Feeding the Endurance Athlete (Part 1)

Feeding the Endurance Athlete

Dr Tim Kempton

Stance Equitec.

This series of articles explores and challenges the science of feeding and training of performance of endurance athletes. 

Setting the scene.    Elite athletes, be they human or equine, have specific training requirements depending on the type of activity.  Ursain Bolt holds the world record or 9.58 secs for the 100 m sprint. Stephen Kiprotich from Uganda won Gold in the 2012 Olympics marathon. Imagine in your mind the physique, training and nutrition of these athletes.  In the equine world, Ursain Bolt is the racehorse and Stephen Kiprotich is the endurance horse. Their physiques are completely different.  The fundamental difference is that the sprinter derives energy for short bursts of speed from the anaerobic (without oxygen) chemical pathways in the body, whereas the marathon runner uses the aerobic (with oxygen) pathways to supply energy for hours of running. The muscles need oxygen to perform for these long periods of time.

Endurance horses are marathon runners, they need a feed to supply energy for hours.  So why are they often fed feeds designed for racehorses that provides energy for minutes?   Many of the issues seen in endurance horses (inflammation, nervous behaviour, ulcers, tying up, colic, lameness) can be attributed to feeding the wrong feeds.  We need to explore some science to explain why.

Energy supply.  The most important nutrient for endurance horses is energy (assuming protein, fibre and minerals and vitamins have been optimised).  Energy is derived primarily from two sources, oil and carbohydrates (sugar, starch and fibre).  Oil has twice the energy content compared to carbohydrate. There are some good oils, and also many bad oils. The sugar and starch content of carbohydrates is called Non Structural Carbohydrate (NSC) and is similar to Glycaemic Index (GI).  In all animals, the chemical production of energy occurs either under anaerobic (without oxygen) or aerobic (with oxygen) conditions. The energy is supplied to the cells as ATP (Adenosine Triphosphate). ATP is simply the term to describe the currency of energy supply (its like $).  ATP cannot be stored in the body, and must be produced continuously from the carbohydrate and oil in the feed.  Oil produces more ATP than carbohydrates under aerobic conditions.

Energy storage.  Energy is stored in the body either as animal starch (glycogen) or fat.  Based on human studies, it is estimated that a 400 kg horse stores approximately 13,000 cal/kg  as glycogen and 590,000 cal/kg as fat . The constraint is however that the energy from fat can only be released when the carbohydrate intake is low, ie when the level of the hormone insulin is low.  Insulin is the hormone associated with diabetes. Horses can get diabetes (insulin resistance) the same as humans. High levels of insulin from grain based feeds can block the release of energy from fat. 

Muscles.  Horses have different types of muscle fibres, which are suited to ether sprint or endurance activities.

Sprint activities include racing, polo, harness racing, polocrosse, campdrafting, show jumping, ie  activities less than 3 minutes.  These horses rely mainly on the Type IIa and Type IIb “fast twitch” muscle fibre groups. Sprint muscles use anaerobic energy supply, and produce lactic acid as a byproduct. These muscles fatigue quickly.

Submaximal or endurance activities include dressage, eventing and  endurance use Type I “slow twitch” muscles that rely on aerobic metabolism. 

These fast and slow twitch muscle groups therefore require completely different feeding strategies. Fast twitch fibres need “sprint” or “explosive” energy over a short term, supplied under anaerobic conditions. Slow twitch fibres need “sub maximal” or “endurance” energy for long term (>10 mins to hours) of activity supplied under aerobic conditions.

Summary.  Endurance horses are marathon runners. They rely on aerobic metabolism to produce ATP and to use the energy stored and supplied for slow twitch muscular function.  The endurance horse cannot efficiently utilise fat for energy if it is fed on high levels of carbohydrate (grain). Grain is suited to sprint activities, and causes an increase in insulin, which can switch off the hormones that allow the horse to use fat as the primary energy source. Simply put, grain can be the enemy of the elite endurance athlete.

Articles in the following QERA newsletters will share the science of endurance nutrition, feeding and training techniques to optimise aerobic metabolism using low NSC, high energy feeds based on fibre, good oil, and strategic supplements such as turmeric to reduce inflammation, and increase nutrient absorption, storage and utilisation.