. Study on lactate metabolism and lactate transporters in Thoroughbreds (2006-2008) (Commissioned research conducted by University of Tokyo) 　This study concerned lactate transporters in Thoroughbreds. Under sustained high-intensity training, no significant increase was seen in MCT1 or MCT4 protein volumes, but MCT1 was greater in Thoroughbreds subjected to longer running times in maximum exercise tests, while MCT4 was larger in Thoroughbreds with extended maximum running time. Next, changes in MCT and other muscle factors related to lactate metabolism depending on the growth stage from foals to two-year-olds were investigated. Of MCT1, MCT2 and lactate dehydrogenase isozymes, the proportion towards lactate acidification and the mitochondria enzyme activity of muscle increased between 2 and 24 months of age. Meanwhile, MCT4, GLUT4 and phosphofructokinase activity were more or less maintained between 2 and 24 months of age. From these results, it was suggested that, in the process of growth between 2 and 24 months of age, the glycolosis capacity of muscle is maintained while the oxidation capacity and lactate acidification capacity of muscle increase. Establishment of a performance testing system for racehorses and its application II (2004-2006) Purpose 　To breed horses of exceded performance in racing, it is of vital importance for everyone involved in the field that exercise physiological information on racehorses should be accumulated and shared, as well as experience and intuition. The first phase of this research project Iﾓ was to introduce sports science into sites of racehorse training. In the first phase of this project, we developed a system for automatically measuring the heart rate and speed of racehorses while training them on tracks at the JRA Training Centers, using a GPS device. In this way, we have accumulated data during the training of active racehorses. To more accurately evaluate the physical fitness of individual racehorses, however, it is vital that we construct a database allowing us to compare data by age, gender, race condition or other attributes. In the second phase of the project, therefore, we constructed such a database and verified the manual for exercise tests created during the first phase. Results 　1. We used Equi PILOT to record the heart rate and running speed of 123 Thoroughbred racehorses (73 stabled at the Miho TC and 50 at the Ritto TC) during exercise. We then calculated VHRmax (speed at maximum heart rate) based on these records, and created a database. As a result, the VHRmax (14.5±1.3m/s; n=101) of 3-year-olds and above was higher than that of 2-year-olds (13.5±0.8m/s; n=22). The VHRmax (14.4±1.3m/s; n=75) of stallions tended to be higher than that of mares (14.0±1.3m/s: n=48). In terms of race condition, the VHRmax of non-winner horses was 14.0±1.3m/s (n=27), that of horses with earnings of up to 5 million yen was 14.3±1.2m/s (n=29), and that of horses with earnings of up to 10 million yen was 14.5±1.1m/s (n=19). The equivalent figure in open conditions was 15.2±1.4 m/s (n=26), showing that the VHRmax tends to rise as the race condition increases. The VHRmax of the top-performing racehorses Deep Impact and Meisho-Samuson was 16-17m/s, showing a clearly high value. 　2. To ascertain changes in the heart rate of racehorses during actual racing, we recorded heart rates in simulated races held at the Nakayama Racecourse between departure from the stables and the end of the race. As a result, 1) the times in practice races (1200m) held one week earlier were 1 minutes 13.5 seconds (1st year), 1 minute 14.6 seconds (2nd year) and 1 minute 15.6 seconds (3rd year). The times in the simulated races under study (1800m) were 1 minute 58.5 seconds (2nd year) and 1 minute 56.9 seconds (3rd year). All of these were more or less consistent with times in the 2-year-old non-winner class. Moreover, 2) it became clear that heart rate tends to rise from the stable area until entering the underpass, is relatively calm while parading around the paddock but tends to rise when the jockey mounts, and finally rises on entering the starting gate. The impact of warming-up intensity on exercising performance by studying running speed and distance (2002-2006) Purpose 　Warming-up (W-up) is seen as vital in order to bring out the maximum sporting ability of the body and improve performance, while also enhancing the flexibility of the body by raising body temperature, and finally preventing injuries during exercise. As such, it is always practiced before training or races by both humans and racehorses. While a number of studies on W-up have been carried out for racehorses, the impact of differences in W-up intensity on the oxygen transport capacity of horses has not been adequately demonstrated. In this study, therefore, we set different levels of W-up intensity and studied how oxygen transport capacity is affected by differences in this intensity. Results 　1. We conducted an incremental step exercise test in advance to determine W-up intensity, and set four levels of W-up intensity for the test. The four levels were 1) No W-up, 2) Low (blood lactate concentration of around 2mM), 3) Mid (blood lactate concentration of around 6mM), and 4) High (blood lactate concentration of around 10mM). At Low, Mid and High intensity, horses were made to run at that intensity for 1 minute, then walked for 10 minutes, and finally run at 115% VO2max as sprint exercise. ﾒNo W-upﾓ consisted of 10 minutesﾕ walking followed by sprint exercise. 　As a result, blood temperature increased by an average 1.5｡C following W-up, and more or less maintained this value while walking for 10 minutes. The higher the W-up intensity, the faster the acceleration of oxygen consumption kinetics during subsequent sprint exercise tended to be. 　2. While referring to the results of the previous test, we then set three different levels of W-up intensity, namely 1) No W-up, 2) Mid (70% VO2max) and 3) High (115% VO2max). At Mid and High intensity, after running at this intensity for 1 minute, horses were walked for 10 minutes. “No W-up” consisted only of walking for 1 minute. The intensity of the sprint exercise was set at 115% VO2max. As a result, a tendency was seen for the acceleration of oxygen consumption kinetics during subsequent sprint exercise to be faster with higher W-up intensity. The possibility was suggested that this acceleration could be impacted by factors such as arterial-venous difference in O2 concentration. As with the previous test, the possibility was also suggested that the supply of energy during sprint exercise could be altered by differences in W-up intensity. 　3. We set three different levels of W-up intensity at uniform W-up distance, namely 1) Low intensity level (30% VO2max: 400 sec.), 2) Mid intensity level (60% VO2max: 200 sec.) and 3) High intensity level (100% VO2max: 120 sec.), and followed W-up with 10 minutesﾕ walking. We set the intensity of sprint exercise at 115% VO2max. As a result, VO2 during sprint exercise was significantly high at High and Mid intensity, and the possibility was suggested that this was caused by cardiac output and stroke volume. Meanwhile, blood lactate concentration immediately after W-up showed no change at Low and Mid intensity, but increased to around 6mM at High intensity. Blood lactate concentration rates were significantly low at Mid, High intensity compared to Low intensity. The fact that the respiratory quotient at the beginning of the exercise was lower at High intensity than at Low intensity suggested that High intensity W-up provides more aerobic exercise. No significant difference in running time was observed between the three types of W-up. If the W-up intensity is too strong, conversely, a tendency was recognized for running time (performance) to be reduced. From these findings, it was thought that, by carrying out W-up, the supply of energy during sprint exercise become more aerobic, although excessively strong W-up intensity is not desirable.