THE ART OF BREATHING
Do the muscles of the respiratory system affect performance?
OWEVER, until recently, the role of breathing in exercise performance in both human and equine athletes was largely unknown, as was the response of the respiratory system to training. Although it has been understood for many years that human lungs do not adapt to the rigours of aerobic training, it was only recently that is was discovered that the respiratory pump muscles (that is rib cage, diaphragm and abdominal wall) can be improved by training, and the degree which an individual is able to adapt to training influences their performance. Because current knowledge regarding the contribution of respiratory muscle performance in human athletes is very relevant to horses, HBLB is funding research Equine Sports Medicine Centre at Bristol University where techniques established in humans are applied in the thoroughbred racehorse. The respiratory system is divided into the upper respiratory tract – from the nostrils to the trachea (windpipe); and the lower respiratory tract – from the trachea to the lungs.
lower respiratory tract What are the muscles influencing the respiratory tract?
The muscles influencing the lower respiratory tract provide the pumping action that draws air into the lungs. The main respiratory muscle is the diaphragm, but there are accessory muscles in the rib cage (intercostals) and neck. When the muscles of the ribcage and the diaphragm act to expand the chest cavity, air is sucked in (inspiration). During expiration, the ‘elastic’ lungs and rib cage recoil, reducing the size of the chest cavity, which forces air out. The muscles of the abdominal wall also
Over the last two decades the Horserace Betting Levy Board (HBLB) has funded substantial research to understand how various body systems respond to training. For example, because of this HBLB investment we now know that the hearts of thoroughbred racehorses get bigger as a response to athletic training and that big hearts are typically associated with better performers. We also know that bones respond to training by remodelling and hence become better prepared for the strains associated with galloping. WORDS: DR Kate allen, aliSOn MccOnnell PHOtOS: FRanK SORGe
contribute to expiration during exercise, when high breathing rates are required.
What happens to breathing during exercise?
At rest both humans and horses breathe at approximately 12 breaths per minute; in horses the breath volume is around 6 litres, whilst in humans it is around 0.5 of a litre. As the horse exercises, breathing frequency increases, and during canter and gallop it becomes linked to stride frequency – so that one breath occurs every one stride. At gallop breathing frequency increases to on average 120 breaths per minute with volumes in the region of 13 litres. Minute ventilation is the amount of air inhaled per minute, and in the thoroughbred at gallop it reaches values between 1500 - 2000 litres per minute. In contrast, humans are not obliged to breathe in synchrony with running stride, so breathing frequency rarely exceeds 50 breaths per minute and ventilation is typically around 150 litres per
minute at peak exercise in the average man, but can be as high as 250 litres in elite male athletes. In both species, the movement of such relatively large volumes of air so rapidly imposes a huge demand upon the respiratory pump muscles, so much so that in humans the diaphragm can exhibit fatigue during intense exercise. The horse is very interesting in that during gallop the ribcage doesn’t actually change size much – you will have noticed this when riding in that when the horse is galloping you don’t actually feel the ribcage expanding and contracting. What actually happens is that the muscles of the ribcage act to splint or stabilise the chest cavity and most of the work of breathing is done by the diaphragm. As we can’t see the diaphragm it is difficult to appreciate how hard this muscle is working, but we know that it is actually one of the major muscles involved in high-speed exercise.
Differences between human and equine athletes
There are substantial differences between the respiratory systems of human and equine athletes. The majority of humans can maintain blood oxygen levels in the arteries close to resting levels during strenuous exercise, whereas in the thoroughbred ISSUE 49 TRAINERMAGAZINE.COM
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