I enjoy trying different training methods to see how I respond as an athlete and also understand what athletes I coach may be experiencing within the workouts I prescribe. Studies are performed to find what may be the best training approach for athletes. I do not think this question will ever be fully answered since we are all so different and complex. Sleep, motivation, life stress and many other variables will always enter into the equation, so I think the best training comes from day to day adjustments and listening to our bodies. That said, there are trends noted within the literature that can point us in directions that have higher chances of success for athletes in regards to their physiology, goal events and desired training adaptations. I've seen studies that suggest certain intervals are superior to others. The results of the studies typically give percentages of response, such as VO2max or 40 km Time Trial improvements. We need to keep in mind that these results are often the averages of each athlete in the study. For example, one athlete may show 0% improvement and another shows 20% improvement which could be reported as a 10% improvement if we average the two. We might walk away thinking that we can expect a 10% improvement if we give this interval protocol a go. Not necessarily. Not all studies report individual responses so keep that in mind and look for those details when available to help you make your own conclusions. Other questions to consider are: What was the training of the athlete prior to the study? What does trained and untrained mean to the authors? What happened 4 weeks after the study as response to any training may be 4-8 weeks later? Ultimately, we need to try something that has sound science behind it for several weeks, see what happens and adjust if needed - only one way to find out if it works for you or not.
A study by Seiler (2) revealed 4 x 8 minute intervals to be superior to 4 x 4 and 4 x 16 minutes. For the record, there is another study that suggests 4 x 16 is superior (I could not find it again to post here) and I listed a study by Ronnestad (1) that suggests 30/15s are the better intervals. So which is it? I don't know but I do believe there is a time and place for the different interval types and can share that another time. I chose to give the 8 minute intervals a go for one last push to end my 2018 road season for a few reasons: 1) fits with the terrain I have locally, 2) positive response in the past, 3) Seiler's study, 4) WKO4 power duration curve model suggests I would best leverage VO2Max improvements with intervals in the 8 minute duration. Life happens and I wanted to share three of my 4 x 8 minute interval sessions to help show athletes to stay loose and adapt to what life throws at them as well as how a slightly different approach to the intervals yields some subtle differences. We can get into that another time if we want to split hairs as each of these workouts strains the system a bit differently - I'd say that the first workout was intensive FTP work, the second was VO2 work and the third was FTP/VO2 - the rest periods have an impact. At the end of the day, I did 32-40 minutes of work at or above FTP and that is what I think matters most. Do the work and good things happen.
5 x 8 MIN with 3-4 minute recovery periods
The image above is from my first 4x8 min workout planned for this training cycle. I was rested and feeling ready to train. I had 4x8 with 2 minute recoveries planned (4x8x2) and on my way to perform the workout I ran into many large trucks making deliveries to a road construction site. This did not feel safe so I changed plans from the flat terrain that would allow the short recoveries and headed to a quiet ~10 minute hill. The hill would be great for the work interval but the descent down to the start would take longer than 2 minutes. Better than getting hit by a truck. The top part of the image shows the intervals - Yellow is power, Red - HR, Green - cadence, Gray - rolling grade of the terrain. The bottom part of the image is from the 'Relative VO2Max Chart' in WKO4. Red - HR, Orange - EWMA Power and Blue - % of VO2 power. EWMA - exponentially weighted movement average - a way of modeling time in VO2 kinetics. The gist is this chart gives me insight into how much time was spent at intensities compared to VO2 max. You can see how each interval except the last one has the shape of a top hat and power for each interval was: 336 W, 340 W, 336 W, 330W and 340 W. I felt good after rolling back down the hill after the 4th interval and added a 5th since I had the time and felt I could get one more in and not flog myself. You can see the power ramps up within the 5th interval (blue line shows this clearly). What this tells me is that I held back in the workout and had more to give and probably why I could do 5 intervals. I think that is also evident since each interval is about the same power and I do not fade a little through the workout. I am pleased that I was able to hold consistent power throughout the workout but feel I missed an opportunity here and could have gone a bit harder earlier in the workout to make it even better. More on this to come in the next examples.
My second workout in this cycle was planned to be 4-5x8x4 again with the trucks still out there. I knew I held back a little on the last session 3 days ago and wanted to improve on this workout if I could. I went hard for the first interval and power came in at 366 W. I did not give it a full 100% effort since that would end my training session and I had 3 more intervals to try and get in. I'd say this was all of a 95% effort for me. I was pretty cooked after this one so the planned 4 minute rest turned into 8 minutes so I could get another quality interval in. The next one was 352 W, then 339 W and finally 330 W. I needed all of the 8 minute rest periods to get through this workout and perceived effort was much higher than the last session. I feel this was a better workout effort than the first example even though my power fades and I do less intervals. You can also see that I held back again on the last interval as power ramps up in the second half - I can do better here. As a coach, I am looking for this type of effort in VO2 workouts - power slightly fades from the start of the interval to the end and also fades through the workout. This indicates proper pacing to me as compared to the first workout. My opinion on this differs from some that are looking for consistent power from interval to interval and through the workout. I do like that strategy for FTP or longer interval work. I think the effort I showed here is more likely to lead to positive adaptations and it takes very hard work to increase VO2Max. I also had about 8 minutes at power over 90% of my VO2Max whereas the first workout only had about 1 minute. That is significant as the science suggests that the best place for adaptations valuable for endurance athletes is around 90-95% VO2Max.
OK, so here is the third workout in the cycle. Again, I had planned on 4-5x8x4-8 and life happened with work limiting the time I had to train. I find it is important to minimize stress in my life for my overall sanity and health, which also helps my training in a positive way. I could have squeezed this workout in outside but then I felt like I would be pressing my luck. If I got a flat then I might be late for work and also would not get my workout in. It was a nice day but the trainer would keep me on schedule. Adapt. 2 minute recoveries would help with time as well so I decided to give that a go. I thought about using erg mode but decided against it as it might hold me back if I was on a good day or might be too hard if I was on an average day. I do not generate the same power on my trainer as I do outside - usually a 20-30 watt drop and this is common for many athletes that do not use a trainer often. Knowing this, I backed off my power target for interval 1. That came in at 328 W and felt like I gave a solid honest effort. 2 minutes of recovery went by fast and interval 2 was tough as you can see by my HR - I eked out 323 W. 2 minutes gone again in the blink of an eye and now I am fully in the pain cave and come out with 301W for number 3 and finish it off with 296W. I am done. Power is lower than the previous two workouts and time >85% VO2 is 25 seconds. So was this a failure of a workout since power and time in VO2 land was low compared to previous efforts? Not at all and I'd argue that this was the best one yet. Let's think about that. What is power really telling us? It is the stress on the system and I think of it like lifting weights. If someone is bench pressing 225 pounds then that is the external stress. That does not tell us the strain on the system - how hard was it for that individual on that day. Perceived effort and HR can be helpful here as they are indicative of the strain on the system and strain is what creates the need for the body to adapt. I do look at power in workouts as it is valuable but we also need to look at the strain on the system and this workout definitely strained me more than the others even though the power was lower at least partly due to the trainer. I'll have to commit to this protocol for a solid 8+ weeks when I am recharged and motivated - it was hard. I think that is something else to consider with intensive interval work - the mental toll. The key to long term improvement is consistency and balance. Doing these workouts twice a week for a few weeks really adds up if we are truly committing and going all in. I'll probably need a recovery week every 3rd week if I tried the 8+ weeks protocol.
I hope this gives you some insight into different ways to approach and evaluate your workouts. We can get pretty rigid when trying to follow prescribed workouts to the 'T'. it is good to try and follow the plan but also important to not get overly precise and keep perspective. I'm pretty sure my body at the cellular level is not creating positive training adaptations based on the minutia we can get caught up trying to be perfect in training. I note many athletes give themselves a pass/fail solely based on power targets. I think it is best to keep the big picture in mind and look at power, HR, perceived effort, how much fatigue we are carrying from previous training, life stress, etc. The best athletes I know are able to adapt to the situation at hand and that can be during a race and also in a training session. Have fun with your training and focus on quality over quantity.
Rønnestad BR et al. Short intervals induce superior training adaptations compared with long intervals in cyclists – An effort-matched approach. Scandinavian Journal of Medicine & Science in Sports, 2015;25:143-151
Seiler S et al. Adaptations to aerobic interval training: interactive effects of exercise intensity and total work duration. Scandinavian Journal of Medicine & Science in Sports, 2013;23:74-83