Why Ladders Are the Best Interval Workouts

Why Ladders Are the Best Interval Workouts


For years I’ve had a default workout format that I rely on when looking for a good hard effort that doesn’t feel so hard: the descending ladder. The specifics depend on my fitness and what I’m training for, but a typical example would be 5:00, 4:00, 3:00, 2:00 (with recovery jogs for half the length of the previous interval) then 1: 00 hard/1:00 easy as many times as I want. There is something about the mental and physical trajectory of these workouts that appeals to me.

Thus, a recent study by Filippo Vaccari and his colleagues from the University of Udine in Italy, published in the European Journal of Applied Physiology, caught my attention. The title of the study talks about “Optimizing Oxygen Uptake” and “Exponential Replenishment Behavior of D'”, but when you dig into the details, you realize that this is a physiological argument for magic of descending ladder training. Call it confirmation bias, but I find it quite compelling.

The ideas in the article are based on the concept of “critical speed”, which has appeared in endurance-related research with increasing frequency in recent years. Basically, it’s the threshold that separates sustainable efforts from unsustainable ones. Once you run faster than critical speed, time is running out and you will soon be exhausted. How long? It depends on your anaerobic capacity, sometimes called D’, which is a kind of auxiliary gas tank that allows you to maintain paces above the critical speed until it is exhausted.

The key point of anaerobic capacity is that it starts to recharge as soon as you drop below critical speed. This is the basic dynamic of interval training: you run hard to (almost) exhaust your anaerobic capacity, then run or rest briefly to recharge, then repeat until you’re nauseous (sometimes literally). By doing so, you are able to accumulate significantly more time at a relatively high level of physiological distress than if you were running hard without recovery periods. (For a more technical discussion of anaerobic capacity in interval training, see Philip Skiba’s recent book, Scientific Training for Endurance Athletes.)

According to Vaccari, what makes ladder workouts special is How? ‘Or’ What anaerobic capacity recharges: the emptier the tank, the faster it recharges in a given amount of time (this is the title’s “exponential replenishment behavior”). If you’re mildly fatigued, you’ll get a minor benefit: your anaerobic capacity might jump to, say, 80-85% during a minute of recovery jogging. If you are on the verge of exhaustion, on the other hand, it can go from 10% to 50% over the same period. This means you get more bang for your recovery buck when you’re tired – and suggests you should start your training with longer intervals, then move to shorter intervals with more frequent recovery as you get more tired .

Vaccari and his colleagues first tested their idea on cyclists in a 2020 study, and their new study extends it to runners. They started with a simple test to confirm that anaerobic capacity recharges faster when you’re tired. The subjects did three runs to exhaustion at a pace they could normally sustain for about six minutes. In one trial, they got a two-minute break after 30 seconds. In the second try, they got the same break after 3:00. And on the third try, they ran until exhaustion, then got a two-minute break, then resumed running at the same speed until they reached exhaustion a second time.

The results were clear: subjects reached exhaustion the earliest (after 308 seconds of running) when they had a break after 30 seconds; had an average result (388 seconds) with a break after three minutes; and lasted the longest (464 seconds) when they ran to exhaustion before taking their two-minute break. In other words, the more tired they were when they took that break, the more they benefited from it, probably because they could recharge their anaerobic capacity at a higher rate.

How does this translate to full interval training? The researchers tested two common training patterns: long intervals (3 min hard, 2 min easy, repeat until exhaustion) and short intervals (30 seconds hard, 20 seconds easy, repeat until exhaustion). They compared them on a descending scale with intense efforts of 3:00, 2:00, 1:00, 0:45, then 0:30 repeated to exhaustion, with recovery jogs two-thirds the length of the previous hard interval. . The idea is to start with long intervals while your anaerobic capacity is fairly full, and gradually move to short intervals as it wears down, so that you always start your recovery interval in a sufficiently tired state.

The results were, once again, impressive. Here is a graph showing the total time spent above 90% VO2 max, which is a zone believed to stimulate big fitness gains. On the left, short intervals (SI); in the middle is ladder training, which they call “high-intensity descending interval training” or HIDIT; on the right, the long intervals (LI).

(Drawing: European Journal of Applied Physiology)

Even though all three workouts involved running to voluntary exhaustion, runners spent almost ten minutes (579 seconds) working at over 90% VO2 max during ladder training, compared to about half of this time during the other two protocols. This is a dramatic difference, due mainly, but not entirely, to the fact that the subjects were able to continue producing 30-second intervals at the end of the workout longer than in the other protocols.

For me, that increase in time above 90% VO2 max isn’t necessarily the selling point. It’s potentially useful if you’re looking for a real pain fest, but in practice I rarely train to voluntary exhaustion. Instead, I look at it the other way around: accumulating the same amount of time greater than 90% as in short or long interval training, I can stop ladder training long before exhaustion. I will get a similar physiological stimulus, but it will feel easier and put less wear and tear on my body.

There is also a deeper philosophical question to wrestle with here. Is making training easier a good or a bad thing? It’s like the debate about wearing super carbon shoes in training. Is it better to wear them and rack up faster training times, or avoid them and force yourself to work harder in training so the race is easier? There are good arguments both ways, but the key for me is that I generally direct my workouts based on effort rather than pace. That means I’m not looking for an easy way out: I push as hard as I see fit that day, whatever workout I choose. Within these constraints, I always felt I got the best out of myself in ladder workouts – and Vaccari’s data suggests I may not be crazy after all.

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