Thoroughbred Conditioning and the Bathtub Analogy
Think of your thoroughbred as having millions of tiny bathtubs in each of his muscles. Inside this bathtub is where lactic acid accumulates during exercise. The floor outside of the bathtub can serve as the muscles themselves. Analogy-time:
When you begin exercise, the faucet is turned on and the tub begins to fill with lactic acid. The drain in the bottom is open – constantly removing lactic acid from the tub – some is being neutralized, and some is being recycled to provide energy. Both good things, as science is finally starting to recognize that lactic acid by itself is not all bad.
If the intensity of exercise is kept low, the drain is able to remove most of the lactic acid filling the tub, as the faucet itself is not turned on full blast just yet, but more of a dripping is taking place. Think a jog or slow canter for most sound horses. But that is not interesting, what takes place as exercise intensity increases is where the magic happens.
Let’s pick up the pace for our fictional racehorse, who we’ll anoint a stakes quality athlete, not graded stakes, but a step above the allowance level. As he approaches the 2:00 minute lick/15sec to the furlong speed barrier, that faucet starts to increase its flow rate – filling up the tub quicker than the drain can reduce the rising level of lactic acid. As he rounds the final turn and is allowed to pick up the speed a bit down the stretch this morning, he approaches the 12-13sec/furlong barrier, and the lactic acid level soon overwhelms the tub and spills onto the floor of the bathroom, bathing the muscles in a highly acidic environment. Depending upon his anaerobic fitness, fatigue sets in soon thereafter – and the stride becomes shortened.
The bigger the bathtub, the bigger the drain – the longer our horse can stave off fatigue due to lactic acid accumulation and protect the muscles from the flood of hydrogen ions that interfere with muscular contraction and athletic performance.
So how do you turn a tiny apartment bathtub into a big 8 person jacuzzi?
Simple. You exercise at the intensity that keeps that tub nearly full of lactic acid, but not so fast that the spillover occurs. The body’s natural response in this scenario is to increase the size of the bathtub in question, as well as increasing the size of the drain to neutralize/remove lactate. This takes place just before OBLA – or the onset of blood lactate accumulation. For most horses, this takes place around 85% of the maximal heart rate, or 85% of the aerobic capacity. It is this intensity of effort that generally leads to a blood lactate level of 4mmol in the bloodstream – any greater metabolic effort and lactic acid begins to accumulate exponentially.
So, what a trainer does is find out the pace his horse can hold with a working heart rate at 85% of max, or 85% of the highest HR during a 4F breeze. Most horses will max, on average, at 230bpm – making that 85% number a nice even 200 beats per minute. But the work is not done. Then one must deduce the speed/pace that elicits that intensity, which I term V200 – or velocity at 200bpm.
For our stakes level theoretical horse above, that pace will be close to 2:00 min/mile, or 15sec/furlong.
A young 2yo months away from seeing the races?
2:45 to the mile, or 20-21sec per furlong.
A $25k claimer?
Typically closer to 2:20 to the mile, or 17.5sec/furlong.
A Grade 1 superstar?
Experience tells me he can do a mile in 1:45 or so, roughly 13sec/furlong, keeping his HR at 85% of max, and his blood lactate just under 4mmol.
This V200 pace gives you the most bang for your buck on the so-called ‘slow’ or ‘off’ days, generally the 3-4 days a week an actively campaigning horse sees the track outside of speedwork/breezes. Please note above, this pace increases with physiological ability, but it is the horseman’s job to determine psychological capacity – a precocious 2yo may have G1 ability at a very early age, but is not yet mentally mature enough to push the 2min/mile pace just yet, for instance.