Don't Train Your Border Collie Like a Husky: Why Coaching Philosophy Needs Phenotype Awareness
A lot of what happens when athletes improve within a coaching system comes down to something coaches rarely talk about: the system accidentally matching the athlete's natural phenotype.
You build a coaching philosophy around what works. Specific threshold sets that improve FTP. VO2 max intervals that build aerobic ceiling. Long aerobic blocks that build base endurance. You've tested the system. You've seen results.
Then the right athlete comes along. The one who adapts beautifully to the stimulus you prescribe. They progress exactly how the system predicts. You think, "This philosophy works."
And it does. But not always for the reason you think.
Take 4x4 Norwegian VO2 max intervals as an example. Four minutes at around 90% max heart rate, three minutes easy recovery. It's a classic VO2 max prescription. And for certain phenotypes—specifically for Type I-dominant athletes—it's brilliant.
A husky with 60-70% Type I fibres recruits its dominant fibre pool at high intensity. Those Type I fibres are aerobic specialists. Four minutes is hard but sustainable. The stimulus forces aerobic adaptation exactly where the athlete's strength is. The progression is predictable. The athlete improves.
But a border collie with 30-40% Type I and abundant Type IIa fibres recruits that same interval very differently. The intensity is too high for pure Type IIa aerobic development—that needs threshold or tempo work. But it's not low enough to make the effort feel sustainable on Type I fibres alone. So the border collie recruits Type IIx power fibres just to hold the pace. What was meant to be VO2 max work becomes glycolytic work. The athlete is layering fatigue—accumulating lactate, depleting carbohydrates—without the training effect that the prescription was supposed to create.
Same interval. Same coach. Different phenotype. Different outcome.
It looked like the system was universal because—for the first athlete—it was. But the system worked beautifully for that athlete because the system was accidentally built around their phenotype.
The question isn't whether your coaching philosophy works. It's whether it works for this athlete's actual physiology.
What You're Actually Looking At: Phenotype and Fibre Composition
Every athlete has an innate muscle fibre distribution. This isn't about genetics in the vague sense. This is about the actual composition of their skeletal muscle—and how many of those fibres they can recruit at different intensities.
Your muscle is made up of three primary fibre types, and their proportion determines how your physiology recruits fibres and generates energy.
Type I fibres (slow-twitch oxidative): These are the aerobic specialists. They have high mitochondrial density. They're oxidative, they use oxygen efficiently to produce energy continuously. They're resistant to fatigue because they rely on aerobic metabolism, which doesn't accumulate lactate quickly. They produce power slowly, but they can sustain that power for hours. They're recruited first, at low intensities, and stay recruited as intensity increases.
Type IIa fibres (fast-twitch oxidative): These are the hybrid workers. They have moderate mitochondrial density—more than Type IIx, less than Type I. They can work aerobically at moderate intensities, but they also have glycolytic capacity for higher intensity work. They're reasonably fatigue-resistant but not as durable as Type I. They're recruited when intensity increases and Type I alone can't meet the power demand.
Type IIx fibres (fast-twitch glycolytic): These are the power specialists. They have low mitochondrial density. They're primarily glycolytic—they produce energy quickly through carbohydrate breakdown. They produce force rapidly and create power explosively. But they fatigue quickly and accumulate lactate. They're recruited last, only when high power output is needed, and they recruit heavily during intense efforts.
Here's the critical part: recruitment order is fixed. Your Type I fibres are always recruited first. As intensity increases, Type IIa fibres get recruited. Only at very high intensity do Type IIx fibres come in.
This is why phenotype matters. The proportion of each fibre type determines which fibres dominate the work at any given intensity. And different fibre types respond to different training stimuli.
The Two Phenotypes: Husky and Border Collie
Not all endurance athletes have the same fibre composition. And young athletes especially don't arrive fully formed in one phenotype.
Phenotype Fibre Composition
What makes each phenotype different at the muscle fibre level
A husky is built for high-volume aerobic training because it has the fibre base to support it.
A border collie's physiology is mixed. It has some Type I fibres, but they're a minority. It has abundant Type IIa fibres that can work aerobically, but they need higher intensity to be recruited. It has significant Type IIx capacity for power and explosiveness.
The Right Stimulus for Each Phenotype
This doesn't mean the coaching philosophy of high-volume aerobic training is wrong. It doesn't mean VO2 max development is unnecessary. It means the stimulus needs to match the phenotype, and the timing matters.
Why High-Volume Works for Huskies
High-volume aerobic training works beautifully for huskies. And coaches are right to prescribe it. A husky with 70% Type I fibres has the muscle fibre base to handle high-volume aerobic work. When you load a husky with long, easy efforts week after week, those Type I fibres adapt as intended. The aerobic system develops. Efficiency improves. Lactate clearance improves. The training effect is exactly what you expect. The progression makes sense. The athlete feels like the work is sustainable. The pace keeps improving. The coach sees confirmation that high-volume works.
And it does. For huskies.
More importantly: endurance sport requires volume. There's no way around it. Even the shortest triathlon requires aerobic endurance. You can't prepare for those demands without accumulating aerobic volume. Huskies are built for exactly this kind of preparation So when coaches say, "You need to do more volume," they're not wrong. Endurance sport does require volume accumulation. The issue isn't the principle. The issue is when that principle gets applied to every athlete before they're ready.
The Border Collie Problem
A border collie with only 35% Type I fibres can't handle the same high-volume prescription as a husky at least not early in training. When you load the same high-volume aerobic training on a border collie, something different happens than what happens with a husky. The border collie's limited Type I fibres get excellent stimulus. They're developing aerobically. But they're a minority of the muscle. Meanwhile, the border collie's abundant Type IIa fibres aren't being recruited enough to develop aerobically. They're sitting there, capable of aerobic work, but not being asked to do it in this easy aerobic volume. and why sometimes athletes perform exceptionally well as youth / juniors when the duration of their event is shorter and having some glycolytic power can actually help them but as they develop into seniors and the race duration increases they seem to struggle or end up constantly injured.
So what happens over weeks and months of high-volume training?
The Type I fibres get stronger and more efficient. But the overall muscle isn't becoming proportionally more aerobic. The border collie has limited ability to recruit more aerobic muscle because the intensity is too low. The high-volume work is only training a small subset of available muscle. Progress is slow. The athlete feels like they're putting in the work but not seeing the adaptation. The coach thinks the athlete needs even more volume, or more discipline, or isn't built for distance. So the coach loads more volume. More long easy runs. More time on the bike. And the border collie gets tired. Recovery takes longer. Motivation drops. But it's not because the athlete isn't tough enough. It's not because they don't want it badly enough. It's because the high-volume system designed for huskies is counterproductive for a border collie who hasn't yet developed aerobic capacity in their Type IIa fibres.
The system—which works brilliantly for huskies—is burning out a border collie.
The Coaching Reframe
The high-volume aerobic training philosophy isn't wrong. The principle is sound: endurance sport requires aerobic volume, and high-volume aerobic training builds it. The issue is applying that principle universally, to every phenotype, before the athlete has the fibre base to support it.
A border collie doesn't need less volume than a husky. It needs different volume at a different time.
For a Husky: High-volume aerobic training from the start. The phenotype is built for it. The adaptation is direct. Accumulate volume and build VO2 max development alongside.
For a Border Collie: Build aerobic capacity in Type IIa fibres first (threshold and tempo work). Then, when the fibre base is developed, gradually introduce high-volume aerobic training. Now the system works the way it does for huskies—because the athlete has developed the aerobic fibre dominance to support it.
This isn't a different philosophy. It's the same philosophy—high-volume aerobic training builds endurance—applied with understanding of phenotype. The border collie still accumulates volume. Still builds aerobic capacity. Still develops the endurance needed for the event. But it gets there via a different pathway and a different timeline.
The coaches who understand this stop saying, "You're not tough enough for distance." They start saying, "We're going to develop your aerobic fibres first, then build volume." And the border collie that could have been burned out by early high-volume training becomes an elite endurance athlete—because the system was adapted to the phenotype, not the other way around
Understanding Fibre Composition and Training Response
Fiber Recruitment Across Training Intensities
Same intensity. Different recruitment. Different adaptation.
The question coaches should be asking isn't, "What training works?" It's, "What training works for this athlete's natural phenotype?"
Two athletes can have the same 10km time. Same fitness level on paper. But different fibre compositions. It's not because one athlete is more committed or more talented. It's because the training stimulus doesn't match the fibre composition in the second athlete.
Once you understand fibre type and recruitment, you start asking better questions:
What intensity recruits the fibre types this athlete actually has?
What stimulus will develop aerobic capacity in those fibres?
When are the fibres developed enough for higher intensity work?
Is this athlete struggling because they're weak, or because the stimulus doesn't match their phenotype?
These questions take time to answer. But they separate coaching that works for the right athlete from coaching that works for all athletes.
Why Young Athletes Are Often Border Collies
Most young endurance athletes aren't highly developed in either direction yet. They're mixed phenotype: some Type I capacity, abundant Type IIa capacity, significant Type IIx power.
They're border collies. So when we prescribe husky-level training (high-volume aerobic, 4x4 VO2 max intervals) to young border collies, we're often getting suboptimal results.
The athlete struggles in Zone 2. We tell them to go slower. They struggle in 4x4 intervals. We tell them to work harder. But the issue might not be effort. It might be that the training stimulus doesn't match the fibre composition the athlete currently has.
A young border collie trained correctly—starting with threshold and tempo work to develop Type IIa aerobic capacity, then progressing to higher intensity work—will eventually become capable of the same training volume and intensity as a natural husky. The same is true when we give too much sprint work to the natural husky (we’ll discuss this in a different blog)
But the pathway is different. And the timeline is longer. Coaches who understand this stop blaming the athlete. They start asking what stimulus the athlete actually needs.
The Group Training Problem
When we write training for groups—clubs, squads, teams—we make an assumption. We assume that because two athletes have the same 10km time or the same 400m time, they need the same training. Same performance level = same training prescription. And sometimes it works. Sometimes it adds up to progress for everyone in the group.
But sometimes it doesn't. Sometimes we're training a border collie like a husky while congratulating ourselves for the progress we're making. Sometimes we're layering fatigue on an athlete whose phenotype isn't ready for the stimulus we're prescribing—and we don't even realise it and also why athlete who change clubs / training groups can get better results but also why some athletes who join a high performance programme burn out and seem unable to reach their true potential.
The problem is that performance time doesn't tell you fibre composition. Two athletes with identical 10km times could have completely different fibre distributions. One might be a 70% Type I athlete who thrives on high-volume aerobic work. The other might be a 40% Type I athlete who needs threshold work first. The same training prescription produces different outcomes for different fibre compositions. And we assume the problem is athlete effort, not coaching stimulus.
Personal Reflection: From System to Physiology
The more of the physiology I understand, the more questions it throws up. And the more questions I ask, the longer it takes me to write training plans. A year ago, I could build a training plan by simply plugging in percentages of FTP - Threshold sessions at 95-105% of FTP. VO2 max work at 110-120%. Easy aerobic at 65-75%. Prescribe the sets, trust the system.
And it worked. The athletes in the system improved. But over the last few months, I've started asking different questions. Not "What sets improve FTP?" but "Why does this athlete respond to this intensity?" Not "What's the standard prescription?" but "What's stopping this athlete from improving and why?" Those questions take time. They require thinking about actual physiology—about fibre types and recruitment patterns and energy systems—instead of just percentages. And they require acknowledging what I don't know about each athlete's actual phenotype.
So I started asking: What is this athlete's fibre composition? Why do they struggle in Zone 2 while another athlete thrives? Are they actually not fit for endurance, or is the training stimulus not aligned with their phenotype? What happens if I change the intensity progression? What if I develop the fibres they actually have instead of assuming they have the fibres the system requires?
The planning takes longer now because I'm not just writing training sets I'm trying to understand the athlete - are they a border collie trying to become a husky or maybe their a Pitbull trying to become a better endurance dog (my thoughts on this will follow in the next blog), what ever phenotype they currently are needs me to think beyond just the same generic percentages and start prescribing training that is targeted to what stimulus the athlete needs based on what they are and what they need to be to achieve their goals.
Don't train your border collie like it's a husky. Train it so it develops the aerobic capacity to one day train like a husky.