according to the studies of matsuba and shimamura in 1933 , 
 respiratory frequency ( rf ) increased by 1.2 times ( all values compared to with those at rest ) when walking 200 
 m , by 1.5 times during a 200 m trot , and by 45-fold during a 5,0006,400 m canter .
however , these numbers were 
 obtained by determining the rf just after exercise by counting the movements of the ribcage and upper flank with 
 naked eye of an observer based on the assumption that the rf immediately after exercise is equivalent to the rf 
 during exercise . in 1944 ,
okabe and sugiyama   measured rf continuously during 
 exercise at a walk , trot , and canter by recording expiratory sounds with a microphone attached near the nostril 
 that was connected to an amplifier and speaker pulled on a drafting vehicle .
the rf and stride frequency ( stf ) 
 during exercise were recorded for a total of 42 min consisting of a 30 min trot ( 170 m / min ) , 3 min canter 
 ( 300400 m / min ) , and 9 min walk ( 100 m / min ) in 20 horses . as shown in fig . 

1.changes in respiratory frequency ( rf ) , stride frequency ( stf ) , and velocity during exercise .
the authors 
 generated this graph using data from a table in a study by okabe and sugiyama .
, the stf during trotting was about 84 str / min ( where str is strides ) 1 min after starting the trot and 
 remained almost constant throughout , and the average stf for a 30 min trot was 83.1 str / min .
the rf during the 
 first 1 min of trotting was 73 br / min ( where br is breaths ) , then it increased to 100 br / min at 12 min and it 
 increased to more than 110 br / min thereafter .
the stf during 
 cantering was 103 str / min 1 min after starting cantering and remained constant .
the average stf during cantering 
 was 105.3 str / min and the rf during cantering was synchronized with the stf , with expiratory sounds occurring 
 during stance phase of the trailing forelimb .
the stf during walikg just after finishing cantering was 63 
 str / min , and then it remained at 5759 str / min thereafter .
the rf at the end of the canter was 108 br / min , it 
 decreased to 97 br / min shortly after finishing cantering , and then it remained around at 110 br / min during 
 walking .
immediately after the horse stopped walking , the rf decreased dramatically to 80 br / min .
the authors 
 concluded that the rf immediately after exercise while standing was completely different from the rf during 
 exercise because of the very rapid decrease in rf that occurred after finishing exercise .
changes in respiratory frequency ( rf ) , stride frequency ( stf ) , and velocity during exercise .
the authors 
 generated this graph using data from a table in a study by okabe and sugiyama .
it was also noted that several different respiratory sounds , such as snorting and booming , were heard during 
 exercise , and a booming sound was recorded during the stance phase of the trailing forelimb .
it was also noted 
 that the tone of the respiratory sounds changed during exercise . during trotting
, the strength , pitch , and 
 length of respiratory sounds tended to become irregular 1620 min after starting trotting , but they became 
 regular when the horse began cantering .
compared the rfs under 4 different 
 workloads including plowing , cultivating ( tilling with a cultivator ) , harrowing ( crushing soil with a harrow ) , 
 and free walking ( as a control ) using the same equipment as okabe and sugiyama . according to their observations ,
the rf increased in a fluctuating manner and reached a steady 
 state at each intensity of exercise .
the average work resistance during plowing and harrowing ( 3035 kg ) was 
 greater than that of cultivating ( 2025 kg ) . because horses have to walk on softer ground when
harrowing 
 compared with plowing , it is generally considered that harrowing is heavier work than plowing . because the rate 
 of increase in rf tended to be higher when harrowing than plowing and higher in plowing than cultivating
reported the rf during trotting at a small riding ground ( 380 m / lap ) with 
 different exercise protocols : a , 300 m / min for 14 min ( or 20 min ) , and b , 200 m / min for 30 min ( or 45 min ) . the 
 rf reached steady state in both protocols approximately 10 min after starting and remained constant thereafter . 

the rf in the steady state was higher during the 300 m / min trot ( 95100 br / min ) than the 200 m / min trot ( 7580 
 br / min ) .
the authors suggested that there was a relationship between stf and rf , because rf was sometimes 
 synchronized with stf systematically in 1:1 , 1:2 , or 1:3 ratios when trotting in a straight line .
these 
 systematic relationships tended to disappear when horses ran around a curve . in 1978 , attenburrow recorded both inspiratory and expiratory respiratory sounds with a radio - stethoscope 
 during walking , trotting , cantering , and galloping .
he also recorded 
 respiratory and limb cycles simultaneously and found that the respiratory cycle and limb cycle were synchronized 
 only at a canter and gallop .
later , kai and kubo   of the equine research institute of the japan racing association recorded 
 respiratory and stride frequency simultaneously during galloping just after a start dash from the starting gate 
 and reported that a 46 sec apneic pause occurred just after starting , after which respiration restarted and 
 synchronized with the stride frequency .
pulse rate immediately after exercise was measured by auscultation in the study of matsuba and shimamura . because direct measurement of heart rate ( hr ) during exercise was 
 impossible at that time ( 1933 ) , pulse rate immediately after exercise was assumed to indicate hr during 
 exercise .
later , tatsumi et al .   showed that there 
 is a close relationship between oxygen consumption of horses during exercise as measured by the douglas bag 
 method and the pulse rate immediately after exercise .
researchers then recognized the importance of hr 
 measurements during exercise and began developing methods for measuring hr during exercise .
it was difficult to 
 obtain an ecg necessary for calculating hr during exercise , although it could be recorded at rest [ 30 , 39 , 83 ] . in 1960 , nomura and tominaga   recorded ecgs from a horse walking on 
 a specially constructed treadmill at a speed of 70 m / min while drafting 5 different weights .
the ecgs were 
 obtained by transmitting the signal to a receiver using a 20 mhz carrier wave and reproducing the signal with an 
 electromagnetic oscillograph .
changes in hr during exercise and the recovery period were calculated by creating 
 diagrams of r - r intervals from the ecg recording .
heart rate increased immediately when the horse started 
 exercising and returned to a steady state within a short time when the workload was light .
even when the 
 workload was heavy , the heart rate became to a steady state within 3 min , with a second increase in hr occurring 
 about 10 min after the beginning of exercise .
although recording of ecgs from a horse exercising on a treadmill 
 had become possible by using a transmitter set near the horse and a carrier wave , it was still very difficult to 
 record the ecg of a horse exercising under field conditions . a research project to record equine ecgs during exercise using radiotelemetry was performed as a collaborative 
 study between nomura of the university of tokyo and the equine health laboratory of the japan racing 
 association . for the research study , a custom - made radiotelemetry system that could record ecgs within 100
m was 
 developed , and the performance of the system evaluated . during exercise at intensities ranging from walking to 
 intense galloping ,
the 
 investigators concluded that ecgs obtained by this system were clear enough to calculate hr or r - r intervals 
 during exercise .
ecgs were recorded using the newly developed system during both low - intensity exercise with a 
 horse riding on the ground or jumping low hurdles and during high - intensity sprint - galloping on a track in order 
 to calculate changes in hr during exercise .
the major findings regarding changes in hr were as follows : 1 ) 
 during low intensity exercise including the walk , trot , canter and extended canter , hr increased from 45 
 beat / min during pre - exercise to 150 beat / min at an extended canter , and ; 2 ) hr increased to 200 beat / min or more 
 in most horses during 100 m high - intensity sprint galloping ( fig . 

the authors generated this graph using data from a 
 table in a study by nomura et al . . ) .
the first report of ecgs measured during field exercise in the horse was from this study by nomura 
 et al . in 1964
[ 41 , 42 ] . a similar report by nomura was also published in 1966 in another journal .
banister et al . in 1968   reported ecgs measured during field exercise in horses . in order to carry out a reliable 
 recording of ecgs during exercise of a horse running on a large track ,
a high - power telemetric transmitter was 
 constructed on special order and operated under a license from the radio regulatory bureau . because the high transmitting power of 1 w enabled an effective 
 transmission range of 5 km or more , it became possible to record ecgs for horses exercising in large areas , 
 e.g. , on an oval track at a racecourse .
the authors generated this graph using data from a 
 table in a study by nomura et al . .  
although it had become possible to measure instantaneous changes in an ecg during exercise using 
 radiotelemetry , this system had certain disadvantages , such as the fact that it could only be used for recording 
 from a single horse and could only be used within the effective transmission area of the radio waves .
therefore , 
 a portable electrocardiograph with a magnetic tape recording system for exercising horses was devised [ 2 , 29 ] . because the portable magnetic 
 tape electrocardiograph allowed recording of ecgs from many horses exercising simultaneously
, it became a useful 
 tool for evaluating equine arrhythmias and hr during exercise tests performed at large race tracks .
currently , 
 digital holter ecg systems are widely used for exercise electrocardiography in racehorses .
nomura   also developed a beat meter to measure the hr of draft 
 horses during heavy pulling work at slower speeds in the field .
although this device could not record a raw ecg , 
 it enabled hr to be measured by counting the popping sounds per unit time that were created when the meter 
 detected larger amplitude signals in the ecg , e.g. , the qrs complex .
matsuba and shimamura evaluated the fitness of racehorses by analyzing 20 parameters they considered as being 
 important for exercise physiology and that were possible to measure at that time ( 19331939 ) . among them , 5 blood 
 parameters - fragility of erythrocytes , blood viscosity , erythrocyte sedimentation rate , freezing point 
 depression , and ph - changed with time during training , so they recommended that these parameters would be useful 
 indexes for future training studies .
in addition to the aforementioned parameters measured in their studies , other parameters such as the 
 o2 concentration , co2 concentration , and blood lactate concentration were also measured . 
 in 1937 , shijo   reported that the o2 concentrations in 
 arterial and venous blood were 20.81% and 12.08% , respectively , and showed that plasma co2 
 concentrations in arterial and venous blood were 46.60% and 57.85% , respectively , using 26 horses .
shijo   measured venous o2 and co2 concentrations weekly 
 for about 3 months during a training period in 4 horses and showed that the average co2 concentration 
 was 61.6% and almost the same in each horse .
the o2 concentration was 12.7% , and there was relatively 
 high correlation between the o2 concentration and erythrocyte count throughout the training period 
 ( fig . 3fig .
the authors 
 generated this graph using data from a table in a study by shijo . ) .
shijo   also examined the effect of exercise on blood counts 
 and showed that erythrocyte and leukocyte counts increased with intense exercise and numbers of neutrophils 
 increased but that numbers of lymphocytes decreased .
the authors 
 generated this graph using data from a table in a study by shijo .
although the blood lactate concentration was not measured in studies by matsuba et al . , the blood lactate 
 concentration is considered to be one of the most important parameters in assessing performance in equine 
 exercise physiology . in 1934 , yasuda   measured blood lactate 
 concentrations during 3 days of draft work ( total distance 111 km ) in 12 warhorses . because the exercise 
 intensities were low ,
the authors generated this graph using data from a table in a 
 study by yasuda .
( pre , before exercise ; post , just after 
 exercise ; 30 min , 30 min after exercise ; and 60 min , 60 min after exercise ) ) .
this was the only study that had measured the blood lactate concentration up to that time . if blood 
 lactate had been measured in the studies of matsuba et al .
the authors generated this graph using data from a table in a 
 study by yasuda .
( pre , before exercise ; post , just after 
 exercise ; 30 min , 30 min after exercise ; and 60 min , 60 min after exercise ) in 1967 , sakurai et al .   compared the effects of 
 exercise intensity ( 1,100 m at 6.7 m / s , 1,100 m at 11.1 m / s , and 1,600 m at 12.5 m / s ) on changes in blood 
 characteristics and reported that the red blood count , white blood cell count , hemoglobin concentration , 
 hematocrit , erythrocyte resistance , and blood lactate concentration increased but that eosinophils , erythrocyte 
 sedimentation rate , and blood water content decreased . in this report , the blood lactate concentration was 0.7 

mmol / l after 1,100 m ( at 6.7 m / s ) , 7.3 mmol / l after 1,100 m ( at 11.1 m / s ) , 
 and 12.1 mmol / l after 1,600 m ( at 12.5 m / s ) .
the glucose , pyruvate and lactate concentrations 
 were also measured after 2 different kinds of exercise - relatively short distance cantering and long distance 
 trotting - and the authors reported that both the lactate and pyruvate concentrations increased after cantering 
 .
the question as to whether or not changes in the thyroid hormone concentration in plasma ( t3 and 
 t4 ) at rest might be useful as an indicator of physical fitness of a racehorse was investigated 
 during the training period from september of the yearling year to may of the 2-year - old year .
the concentration of t3 in plasma , which was used in that 
 study as the t3 binding capacity index , decreased clearly during the early period of training and 
 remained constant during the latter half of the training period .
the authors found that greater function of the 
 thyroid gland during training correlated with changes in t3 in the horses .
therefore , they speculated 
 that changes in t3 might be used to evaluate the physical fitness of active racehorses .
the 
 concentration of t4 in plasma decreased clearly in the middle stage of training , but it increased 
 markedly in the final stage . because it was presumed that the horses were able to train more intensely in the 
 final stage of their investigation , the authors considered that the elevation of t4 was useful for 
 evaluating the reserve of strength in the horse .
relationships between changes of some blood enzymes and physiological conditions in exercising horses were 
 investigated using 3 horses subjected to long distance running .
they ran 22,000 m / day for 5 consecutive days 
 mainly at an extended trot but partially at a slow canter .
blood 
 samples were collected before , in the middle , immediately after , and 1 and 5 hr after exercise every day during 
 the exercise period and at 1 , 2 , 3 , 5 , and 7 days following the exercise period to document the recovery 
 process . in this experiment ,
changes in the activities of creatine kinase , aspartate amino transferase , and 
 fructose diphosphate aldolase were measured .
the magnitude of the rate of increase became larger as the exercise intensity increased . 

although aspartate amino transferase activity failed to increase markedly as the intensity of the exercise 
 increased , it remained at a relatively high level and then increased gradually during the exercise period . 

fructose diphosphate aldolase activity changed in an intermediate manner between the two enzymes mentioned 
 above .
these results suggest that creatine kinase might be utilized as the most useful index of the severity of 
 exercise and that aspartate aminotransferase might be utilized as an index for overtraining .
however , the 
 significance of changes in fructose diphosphate aldolase activity with exercise is unclear .
the erythrocyte sedimentation rate ( esr ) is the rate at which erythrocytes form a sediment during a fixed 
 period of time , typically 1 hr ; it considered to be a nonspecific parameter of inflammation .
although this 
 parameter has been used mainly as a nonspecific index of inflammation , it must be considered that it can be 
 influenced by various factors . however , the relationship between the esr and exercise was previously unknown , 
 especially in horses .
yasuda and coworkers , who studied the exercise physiology of the warhorse , examined 
 relationships between the esr and exercise and fatigue in warhorses .
examined the effects on the esr of 
 faster and slower speeds during exercise using 15 warhorses and 6 local horses .
the faster exercise consisted of 
 long distance riding for 3 days , and the total distance was 142.5 km .
the slower exercise was draft exercise for 
 4 days , and the total distance was 116.5 km .
the esr was calculated as the median value from the sedimentation 
 at 1 hr and 2 hr ( ( 1 hr + 2 hr/2)/2 ) .
it was found that the esr after faster exercise was 14.5 mm lower than the 
 values before exercise . on the other hand , the esr after slower exercise did not differ between before and after 
 exercise , and the esr tended to be low when the erythrocyte count was large .
the authors suggested that 
 measurement of the esr might be a useful tool for evaluating fatigue , especially with faster riding exercise . 

hiroe et al .   also reported the effects of similar 
 exercise on blood viscosity in 25 warhorses .
blood viscosity was expressed as a relative value using distilled 
 water as a reference ( 1.0 ) .
the average blood viscosity at rest was 4.89 and increased to 12.6 after faster 
 exercise , and recovery took about 21 hr . on the other hand , blood viscosity was not changed after slower 
 exercise compared with the pre - exercise value .
the authors suggested that blood viscosity might be a useful 
 index for evaluating fatigue during intense exercise in conjunction with the esr . in 1937 , shijo   examined relationships between both changes in esr 
 after exercise and changes in blood characteristics ( blood o2 concentration , plasma co2 
 concentration , erythrocyte count , hemoglobin concentration , and plasma volume ) , and clinical findings ( pulse 
 rate , respiratory frequency , and blood pressure ) .
measurements were performed using 9 different exercise 
 protocols and 4 racehorses as follows : 1 ) walk , 200 m ; 2 ) walk , 800 m ; 3 ) walk , 1,600 m ; 4 ) trot , 200 m ; 5 ) 
 trot , 800 m ; 6 ) trot , 1,600 m ; 7 ) canter , 200 m ; 8) canter , 800 m ; and 9 ) canter , 1,600 m. the esr was 
 calculated as a median value based on the values at 1 hr and 2 hr .
the average esr at rest was 92.2 mm ( 84103 
 mm ) and decreased after exercise .
the authors 
 generated this graph using data from a table in a study by shijo .
( w , walk ; t , trot ; and c , canter ) ) . because the esr decreased when the erythrocyte count and o2 concentration were increased
, 
 the authors suggested that there were close relationships between the esr and erythrocyte count and 
 o2 concentration .
the authors 
 generated this graph using data from a table in a study by shijo .
( w , walk ; t , trot ; and c , canter ) during the period from 1938 to 1941 , kikuchi published 4 papers on the esr in horses : one on the esr during 
 normal status , one on the esr during pregnancy and the postnatal 
 period , one on the esr with various diseases , and one on factors influencing the esr . in 
 the first paper , 54 female horses ( 220 years old ) , 22 male horses 
 ( 219 years old ) , 13 geldings ( 519 years old ) , and 37 foals ( 2170 days old ) were investigated , and showed that 
 the esrs of each group were 66100 mm , 71100 mm , 71100 mm , and 2880 mm , respectively .
the esr of foals 6 days 
 after birth was the lowest and it increased with growth . in the final paper ,
the author reported that the esr decreased after exercise , as had been reported by hiroe 
 et al .   and
shijo , and also reported that differences between pre - exercise and post - exercise values were smaller in 
 trained horses than in untrained horses .
in the same paper , kikuchi also investigated effects of various 
 factors , such as temperature , congestion , concussion , feeding , and sodium citrate on the esr of horses .
kikuchi wrote interpretive articles on measurement of the esr and its 
 significance for clinical diagnosis . in these articles
, he described several methods of 
 measuring the esr , normal values of the esr in the horse , cattle , dog , goat , sheep , and pig , factors influencing 
 the esr , the esr in various diseases , and the mechanism of the esr .
ohi performed a series of experiments on species variation of the esr in domestic animals using horses , pigs , 
 dogs , cattle , sheep , and goats to evaluate variations of the erythrocyte sedimentation curve , shape of the erythrocyte sedimentation curve , correlation between the esr and temperature of the laboratory , influence of measurement temperature on erythrocyte sedimentation , correlation between esr and inclination of the tube , influence of tube inclination on erythrocyte sedimentation , correlation between the esr and diameter of the tube , 
 influence of tube diameter on erythrocyte sedimentation , correlation 
 between esr and height of the blood column , and influence of the 
 height of the blood column on erythrocyte sedimentation .
.   showed in 2-year - old thoroughbreds 
 that the esr decreased as training advanced ( fig .
6.changes in erythrocyte sedimentation rate ( esr ) in relation to training in 2 horses .
the authors generated this graph using data from a table in a study by matsuba 
 et al . . ) .
after working on equine exercise physiology with matsuba , sakurai started working on exercise 
 physiology of racehorses trained at racecourses , mainly studying blood characteristics , especially the esr . 

sakurai   examined the esr in 100 horses , including 46 racehorses 
 purchased at sales ( referred to as  yobiuma  at that time ) , 31 racehorses purchased by an organization that held 
 horse races ( owners of these horses were determined by lottery ; these horses were referred to as  chusenba  at 
 that time ) , 10 trotters , and 13 riding horses .
the chusenba lottery system was a unique system in japan . because 
 the yobiuma horses were purchased at sales by owners , the yobiuma horses were generally considered to be higher 
 quality horses than those acquired in the chusenba system .
sakurai s measurements were carried out throughout 
 the 26-day horse race meeting at tokyo racecourse in 1940 .
the esrs of the yobiuma were the lowest , and they were progressively higher 
 in chusenba horses and trotters .
sakurai concluded that the esr of 
 high - quality or high - performance horses tends to be lower .
changes in erythrocyte sedimentation rate ( esr ) in relation to training in 2 horses .
the authors generated this graph using data from a table in a study by matsuba 
 et al . .
changes in esr during the duration of a horse race meeting that included daily training and racing were 
 investigated in 13 racehorses and compared to other parameters .
the 
 esr changed in relation to the state of the general condition of the horse , and it correlated highly with the 
 erythrocyte count and hemoglobin concentration .
this result was similar to the findings of shijo   and matsuba et al . .
sakurai measured the esr , plasma protein concentration , specific viscosity , and albumin content 
 in 101 racehorses in order to examine relationships between the esr and the other variables , and he found that 
 total plasma protein correlated with specific viscosity .
the esr in 
 horses with good racing performance was low and albumin content in these horses was higher .
six horses were trained 
 for about 1 month and able to perform a maximal speed run of 1,500 m at the end of the training period .
while the general physical condition of the horses improved , the esr and 
 body weight decreased .
in contrast , when the condition of the horses by general inspection worsened , the esr 
 increased .
sakurai et al .   performed intensive research 
 throughout a long period of training from july to october using 110 racehorses trained at the tokyo racecourse . 

changes in esr , body weight , pulse rate , cardiac sounds , and nutritional status were observed , and the following 
 results were reported : 1 ) the esr decreased when a horse s condition by general inspection improved and 
 increased when a horse s condition by general inspection worsened ; 2 ) body weight decreased when the training 
 intensity was higher and increased when the training intensity was reduced ; and 3 ) pulse rate increased and 
 cardiac sounds became weaker when the horse s condition worsened , while pulse rate decreased and cardiac sounds 
 strengthened when the horse s condition improved .
they concluded that measurement of these 4 parameters were 
 useful for evaluation of a horse s condition .
sakurai   also performed 
 similar experiments regarding the effects of training over intervals ranging from several months to 1 year on 
 clinical and blood parameters using 14 racehorses and concluded that changes in esr and body weight would be 
 good parameters for evaluation of the condition of a racehorse . from these results ,
sakurai suggested that 
 measurement of the esr , body weight , pulse rate , and cardiac sounds was useful for evaluation of a horse s 
 condition .
sakurai made similar observations on 18 riding horses trained for 2 months according to training 
 regimens typically used for racehorses and reconfirmed that both the esr and body weight decreased as training 
 advanced . in order to validate the usefulness of changes in esr and body weight for evaluation of fatigue ,
sakurai   observed changes in esr and body weight once a week during a 6-week 
 period of training using 2 horses . during the first 2 weeks of low - intensity training , the esr decreased and 
 body weight increased . during the next 2 weeks
, the exercise intensity was increased gradually , and the esr 
 became much lower , and body weight decreased . during the final 2 weeks , higher - intensity training was carried 
 out , and the horses showed signs of fatigue while esr increased and body weight decreased further .
these results 
 suggested that changes in esr and body weight were useful parameters for evaluation of fatigue or the condition 
 of a racehorse .
sakurai named this method as the  esr - body weight method  and concluded that it would be a 
 useful index for screening tests of the effects of training on conditioning and fatigue . because previous research was conducted using adult horses trained at a racecourse or on retired racehorses , in 
 1961 , sakurai and ogawa observed effects of training and growth on the esr and body weight using 19 young 
 racehorses trained at the utsunomiya yearling training farm of the japan racing association .
measurement of blood characteristics was performed at the beginning of 
 june of the yearling year ( 1st ) , the end of september of the yearling year ( 2nd ) , the beginning of december of 
 the yearling year ( 3rd ) , and the beginning of march of the 2-year - old year ( 4th ) .
the esr was measured as a 40 
 min value and converted to the value at 20c .
the average esr for the 1st period was 74 mm , and it then 
 decreased to 61 mm for the 2nd period , 40 mm for the 3rd period , and 39 mm for the 4th period . on the other 
 hand ,
average body weight increased from 338 kg for the first period to 457 kg for the 4th period . in 1964 , sakurai et al .   performed a more intense 
 and longer study than in 1961 with 102 racehorses trained at the utsunomiya yearling training farm .
table 1table 1.summary of training and testing ( ponying , that is , running on courses without rider with 2 lead 
 horses with riders)agetrainingtestyearlingponying ( from september ) an breaking ( from december ) at the utsunomiya 
 yearling training farm.1st : october to november ( n=102)2 years oldtraining at a racecourse ( from the end of march or the beginning of 
 april ) .
most horses could join races until the end of 
 december.2nd : february to march ( n=103 ) 3rd : june ( n=49)3 years oldtraining at racecourses and participating in racing.4th : march ( n=39 ) shows the training protocols .
these horses were trained with a method referred as  oi - undo  
 ( ponying , that is , running on a track without a rider , with 2 lead horses with riders ) until the horses were 
 broken .
breaking was carried out in december of the yearling year , and running exercise with a rider was started 
 thereafter with the exercise intensity gradually increasing .
the 2nd study was conducted in february and march of the 2-year - old year .
the 
 horses were moved to racecourses in march to april and were then trained with high - intensity exercise in their 
 trainer s stable .
the 3rd study was performed in june of the 2-year - old year . from july onward ,
horses began to 
 join racing meets , and most of the horses could race until december , except for those horses with 
 musculoskeletal disorders .
the 4th and final study was performed in march of the 3-year - old year .
although the 
 number of horses examined was about 100 for the 1st and 2nd studies , the number decreased to 49 for the 3rd 
 study and 39 for the 4th study .
the average esr during the 1st study was 60 mm , and it decreased as training advanced to 11 mm by the 4th study 
 ( fig . 7fig .
7.changes in erythrocyte sedimentation rate ( esr ) and body weight during the training periods from october 
 to november of the yearling year ( 1st ) , february to march of the 2-year - old year ( 2nd ) , june of the 
 2-year - old year ( 3rd ) , and march of the 3-year - old year ( 4th ) .
the authors generated this graph using data 
 from a table in a study by sakurai et al . . ) .
although individual variation was larger in the 1st survey , the variation became smaller and dispersion 
 among horses decreased as training advanced , with 77% of the horses having values of 15 mm or less in the 4th 
 study .
the authors suggested that decrease of the esr in relation to time during training might be a response to 
 the stress of training . on the other hand , although body weight increased when the horses were trained at 
 utsunomiya yearling training farm , where the training intensity was low , body weight decreased after moving to 
 racecourses where the training intensity was high ( fig .
changes in erythrocyte sedimentation rate ( esr ) and body weight during the training periods from october 
 to november of the yearling year ( 1st ) , february to march of the 2-year - old year ( 2nd ) , june of the 
 2-year - old year ( 3rd ) , and march of the 3-year - old year ( 4th ) .
the authors generated this graph using data 
 from a table in a study by sakurai et al . .
in order to investigate relationships between the esr , fibrinogen , and packed cell volume ( pcv ) , 39 young 
 horses were trained from september of the yearling year to may of the 2-year - old year , and changes in these 
 parameters during the training period were measured .
the esr during 
 the early stage of training slowed , and fibrinogen decreased , as shown in fig . 8fig .
8.changes in fibrinogen concentration and erythrocyte sedimentation rate ( esr ) during the training period . 

the authors generated this graph using data from a study by takagi et al . .
all the three factors , however , were unchanged during the latter 
 half of the training period .
additionally , there was a positive correlation between fibrinogen and the esr at 
 each experiment .
when the coefficient of correlation was compared among changing values , the esr appeared to be 
 influenced mainly by the changes in fibrinogen , at least when the esr was greatly decreased , or by the 
 racehorse s condition progressing to good condition .
however , the authors considered that the esr might interact 
 with the pcv and fibrinogen and result in the lack of observed changes .
changes in fibrinogen concentration and erythrocyte sedimentation rate ( esr ) during the training period . 

the authors generated this graph using data from a study by takagi et al . .  
although the esr was first measured in a warhorse , esr recording in racehorses became popular following studies 
 by matsuba , shijo , and sakurai as mentioned above .
a small number of studies were being performed in foreign 
 countries on the relationship between the esr and exercise in horses [ 7 , 
 81 ] . based on studies comparing the esr in various species [ 22 , 57 ] ,
it was reported that the esr 
 of the horse was high and that the esr in ruminants were low , although the reason was unknown .
it was also 
 reported that the esr in active animals , such as pronghorn antelope , dog , and horse , was higher and that 
 inactive animals , such as sheep and cattle , was lower .
therefore , 
 sakurai s finding that fit racehorses tend to have a low esr is an interesting phenomenon that contradicts other 
 studies .
several papers have evaluated factors influencing the esr [ 1 , 
 20 , 70 , 76 ] .
sakurai indicated in a review article   that the individual variation 
 and dispersion of the esr among horses became smaller as training advanced , suggesting that this index would be 
 useful for evaluation of the condition of individual horses but it would be difficult to use as the basis for 
 comparison of racing performance between different individual horses .
he had evaluating conditions of large 
 numbers of racehorses according to criteria for evaluated conditions associated with fatigue as shown in table 2table 2.criteria for judgment of condition by using the erythrocyte sedimentation rate ( esr ) and body 
 weightesrbody weightjudgment of condition1fastheavyuntrained2became fastbecame heavyso - called  horse is heavy  .
it is ok to increase the training intensity.5became fastremarkably became lightneed to reduce training due to fatigue.6remarkably became slowbecame lightanorexia .
intensive training will worsen condition.cited from sakurai .. although there is no clear relationship between the esr and a horse s  condition  , there may be 
 an association between the two . cited from sakurai .
the history of research on exercise physiology of the horse in japan began in the 1920s during a time when the 
 role of the warhorse was still most important , and then studies on racehorses started .
matsuba and 
 shimamura of the university of tokyo played major roles in studies of racehorses performed during the 1930s . in 
 particular , the first study they published in 1933   was a seminal 
 study , as mentioned above , and what is surprising is that they already had tried to evaluate performance of 
 racehorses in the 1930s at the dawn of modern horse racing in japan .
although it seems that they evaluated the fitness of racehorses using many blood parameters that were 
 considered to be important in exercise physiology and were possible to measure at that time , it was difficult to 
 evaluate the performance of a racehorse and the effects of training at that time .
however , based on their 
 studies , new approaches for evaluating performance and conditioning of racehorses by using characteristics of 
 the blood were developed by their successors [ 58,59,60,61,62,63,64,65,66,67,68 , 71,72,73,74 ] .
additionally , techniques were developed for measuring cardiopulmonary 
 variables such as respiration [ 56 , 69 , 70 ] , heart rate , and oxygen consumption during 
 exercise [ 78 , 79 ] , leading to 
 additional understanding of equine exercise physiology . in the present day , studies on cardiopulmonary function during exercise are mainly performed by measuring 
 cardiopulmonary parameters such as oxygen uptake . although the numbers of studies on blood characteristics is 
 not large in japan , studies on the fragility of erythrocytes were carried out intensively at the end of the 
 1990s .
reported the effects of exercise and splenectomy on the osmotic 
 fragility of circulating erythrocytes .
in addition , studies of blood lactate changes during exercise have been 
 carried out intensively .
anaerobic work capacity estimated by the lactate accumulation rate has added new ideas 
 regarding energy expenditure during exercise .
studies of lactate 
 metabolism during high - intensity exercise and of the monocarboxylate transporter as it relates to lactate 
 metabolism   are providing new perspectives and further insights into equine exercise physiology .
 abstractafter publication of the epic report on equine exercise physiology by matsuba and shimamura in 1933 , papers 
 on exercise physiology of the racehorse in japan began appearing in scientific journals and increased in 
 number . in 1944 , respiration during exercise at a walk , trot , and canter was measured by recording expiratory 
 sounds with a microphone attached near the nostril . 
 respiratory frequency during cantering was synchronized 
 with stride frequency , and expiratory sounds were found to occur during the stance phase of the trailing 
 forelimb . 
 development of a radiotelemetry system in 1964 for electrocardiogram recording enabled the first 
 recording of an equine electrocardiogram during field exercise that included fast galloping and calculation of 
 heart rate ( hr ) during exercise . during low intensity exercise including walking , trotting , cantering and 
 extended cantering , 
 hr increased from 45 beat / min during pre - exercise to 150 beat / min at an extended canter . 
 
 hr increased to 200 beat / min or more in most horses during 100 m of high - intensity sprint galloping . 
 when 
 blood lactate was measured after 3 days of draft work in 12 warhorses in 1934 , no increase in blood lactate 
 was found . 
 the erythrocyte sedimentation rate ( esr ) was decreased by intense exercise and also decreased as 
 training increased . 
 it was suggested that measuring changes in esr and body weight in relation to training 
 might become useful as a screening index of training , condition , and fatigue . 
 this evaluation method was named 
 the  esr - body weight method .  
Respiration during Exercise
Heart Rate during Exercise
Effect of Exercise on General Blood Characteristics
Effect of Exercise on Erythrocyte Sedimentation Rate
Conclusions