Adenosine triphosphate — ATP — is the only molecule a muscle cell can actually spend to produce movement. Every stride a racehorse takes requires ATP. Every training adaptation is ultimately about the body getting better at producing and regenerating ATP faster than it is being consumed.
Everything a horse eats — carbohydrate, fat, protein — must first be converted into ATP before a single muscle fibre can contract. Feed is not fuel until it becomes ATP. This is why feeding decisions and training decisions are inseparable: the goal is always to supply enough raw material to regenerate ATP at the rate the work demands.
A horse's muscles can only store enough ATP for 1–2 seconds of maximal effort. Everything beyond that relies on regeneration systems working in real time.
The three energy systems — phosphocreatine, glycolytic, and aerobic — are simply three different ways to rebuild ATP. Speed, endurance, and recovery all come back to this single molecule.
"When your horse tires mid-race, what is actually running out — and what does that tell you about what to train?"
Every training session, every feed choice, every rest day has one ultimate purpose: ensure the horse can regenerate ATP fast enough for the work being asked of them. When you understand ATP, training stops being routine and starts being deliberate.
The aerobic system uses oxygen and mitochondria to burn carbohydrate, fat, and some protein, producing large amounts of ATP per fuel molecule. It is not the fastest system — but it is by far the biggest, most efficient, and most trainable of the three energy systems.
For any race distance beyond a short sprint, the aerobic system is doing the majority of the work. Even in a 1200m race, aerobic metabolism contributes over 70% of total energy production. Trainers who underestimate this system and focus only on speed work are leaving the most trainable system underdeveloped.
At lower intensities: fat is the primary fuel, sparing glycogen. As intensity rises, carbohydrate takes over. Training improves fat-burning efficiency — a critical adaptation for stamina horses.
Long, lower-intensity work builds the aerobic base. Short high-intensity bursts early in a session drive mitochondrial growth in fast-twitch fibres. Both are needed.
"How much of your weekly programme is genuinely building the aerobic engine — versus sharpening speed that doesn't yet have a base to sit on?"
Your slow, long work days are not easy days — they are aerobic engine days. The horse that can sustain a high aerobic output for longer, and recover faster between efforts, wins more races over a season. The aerobic system is the foundation everything else is built on.
Wednesday #3: The anaerobic system bridges the gap when aerobic supply cannot keep up — understanding both together explains every race fade. | Friday #5: VO₂max is the ceiling of aerobic capacity — the number that quantifies how big this engine actually is.