The above statement is very accurate. When doing research for my MS, I came across doctoral research from a 1978 dissertation on the effect of varying rest intervals in swimmers. Unfortunately for me, it took a long time before I figured out how to work this concept into my team's training.
It goes like this. If you take a longer rest interval, your HR will slow more and when you start the next rep, you will be getting a larger portion of your energy from the glycolytic pathways while your HR and other aerobic factors ramp back up. So, for the same reasons that keeping the rest interval allows you to spend more time at or near max HR throughout the workout, lengthening the rest interval allows you to more fully develop the anaerobic pathways even at sub-maximal paces.
The way this works out for my teams is as follows:
If you're a standard 1600-3200 type, you're going to do your VO2 max type of stuff at somewhere between 3200 and 5k pace and the rest interval will be fairly short. More likely though, you're going to do CV reps with 1 minute rest or tempo runs at 75-80% vVO2 max (as measured by a 6 minute run for distance).
If you're a 400-800-1600 type, VO2 max type stuff will be done at goal 3200 pace, but with more rest. Threshold stuff will likely be done in 5 minute intervals at 85% vVO2 max with 1 minute recovery OR CV paced reps of 3 minutes at 90% vVO2 max with 1 minute recovery. For the VO2 max type work. A standard progression for the kids in this group coming out of winter break would be
- 3-4 x 600 @ goal 3200 pace (probably 95% vVO2 max). Up to 4 minutes of active recovery
- 4-5 x 600
- 4 x 800
- 5 x 800
- 4 x 1000.
By the time the athlete is able to do 4 x 1k comfortably at the same pace as s/he was doing the 600s coming out of winter break, we are getting into racing season, and races take over as our primary developer of race pace training. Ideally, I like them to be able to successfully complete the 4 x 1k workout twice. It might take us 8-10 weeks to work through this progression. Usually the week's other big aerobic session for this group would be EITHER 4-5 x 800 @ CV with 1 min recovery OR 4-5 x 5 minutes at estimated threshold (80-85% vVO2). Sometimes, these kids will run a 2.75 mile loop we have as a continuous threshold run, but I only have the ones that will be faster than 16:30 or 17:00 do that. The weaker kids might do only a 2 mile continuous threshold run on this day.
The quality days listed above always include a number of drills, strides, stadium ramps, circuit training type stuff......
I'll use the example of our most unlikely league champion. He was a kid that ran track and cross for me all 4 years. He would usually run well part of the way through the season then start to regress. He had mostly been doing the standard stuff we do with our 3200m kids. He could run 6 mile tempo runs fairly comfortably in 37 - 38 ish minutes. Going into his senior year, he had neither broken 5:00 for 1600, nor 11:00 for 3200. We moved him to the mid distance group for his senior year.
He opened up his season at distance carnival in the last week of February with a 4:47 and 10:53. The really cool thing is that he hadn't done any longer reps faster than 80 second pace. He started the year with 600s at 2:00-2:02 and worked up to 1000s at low 3:20s. These were all done with 3-4 minutes of recovery.
He had a setback in April where he was sick for about 2 weeks, so worried about his aerobic fitness, we made the decision to drop to the 800 despite coming into the season with only a 2:18 PR. He ran 2:15 in his first attempt then at a late season relay meet twice ran 2:09. At our league finals meet, the fast heat (heat 1, luckily) got all tactical and the heat was won in only 2:08. My guy saw his chance and took his heat out at 57 seconds, then barely hung on for a 2:07 to be league champion.
I'm not trying to say that this kid was great or anything. 2:07 certainly isn't a world beating time, but for a guy that had run 3.5 years already, the change in training allowed massive improvement.
My hypothesis is that the FT type kids will just break down quicker if you try to have them do the training that your longer groups do. The year before our unlikely league champ, I had a kid that had been hovering around 1:59-2:00 minutes for 2 years until we switched up his training and he ended up going 1:56. He moved on to the local D2 school and 2 years later, following the same type of plan he did at the end of his senior year, he ended up going 1:50.03
It's to my discredit that it took me until after 2010 to figure this out when I first read the doctoral dissertation way back in 1996. It was just one of those little nuggets of info that I sort of filed away without thinking too much about because it was one of scores of articles I had read and then once I got out into the coaching world the CW of the time didn't really allow for long rest intervals unless people were doing supramaximal type intervals.