of the Completed Research
@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.
@Hypoxic training is a common method used by human athletes to improve aerobic performance. In skeletal muscle, PGC-1ฟ is a major regulator of exercise-induced mitochondrial biogenesis. The purpose of this study was to investigate the effect of hypoxic training on PGC-1ฟ 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-1ฟ 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.
@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.
@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.
Study on the effect of high-intensity training on lactate transporter in Thoroughbred horses (2009P2011) (Joint research conducted with Tokyo University)
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.
The effect of feeding and exercising on appetite controlled hormones (ghrelin and GLP-1) in Thoroughbred horses (2009P2011) (Joint research conducted with Hiroshima University)
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.
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 horseีs 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)
@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 ะCa2+ะATPase 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)
@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)
The impact of warming-up intensity on exercising performance by studying running speed and distance (2002-2006)
@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-uph 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.
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 minutesี
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.