What High-Intensity Training Actually Does

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DEEP DIVE

What High-Intensity Training Actually Does

Last week I explained why sprint training requires both high and low-intensity work. This week, let's talk about what happens during those high-intensity sessions and what determines whether they actually work.

High-intensity training is where speed gets built.

These are the sessions where you sprint at 90-100% effort, perform explosive plyometrics, and lift heavy. The work that creates the specific adaptations that make you faster.

But there's a critical detail: high-intensity training only works when it's actually high intensity.

That sounds obvious until you see what can happen in practice.

An athlete runs six 30-meter sprints with 90 seconds rest between reps. By rep four, times are slowing. By rep six, they're grinding through on willpower rather than speed.

The volume got completed. The work was hard. But the session didn't accomplish what high-intensity training is supposed to accomplish.

Here's what's happening physiologically during a maximal sprint.

Your body uses the ATP-CP energy system, which relies on adenosine triphosphate and creatine phosphate stored directly in your muscle cells. This system provides immediate energy for roughly 2-10 seconds of maximum effort before depletion starts affecting performance.

At the same time, your central nervous system is coordinating thousands of muscle fibers in precise sequences to produce the coordinated movements needed for efficient force application. This neural demand is extraordinarily taxing.

When you don't allow adequate recovery between sprints, two things happen.

First, your creatine phosphate stores don't fully replenish. You're asking your body to produce maximal output without the fuel to do it.

Second, your nervous system can't recover enough to maintain the muscle contraction rates needed for true speed. Your stride frequency drops. Technical quality degrades.

You're still working hard, but you're no longer training the qualities that make you faster.

The general rule is 60 seconds of rest for every 10 meters you sprint at 100% effort. A 30-meter sprint needs roughly 3 minutes of recovery. A 60-meter sprint needs closer to 6 minutes.

When rest intervals fall short of this, problems emerge.

The temptation is to think more volume equals better training. Or to feel guilty standing around for 5 minutes between sprints. Or to want to maximize training time.

But high-intensity training isn't about volume. It's about quality.

These extended rest periods allow both creatine phosphate stores and the nervous system to recover adequately.

For shorter acceleration work, rest ratios around 1:12 to 1:20 may suffice for metabolic recovery.

But for maximal velocity sprints where neural demand is highest, the practical application of 60 seconds per 10 meters creates longer effective rest periods to ensure genuine maximum output on each repetition.

If you can't maintain 90% or better of your maximum capability, the session should end, even if you haven't hit your prescribed volume.

This is the quality imperative.

Fatigue-compromised repetitions performed at 80 or 85% might provide some conditioning benefit, but they won't drive the neural and mechanical adaptations necessary for sprint performance. You're just accumulating fatigue without the stimulus that triggers improvement.

The type of high-intensity work also matters for how much volume you can handle.

Acceleration training uses shorter distances, typically 5-40 meters. The neural fatigue from these efforts is less than maximal velocity work, which allows for higher repetition counts. You might do 4x10m, 4x20m, 4x30m in a single session for 200-400 meters total volume.

Maximal velocity training uses longer distances, 20-60+ meters, to allow you to actually reach top-end speed. These efforts are far more demanding on the nervous system and musculoskeletal system. Total volumes stay in the 250-400 meter range, but distributed across fewer, higher-quality repetitions with longer rest periods.

The forces experienced during maximal velocity sprinting create enormous stress on muscles, tendons, and connective tissue. This is why top-end speed work requires such careful progression and monitoring.

You can't just jump into high volumes of maximum velocity sprints without building the tissue capacity to handle those forces first. Acceleration work provides a safer environment for developing speed because the ground contact times are longer and peak forces are somewhat lower.

Between high-intensity sessions, you need 48-72 hours of recovery.

Not just rest days. Actual recovery time where your muscles, connective tissue, and central nervous system can fully adapt to the stimulus you created.

Trying to do high-intensity work on consecutive days, or even with only one day between sessions, typically results in compromised training quality and increased injury risk.

This is where the alternating model of high and low-intensity training becomes essential. The low-intensity days aren't wasted time. They're what allow you to show up to the next high-intensity session actually ready to produce maximum output again.

Most sprint programs prescribe 2-3 high-intensity sessions per week. Less experienced athletes might handle two sessions comfortably. More advanced athletes during intensive preparation phases might manage three.

But regardless of experience level, the principle stays the same: each high-intensity session needs to be executed with genuine maximum or near-maximum effort, with adequate rest between reps, and with enough recovery before the next high-intensity session.

The mental discipline required to end a session early when quality drops is harder than the physical discipline to push through fatigue. But it's also what separates athletes who keep improving from those who plateau.

From my coaching experience, there's often a gap between what athletes understand intellectually and what actually happens in training.

Everyone agrees that quality matters. But when it comes time to take 5+ minutes between sprints, or to call a session after four reps instead of six, the competitive instinct pushes them to do more.

That instinct is valuable in competition. It's counterproductive in high-intensity training.

High-intensity work creates the stimulus for speed development. But only when it's actually performed at high intensity with adequate recovery to maintain quality across the session.

Next week, I'll break down what low-intensity training accomplishes and why it's harder to execute properly than most athletes realize.

But first, you need to make sure your high-intensity sessions are actually high intensity.

If your sprint times are dramatically slowing across a session, you're not resting enough. If you're grinding through reps on determination rather than speed, the session should end.

Quality over quantity isn't a platitude. It's the fundamental requirement for high-intensity training to work.