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Looking for a new workout, or just a way to round out a shorter one? A fun choice, especially in hot weather when you might need frequent breaks to keep from overheating, is what I call rat-a-tat 400s.
Rat-a-tat 400s are a variant on what Jack Daniels, author of Daniels’ Running Formula, calls cruise intervals.
Intervals at Cruise Pace
Cruise intervals are tempo repeats done on short recovery. The idea is that they are not only a bit less stressful than longer tempo runs (especially in heat), but the frequent breaks allow you to run a higher volume of tempo work than you could in a single, continuous session. That means they can be a very effective, low-stress way of building speed-endurance.
Scientifically, cruise intervals work the lactate shuttle, which is the process by which the body moves lactate from hard-working leg muscles to better-oxygenated tissues like the heart, arms, brain, and liver, all of which can use it more efficiently than oxygen-depleted leg muscles.
Lactate-shuttle training, championed by the likes of elite coaches Renato Canova and Peter Thompson, works by running fast enough to build up lactate in the blood, then taking a short recovery to teach the body to clear this lactate quickly before the next repeat begins. In the process, you become more efficient in processing energy, and, hopefully, faster.
Classic cruise-interval training tends to involve 1000m to 3K repeats run at lactate threshold pace (about the pace you can sustain for a race lasting 60 minutes), with about one minute of recovery for each 5–6 minutes of running. Thus, a 40:00 10K runner might do 1000s on 45-sec recoveries, miles on 60–75 sec recoveries, and 3K repeats on perhaps 2-minute or 2½-minute recoveries.
But there’s no reason these repeats need to be that long. For years, one of my go-to workouts has been 600m cruise intervals, on 20–25 seconds recovery.
Short Repeats, Shorter Recovery
Rat-a-tat 400s come from realizing that you can shorten the cycle even further.
Specifically, you run 400m repeats on 15 sec recoveries. The protocol is to run a lap, cross the line, then circle back at a slow jog so that 15 seconds later you are ready to go. Keeping an eye on the clock is critical, because 15 seconds isn’t a lot of time. But once you get the hang of it, your internal clock can get you back to the start line with remarkable precision. (And the difference between 15 seconds and, say 14, or 17, isn’t important; this isn’t rocket science.)
The target pace is little faster than threshold, so you have a chance for lactate to mount, even during such a short interval. But you don’t run them wickedly fast. If you’re looking for a specific target, 10K race pace is usually about right. They need to be faster than in Daniels’s traditional cruise intervals, so you can actually build some lactate before the 400 is over, but not so fast you don’t have time to recover.
Also, you should adjust the recovery times for your speed. Fifteen seconds is good for folks speedier than around 6:15 per mile. If that’s too fast for you, you might want to make the recoveries 20 seconds, or even a bit longer. They key thing is that they are short: no more than 1/5th the time it took you to get around the lap.
Lots of Repeats, or a Tag On
A full workout is probably 16–20 repeats (4 to 5 miles of total work). That’s a lot of repeats, but, says 18:14 5K runner Lauren Elgee of Portland, Oregon, “I really liked this workout because I got to focus on maintaining pace.” Initially, she adds, it felt easy. Then, about ¾ of the way in, the short recoveries started to add up and it got “very, very real.”
Another way to use this workout is at the end of a longer session. That, in fact, is how I initially came up with the workout. I was working with a runner who was planning to end her workout with a few 600s on 20-25 sec recoveries. But she was on lunch break and had an appointment looming. “What about 400s?” she asked. To which I could only think, “why not?” And it worked so well we kept doing them.
Cruise intervals are a good way to break up the monotony of a long workout, says Thom Hunt, a former American 10K record-holder who now coaches at Cuyamaca College in San Diego. Personally, he says, he prefers longer intervals, but that doesn’t mean something different can’t be tried as an alternative or as an add-on at the end of a workout. “Work is still work,” he says.
Elgee’s teammate, Corrina Jackson (also an 18:14 5K runner) likes rat-a-tats 400s for another reason. “When I do a few of these at the end of a workout,” she says, “I feel less fatigued than if I immediately shift to recovery-jog mode.”
Why that works, she’s not sure. “But the tempo effort suddenly feels easy in comparison to what I’d been doing.” A small number of these (she likes 4-5 of them, so long as the prior workout isn’t too taxing to make that unwise), also boosts her confidence. “It feels good to turn my legs over a bit,” she says. “Seeing that I can do this helps me not feel so fatigued and burnt out. I really like ending with a few of these.”