Objectives, Principles, and Methods of Strength Training for Horses

Accepted Manuscript Objectives, Principles and Methods of Strength Training for Horses Cristina Castejon-Riber, Cristina Riber, María Dolores Rubio, Estrella Agüera, Ana Munoz PII:

S0737-0806(16)30715-8

DOI:

10.1016/j.jevs.2017.04.011

Reference:

YJEVS 2317

To appear in:

Journal of Equine Veterinary Science

Received Date: 22 December 2016 Revised Date:

15 March 2017

Accepted Date: 17 April 2017

Please cite this article as: Castejon-Riber C, Riber C, Rubio MD, Agüera E, Munoz A, Objectives, Principles and Methods of Strength Training for Horses, Journal of Equine Veterinary Science (2017), doi: 10.1016/j.jevs.2017.04.011. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Title Page: Manuscript number: JEVS_2016_418 Title: Objectives, principles and methods of strength training for horses

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Article type: Review article

Order of authors: Cristina Castejon-Riber, Cristina Riber, María Dolores Rubio, Estrella Agüera, Ana Munoz

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Affiliation: Universidad de Cordoba, Equine Sport Medicine Center, University of Córdoba, Campus Rabanales, 14017 Cordoba, Spain, Spain

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Corresponding Author: Dr. Cristina Castejon-Riber, Universidad de Cordoba, Equine Sport Medicine Center, University of Córdoba, Campus Rabanales, 14017 Cordoba, Spain, Spain. Email: [email protected].

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Abstract: The use of the horse for athletic competition involves conditioning and training for specific types of performance. The present review focuses on one of the four main components of basic fitness, strength. First, some concepts, such as, the different types of contractions are presented in order to fully understand this article. Then five main objectives of general training are established: to improve or maintain maximum performance, preparing the horse for the competition; to delay onset of fatigue; to improve skills or work capacity; to minimize the incidence of injuries or metabolic disorders; and to maintain willingness and enthusiasm for exercise. Furthermore, we have developed 7 principles of training based on scientific literature and our own experience, which are: 1. To avoid or to minimize the incidence of injuries; 2. Overcompensation; 3. Periodization; 4. Progressive loading; 5. Individuality; 6. Specificity; 7. Unity. Finally, several methods of strength training are presented to be used in different disciplines. In conclusion, there is a need for research about strength training in horses. Most of the conditioning programs used nowadays are based in empirical knowledge. In this paper we present objectives, principles and methods of strength training for horses based on human strength training applied to horses and based on our experience and some other authors. Until further researcher, we recommend trainers to use this article as a guide when designing the training program of their horses and developing the strength exercises of each session.

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Keywords: Horses; training objectives; training principles; strength training.

1. Introduction

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The use of the horse for athletic competition involves conditioning and training for specific types of performance. In contrast to developments in human athletes, selection of individuals [1] and training strategies for the equine athlete are based largely on subjective judgment and empirical traditional training methods [1,2] with too little influence from scientific knowledge [3]. Furthermore, it has been suggested that conventional techniques are not always adequate. In addition, the performance of, for example, racehorses [4] and elite event horses [5] could be improved; and injury rates reduced [6] by the use of more scientific protocols. Moreover, Rose and Evans [7] asked if training a horse was art or science, and they concluded that the combination of both is necessary to produce better results for performance and fitter horses. Although they focused on the racehorse, this conclusion can be extrapolated to other disciplines. In 2011 Campbell [3] stated that there is still too little influence from scientific knowledge into equine conditioning programs. There are not scientific protocols designed for strength training on horses that can help the hard work of the trainers and/or riders. It may be for several reasons but we believe that the high economical cost of this research and the difficulty of evaluating strength on a horse may be the main reasons. In this review we would try to bring science and empiric knowledge together.

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A horse trainer has an extremely difficult task, regardless of whether the job is to prepare a racehorse, eventer, endurance or other type of performance horse. Every trainer must prepare the horse to perform to its full potential regardless of the discipline. The horse must be kept healthy, and ideally not be undertrained or overtrained. It should be presented at competition with no muscle, skeletal, respiratory or other body system disease that could reduce or limit performance [2].

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ACCEPTED Preparation of the horse in any kindMANUSCRIPT of competition involves a combination of conditioning and schooling. Schooling develops neuromuscular coordination and mental discipline while conditioning induces physiological and structural adaptations that maximize performance and maintain soundness [8].There are two main aspects of fitness and conditioning that we should take into consideration when training a horse: 1) fitness of the cardiovascular and respiratory systems and 2) fitness of the musculoskeletal system [9]. Other aspects also important in training a horse, although interrelated with the two above mentioned are: proper energy expenditure and gait, and efficient thermoregulation. "Fitness" is a rather vague expression, but in general is the ability to complete the required amount of physical activity without fatigue, stress, or injury. Any horse that is used for high-level competition or weekend trail riding should be fit for the task.

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Strength is one of the four main components of basic fitness which also include, speed, stamina and flexibility. There are also other components of fitness that are important for the horse performance such as, coordination, agility and balance. We should take into consideration that strength improvement is also highly dependent on neuromuscular control which is also related to coordination and speed. In humans, is well stablished that the first improvements in strength in a training programs are related to neuromuscular adaptation, musculoskeletal adaptation take longer [10]. There are many different kinds of exercise tests to evaluate fitness of the horse [2, 11- 13]. These kinds of tests evaluate cardiovascular, respiratory and muscle (metabolic) systems. To our knowledge there are not exercise tests that evaluate the strength of the horse. The only way we could evaluate the strength of a horse is by a biopsy. This is due to an existing relationship between muscle mass and muscle strength. This relationship is explained by the physiological cross-sectional area of a muscle, defined as the sum of the cross-

ACCEPTED MANUSCRIPT sectional area of their constituent muscle fibers. Hence, larger muscles will have an increased capacity for powerful contractions [14]. However, this kind of measure is not really practical in the trainer´s routine.

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In the present review we will focus on the strength part of the conditioning training. However, since every exercise requires more than one component of fitness other components as well as schooling will be also taken into consideration. For example, jumping one fence requires at least, strength, flexibility, coordination and balance. Furthermore, it is recommended that supplying exercises (exercises that improve flexibility) should be performed in conjunction with a strength training in other to maximizing the horse´s athletic ability and for minimizing the risk of injury [15]. To our knowledge there are not scientific articles about strength training in horses. Recently, Sommer et al. [11] published an article about training of show jumping horses. However, they did not evaluate the strength of these athletes.

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Objectives of training

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The main goal of this article is to provide guidance to trainers and riders about training horses for sport performance in general, and strength conditioning training in particular, since there is very little information about this type of training in the literature.

Objectives should be individualized to each individual and specific for each discipline, as will be mentioned in training principles. However there are some basic objectives presented by different authors:

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(1) To minimize the incidence of injuries or metabolic disorders [7,16, 17]. For us this will be the main objective in any discipline.

ACCEPTED MANUSCRIPT (2)To improve or maintain maximum performance, preparing the horse for the competition [7,16-18]. (3) To delay onset of fatigue [7,17,18]. (4) To improve skills or work capacity [7,16-18]. (5) To maintain willingness and enthusiasm for exercise [7,18].

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The emphasis placed on each of these aspects varies, depending on the type of horse and activity being undertaken. For example, a horse trained for show jumping requires more improvement of biomechanics skills and strength fitness, than a horse being trained for endurance events where an improvement in stamina is the main aim [7].

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Regarding to the goals of strength training there are some considerations that should be taken, adapted from humans [19]. Strength training programs may be used to increases in muscle size, strength, power, speed, local muscular endurance, balance, coordination, and flexibility and rehabilitation from injury (in this review will not focus on rehabilitation). Most programs should aim to collectively improve several of these components in an integrative approach as opposed to only focusing on one of them.

Musculoskeletal adaptations to training

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The musculoskeletal system of the horse is highly developed and specialized, allowing the horse to travel long distances to feed itself and to attain high speed to evade predators. One of the major reasons for training horses is to increase musculoskeletal strength that would prevent injuries [20]. Injury results when the load applied to a structure

exceeds its capacityACCEPTED to sustain it. SoMANUSCRIPT in order to reduce injury, the structure is required to increase its ability to sustain load. In humans exercises to increase neuromuscular adaptation, such as, strength and balance are proposed for injury prevention [21].

3.1.

Muscular adaptation to training

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There are different physiological adaptations to training or conditioning depending on the training and the type of tissues involved. Some tissues or functions are highly malleable and are significantly improved by conditioning, i.e. muscles [22] and cardiac function [23,24] while others remain unchanged i.e. lung and respiratory function [25]. Over all, among the adaptable biological systems, the soft tissues (skeletal and cardiac muscles for example) adapt rather rapidly while hard tissues (tendons, bones and joints) take longer to improve [17]. If we want to avoid injuries, our main goal, we should take into consideration the time required to adapt of these different tissues.

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Studies in horses have shown that performance is correlated with selected muscle characteristics. The adaptation of equine skeletal muscle during training is largely mediated by the structural and functional plasticity of the myofibers. Depending on the nature of the training the adaptive response can take the form of [14,26]: - Hypertrophy (when myofibers increase in size but otherwise retain their basal structural, physiologic, and biochemical properties);

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- Remodeling without hypertrophy (where myofibers do not enlarge but acquire markedly different enzymatic and structural characteristics, often accompanied by changes in the microvasculature)

ACCEPTED - A mixed response of both.

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- Hyperplasia: an increase in the number of muscle fibers.

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The effects of training on equine muscle fiber size are still some controversial. Equine muscles usually respond to training by increasing muscle mass. This adaptation has been associated with hypertrophy rather than with hyperplasia of muscle fibers. However a hyperplasic growth of muscle fibers after training cannot be rejected in some breeds (in particular, Thoroughbreds and Standardbreds), that usually respond with a prominent increase in muscle mass associated with minimal or no changes in muscle fibre sizes [27].

3.2.

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The response is different depending on the basal muscle profile before training [28]. Many studies have demonstrated that muscle fiber type distribution and myosin heavy chain (MYHC) composition are strongly influenced by training. Studies on endurance training in horses have demonstrated increases in the percentage of type IIA fibers and coupled with a decrease in the proportion of IIX fibers. Fiber type transitions during strength training appear to resemble qualitatively those observed in endurance training [26]. When these various training studies are considered in combination, it is reasonable to assume that fiber type transition is graded and in order, typically changes from faster and more glycolytic fibers to slower and more oxidative fibers, i.e. IIX—>IIAX— >IIA—>IIA+I—>I [28]. Functional adaptation of bone, tendon and ligament to training

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The bony skeleton provides structural support for the body and also enables locomotion. The genetically determined bone mass is optimized for energetic efficiency and to accommodate the loads imposed. The process of functional adaptation enables the appropriate adjustments to

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MANUSCRIPT be made to the massACCEPTED and architecture of the skeleton. The biologic signals that induce bone cell activity and control the adaptive process are related to the deformation of the tissue as a consequence of the loads applied by muscle and gravity [29]. In other words, the skeletal system of a performance horse adapts to exercise or the lack of exercise by forming or removing tissue [30]. Since strength training apply larger loads on the musculoskeletal system than other types of training it also may incite in more adaptation (this is well established in humans). Indeed, Santamaria et al [31] performed a jumping training program in foals and looked the results in a longitudinal way. They concluded that carefully controlled exercise at foal age may help in improving strength and resistance of the musculoskeletal tissues. 4. Principles of horse training

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We have developed 7 principles of training based on scientific literature and our own experience. They are not only the general principles of training presented by other authors but also other principles based on medicine, pedagogy and our own experience as a veterinaries and trainers (for human and horses). Some other authors do not present them as a principle but recommend using them for horse training. We believe that following these principles will help trainers to enhance the performance of any horse. 1. To avoid or minimize the incidence of injuries 2. Overcompensation

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3. Progressive loading

4. Periodization ACCEPTED

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5. Individuality 6. Specificity 7. Unity 4. 1. First principle: to avoid or minimize the incidence of injuries

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For some authors this principle is within the definition of training or within the main goals [8,16,18,32]. This principle is one of the main objectives of a training program. We consider that this is the most important principle that a trainer or rider must follow. Exercise-induce injury is the main determinant of failure of an equine athlete to train, to compete, and to perform. Furthermore, it is the mayor cause of loss of incomes and value in the equine industry [20].

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The best way to reduce exercise-induced injury is by applying the scientific knowledge of exercise physiology and training [6]. We mean this principle as principle of health care ethics, non-maleficence. For us and for every trainer taking care of the horse should be the most important principle. Unfortunately, we have seen some trainers worrier about the competition than the health of their horses. 4.2. Second principle: overcompensation

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A basic principle of training is that a single exercise session leads to fatigue and mild cellular damage which, in turn, results in short-term adaptive responses (Fig. 1) [33].

ACCEPTED MANUSCRIPT Figure 1: Overcompensation principle. Adapted from Rogers et al. [33] For training to be effective there must be a degree of ́over-reaching ́. Over-reaching refers to the performance on an activity at sufficient intensity and duration to induce some strain into the organism [32]. If the training stimulus is not intense enough there will be not adaptation. However if there is not enough time of recovery this ́over-reaching ́ can lead to a more serious condition, called overtraining [2, 33].

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Overtraining is defined as a loss of performance ability, despite the maintenance of or an increase in training intensity. Athletic performance decreases, and horses must cease or reduce training for variable periods of time in order to recover. For most horse trainers, there is a delicate balance between attaining and maintaining peak fitness, and lameness or overtraining [2]. For this reason it is very important to identify signs of overtraining. Some signs, including poor appetite, body weight loss, behavioral changes and reluctance to exercise typically accompany the reduction in performance observed in overtrained horses [34]. Overtraining occurs when training is too vigorous and/or rest periods between training sessions too short, performance is reduced due to an imbalance between training stress and recovery [33].

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On the other hand when the load of training is not enough or there is lack of training, another condition occurs called, detraining. Different researches about detraining in endurance horses have shown that maintenance of the trained muscle characteristics during inactivity is more prolonged in horses than other athletic species, lasting throughout 5-6 weeks of inactivity, although not beyond 12 weeks. During detraining, fiber sizes decrease and there is a decline in mitochondrial

ACCEPTED MANUSCRIPT density, aerobic enzyme activities, glycogen content, and a normalization of anaerobic enzymes activities [26]. How do we prevent overtraining or detraining? We should observe our horse for any of the signs mentioned earlier. Furthermore, we have to be sure that the period of time before exposure to the next training session is enough to allow time for the training effect (adaptation) from the previous session to occur [33].

4.2.1. Evaluation of fitness and control of training

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How can we evaluate the adaptation? By the evaluation of fitness and control of the training. However, if the day after any training session the horse appears tired or demonstrates any sign such as swelling or filling in the legs, it is advisable to reduce the training session or give the horse a rest day, to give the musculoskeletal system time to strengthen and adapt to the stresses being progressively applied [35].

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The risk of overloading and overtraining can be reduced with scientifically designed training programs and with a control of the intensity and progression of the training sessions, by means of exercise tests [36]. Although no measure or combination of measurements will ever be perfectly correlated with the ability to perform, results of appropriate fitness tests can guide decisions by horse owners, riders and trainers concerning the training and use of horses for competitions [37, 38].

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One of the main reasons to perform a standard exercise test (SET) [11,36,37,39-41] is to compare the effectiveness of different training programs, to measure the adaptations of the animal to a specific training program and to modify the program according to the progresses achieved. These goals could be adequately reached if only regular tests

ACCEPTED MANUSCRIPT are performed in the same horse and initial acquired data served as reference to assess progress during the training period.

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Horse owners and trainers have long been interested in fitness measurement. These measurements can only be obtained by SET. The ultimate expression of aerobic capacity is maximum oxygen uptake, or VO2max. Measurement of VO2 max currently necessitates use of a treadmill and/or expensive equipment for gas analysis. Alternatives are the analysis of heart rate and blood lactate in response to specific workloads [2].

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Increases in fitness are reflected in decreases in heart rate during submaximal exercise. Furthermore, the lactate response to specific speeds has been used in laboratory treadmill and field testing for assessing performance and fitness. Fitness has usually been described with speed at a lactate concentration of 4 mmol/L (VLa4). As the horse increases fitness, VLa4 increases [2]. In the recent study by Sommer et al. [11], they evaluated the fitness of show jumpers with this index. They found that in professional riders the Vla4 of their horse improves with training while amateurs` horse riders did not. There may be for several reason but we find these results very interesting. 4.3. Third principle: Progressive loading principle

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Every horse needs to have a general training in order to perform properly on their discipline [2], this is the preparatory period in the periodization hierarchy. Furthermore, different disciplines and different horses (Individuality Principle) require a longer or shorter preparatory period.

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ACCEPTED The basis of any training program isMANUSCRIPT to continually provide increased levels of stress to the physiological systems to improve performance. For continual adaptation, this level of stress needs to be continually increased [33]. Furthermore, the success of a conditioning program relies on the body adaptive response to the stress of exercise [8].

Figure 2: Relationship between work-load (blocks) and performance (discontinued line). Adapted from Rogers et al. [33].

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As we see in figure 2 if the level of stress is not increased there will not be increase in performance (discontinued line). On the other hand if the workload is increased there will be a better adaptation to training.

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How do we increase the training load? The training load or the volume is the stress or the workload that we perform on a horse over a period of time. It depends on the intensity, the duration and the frequency of the workout [8]. A good trainer should be able to manage these three variables in order to increase the load of training properly.

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The usual progression of a conditioning program is to maintain a low intensity of exercise in the early stages of the training (when the horses are young for its discipline and at the beginning of each season), while increasing the duration. The next step is to maintain or reduce the

ACCEPTED MANUSCRIPT duration as the intensity increases. In the final stages the program (when the horses are close to an official competition) becomes more sport specific, mimicking the competition [8]. There are different variables that should be increased in this sequence in order to obtain the training objectives: Duration: Is the period of time over which exercise is performed. The duration depends on multiple factors, such as intensity and individuality.

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Frequency: Describe the number of workouts or exercises during a period of time. As the duration, the frequency depends on other factors, such as the volume, the period of the season or the objective.

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Intensity: The intensity of exercise depends on the amount of energy expended over a period of time. Heart rate is a good indicator. Furthermore, speed and high of the jump are the mayor indicator of exercise intensity.

4.4. Periodization principle

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When we train a horse we should have a main objective for example, the World Equestrian Games, and we must plan based on this objective. Setting smaller objectives will help the horse to be in its best performance in our main objective. However, we cannot only follow the progressive loading principle because the horse also needs recovery time in other to improve, as mentioned before.

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‘Training periodization’ was described as the purposeful sequencing of different training units (long duration, medium duration and short-term training cycles and sessions) so that athletes could attain the desired state and planned results [42].

ACCEPTED MANUSCRIPT Variation, or periodization, entails the systematic process of altering one or more program variable(s) over time to allow for the training stimulus to remain challenging and effective. The main goal of any training or conditioning program in sport horses is to stimulate physiological adaptations within the animal’s body to improve performance [43]. These physiological adaptations are obtained by the chronic repetition of exercise at the level of all systems involved in the realization of exercise [25].

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Exists a hierarchy of periodized training cycles, here we present the traditional theory, and for more information about periodization we recommend the excellent review of Issurin [42]: The upper level of the hierarchical periodized system belongs to multi-year preparation, where the Olympic quadrennial cycle is of particular importance in our case also the World Equestrian Games. The next level of the hierarchy is represented by the macrocycles, which usually last one year but can be shortened to half a year, this is usually a season. The macrocycles are divided into training periods, which full a key function in traditional theory: they divide the macrocycle into two main parts, the preparatory period, with more general training, and the competition period, with more specific kind of training. In addition, there is a third and the shortest period of active recovery. The next two levels of the hierarchy are reserved for the mesocycles (medium-size training cycles, weeks) and microcycle (small-size training cycles, days); the bottom part belongs to workouts and exercises, which are the building blocks of the entire training system.

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In conclusion, we need to have a plan when training our horses that we will most probably have to redo due to some conditions such an injury or climatic conditions. However, remember that having a bad plan is better than not having a plan at all.

ACCEPTED 4.5. Individuality principle

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Each horse is an individual, we should take into consideration several factors, such as age, breed, how it was raised, if the horse is coming from an injury or any factor that you feel can be relevant, when designing a periodization. For example, in race horses sprint work is essential in conditioning two-year-olds, but they are not mentally mature enough to handle very much of it [44]. Furthermore, different breeds could be more suited for some disciplines than others. For example, in 2012 we compared Andalusian (AN) horses with Arabian (A) horses and we concluded that even when AN and A horses are selected for morphological purposes, A horses have a greater aerobic potential [45]. Not only the characteristic of the individual horse but also other conditions, such as the ridder, the environment where the horse works, the economy of the team, the individual goals of the season, etc., should be taken into consideration when training a horse.

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4.6. Specificity principle

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In order to prepare a horse adequately for competition, the horse should regularly perform the type of activity that it will perform in competition, at an intensity that will induce the physiologic changes needed to permit optimal performance [32]. Strength training should mimic the range and speed of the joint motion used in the sport [15].

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Being specific, or "specificity of exercise", means that the type of work must emulate the competitive event in which the horse will later be required to participate [46]. For example, for show jumpers, strength training exercises that use a similar motion pattern include gymnastic jumping and bounding up steep gradients [15]. Specificity of training signals the bone to remodel in a fashion that will prepare the horse for

ACCEPTED MANUSCRIPT the rigors of competition [46]. The goal in this process is to increase stress gradually (Principle 4. progressive loading), using specificity and gradual overloading, without causing injury [30,47].

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Using cross-training or other exercises that are not specific for your discipline can have beneficial or disadvantageous effects. For example, endurance conditioning benefits a sprint horse by improving aerobic metabolism, which reduces the horse`s dependency on anaerobic energy production, so less lactate is produced [48]. On the other hand, enhanced power through training comes with the cost of a corresponding theoretical ́decline` in aerobic capacity, because the increased mass of recruited fibers and concomitant rise in ATP utilization, occurs simultaneously with a relative inability of oxygen to diffuse into the larger fibers. In practice, this means that training-induced myofiber hypertrophy might well be a handicap not only for long- distance endurance horses, but also for trotters and gallopers competing over middle or long distances [49].

5.7. Unity principle.

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For these reasons we should be careful when programming a training session or season. Some exercises or training method may be beneficial for your horse however others may be harmful. For example, we want our endurance horse to be schooling in dressage, however, elevated movement are not beneficial for our main objective, which is move as fast as possible expending the least energy as possible.

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We should take into consideration every part of the horse when designing a training session or season. Horses as equine athletes must be conditioned and trained to optimize the whole animal for the particular type of athletic activity [29]. When training a horse we should not only take care of its physical state but also its psychological state. For

ACCEPTED MANUSCRIPT optimal individual performance horses must be in peak physical condition and have the correct psychological state [50].

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For example, regarding unity in its physical state; although it only takes about 1 month to develop a significant amount of aerobic, cardiovascular fitness in horses, effects on tendons and bones often take much longer[15,47]. Furthermore, if we want a durable athlete, we should consider the necessary dedication of time to develop strength of all parts of the horse`s body attending to the specificity principle [48]. For these reason, if we do not take the horse as a unit, in this case only taking into consideration its cardiovascular fitness, we can produce some injury on its bones and tendons that may not be ready yet for a more intense training, as its vascular system.

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5. Concepts of strength training

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For example, regarding its psychological state; highly motivated horses can be exposed to behavioral modification techniques in order to attenuate specific unwanted behaviors [50]. For more information about Psychological factors affecting equine performance please read McBride and Mills [50].

There are some basic concepts that are present in strength training that should be introduced in order to understand this kind of training in horses. These concepts are well establish in humans, we will try to adapt them to horses [51,52]:

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It is widely accepted that strength is the ability to exert force. However in any sport strength and speed are highly correlated. For this reason Knuttgen and Kraemer [51] define strength as: “the maximal force that a muscle or muscle group can generate at a specified velocity”. A muscle

ACCEPTED MANUSCRIPT contraction (the active state of muscle tissue, the attempt of muscle to shorten) is needed to generate strength”. There are different types of muscle contractions: - Isometric contraction: the muscle does not shorten because either the bony attachments are fixed or the forces functioning to lengthen the muscle are exactly the same, for example, the back musculature of the horse holding the rider.

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- Concentric contraction: it is a dynamic action in which the end of the muscle (bony attachments) is moved closer together and movement of the skeleton occurs. In concentric contractions either a body part or the total body is elevated. For example, when the horse jumps or when the horse elevates a limb.

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- Eccentric contraction: when the active muscle is forcibly lengthened, for example landing of the jump.

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- Stretch-shortening cycle (known by trainers as plyometric exercises) describes an event in which activated muscle that is forcibly lengthened (eccentric contraction) is successful in reversing the lengthening activity by accomplishing an immediate concentric contraction, for example, gymnastic jumping.

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The stretch-shorting cycle refers to a natural part of most movements. For example, in humans, every time the foot hits the ground during walking, the quadriceps go through a stretch-shortening cycle. When a foot hits the ground, the quadriceps first go through an eccentric action, then a brief isometric action and finally a concentric action. When a reversal of the eccentric action is performed quickly, the muscle is stretched slightly and the resultant concentric action is more powerful

ACCEPTED than if a slight stretch did not occurMANUSCRIPT [52]. This may explain why horses want to canter when we are climbing a very high slope, for sure most of you can relate to this, they use the stretched muscle to generate more power, since the slight stretching store elastic energy. Other common explanation for the more forcible concentric action is that the neutral reflex results in a quicker recruitment of muscle fiber or a recruitment of more muscle fibers [52]. - Repetition, means each time you do an exercise, for example a jump.

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- A set: is a group of repetitions performed continuously without stopping or resting. For example a jumping course or climbing a hill.

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- The percentage of the maximal strength of you horse is very useful for jumping or eventing horses and probably for reining horses since as we mentioned earlier speed and strength are highly correlated. We should take into consideration that maximal strength of the horse is not the same as maximal jumping capacity of the horse. The last one partly depends on the anatomic and physiologic properties of the musculoskeletal system that allow the horse to project its body sufficiently high into the air to clear the obstacle. Nevertheless, the horse also needs to rotate and fold its body around the obstacle without touching it. Theoretically, the latter jumping technique could be a matter of talent, could be acquired by training, or a combination of both [31]. You will probably never know the maximal strength of your horse however you can estimate the percentage of intensity used. We recommend to be careful, you should remember the first principle of training (Avoid or minimize the incidence of injuries). As a general rule, the higher the jump or the slope of the hill, less repetitions should be performed. We should take into consideration that in contrast to the

situation in human ACCEPTED athletes, strengthMANUSCRIPT training is not continued to the point of exhaustion in horses because the risk of injury. Instead, the workout is terminated when signs of muscular fatigue are evident [15]. - Rest periods between sets of an exercise, between exercises, and between training sessions allow recovery and are important for the success of any program.

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- Power: is the rate of performing work. Power during a repetition is defined as the weight moved (it can be the own weight of the horse, or the weight of the horse and the ridder) multiplied by the distance the weight is moved divided by the time to complete the repetition. To have an idea, although other factors can take part, if the horse weights 500 kg and the rider weights 70 kg and both are moved 1 meter in 1 second, the power is 570 kg multiply by 1 meter and divided by 1 second or about 570 Watts. Power during a repetition or a set can be increase by: - Moving the same weight the same distance in a shorter period

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of time.

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- Moving a heavier resistance (adding weight to the horse) with the same distance and the same period of time.

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Thus, the only ways to increase power are to increase movement speed or moving a heavier resistance with the same or greater movement speed than a lighter resistance. For example, when climbing a hill, the horse will generate more power if he does the same distance in a less period of time or if we add weight to the saddle. Some endurance competitors use a training saddle heavier than his competition saddle, so the horse are used to generate more power during training and will move lighter in competition.

ACCEPTED MANUSCRIPT As mention in the introduction, there is neuromuscular contributions to the improvement of strength. In order to development of maximal muscle power, the neuromuscular contribution is crucial and it contribution may include: 1) maximal rate of force development; 2) muscular strength at slow and fast repetition velocities; 3) stretch- shortening cycle performance; and 4) coordination of movement pattern and skill [19].

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6. Types and methods of strength training

Many different method can be used to improve strength, in humans, these methods has been grouped into three contents areas [53].

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a) Resistance training: is the strength training when you use any kind of extra resistance to your body weight. For example, walking in water or adding extra weight to the horse.

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b) Plyometric training: plyometric exercise refers to those activities that enable a muscle to reach maximal force in the shorter possible time. It has been explained before. This is the kind of exercise usually used by jumpers. c) Speed, agility, and speed-endurance development [54]: Although, speed, agility and endurance are other components of fitness, as mention before, they are very correlated with strength.

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- Speed is the ability to achieve high velocity. It is a manifestation of explosive force applied to a specific task.

MANUSCRIPT - Agility is the ACCEPTED ability to explosively brake, change direction, and accelerate again. - Speed-endurance: provides the metabolic conditioning needed to support speed, agility, and speed strength.

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In humans, these three method are used together in order to improve strength [53]. Since horses cannot be trained to lift weight to work resistance machines, we must use other kind of strength training exercises that load the relevant muscle groups in an appropriate manner in order to get results [8]. Hills, gradients and gymnastic jumping exercises have been used to good effect [8,15,48], these are the types of conditioning training “b” and “c” mention before. Moreover, conditioning on a loose, deep surface and riding through snow or water not only strengthen specific muscle groups, but also increase cardiovascular loading and encourage active joint flexion through a wide range of motion [8,48] this is type of conditioning training “a”, conditioning in these kind of surfaces, as will be explained latter, should be taken with caution to prevent injuries. And finally, pulling exercises that may increase strength are not very well described in the literature, however, there are places where this method is used [55] also type of conditioning training “a”. There are different types of strength training. Except if you are training to beat the world record of high jumping, which you will train your horse for maximal strength, or you want to increase your horse muscle, training for muscle hypertrophy, you will most probably train your horse for muscular endurance or muscular power.

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There are several resistance training exercises to select, when designing a program for a horse, however, they can be divided into two categories: core or main exercises and assistance or supplying exercises (Adapted to

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ACCEPTED MANUSCRIPT horses from, Baechle [56]). Core exercises recruit one or more large muscle areas such as, hind legs, forearm, and shoulder muscles, and receive priority when selecting exercises because of their direct application to the sport. Assistance or supplying exercises usually recruit smaller muscle areas, such as neck muscles, involve only one primary joint and are considered less important to improve sport performance. We should take into consideration that some core exercises in one discipline can be supplying exercises in other. For example, downhill walking can be a supplying exercise for a dressage horse but a main exercise for an endurance horse; or the opposite, turns, circles, voltes, and lateral movements, can be main exercises for a dressage horse but supplying exercises for an endurance horse.

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A common application of assistance or supplying exercises is for injury prevention and rehabilitation [15,35,56]. For example, the back of a horse is highly susceptible to injury and remodeling if subject suffers intense pressure too early. Working the horse to strength the back and abdominal muscles, for instance, some dressage, long reining training, and hill work at different angles can help develop the epaxial musculature of the “top line” of the horse [35]. Although recently core strength training for horses in physiotherapy is been more used [57], its clear that type of assistance training should be used not only to treat but also to prevent injuries, for more information about this topic please read, Clayton [57]. 6.1. Different types of strength training (adapted from Baechle et al. [56]):

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Training for muscle maximal strength: All types of weight training will improve your strength. But this technique aims to improve absolute strength. It involves one to six repetitions of each exercise performed

relatively slowly atACCEPTED more than 85 %MANUSCRIPT of the maximal strength of your horse. This can be done for three to six sets with a rest interval of 1-2 or 2-3 minutes, depending on the exercise. As mention before this type of strength training is not usually needed for regular competitions.

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Training for muscle hypertrophy: This type of training aims to increase the amount of lean muscle in your horse. It involves doing 6 to 12 repetitions relatively slowly, generally for one to three sets per exercise at 67-85 % of the maximal strength. Rest periods of 1-2 or 2-3 minutes are advisable between sets, depending on the exercise. An example of this kind of training will be doing a jumping course of 10 jumps which are not really challenging for your horse, either in hight or technique and repeat this 3 times. As mention before this type of strength training is not usually needed for regular competitions.

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Training for muscle power: This technique aims to improve a muscle’s explosive power, meaning its ability to perform a powerful movement in minimal time. Examples include launching into a fast sprint or jumping. It involves doing one to 2 repetitions of each exercise at maximum speed at 70-90 % of the maximal strength of your horse depending on the number of repetitions. Depending on training goals, a power program can consist of one to three or three to six sets. For high-intensity exercises, a rest period of at least two to three minutes per set is recommended. Your horse should be totally rest before starting a new set.

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Training for muscular endurance: This kind of training helps muscles to be able to keep performing a movement for a prolonged period. This is the type of strength more important in horse training because it is the most specific for almost any kind of competition. Training for muscular endurance involves doing more than 12 repetitions or more at a

ACCEPTED controlled speed, generally for one MANUSCRIPT to three sets. It is recommended that short rest periods be used for muscular endurance training - 1-2 minutes between sets of 20 repetitions and even less than a minute if you are doing a more moderate number of repetitions, such as 10-15. Hill work or gradient will be an example of this type of training. 6.2. Strength training Methods 6.2.1. Hill

work or gradients.

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Gradients are the foundation of equine strength training [8]. Working the horse on a gradient makes use of the effects of gravity to selectively load the hind limbs on an incline or the forelimbs on a decline [57]. Furthermore, an inclined grade or a hill challenges and strengthens the horse`s body muscles. Indeed, Self et al. [58] examined the speed of 373 racehorses on different gradients on an undulating racecourse. Their results showed that highest speeds were in fact achieved on a level gradient and horses were slower on both incline and decline slopes. Human athletes run faster on a decline, which can be explained by the energy gained by the center of mass from height loss. This study showed that horses go slower, which may be attributable to the anatomical simplicity of their front legs limiting weight support and stability when going downhill. Furthermore, the results of Eto et al [59] indicated the possibility that up- hill running results in the same training effect as faster running on a flat track. In research, many authors use inclined treadmill because the can achieve higher intensities without the dangerous implications of speed [59,60].

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The slope or and the direction of the gradient, and the horse´s gait and speed are manipulated to enhance the specificity of the exercise for a

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ACCEPTED MANUSCRIPT particular sport. Different fitness components are improved with this kind of training, such as, stamina, balance and of course strength [8]. The resistance of a horse´s body weight and in most cases its rider´s weight, as he climbs a hill develops: hind leg, forearm, and shoulder muscles. Walking or trotting a hill develops independent muscle in each hind leg. On the other hand, at canter or gallop, the horse propels himself forward by pushing off the ground with both hind legs at about the same time. At these gaits, the horse use both legs as a unit with considerable strain on the rump and back muscles. Downhill work strengthens pectoral, shoulder, and forearm muscles, while braking strengthens the quadriceps muscle in the hind legs [8,48].

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Downhill conditioning at trot and canter is necessary for horses that are being prepared for eventing, and endurance racing (specificity principle). However, we should be careful with this type of training because creates a lot of stress on the joints, and should be limited. An interesting fact is that sometimes is beneficial to work across a slope, especially in horses that are markedly asymmetrical. This kind of training makes help to use both hind legs [8].

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Uphill gallops that require the horse to be pushing all the time are the shorter most intense training gallops, with the incline of the slope and the evenness of the chamber of the ground determining the intensity, this intensity may overburden the horse´s musculoskeletal system compared with flat ground [9].

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Clayton [57] recommends as with other types of exercise, gradients should be incorporated gradually into the exercise routine (progressive loading principle) starting with a small number of repetitions on a gentle slope and incrementally increasing the work by performing a larger number of repetitions or by including steeper gradients. However,

ACCEPTED MANUSCRIPT she does not provide information about the incline, height and length of a hill. Moreover, it seems that increases in speed and in inclination lead to an increase in the integrated electromyographic activity on the muscles and hence to a higher workload [61].

6.2.2. Cavalleti

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When training jumpers Van Weeren [15] also recommends the use of gradients. This author states that several sets should be performed and the appropriate work-rest ratio is 1:6, in which bounding up the gradient is the work and descending at a walk is the rest period.

or pole work

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Cavalleti are series of parallel rails or low obstacles placed for the individual horse at a walk, trot, or canter. Its use requires the horse to undergo disciplined exercise, using and developing the correct muscle. He must lift his legs higher, arch his back, and stretch his neck, both loosening and strengthening muscles, and improving suppleness and flexibility. By engaging his hindquarters, he increases impulsion [62]. Cavalleti or pole work, is an excellent training tool, as it can provide both an interesting variation of flat work and a degree of gymnastic work [9]. Furthermore, it is an excellent assistance exercise. When the trainer understands how to use it, cavalletti works open many possibilities for improving the horse´s suppleness and strength [63].

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There are many possibilities using this training method. Poles or cavalletti can be set either in straight lines o around the perimeter of a circle can be very helpful to increase lift and length of the stride in trot [9, 63]. Furthermore, the horse can work with or without the rider [63]. Pole work is used training young horse in preparation to jumping, the added advantage of this method of training is that even with mistakes,

ACCEPTED MANUSCRIPT injuries are rare [9]. Furthermore, they can also be used for dressage and experience jumpers [63]. Moreover, trotting over poles it been used for core training because strength the extrinsic forelimb musculature (extensors and adductors) and may also recruit the core stabilizing musculature [57].

6.2.3. Gymnastic

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The lowest height of most cavalletti is 15-20 cm (best for walk and trot), the highest setting is generally 50 cm which is ideal for canter, there are also some height in the middle. Furthermore, a reference distance between cavalletti are: for walk about 0.8 m and for trot about 1.3 m [63]. For more information about this training method please read Klimke and Klimke [63]. Jumping

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Gymnastic jumping is a highly sport-specific strength training method for show jumpers [15] and eventers. By adjusting the height and the width of the fences and the distances between them, the trainer can improve not only the horse´s muscular strength but also its mental and physical agility [8,15] to fulfill the requirements of different sport [8]. Each time the horse takes off over a fence, the joints of the hind legs flex then extend in an eccentric-concentric cycle of contraction [8].

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Van Weeren [15] presented two key criteria for using gymnastic jumping as a strength training tool: first, the horse must be familiar with the technical skill (avoid or minimize the incidence of injuries principle), and second sufficient repetitions must be performed to stimulate muscular adaptation. Depending on your objective, such as for example hypertrophy or muscular endurance, you should follow the repetitions and sets, with the appropriate recovery time mentioned earlier. This method of training should be used at least once a week, even for

ACCEPTED MANUSCRIPT experienced jumpers in other to maintain the strength of the musculoskeletal system.

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For sports that need a high degree of collection, it is appropriate to use small fences (70-80 cm high) set at bounce distances (creating a stretchshortening cycle), so the horse lands the take off immediately, without any intervening strides [8]. When the development of muscular power is of the prime importance (show jumpers and eventers), the use of series of small fences (60-90 cm high) leading to two or three large fences at the end of the gird is effective, it also prepare the horse for jumping through combinations [15]. As when training hills, if a horse`s strength is very one-sided, the jump can be set on a curve because at take off the inside leg is selectively loaded, which increases the strength on that side of the body [8]. 6.2.4. Steps

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Both uphill and downhill steps can be incorporated in a strength training program [8]. However, we should be careful when introducing this method of training because horses are used to finish the movement in an eccentric-concentric cycle of contraction, like in a jump. However uphill steps are concentric muscular contractions, while down steps emphasizes the eccentric contractions in the muscle. As mentioned earlier, horses do not use single contractions and may get injured very easily. Being said that, uphill steps develop explosive power in the hind legs and jumping down steps emphasizes the eccentric contraction in the muscles of the front legs, very beneficial for eventers [8].

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A particular useful exercise is one in which the horse jumps down a drop followed immediately by jumping up a step [8]. This is like to plyometric training in humans or stretch-shortening cycle as mention before.

6.2.5. Different

ACCEPTED MANUSCRIPT surfaces or deep footing.

Exercise in deep footing, like sand, snow, or a spongy meadow, create resistance in thigh and pectoral muscles. Slow and careful conditioning accustoms a horse to deep footing, preventing tendon strain. However, if mud is incorporated into training routine, restrict exercise to exclusively walk [48]. We should be careful with this method of training because it may produce injury on the horses.

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Lately, treadmills submerged in water (water treadmills) are being used for rehabilitation and conditioning of horses [64-67]. This method of training can be good to increase strength in horses coming from a surgery or a injury, or as a supplying exercise for any kind of horse because the range of movement of the joints is increased [67]. 6.2.6. Calisthenic exercises

7. Designing

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In humans, body weight exercises, often called calisthenics, use body weight as resistance with the intent to improve strength through a variety of movements such as pushups, pullups, and situps [68]. In horses, an example of these exercises is when we train the horse to accept bit contact. The horse´s neck and head arch and the hose activate the muscle on the top of its neck. The head acts as a weight to provide some resistance to the exercise. Continual exercise of the neck muscles develops them over time and bulks up the neck [48].

a Strength Training Program

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In the annual conditioning cycle, the ideal time to improve strength is during off season [15]. The gains in strength are maintained through the competition season by a single workout each week [8]. The American

ACCEPTED College of Sport Medicine (ACSM)MANUSCRIPT [69] recommends in its position stand that in order to improve strength (in humans) the recommendation for training frequency is 2-3 days per week for novice training, 3-4 days per week for intermediate training, and 4-5 days per week for advanced training.

8. Conclusions:

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Van Weeren [15] presents general recommendation to show jumpers, which are similar to the ACSM, this author recommend that strength training should be introduced after completion of the slow, longdistance phases and is to be performed two or three times a week, which balances the need for sufficient muscular stimulation with enough rest but does not provide any reference about this. Moreover, this author does not include specific recommendations. Therefore, we suggest following the ACSM recommendations using different methods of conditioning training during the week, however the methods should be combined to avoid overtraining and injuries. For example, one day plyometrics, one day hills and one day regular jumping, for jumpers. For endurance horses, two days of supplying exercises (dressage) and one day of hills. For an advance eventer during pre-season, one day of cavalletti, one day regular jumping, one day of gymnastic jumping and two days of hills work. Until more research is done in horses about this matter we recommend to be cautious and follow the principles of training mention before when designing a strength training program for horses.

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In conclusion, there is a need for research about strength training in horses. Most of the conditioning programs used nowadays are based on empirical knowledge. In this paper we present objectives, principles of

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training in general ACCEPTED and methods of MANUSCRIPT strength training in particular based on human strength training applied to horses and based on our own experience and some other authors. Until further researches, we recommend trainers to use this article as a guide when designing the training program of their horses and developing the strength exercises of each session.

9. References:

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[2] Evans DL. Training and fitness in athletic horses. A report for the Rural Industries Research and Development Corporation. Sydney: Publication No 00/1, Project No US-772; 2000.

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[63] Klimke I, Klimke R. Cavalletti: For Dressage and Jumping. 2nd Ed. North Pomfret, Vermont: Trafalgar Square Books; 2014. [64] Voss B, Mohr E, Krzywanek H. Effects of aqua-treadmill exercise on selected blood parameters and on heart-rate variability of horses. J Vet Med A 2002; 49: 137-43.

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[66] Lindner A, Wäschles S, Sasse HHL . Physiological and blood biochemical variables in horses exercising on a treadmill submerged in water. Journal of Animal Physiology and Animal Nutrition 2012; 96(4): 563-9.

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[67] Mendez-Angulo J L, Firshman A M, Groschen D M, Kieffer P J, Trumble T N. Effect of water depth on amount of flexion and extension of joints of the distal aspects of the limbs in healthy horses walking on a underwater treadmill. Am J Vet Res 2013; 74:557- 66.

ACCEPTED [68] de Souza Santos D, de OliveiraMANUSCRIPT TE, Pereira CA, Evangelista AL, Sales D, Bocalini RL, et al. Does a calisthenics-based exercise program applied in school improve morphofunctional parameters in youth? Journal of Exercise Physiology. JEP online. 2015 Dec 1; 18(6):52-62.

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[69] American College of Sports Medicine. American College of Sports Medicine position stand. Progression models in resistance training for healthy adults. Med Sci Sports Exerc 2009; 41(3):687

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ACCEPTED MANUSCRIPT

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RI PT

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT

EP

TE D

M AN U

SC

RI PT

The use of the horse for athletic competition involves conditioning and training for specific types of performance. • Most of the conditioning programs used nowadays are based in empirical knowledge. • Until further research, when training horses, the principles of training presented in this paper should be followed. • Different methods of strength training can be used when training horses depending on the objetive.

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