@Outline of the Completed Research

Sports Science


Analysis of training programs of Thoroughbred racehorses: physiological responses and adaptations to training (2013|2015)

@We investigated the training programs of racehorses in Japan tested the hypothesis that higher-ranked trainers (HI) exercised horses differently from lower-ranked trainers (LO). Total exercise distance\especially the distance at a walk (as a warm-up) and at moderate intensity (>6.9 and <13.3 m/s)\was longer at the Miho training center than at the Ritto training center. We also analyzed the relationship between risk of injury and training programs, and we showed that the incidence of injury increased only with longer distance at moderate intensity. The training programs of HI were of shorter distance than those of LO at moderate intensity and of longer distance than those of LO at high intensity (>13.3 m/s). To determine whether these differences in training protocols could change physiological responses and skeletal muscle adaptation in horses, we conducted treadmill exercise tests to simulate the typical training protocols of HI and LO. The training programs of HI covered less total distance but greater distance at higher intensity than those of LO, presumably providing greater stimulation of aerobic and glycolytic energy pathways than those of the LO. A single training bout with HI induced greater adaptations in mitochondrial biogenesis and angiogenesis of skeletal muscle than a single bout with LO.

Techniques of recovering the water and electrolytes lost in sweat during exercise (2013|2015)

@We examined methods of recovering the water and electrolytes lost in sweat during exercise. First, methods for estimating the total sweating rate of the whole body of the horse were examined. There was a significant correlation between total body water (TBW) and unit area sweating rate (SR) on the neck (R2 = 0.884; P < 0.001), and it was thus possible to estimate TBW by measuring SR on the neck. We then examined the effects of the type of replacement solution on recovery of the water lost with sweat were examined. Water (Water group) or electrolyte solution (Electro group) was administered by transnasal catheter 1 h before exercise, and recovery of TBW was measured by the stable isotope dilution method. There were no differences between the two groups. We then examined the effects of the timing of administration of electrolytes on TBW. Electrolyte solution was administered by transnasal catheter 1 or 3 h before the start of exercise, and TBW was measured by the same method as above. No differences in TBW 3 h after the end of exercise were seen between the two different timings of administration of electrolyte solution. There is a need for further examination of appropriate water and electrolyte administration in future.

The effects of exercise and nutrition on protein synthesis in skeletal muscle of Thoroughbred horses (2011-2013)

@The present study aimed to clarify the effects of treadmill exercise and of nutrient ingestion following treadmill exercise on muscle protein synthesis and degradation of Thoroughbred horses. The mammalian target of rapamycin (mTOR) signaling pathway plays a significant role in stimulating translation initiation and muscle protein synthesis. mTOR signaling to its downstream effector, ribosomal S6 kinase 1 (S6K1), is involved in the regulation of mRNA translation initiation and appears to be a critical regulator of exercise-induced muscle protein synthesis and training-induced hypertrophy. Inasmuch as the levels of phosphorylation influence the activities of S6K1 in the initiation of protein synthesis, the phosphorylation states of S6K1 were examined in the gluteus medius muscle. The phosphorylation of S6K1 was increased following treadmill exercise in both gelding and female horses. Oral administration of whey protein at 30 min after exercise further enhanced the phosphorylation of S6K1. There are two protein degradation systems in mammalian cells, namely autophagy and ubiquitin/proteasome systems. Both systems are activated during muscle atrophy and variably contribute to the loss of muscle mass. Importantly, autophagy is physiologically induced by exercise including both endurance and resistance exercise and mediates the metabolic beneficial effects of physical activity on glucose homeostasis. The ratio of LC3II to LC3I, an indicator of autophagy, was not changed either by exercise alone or by exercise plus whey administration. These data suggest that immediate administration of protein after exercise could improve the stimulation of muscle protein anabolism by treadmill exercise.


The effect of hypoxic training on peroxisome proliferatoractivated receptor ƒม coactivator-1 ƒฟ (PGC-1ƒฟ) in Thoroughbred horses (2010-2013)

@Hypoxic training is a common method used by human athletes to improve aerobic performance. In skeletal muscle, PGC-1ƒฟ is a major regulator of exercise-induced mitochondrial biogenesis. The purpose of this study was to investigate the effect of hypoxic training on PGC-1ƒฟ in Thoroughbred horses. After treadmill training in normobaric hypoxia 3 days/week for 4 weeks, hypoxia group increased significantly more than normoxia group in time to exhaustion and maximal O2 consumption. Specific cardiac output and stroke volume at exhaustion increased only in hypoxia group. PGC-1ƒฟ protein content in hypoxia group tended to decrease and cytochrome c oxidase (COX IV) protein content significantly decreased compared to normoxia group. These results suggest that hypoxic training in Thoroughbred horses improves their performance and aerobic capacity, which is independent of mitochondrial biogenesis.


The effects of fatigue in the superficial and deep digital flexor muscle to the injury of the superficial digital flexor tendon (2011-2013)

@One of the causes of the injury in the superficial digital flexor tendon is assumed that the force to the superficial digital flexor tendon increase with fatigue. The reason of this increase of force is assumed as follow. The deep digital flexor muscle may fatigue earlier than the superficial digital flexor muscle, because the percentage of fast twitch fiber is higher in the deep digital flexor muscle compare to the superficial digital flexor tendon. The force produced by the deep flexor muscle may decrease with fatigue. The force to the superficial digital flexor muscle and tendon may increase, because the deep digital flexor muscle supports the fetlock joint with the superficial digital flexor muscle. Therefore, we examined the time of developing the fatigue and the effect of fatigue to the force in the superficial and the deep digital flexor tendons. The results suggested that the deep digital flexor muscle tended to fatigue earlier than the superficial digital flexor muscle. After the exhaustion running, however, the force did not change in the deep digital flexor tendon, although the force tended to decrease in the superficial digital flexor tendon, and significantly increased in the suspensory ligament. Because the force in the superficial digital flexor tendon decreased, the injury of this tendon might not be caused by the fatigue of the deep digital flexor muscle.


Effects of training on oxygen consumption (2010–2012)

@In repetitive high-intensity exercise, oxygen consumption in the second run was higher than in the first one when the interval between runs was shorter. Oxygen consumption at high speed did not differ significantly between running downhill and on a flat course.

Influence of different feeds on energy metabolism in racehorses: Effects of beet pulp plus vegetable oil (2010–2012)

@Nine Thoroughbred horses exercised daily on a treadmill were fed for 3 weeks or more on high-starch feed (HS) or high lipid and fiber feed (FF); the feeding trial was then repeated with the two types of feed switched. We investigated the effects of the two feeds (i.e. either starch or lipid + plant fiber) on the rates of use of carbohydrate and lipid for energy during and after high-intensity exercise.
@Stable isotope-labeled carbohydrate (glucose) and lipid (glycerol) were infused intravenously; the rates of use of carbohydrate and lipid for energy were then investigated by measuring the changes in the ratios of the stable isotopes of glucose and glycerol (enrichment) and origin those in the living body. In the HS and FF treatments, there were no differences in the rates of carbohydrate and lipid use for energy during and after exercise. The influence of oil and fiber on racehorse performance was equivalent to that of a high starch diet in respect of energy production. Vegetable oil or beet pulp, or both, are recommended for use in appropriate amounts in racehorses as racehorse feeds.

Study on the effect of high-intensity training on lactate transporter in Thoroughbred horses (2009P2011) (Joint research conducted with Tokyo University)

@The aim of this study was to investigate the effect of high-intensity training and detraining or reduced training on lactate transporters (monocarboxylate transporters (MCTs)) in Thoroughbred horses. Fourteen proteins have been identified in the MCT family. MCT1 and MCT4 are two of the major MCTs in the skeletal muscle. MCT1 uptakes lactate within the muscle cell and MCT4 releases lactate from the muscle cell.
@Both MCT1 and MCT4 protein expressions significantly increased after 18-wk high-intensity training. Following 18-wk training, MCT1 protein expression of 6-wk detraining group decreased and that of 6-wk moderate-intensity training group maintained the post-training level. However, MCT4 protein expression declined after both 6-wk detraining and moderate-intensity training.
@Moreover, MCT1 and MCT4 protein expressions significantly increased 6 h after a single bout of high-intensity exercise and returned to the baseline 24 h after exercise. These results suggest that increased MCT1 and MCT4 protein expressions after 18-wk training may follow repeated exercise-induced transient increases in these proteins.

The effect of feeding and exercising on appetite controlled hormones (ghrelin and GLP-1) in Thoroughbred horses (2009P2011) (Joint research conducted with Hiroshima University)

@The aim of this study was to investigate the effect of feeding and exercising on ghrelin and glucagon-like peptide-1 (GLP-1) in Thoroughbred horses. Ghrelin have an appetite-enhancing action and GLP-1 have an appetite-suppressing effect. Both hormones showed diurnal variation mainly in response to feeding, however, this diurnal variation was disturbed by application of a highly-intense exercise after feeding. The disturbance was stabilized by prolonging the interval between feeding and exercise and by keeping the pre-exercise energy allowance low. The changes in the levels of these hormones were likely associated with feeding-related increases in blood glucose levels and blood insulin levels.
@In conclusion, it may be possible to prevent the loss of appetite caused by exercise by varying both the interval between feeding and exercise and the pre-exercise energy allowance.

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 horses 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 Ca2+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 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. No W-up consisted of 10 minutes walking followed by sprint exercise.
@As a result, blood temperature increased by an average 1.5C 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. gNo W-uph 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 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.