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.

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About bpressey

Equine Exercise Physiologist

Posted on November 29, 2012, in Uncategorized. Bookmark the permalink. 8 Comments.

  1. Nice analogy Bill, makes it easy to understand a rather complicated process.

  2. Agree. Good post! I was guessing :14s as the 85% heart rate. Are u getting 85% heart rate at 15s with conditioned athletes? Any estimates of heart rate doing :14s?

    • I am getting 85% heart rates and 15’s with many stakes-caliber winners RR. Not yet in any 2yo. I have seen some 14’s at this intensity, but only a few times and in world class horses, mostly in Europe.

  3. Bill

    Good analogy. The only nuance I would add is that where you said “fatigue sets in soon thereafter – and the stride becomes shortened”.

    In terms of class, horses are generally separated in terms of stride length but more importantly elite performance is separated by stride frequency and duration of ground contact. If two horses have the same stride length, let’s say 23 feet, then the better horse is the one that can maintain superior stride frequency throughout the race and have a low percentage of the stride with a limb with ground contact (thus having greater inspiration time and allowing greater oxygen to be transported via RBC’s to combat lactic overflow in the first place). When horses do start to fatigue, it is the frequency that drops off and the contact time that increases first, then the length of the stride is compromised.

    Of course if a horse has a massive stride, and is able to maintain frequency across multiple furlongs they are unbeatable. There is an article somewhere that talks about how Black Caviar has not only a massive stride length (I believe measured at around 26 feet) but she can maintain a stride frequency of 7.5 strides per furlong for multiple furlongs and has extraordinary low contact time in a stride. A pretty hard combination to beat!

    Byron

    • I am getting ready to post about Lance Armstrong. Before he was a household name, he was a middle of the pack cyclist (and likely using drugs along with the rest of them at this time).

      After getting cancer, he lost some bodyweight – and when he returned to the races his trainer formulated a strategy of a higher pedal cadence (stride frequency) than he had rode with in the past, and 20% higher than all of his competitors.

      This change shifted the stress of cycling from his muscles to his CV system, leading to much improved performances and no doubt lessening the accumulation of lactic acid in the process. He was thus able to maintain higher speeds for longer distances all the while buffering lactate build up.

      So I would add Byron, stride length + stride frequency + metabolic cost of that combination = performance.

      He actually broke this down to a number: 6.7. As in 6.7 watts of power generated on the bike per kg of rider bodyweight. That number was necessary to be in peak condition. I think since then many other successful riders have arrived at nearly the same data.

      Then, of course, the question becomes – if they are born with a certain stride length due to conformation, can we impact the stride turnover through conditioning?

      In Australia horses like Black Caviar have been known to finish some gallops with a 10sec furlong. Pierro recently did also. If there is any method to improve the energy cost of a quick turnover, that would be the way to do it.

      • “Then, of course, the question becomes – if they are born with a certain stride length due to conformation, can we impact the stride turnover through conditioning?”

        Interesting question, but then not all stride length is the same. Lets take those same two horses at 23 feet stride length. If one horse is 160cm tall and the other horse is 150 cm tall then the “relative stride length” (stride length divided by height) for each horse is different. Which one do you want? This is why looking at gross stride lengths like BiodataTrack, EQB and Equix do at sales is not that informative as the smaller horse with a longer stride has completely different joint angles and muscle architecture to allow a 23ft stride.

        Biomechanics would be one part of a quick turnover, but you would also have to consider internal muscle architecture. The question then becomes, of which muscles? There was a recent paper that showed that the ECR muscle (the one that goes down the front of the forearm of the horse) is the only muscle that engages in the swing phase of the foreleg stride with the other muscles primarily used in the stance phase (effectively to hold the trunk up). Is the ECR muscle the one that fatigues in racing resulting in a “breaking effect”, reducing turnover, increasing foot contact time and reducing stride length?

  4. From blog reader Barry in NZ: ‘I may have mentioned what I have written below to you before, but I think it is worth mentioning again.

    Richard Otto, a Trainer I know here in NZ spent some time working for Bart Cummings in Melbourne when he was younger. Bart never had the Benefit of Heart rate monitors GPS etc, and as a consequence never was able to exactly program the work for individual horses, but after basic conditioning and leading up to sharpening work, According to Richard, Bart would work most of his horses at 15/ flg 2 – 3 times a week. mixed with other work .. Sprinters would cover 1400 – 1600m at this pace, middle distance and stayer’s 1600 – 2000 – or even 2400 metres for Melbourne Cup horses.

    For some horses it was probably too much pace for their V200, for others not enough pace. but what he was achieving whether he realised it or not was the same effect as what you Bill are trying to get across in your article.’

    That comment came from my email, thanks Barry – interesting to see perhaps the greatest trainer of all time varied the work requirements for sprinters/middle distance/stayers – while here in the US a 5F turf horse gets the same exercise (generally) as a 1.5F marathon runner.

  5. Nice work. A little complex for me right now or I’d comment further. Hoping to have actual input soon here at the RR stables. Very helpful stuff. Keep it coming!

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