I've finally got the manuscript written for the book on aging athletes I've mentioned here several times. The working title is "Fast After 50," and it will probably be ready by the end of the year - in both English and German. The weight of the world is off of my shoulders and I'm getting back to a normal life which includes posting to this blog. Another big project is looming and so I've been reading a lot of training-related research recently. That's how the following post came about.
One of the best workouts for building fitness is intervals. That’s a session with alternating hard and easy segments. I previously wrote a series of five posts describing the details of interval training (part 1, part 2, part 3, part 4, part 5). Early in that series I explained that the word “interval” actually refers to the easy segments, but most of us use the term to mean the hard parts. So to hold down the confusion in this update on the topic I’ll refer to the hard segments as “Work Intervals” (WI) and the easy portions as “Rest Intervals” (RI).
When doing intervals, or any workout, the key question must always be: What is the purpose of this session? If you can’t answer that question with something other than a vague to improve my fitness, then the workout may not be appropriate. You could be doing something that has little merit in terms of the race or event for which you are training. For example, a marathon runner gets little or no race-specific benefit from doing sprint power intervals. A win is unlikely to come down to an eight-second, all-out sprint at the line. But for a road cyclist such a workout may be perfect.
The second most basic question has to do with timing: Is this the best time in my season to do this workout? Something I often mention in this blog is that the purpose of periodization is to improve performance for a given event on a given date. I also frequently point out the way to periodize training is to have the workouts become progressively more like the event in the last few weeks prior to that date. Doing the opposite – making the workouts less like the event as you approach race day – only results in poor to mediocre performance. Increasing race specificity in training is one of the keys to good planning.
In this post I want to look only at interval duration, primarily for the length of the Work Interval (WI) in an anaerobic endurance interval workout. The physiological reason for doing this type of high-intensity session is to improve aerobic capacity (VO2max). Athletes in a wide range of endurance sports do anaerobic endurance intervals at some points in their seasons. For endurance events that are raced at high intensity (for example, bicycle road races and criteriums, 3- to 5-km running races, short mountain bike races, 100- to 1500-m swim races, sprint triathlons) anaerobic endurance intervals are commonly done in the Build period (the last 8 weeks or so prior to tapering/peaking). For events done at a low to moderate intensity (for example, running marathons, mountain bike marathons, half Iron and Ironman triathlons, very long bike time trials) such high-intensity intervals are perhaps best done in the latter portion of the Base period some 12 to 18 weeks prior to the A-priority race. For those events between the two categories – such as those raced at near the lactate threshold - the timing of anaerobic endurance intervals is much more open to debate. (I’m being a bit vague on this because when it comes to periodization there are a lot of “it depends,” such as age, ability, experience in the sport, capacity for work, susceptibility to injury and many others).
With all of these details out of the way, let’s get back to the purpose of this article: How long should you make the WI in a high-intensity, anaerobic endurance interval session with the purpose of improving aerobic capacity and, therefore, race performance? It just so happens that a recent research study out of Lillehammer University in Norway took a look at that question. (This team of sport scientists has recently produced some excellent studies that can be directly applied to training in the real world. I intend to feature more of their research in future posts.)
The Norwegian researchers compared short and long intervals to see if there is any benefit one way or the other when it comes to aerobic capacity and performance benefits. They divided a group of 16 competitive cyclists into two groups with both doing anaerobic endurance intervals at the same intensity - about 90 to 100% of VO2max - with WI being the main difference. For 10 weeks they did either short or long WI workouts twice weekly.
The short intervals (SI) group did 3 sets of 13 x 30 seconds with 15-second rest intervals after each WI and 3 minutes of extended recovery between each of the 3 sets. The long intervals (LI) group did 4 x 5-minute WI with 2.5-minute RI. The recoveries for both groups were active, meaning they continued to pedal at a low intensity. The combined high-intensity time of the interval sessions were similar between the two groups. The SI workout resulted in 19.5 minutes of total hard effort while the LI group did about the same with 20 minutes of high intensity per session.
These are extremely hard workouts. A cyclist can typically sustain 100% of VO2max for about 5 minutes. Doing it 4 times in a session with only 2.5 minutes to recover after each as LI did is a lot of suffering, especially when you consider that this was done 20 times in 10 weeks. But 13 x 30 seconds with a paltry 15 seconds to recover in each of the 3 sets was no walk in the park for SI either. These were both certainly sufferfests. Perhaps the only saving grace from the riders’ perspective was that the WI were done at 88 to 100% of max heart rate. Since heart rate tends to drift upwards during such a session and come down more slowly with each succeeding RI, it would become somewhat easier to achieve the goal intensity on each subsequent WI. Easier but by no means easy. Cycling power is a better way of gauging the intensity of interval workouts as it stays constant throughout. There is no power drift meaning each WI from beginning to end would be of the same quality. And, in fact, power was measured during each interval for both groups. The LI group produced a slightly lower average power due to the length and sustainability of their longer WI. (The closest equivalent to power for runners is pace.)
The results of the groups’ training were interesting. The LI group improved their VO2max by 2.6% on average over the course of the 10 weeks, but the SI riders had a huge average improvement of 8.7%. SI also made greater performance gains in 30-second, 5-minute and 40-minute time trials.
Other studies of long versus short WI in well-trained athletes have found little difference in the physiological benefits. This study is unique, however, in that the total intervention period—10 weeks—was much greater than in previous such studies. The relatively short RI were also unique. At a duration of 50% of the WI they were shorter than is commonly done. This meant that the athletes’ stress throughout each interval session was at or near VO2max for a longer total time than is common with a longer RI. With long RI the density of the stress is reduced thus somewhat lessening the benefit.
This last point probably also explains why the SI athletes improved to a much greater amount than the LI. With only 15 seconds to recover after each WI they never even came close to full recovery for 6 minutes in a set. The LI group, however, would have experienced slightly less total continuous stress per session due to the longer RI.
The researchers point out that such high-intensity interval sessions are better for performance the more highly trained the athlete is. This, again, may explain why the very brief WI of the SI group produced results that were so much better than was found in other studies with relatively long RI. The subjects in this study were highly fit with average VO2max values in the high 60s. Subjects in previous studies of interval duration were much less well-conditioned. What this means is that if you are not at or near a very high absolute level of performance (not merely at an elite level in your age group) as indicated by a high VO2max, then using very short RI after also short WI may not be the best way for you to do intervals. In this case, a 1:1 ratio of WI to RI may be better for you. That would be something like a 30-second WI followed by a 30-second RI.
If you have not previously done high-intensity interval sessions in training or if there has a been a break of several weeks since you last did them, it’s probably best to start at a much lower level of total interval time in a session than was used in this study. That could be something such as one set of 10 x 30 seconds with 30-second recoveries or 5 x 1 minute with 1-minute recoveries. But if you are an elite athlete (meaning you’re a contender for the overall podium positions in races) and have been doing high-intensity training recently, then the SI type of workout described above may be a good training option when the time is right to build aerobic capacity.