Effects of training of the Standardbred racehorse
By Sune Persson, Professor em.
Racing performance is the amalgamated result of many genetic and acquired traits involving locomotory and energy producing capacities. A number of these are trainable, i.e. may be improved by proper adaptation to the performance required. When training a trotter it is important, however, to consider which traits are likely to be limiting. The objects of most training methods are to enhance energy production and utilization, thereby improving fitness and stamina. Factors associated with these properties are:
aerobic power (energy produced through oxidation)
anaerobic power (energy produced without oxygen)
fatigue and lactate threshold
In the racing horse all energy production starts with anaerobic breakdown of energy-rich compounds stored in the muscle cell. This energy source is rapidly recruited, but, very limited and inefficient and must be replenished continuously with energy from aerobic processes in the muscle. The fuel for this is primarily carbohydrate (glycogen) also stored in the muscle cells. Thus, the energy provision is gradually taken over by aerobic production the longer the work is lasting, both sources being equally important after approximately two minutes. Physiologically, the Standardbred racehorse is comparable with a human middle distance runner, i.e., depends on both anaerobic and aerobic metabolic pathways during the race, the latter dominating. Therefore, the capacities for uptake and utilization of oxygen are crucial for racing performance and most training regimens are aiming at increasing the aerobic potential by improving the oxygen transport from the inhaled air in the lungs to the working muscles. This involves a number of "links in the oxygen transport chain" some of which can be measured and evaluated in relation to effects of training and racing performance, e.g. maximal oxygen uptake capacity, the capacity of the heart as a pump, the total blood volume as a transport vehicle and the capacity of the muscle to utilize the oxygen offered.
Commonly used markers for aerobic potential are values for oxygen uptake during maximal work or at a heart rate (HR) of 200 beats/min which approximately denotes the lactate threshold, i.e., the work intensity when a rapid accumulation in the blood of lactic acid starts which is above a concentration of 4 mmol/1. Further, the speed causing a HR=200 (V200) is a useful indicator of "the heart capacity" and the speed producing a blood lactate level of 4 mmol/1 (VLA4) is a useful marker for the oxidative capacity of the muscles. Determination of the total blood volume has been found to be extremely valuable clinically for detection of overtraining, but, also as an indicator of the "overall" aerobic adaptation to training and performance potential.
Several metabolic properties of the muscle cells are possible to identify and evaluate by analyses of muscle biopsies, i.e. in small pieces of muscle taken with a biopsy needle under local anaesthesia. Thus, both muscle fibre types and their biochemical characteristics provide useful information concerning adaptation to training and, possibly, may indicate whether the horse is to be considered to be a sprinter or a long distance athlete. There are three muscle fibre types with different properties:
|Type 1||Type 11A||Type 11B|
|aerobic capacity||very high||high||low|
The metabolic pathway used for energy production during fast work training and racing is influenced by the aerobic capacity, the enzyme profiles of the muscle fibres, blood supply (capillarization) of the fibres, and fibre recruitment pattern. These traits all vary with age, sex, and state of training. The recruitment of the muscle fibres during exercise appears to follow the order of Type I through Type IIA to IIB as the speed increases and recruitment of Type IIB fibres approximately coinciding with the lactate threshold. Thus, in conclusion, there are a number of physiological qualities related to performance potential of the athletic horse available in evaluation of optimal training regimens.
Training of the Standardbred race horse
When training the race horse it is imperative to be aware of what kind of work the horse is required to do with respect to duration and possible intermittent rapid accelerations fighting for position and at the finish.
In general the objects of training should be:
Increase of maximal oxygen uptake capacity => stamina
Increase of lactate threshold => muscular endurance
Muscle fibre changes => strength, speed, endurance
Tissue adaptation => durability => prevention of injuries
Neuro-muscular coordination => speed, durability
Various training schedules have been applied through the years of Standardbred racing, but, generally, four main kinds are practiced in different combinations:
Fast speed training as heat or interval training ("lactate training")
Slow work endurance training ("lactate threshold training")
Long, slow "road work" training
The fast work training is performed at near maximum speed, i.e. above the lactate threshold, and is primarily aiming at improvement of the oxygen uptake capacity, but, also at increasing the anaerobic capacity and the ability to ensure high muscle lactate concentrations and tolerance to fatigue. Effects can be monitored as e.g. increased total blood cell volume, increased speed and power output at the lactate threshold (V200 and W200 ), a higher Type IIA/IIB ratio and CS-enzyme concentration in the muscles, increased speed and power output at a blood lactate concentration of 4 mmol/1 (VLA4 and WLA4 respectively), and oxygen uptake at V200 (VO2-200) or maximally (VO2-max). Some of these markers can be estimated fairly accurately on the track, e.g. heart rate and blood lactate responses to a standardised exercise test.
The "lactate" threshold training" implies slow speed trotting at or below VLA4 and aims essentially at the same results as by the lactate training with the exception of effects on anaerobic capacity. The advantage with this kind of training is that long distance work can be done without accumulation of lactate in the muscles and, therefore, with less risk of fatigue related injuries. The overall training effect is, however, less pronounced.
The strength training is usually done either as trotting uphill or by draught loaded trotting using a sulky that can be breaked intermittently. Other methods are also employed like riding the horse in hilly terrain or longing it in deep snow or in a sand pit. The principal effects are found in muscle fibre properties indicating improved endurance traits and also as a lower blood lactate accumulation during a standard exercise.
The main object with the slow "road work" type of training is to improve the strength and durability of supporting tissues such as bone, tendons, and joint cartilage in order to minimize fatigue related injuries. This kind of exercise has only a marginal effect on energy metabolic processes, but, should not be neglected if a long racing career is expected.
There is however an inherent limitation to the horse's ability to adapt to training and racing. Sooner or later during the racing career, the horse competing in gradually tougher races due to increasing accumulated purse he will reach his genetically determined performance limit. If this is not realized and accepted by the trainer and/or owner the training is often intensified to improve racing results. The result will then be the opposite to the intended, i.e. a loss of performance syndrome with fading racing form. If this is not recognized in time the horse will develop a stress induced polycythemia, i.e. an abnormally increased total red blood cell volume. It is not unusual to find a volume 50% above normal in an advanced case. If so, the career as a race horse is usually to be considered to be more or less over. Consequently, it is imperative to consider this possibility if the horse is showing unexpected fading racing form without obvious clinical symptoms explaining it. Development of this chronic stress syndrome with abnormally increased blood volume is by far most common in male, five years old and older, horses. If this is recognized at an early stage with a blood volume determination it is usually possible to prevent a "disaster" by modification of the training schedule and accepting the fact that the horse can only be entered in less tough competitions in the future.