Effects of a draft-loaded interval-training program on skeletal muscle in the horse

Effect of high-starch or high-fibre diets on the energy metabolism and physical performance of horses during an 8-week training period

Large amounts of high-starch concentrates are traditionally fed to horses in training. However, this has been associated with digestive or muscle diseases and behavioural modifications. In parallel, it has been demonstrated that horses fed high-fibre, low-starch diets achieve the same performance over an exercise test as the ones fed high-starch diets. However, whether the same performance level can be maintained over a longer training cycle is still being determined. This study aimed to compare the evolution in physical performance and cardiorespiratory responses of two groups of French Trotters fed either a control high-starch (15.0 g dry matter hay/kg body mass/day + 6.6 g dry matter oats/kg body mass/day) or a high-fibre diet (75% of oats replaced by dehydrated alfalfa) over an 8-week training period. The horses that entered the trial were untrained for ≥4 months and previously fed hay only. Track training with speed monitoring included interval training sessions and 2400 m performance tests from week 1 to week 8 (W8). Before (week 0, W0) and after (week 9, W9) the training period, horses performed an incremental continuous exercise test during which cardiorespiratory parameters were measured. Both groups progressed to the same extent regarding physical performance measured during interval training sessions (acceleration: 0.16 m.s-2 at W0 and 0.40 m.s-2 at W8; p < 0.0001), the 2400 m performance test (average speed: 8.88 m.s-1 at W0 and 10.55 m.s-1 at W8; p < 0.0001), and the incremental continuous exercise test (speed during the fastest stage: 9.57 m.s-1 at W0 and 10.53 m.s-1 at W9; p = 0.030). Although oxygen consumption increased with training (p = 0.071), it was not influenced by the diet. On the contrary, carbon dioxide production increased in the high-starch group only (high-starch group: 84.0 vs. high-fibre group: 77.7 mL.kg-1.min-1 at W9; p = 0.031). The results illustrate that horses in both groups progressed similarly but did not use the same metabolic pathways during exercise. This hypothesis is supported by carbohydrate oxidation, which tended to increase in the high-starch group at W9 but decreased in the high-fibre group (p = 0.061). In conclusion, the substitution of high-starch by high-fibre diets enabled similar performance over an 8-week training period and altered energy metabolism in a way that could be beneficial during high-intensity exercise.

Assessing the impact of draught load pulling on welfare in equids

About 112 million working equids are the source of income for 600 million people globally. Many equids are used for pulling loads (up to 15,000 kg per day) to transport goods. Most of them are associated with brick kilns, mining, and agriculture industries in developing countries. They may suffer from welfare issues such as overloading, being beaten, and being forced to work for long periods. These issues may occur due to a poor understanding of load-pulling equids. Understanding their capabilities and the elements that influence them is critical for efficient performance and welfare. The measurement of stride characteristics and gait kinematics can reveal loading adaptations and help identify loading limitations. It is known that both loading and fatigue change the locomotor patterns of load-pulling horses. Heart rate is a stress quantifying metric and an important representative of the speed of work and draught force. Heart rate variability is a regularly used statistic to quantify a physiological response to stresses, but it has never been used for load-pulling equids. Changes in blood lactate, nitrogen, oxygen, and carbon dioxide contents are reliable biochemical indicators of the effects of load pulling. Changes in plasma cortisol levels reflect the intensity of exercise and stress levels in horses while pulling a load. However, eye blink rate is a cheap, simple, and immediate indicator of acute equine stress, and we suggest it may be used to aid in load-pulling equine welfare assessment. However, further research is needed for a standardized and evidence-based draught load pulling capacity of working horses, mules, and donkeys.

Flexibility of equine bioenergetics and muscle plasticity in response to different types of training: An integrative approach, questioning existing paradigms

Equine bioenergetics have predominantly been studied focusing on glycogen and fatty acids. Combining omics with conventional techniques allows for an integrative approach to broadly explore and identify important biomolecules. Friesian horses were aquatrained (n = 5) or dry treadmill trained (n = 7) (8 weeks) and monitored for: evolution of muscle diameter in response to aquatraining and dry treadmill training, fiber type composition and fiber cross-sectional area of the M. pectoralis, M. vastus lateralis and M. semitendinosus and untargeted metabolomics of the M. pectoralis and M. vastus lateralis in response to dry treadmill training. Aquatraining was superior to dry treadmill training to increase muscle diameter in the hindquarters, with maximum effect after 4 weeks. After dry treadmill training, the M. pectoralis showed increased muscle diameter, more type I fibers, decreased fiber mean cross sectional area, and an upregulated oxidative metabolic profile: increased β-oxidation (key metabolites: decreased long chain fatty acids and increased long chain acylcarnitines), TCA activity (intermediates including succinyl-carnitine and 2-methylcitrate), amino acid metabolism (glutamine, aromatic amino acids, serine, urea cycle metabolites such as proline, arginine and ornithine) and xenobiotic metabolism (especially p-cresol glucuronide). The M. vastus lateralis expanded its fast twitch profile, with decreased muscle diameter, type I fibers and an upregulation of glycolytic and pentose phosphate pathway activity, and increased branched-chain and aromatic amino acid metabolism (cis-urocanate, carnosine, homocarnosine, tyrosine, tryptophan, p-cresol-glucuronide, serine, methionine, cysteine, proline and ornithine). Trained Friesians showed increased collagen and elastin turn-over. Results show that branched-chain amino acids, aromatic amino acids and microbiome-derived xenobiotics need further study in horses. They feed the TCA cycle at steps further downstream from acetyl CoA and most likely, they are oxidized in type IIA fibers, the predominant fiber type of the horse. These study results underline the importance of reviewing existing paradigms on equine bioenergetics.

The effect of rider weight and additional weight in Icelandic horses in tölt: part I. Physiological responses

This study examined the effect of increasing BW ratio (BWR) between rider and horse, in the BWR range common for Icelandic horses (20% to 35%), on heart rate (HR), plasma lactate concentration (Lac), BWR at Lac 4 mmol/l (W₄), breathing frequency (BF), rectal temperature (RT) and hematocrit (Hct) in Icelandic horses. In total, eight experienced school-horses were used in an incremental exercise test performed outdoors on an oval riding track and one rider rode all horses. The exercise test consisted of five phases (each 642 m) in tölt, a four-beat symmetrical gait, at a speed of 5.4±0.1 m/s (mean±SD), where BWR between rider (including saddle) and horse started at 20% (BWR₂₀), was increased to 25% (BWR₂₅), 30% (BWR₃₀), and 35% (BWR₃₅) and finally decreased to 20% (BWR_20b). Between phases, the horses were stopped (~5.5 min) to add lead weights to specially adjusted saddle bags and a vest on the rider. Heart rate was measured during warm-up, the exercise test and after 5, 15 and 30 min of recovery and blood samples were taken and BF recorded at rest, and at end of each of these aforementioned occasions. Rectal temperature was measured at rest, at end of the exercise test and after a 30-min recovery period. Body size and body condition score (BCS) were registered and a clinical examination performed on the day before the test and for 2 days after. Heart rate and BF increased linearly (P<0.05) and Lac exponentially (P<0.05) with increasing BWR. The W₄ was 22.7±4.3% (individual range 17.0% to 27.5%). There was a positive correlation between back BCS and W₄ (r=0.75; P=0.032), but no other correlations between body measurements and W₄ were found. Hematocrit was not affected by BWR (P>0.05), but negative correlations (P<0.05) existed between body size measurements and Hct. While HR, Hct and BF recovered to values at rest within 30 min, Lac and RT did not. All horses had no clinical remarks on palpation and at walk 1 and 2 days after the test. In conclusion, increasing BWR from 20% to 35% resulted in increased HR, Lac, RT and BF responses in the test group of experienced adult Icelandic riding horses. The horses mainly worked aerobically until BWR reached 22.7%, but considerable individual differences (17.0% to 27.5%) existed that were not linked to horse size, but to back BCS.

Effects of training at a walk on conventional and underwater treadmills on fiber properties and metabolic responses of superficial digital flexor and gluteal muscles to high-speed exercise in horses

OBJECTIVE

To compare effects of training on conventional and underwater treadmills on fiber properties and metabolic responses of the superficial digital flexor (SDF) and gluteal muscles to high-speed exercise in horses.

SAMPLE

6 unconditioned Quarter Horse-type horses.

PROCEDURES

6 horses were walked on underwater and conventional treadmills for 5 d/wk (maximum, 40 min/d) for 8 weeks in a randomized crossover design (60-day detraining period). Horses underwent a standardized exercise test (SET) at high speed before and after training. Analyte concentrations and fiber characteristics were measured in muscle biopsy specimens obtained from horses before and after each SET.

RESULTS

Lactate concentration increased 2- to 3-fold in SDF and gluteal muscle after SETs. No training effect was identified on muscle fiber type composition, type II fiber diameter, muscle analyte concentrations, blood lactate concentration, or heart rate responses. Maximum diameters of type I fibers decreased significantly in gluteal muscle with conventional treadmill training and decreased in SDF muscle with both types of training, with maximum diameters greater for horses after underwater versus conventional treadmill training. No change was identified in minimum fiber diameters.

CONCLUSIONS AND CLINICAL RELEVANCE

SETs involving near-maximal exertion resulted in an anaerobic response in SDF and gluteal muscles of horses. Eight weeks of conventional or underwater treadmill training resulted in minor changes in type I muscle fiber sizes, with no effect on muscle metabolic or heart rate responses to SETs. After rehabilitation involving underwater treadmills, training at progressing speeds is recommended for horses to develop the required fitness for speed work.

Muscle fibre type distribution of the thoracolumbar and hindlimb regions of horses: relating fibre type and functional role

BACKGROUND

Although the majority of equine muscles have a mixed fibre type distribution indicative of diverse functional roles, the predominance of a fibre type can indicate the primary function of a muscle. The deep epaxial musculature has an important role in core spinal stability in humans, reflected as a predominantly muscle fibre type (MFT) I or postural fibre type. The fibre type of the deep epaxial musculature has not been determined in horses. The objective of the study was to determine the MFT distribution in selected muscles of thoracolumbar and hindlimb region of horses. This included deep epaxial and hypaxial muscles that were hypothesised to have a postural stabilising role. A second objective was to examine differences in MFT distribution between horses bred for endurance (Arabian) and sprinting (Quarter horse). Muscle biopsy samples were obtained from selected thoracolumbar and hind limb muscles of 5 Quarter horses, 4 Arabians, and 2 Thoroughbreds. The myosin heavy chain distribution was determined by gel electrophoresis. Mann-Whitney rank test was used to compare the proportional MFT and differences between breeds.

RESULTS

Mm. sacrocaudalis dorsalis medialis and diaphragm had the highest proportion of MFT-I. The remaining deep epaxial muscles and the hypaxial muscle m. psoas minor had approximately equal MFT I and II proportions. Mm. psoas major, iliocostalis, longissimus dorsi and the hind limb muscles contained mostly MFT-IIX. The fibre type distribution was similar between Arabians and Quarter horses, although Quarter horses had more MFT-IIX fibres in psoas major (P = 0.02) while Arabians had more MFT-I fibres in m. longissimus dorsi (P = 0.03).

CONCLUSIONS

The fibre type distribution of the deep epaxial muscles, mm psoas minor and diaphragm varied from approximately equal MFT-I and II proportions to predominantly MFT-I suggesting a postural stabilising role possibly important in core spinal stability. In contrast the fibre type proportions of mm psoas major, iliocostalis, longissimus dorsi and the hind limb muscles were mainly MFT-II suggesting a locomotory role. Knowledge of fibre type distribution in such a clinically important area can direct diagnosis, prevention and treatment of muscular or neuromotor dysfunction.

Curriculum vitae paper - Sune G.B. Persson (1931-2009)

Sune Persson was born in Landskrona Sweden in 1931 and grew up on the west coast of Sweden. He graduated from the Royal Veterinary College in Stockholm in 1960 and in 1967 received his PhD entitled ‘On blood volume and working capacity in horses’. Sune pursued an academic career devoted to internal medicine and exercise physiology. He rapidly became Professor of Medicine in 1979 as the veterinary school moved from Stockholm to the Swedish University of Agricultural Sciences in Uppsala.

Differences in the metabolic properties of gluteus medius and superficial digital flexor muscles and the effect of water treadmill training in the horse

REASONS FOR PERFORMING STUDY

Flexor tendon injury may be due to flexor muscle fatigue, contributing to fetlock joint hyperextension and tendon damage. A water treadmill provides resistance training on flexor tendon muscles, which might reduce the risk of tendon injury.

OBJECTIVE

To determine the effect of water treadmill training on the properties of the gluteal and superficial digital flexor (SDF) muscles and on cardiocirculatory response to a standardised exercise test.

METHODS

Five healthy unfit horses were trained on a water treadmill for 5 days/week for 4 weeks, starting with 5 min/day increasing to 20 min/day. Before and after the water treadmill training, an incremental SET was performed on a land treadmill to determine velocity at a heart rate 200 beats/min (V(200)) and resting gluteal and SDF muscle biopsies were obtained for biochemical analyses.

RESULTS

There was no measurable difference in resting concentrations of gluteal or SDF muscle glycogen, lactate, ATP or glucose-6-phosphate (G6P), or activities of citrate synthase (CS), 3-hydroxyacyl CoA dehydrogenase (HAD) and lactate dehydrogenase (LDH) after training and no change in V(200), Lactate, glycogen, G6P and ATP concentrations were 50% lower and type 1 fibres 30% higher in SDF compared to gluteal muscles. CS and HAD activities were similar between SDF and gluteal, while LDH was lower in the SDF muscle.

CONCLUSIONS

A more strenuous water treadmill conditioning protocol may be needed to induce a training effect in gluteal and SDF muscle and heart rate response. The low substrate concentrations and oxidative capacity of SDF may predispose this muscle to catastrophic fatigue during maximal exercise.

Muscle characteristics in young Norwegian-Swedish Coldblooded Trotters and associations with breeding index, body size and early training

REASONS FOR PERFORMING STUDY

The trotting speed of Norwegian-Swedish Coldblooded Trotters (NSCTs) is, although inferior to Standardbred speeds, gradually increasing. This development is mainly attributed to breeding progresses. Characteristics of the middle gluteal muscle have recently been described in a small number of these horses but the actual spread in muscle parameters within the population is unknown.

OBJECTIVES

To describe the characteristics of the middle gluteal muscle and their naturally occurring variability in young NSCT horses and investigate possible association with body size, individual breeding index and early training.

METHODS

Biopsies of the middle gluteal muscle of 144 NSCT horses born in 2005 were collected at age 17-24 months. The horses were randomly selected by stratified sampling with gender and paternal progeny as stratification factors. The muscle samples were analysed for fibre type composition, fibre type areas, capillary supply and the activity of the key metabolic enzymes citrate synthase, 3-OH-acyl-CoA-dehydrogenase and lactate dehydrogenase. Correlation analysis including muscle parameters and body size, individual breeding index and early training was performed.

RESULTS

Large interindividual differences were identified in muscle characteristics. Male horses had higher percentages of type IIA fibres and lower percentages of type IIX fibres than age-matched females. Fibre type areas followed the order type IIX>IIAX>IIA>I, while the capillary supply per fibre type area increased in the opposite order. No gender-related differences were found in fibre type areas or capillary supply. Height was correlated to the relative area of type I fibres. Early training was associated with increased oxidative capacity and increased percentage of type IIA fibres. The lowest breeding index was found in untrained horses.

CONCLUSIONS

Muscle characteristics differ among young NSCT horses, but the innate oxidative capacity seems to be lower than in Standardbreds of comparable age. Early training may influence on these parameters.

Gene expression profiling in equine muscle tissues using mouse cDNA microarrays

REASONS FOR PERFORMING STUDY

Progress could be achieved by using microarrays to understand metabolic adaptations and disorders in equine muscle in response to exercise.

OBJECTIVES

To test the feasibility of using mouse cDNA microarrays to analyse gene expression profile in normal equine muscles.

METHODS

Muscular biopsies of dorsal gluteus medius and longissimus lumborum were done in 4 healthy Standardbreds. Total RNA was extracted from the muscle samples. The concentration and quality of RNA were measured before and after amplification. Gene expression profiles were measured using mouse cDNA microarrays including 15,264 unique genes representing about 11,000 documented genes. Three hybridisation tests were performed to check interspecificity, reproducibility and to compare gene expression in these muscles. For each test, a dye-swap hybridisation with Cy3 and Cy5 fluoromarkers were done and the gene list filtered according the signal level.

RESULTS

According to the specificity test, the mouse cDNA microarrays were correctly hybridised by equine muscle cDNA. All positive control genes (GAPDH, HPRT and beta-Actin) and no negative control gene (yeast, plant) hybridised. The reproducibility test demonstrated a good linearity between the duplicate hybridisations: 99.99% of the significant expressed genes have an expression ratio between 1.4 and 1/1.4 = 0.71. These limits can be considered as the thresholds to qualify as up-regulated (ratio >1.4) or downregulated (ratio <0.71). In the muscle comparison test between gluteus medius vs. longissimus lumborum, 63 genes were found up-regulated and 8 genes down-regulated. The range of gene expression ratios in the gluteus medius was 0.61-8.31 x the longissimus lumborum. This list of modulated genes was classified by functions using a gene ontology data basis.

CONCLUSION

Mouse microarrays could be used to hybridise equine RNA extracted from muscle tissues. For many genes there are large sequence identities that allowed interspecific cDNA hybridisation. The sensitivity of the method allowed quantification of up- and down-regulated genes after applying appropriate filters.

POTENTIAL RELEVANCE

Expression profiling could be used to explore the muscle metabolism changes related to exercise, training, pathology and illegal medication in horses.

Muscle energetics in exercising horses

An optimally functional musculoskeletal system is crucial for athletic performance and even minor perturbations can limit athletic ability. The introduction of the muscle biopsy technique in the 1970s created a window of opportunity to examine the form and function of equine skeletal muscle. Muscle histochemical and biochemical analyses have allowed characterization of the properties of equine muscle fibres and their influence on, and adaptation to, physical exertion. Analyses of exercise responses during standardized treadmill exercise and field studies have illustrated the role of cellular energetics in determining athletic suitability for specific disciplines, mechanisms of fatigue, adaptations to training and the affect of diet on metabolic responses. This article provides a review of the tools available to study muscle energetics in the horse, discusses the muscular metabolic pathways and summarizes the energetics of exercise.

Training-induced alterations of the fatty acid profile of rabbit muscles

The present study was designed to investigate whether meat-type rabbits are able to perform treadmill running as a daily routine exercise, and if so, whether the exercise induces specific proportional changes in the fatty acid composition of their muscles. After a four-week training period 8-week-old rabbits were slaughtered and the total activity of plasma lactate dehydrogenase was measured, showing a significant difference between the exercised and control groups (429 +/- 126 IU/l vs. 639 +/- 203 IU/l). Furthermore the fatty acid composition of m. longissimus dorsi (MLD) and m. vastus lateralis (MVL) was determined by means of gas chromatography. Exercise increased the proportions of oleic acid (C18:1 n-9) in both MLD and MVL as compared to the control group. However, the level of stearic (C18:0) and arachidonic (C20:4 n-6) acids significantly decreased in the MVL after the exercise. Changes in the fatty acid profile resulting from the physically loaded condition were of the same tendency in both muscles, adding that the MVL might have been exposed to the exercise more intensively; alterations there occurred in a more pronounced manner. Based on the inference that the composition of membrane structure was also affected, these alterations may have important consequences on meat quality.

Effects of prolonged training, overtraining and detraining on skeletal muscle metabolites and enzymes

Thirteen Standardbred horses trained intensively for 34 weeks and detrained for 12 weeks to investigate the effects of training, overtraining and detraining on muscle metabolites, buffering capacity and enzyme activities (CS, HAD and LDH). After a standardised exercise test to fatigue at 10 m/s (approximately 100% VO2max), there was significant depletion of [ATP], [PCr] and muscle [glycogen] and accumulation of muscle and plasma [lactate], [NH3] and elevated muscle temperature. After training, associated with increased run time to fatigue (148%), there was reduced depletion of muscle [glycogen] and increased [NH3] and muscle temperature at fatigue. Training resulted in increased muscle buffering capacity (19%) and activities of CS (29%) and HAD (32%) and reduced glycogen utilisation (1.32 mmol/s in week 1 to 0.58 mmol/s in week 32). Plasma [lactate] at fatigue increased with training as opposed to muscle [lactate] implying enhanced ability to remove lactate from muscle. Overtraining resulted in reduced run time and associated effects in overtrained horses. While muscle [glycogen] prior to exercise was lower in overtrained horses, glycogen utilisation/s was not reduced and it may not, therefore, have caused the reduced run time. Prolonged high intensity training caused primarily aerobic adaptations and poor performance associated with overtraining may not be due to metabolic disturbances.

Myosin heavy chain profile of equine gluteus medius muscle following prolonged draught-exercise training and detraining

Fourteen 4-year old Andalusian mares were used to examine the plasticity of myosin heavy chain (MHC) composition in horse skeletal muscle with heavy draught-exercise training and detraining. Seven horses underwent a training programme based on carriage exercises for 8 months. Afterwards, they were kept in paddocks for 3 months. The remaining seven animals were used as control horses. Three gluteus medius muscle biopsies were removed at depths of 20, 40 and 60 mm from each horse before (month 0), during the training (months 3 and 8) and after detraining (month 11). Myosin heavy chain composition was analysed by electrophoresis and immunohistochemically with anti-MHC monoclonal antibodies. Fibre areas, oxidative capacity and capillaries were studied histochemically. After 8 months of training, MHC-IIX and IIX fibres decreased whereas MHC-I and type I and I + IIA fibres increased. Neither MHC-IIA nor the percentage of IIA fibres changed when the data were considered as a whole, but the proportion of MHC-IIA increased in the superficial region of the muscle after 8 months of training. Mean areas of type II fibres were not affected by training and detraining, but the cross-sectional of type I fibres increased after 3 month of training and not further increases were recorded afterward. The percentage of high-oxidative capacity fibres and the number of capillaries per mm2 increased with training. Most of these muscular adaptations reverted after detraining. These results indicate that long term draught-exercise training induces a reversible transition of MHC composition in equine muscle in the order IIX --> IIA --> I. The physiological implication of these changes is an impact on the velocity of shortening and fatigue resistance of muscle fibres.

Skeletal myosin heavy chain composition and carriage training

Three different myosin heavy chain (MHC) isoforms have been identified in the equine gluteus medius muscle: the slow or MHC-I and the 2 fast MHC-IIA and MHC-IIX isoforms. They are distributed in 3 fibre types containing a single MHC (I, IIA, IIX) and 2 hybrid types co-expressing 2 isoforms (I + IIA, IIA + IIX). The aim of this study was to determine if heavy carriage training alters skeletal MHC composition in horses. Fourteen Andalusian mares age 42-46 months were used. Seven horses were used as controls to estimate the effects of growth on muscle. The remaining 7 horses underwent a training programme based on carriage exercise for 8 months. The intensity of exercise was individually adjusted to each horse according to a standardised exercise test. Gluteus medius muscle biopsies were analysed biochemically for MHC composition by electrophoresis, immunohistochemically for fibre types with specific anti-MHC monoclonal antibodies, and histochemically for fibre type areas, fibre oxidative capacity and capillaries. After training, MHC-IIX decreased and MHC-I increased. The percentages of type IIX and IIAX (i.e. fibres co-expressing MHCs IIA and IIX) fibres decreased, whereas the percentage of type I fibres increased. Neither MHC-IIA composition nor type IIA fibre percentage changed with training. The training had no significant effect on fibre areas and capillaries, but the percentage of fibres with high oxidative capacity increased. The control group showed no changes in muscle variables after the 8 month training period. These results suggest that carriage training alters MHC composition in equine skeletal muscle, reflecting a conversion of MHC isoforms in the order IIX-->IIA-->I and suggesting a reduction in the velocity of shortening of the muscle, but an increase in fatigue resistance.

The kinematics of loading and fatigue in the standardbred trotter

The Standardbred trotter must pull a considerable load when racing and, consequently, draught loading is a common method of training in the Standardbred and the effects of loading and fatigue due to loading on the locomotor pattern was the purpose of this investigation. Four mature healthy Standardbred horses trotted with and without a horizontal-pulling loading of 34 kg until the horses were no longer willing to keep pace with the treadmill despite encouragement. Heart rate was monitored every min using a bipolar electrocardiogram. The kinematics for 5 consecutive strides were filmed. Horses exercised on the treadmill for 7-10 mins. The mean heart rate was 206 beats/min at the end of the exercise. Due to draught loading, the horses reduced significantly the time of the stance phase in both the fore- and hindlimb. Three of the 4 horses reduced their stride lengths as the result of increased loading. The general movement pattern of the horses remained similar. More dramatic changes in the movement pattern were observed because of fatigue. The limbs of the horse were significantly more compressed as the result of greater joint excursion during the stance phase. Furthermore, the length of stride was significantly increased as the result of fatigue. The results show that both loading and fatigue change the locomotor pattern of the Standardbred trotter. Although the horizontal loading was considerable, the horse maintained similar joint movement with increases in stride frequency. During fatigue the horse seems to be unable to maintain stride frequency, probably due to a compromised power capacity of the muscles. The increase in joint excursion due to fatigue may have an important influence on certain types of injury to the locomotor system of the racehorse.

Comparison of standardbred trotters exercising on a treadmill and a race track with identical draught resistances

The responses in heart rate, plasma lactate and rectal temperature of standardbred trotters to draught loaded interval exercise on a treadmill and a race track were studied. The horses were exercised with incrementally increasing trotting speeds for two-minute intervals with draught loads of 10, 20 and 30 kilopond (kp) in three different tests. Each trotting interval was followed by two-minute periods at a walk without a draught load. Measurements of heart rate and plasma lactate were made at the end of each interval and the rectal temperature was taken at the end of the exercise. The heart rate and plasma lactate levels were significantly lower on the treadmill than on the track in the tests with 10 kp, but no significant differences were found between the treadmill and track exercise tests with the heavier draught resistances. No differences were observed in rectal temperature between treadmill and track conditions. From these findings it was concluded that the workload was significantly greater on the race track compared to the treadmill when the draught resistance was low (10 kp). Although the workload increased on both the race track and the treadmill as draught resistance increased, at the heavier draught resistances track exercise was no longer more demanding than exercise on the treadmill.

Cardio-respiratory and plasma lactate responses to exercise with low draught resistances in standardbred trotters

Five Standardbred trotters performed treadmill exercise with incrementally increasing trotting velocities for 2 min intervals in three different tests until fatigue. Each test was performed with draught loads of either 10, 20 or 30 kilopond (kp). Each trotting interval was followed by 2 min periods at a walk without draught load. Recordings were made of heart rate (HR), respiratory rate (RR), plasma lactate (PLA) and stride frequency (SF) at the end of each trotting interval. The HR increased to average values of 191 +/- 10,203 +/- 10 and 214 +/- 7 bpm and PLA increased to 3.8 +/- 0.7, 7.3 +/- 3.8 and 10.8 +/- 6.4 mmol/l at 9 m/s in the three tests, respectively. The HR response to exercise was significantly higher with increasing draught loads, and PLA was significantly higher with 30 kp compared to 10 kp draught resistance. The lowest respiratory rate was seen in the test with 30 kp loading. Peak oxygen uptake (VO2peak) was measured in a separate test on a sloped treadmill with increasing velocities without draught load and averaged 70.4 +/- 9.11/min. Muscle biopsies were taken from the gluteus muscle. Individual variations were seen in VO2peak, muscle fibre composition and HR and PLA responses to exercise. In conclusion, at a certain velocity a small increase in draught resistance from 10 to 30 kp significantly increases both the HR and PLA responses. At comparable work intensities the horses differed in circulatory and metabolic responses to exercise.

Cardiovascular, respiratory and metabolic effects of interval training at VLA4

The purpose of this study was to determine if training with short intervals at the velocity producing a lactate level of 4 mmol/l (VLA4) is sufficient to induce adaptations and better exercise tolerance. Five Standardbred mares (4-8 years) were interval trained on a treadmill 3 days a week for 12 weeks and subsequently detrained for 4 weeks. Standardized exercise tests were performed before, during and after the training period and muscle biopsies were taken. Measurements were made of heart rate, oxygen consumption, stride frequency, blood volume and blood lactate. Plasma volume was reduced after 2 weeks of training but then increased to the approximate pre-training value throughout the remaining training and post-training periods. No change was detected in the total cell volume whereas the total blood volume varied in consequence with the plasma volume variation. A significant reduction in heart rate response to exercise was seen after 4 weeks of training. VLA4 increased after 2 weeks of training and remained higher than the baseline value during the rest of the training period. Consequently, the blood lactate at 8 m/sec was decreased compared to baseline concentration after 8 and 12 weeks of training. The post-training VLA4 did not differ significantly either from the end of training or from the pre-training value. Mass specific oxygen consumption (VO2-200/BW) at V200 increased with training and decreased with detraining. The respiratory quotient at a velocity of 8 m/sec decreased from 1.18 +/- 0.02 before training to 1.07 +/- 0.02 (P < 0.05) at the end of training. No changes were found in muscle histo- or biochemical parameters. The results indicate that training at VLA4 is sufficient to cause adaptational changes in exercise tolerance related parameters.

Effects of a 3 month endurance training programme on skeletal muscle histochemistry in Andalusian, Arabian and Anglo-Arabian horses

Twenty adult (5 to 14 years old) sedentary stallions of several breeds (8 Andalusians, 7 Arabians and 5 Anglo-Arabians) were endurance-trained for 3 months. Duplicate biopsies from 2 different depths (20 mm, superficial sampling site; 60 mm, deep sampling site) of the gluteus medius muscle were collected before and after training and after 3 months of detraining. Few significant changes in muscle fibre type composition were recorded in response to training. The percentage of type I fibres in the deep sampling site of the muscle in Andalusian horses and of type IIB oxidative fibres in the superficial region in Anglo-Arabians had increased significantly (P < 0.05) after training. The mean type I and IIA cross-sectional area was increased significantly (range P < 0.05 to P < 0.01) after 3 months' training in the deep site of the muscle in Arabian and Andalusian horses, but not in Anglo-Arabians. The changes seen in fibre sizes disappeared after the detraining period. The mean number of capillaries adjacent to type I fibres in the superficial sampling site of the muscle had increased significantly (P < 0.05) in response to training in Andalusian and Arabian horses. However, a significant decrease in the mean number of capillaries in contact with each fibre type relative to the mean area of that fibre type was observed associated with training in the deep region of the muscle for type I and IIA fibres in Arabians (P < 0.01) and for type I fibres in Andalusian horses (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Stiffness changes and fibre type transitions in rat soleus muscle produced by jumping training

Rat soleus muscles were overloaded with intent to induce a relative increase in fast fibres and modifications in muscular stiffness. The overloading technique was a training period consisting of an 11-week vertical jump programme. The method of controlled releases was used to obtain tension/extension curves characterizing the elastic behaviour of the soleus. Fibre typing was made by myofibrillar adenosine 5'-triphosphatase staining. With regard to a control group, training resulted in a relative decrease in type I fibres for the benefit of type II fibres. Training also induced a decrease in muscle stiffness as attested notably by significant differences in maximal extension. These results are interpreted in terms of modifications occurring in the active fraction of the so-called series elastic component.