I'm currently self-coaching. My information comes from forum posters and podcasts that I deem credible. Here's my perspective.
Both workout types are useful. The first workout is a VO2max workout. The second is a sweet spot workout, which is less intense than a workout at or near threshold, but has similar effects. Each of the workouts has some flaws that I detail below.
The question is also incomplete. You need to consider how to progress - if you keep doing the same length intervals, you eventually won't progress. You also want to consider when each workout fits in to a training plan: in the build phase, usually over winter, we mostly do endurance rides, then we add sweet spot and threshold as you get closer to outdoor season, and then we might add more intensity above threshold just before outdoor season.
Power zones
Power output is organized into zones. Trainer Road has a discussion of the basic zones here. Three relevant zones are:
| Name |
Power range (% of threshold power) |
| Sweet spot |
88-94% |
| Threshold |
95-105% |
| VO2max |
106-120% |
Time in Zone
In weight training, we add repetitions to progress. Then we might add sets. Or we might add weight and reduce the number of repetitions.
For structured cycling intervals, we increase time in zone (TiZ) to progress. For threshold and sweet spot intervals, we also want to build up to fewer and longer intervals able. For VO2max workouts, we try to lengthen the intervals to 4-5 minutes, and aim for 16-20 minutes TiZ.
Further, in both resistance training and cycling, shorter rest durations make the workout harder. Shorter rests can help train your repeatability.
I typically set sweet spot at 90% and threshold at 95%. From the Empirical Cycling podcast, I believe that it's better to do longer intervals at slightly lower power. That said, this isn't set in stone.
VO2max intervals
The first workout a VO2max workout. You're working significantly above functional threshold power (FTP), and your aerobic energy system reaches maximum output. There is more discussion elsewhere on what VO2max means.
The workout has 9 minutes at VO2max, in 3 minute intervals. I think this isn't enough time in zone unless you're an absolute beginner. I'd aim for at least 12 minutes TiZ to start. Build up from there, aiming for 16-20. You can use 2 min intervals to start, i.e. your first VO2max session can be 6x 2 mins. Try to build up to 4-5 minute intervals as able, for reasons discussed below. 4x 4mins is a good target for many people to aim for, and advanced cyclists can consider 5x 4 mins, 4x 5 mins, or more. Typically, you rest the same length as the interval. You can rest longer if you need to. A shorter rest is fine but it is not exactly pleasant.
Sports scientist Andrew Coggan (handle the_Cog) discussed ideal interval length and TiZ in this TrainerRoad thread.
If you are worried that you can't finish, then perhaps you could do, for example, 3x 4 min intervals, then just start the last interval and see how long you can last.
If you want a power target, I think that you could start with about 110% FTP for a 5-min interval, more if you can manage it. 120-125% would probably be fine for 2-3 min intervals.
The percent of FTP where we hit our VO2max can vary a lot. For some people, 110% FTP may be hard. For people with high anaerobic capacity, it might be easy - I can typically do at least 118% of FTP for multiple 5 minute intervals, and there will be people who can do more.
So, ideally, as you advance, consider pacing your own intervals with erg off. Select a power output that lets you maintain power over the duration of the workout. It is OK for your interval power to decrease a bit with time, like in this workout I did, but you want to maintain power well in excess of threshold.
Sweet spot and threshold intervals
The second workout is a sweet spot interval workout, with 40 minutes TiZ and 4 minutes recovery. Note that the OP's target power is a bit low; I usually target 90% FTP for sweet spot and 95% FTP for threshold. Here is a Trainer Road blog post discussing the benefits of sweet spot training and some sample workouts. They accomplish similar things to workouts at threshold, but they're less strenuous than threshold workouts. Both workouts can increase your time to exhaustion at threshold as well as push your threshold up.
I believe that some of TrainerRoad's base plans are relatively less total volume, but a high proportion of sweet spot. The sweet spot is a partial substitute for longer endurance rides, which are not pleasant to do indoors. TrainerRoad may have said on its forums that if they prescribed a real zone 2-heavy plan, many people wouldn't do it.
There are some problems with the workout in the question. 20 minute intervals are quite long. Beginners might not be able to complete them. Feel free to start with 12, 10, or even 8 minute intervals. Furthermore, 20 mins on and 4 mins rest is not much rest for beginners. The standard amount of rest for threshold work is half the length of the interval. For sweet spot, maybe start with a bit less than half (e.g. 12 mins on 5 mins off). Try to reduce this as you progress - I can do 20 on 4 off, or even 30 on 6 off, but I've been at this a while.
I would start by finding a total TiZ that you can accomplish, then add TiZ gradually to progress. This page by FasCat coaching says they prescribe total sweet spot durations as short as 15 minutes for complete beginners. For a fairly advanced cyclist, 40 mins TiZ at sweet spot is quite doable and is a good maintenance workout. As before, longer intervals are better. If your interval blocks are too short, you may be getting a lot of the energy from an anaerobic energy system, and not stressing the aerobic system enough.
Here are some sample progressions for threshold and sweet spot workouts:
- 5x 5, 6, 7, or 8 mins (25-40 mins total, beginners consider starting here)
- 3x 10 mins or 2x 15 mins (30 mins total, intermediate riders consider starting here)
- 4x 10 mins (40 mins)
- 2x 20 mins (40 mins)
- 3x 15 mins (45 mins)
- 2x 25 mins (50 mins)
For beginner cyclists, you can start with 5-8 minute blocks. Get as much TiZ as you can stand. Yes, people can ride blocks that are a lot longer, but your mind and body need a bit of getting used to this. More seasoned cyclists should probably start with 3x10 for threshold or more. If you have trouble completing longer blocks, you might start longer blocks at high tempo pace (e.g. 85% FTP).
Also, you don't have to progress the intervals in 5 min chunks if, say, you've done 45 mins and 50 seems like a lot. Another mental trick to try to stretch yourself is that you can consider taking a 15-30s breather in the middle of a block. Your heart will still be beating fast when you start again.
Workouts more advanced than 2x25 are possible. 2x25 at threshold is already a lot and will get most cyclists pretty far. If you want to push further, simply add more intervals and/or more time.
In strength training, there is the concept of reps in reserve (RiR) - i.e. how many more repetitions you think you could have done at the end of a set. Some research shows that you shouldn't do every single set to failure, because the additional stress on the body can compromise gains. I suspect a similar concept holds in endurance sports. In fact, TrainerRoad's post-workout survey alludes to it. As discussed here, they don't want you to work to failure every workout.
For threshold or sweet spot intervals, I tend to ask myself at the end of the last interval (but before the cool-down) how long more I think I could go after a cooldown. I consider that if I could do 5-10 more minutes, the workout is difficult enough. I push myself closer to failure regularly, but I definitely don't do it all the time! If I'm struggling to finish intervals in the middle of the workout, it was too hard (and I tend to cut it short). Struggling physically to finish the last interval is about equivalent to 0 RiR. Signs of struggling can include needing to take a rest, or needing to decrease the power, or struggling to hold cadence in erg mode.
For VO2max intervals, I tend to just stop at 20 or 25 minutes total time. I'm not sure the RiR concept is as applicable to VO2max work. I am aiming to work at a rate that's sustainable over all 4 or 5 intervals. If I was too tired to sustain over about 105% of FTP, I'd terminate the session.
Periodization
Broadly, we usually vary our intensity through the year. In the cold months, people usually do base training, i.e. long slow distance, aka zone 2 rides. You could do just zone 2 rides with no intensity. TrainerRoad typically uses sweet spot intervals to substitute for some of these longer rides due to time concerns. TrainerRoad also feels that athletes can benefit from doing at least some higher-intensity workouts in the base phase, including some VO2max work. So, the choice is yours, but remember your body and mind do need an occasional break.
As you near the summer events when you have rides or events you want to do, riders would typically add high-intensity rides. You might add more VO2max and over-under workouts than previous. You might add anaerobic threshold workouts if these align with your cycling goals. Properly done VO2max workouts are pretty strenuous. I think that many cyclists probably don't want to do 2 VO2max workouts a week for a prolonged period.
As you near an important event, you usually want to rest in the week of that event, maybe doing one shorter set of intervals.
On a shorter timescale, you should generally do a block of training for 2 or 3 weeks, then have one week with a lighter workload. That lighter week can be just one structured workout, e.g. a 40 minute sweet spot session for maintenance. This prevents overtraining and helps the body to consolidate its gains. In terms of volume, I think that 2 hard workouts, 1-2 longer endurance rides, and maybe a recovery ride during each week is achievable for most. During riding season, I was mainly riding outdoors, and I cut down to one interval session.
Closing
If you're self-coaching, you need to develop intuition for how much of a workload to take on and when to rest. Also, you want to develop a sense for how each type of workout feels - VO2max intervals leave you breathing hard by the time you're halfway through a block; threshold intervals feel effortful but something I could sustain for a while. Now, our FTP might climb or decline in a season. Or your test may have mis-estimated your FTP a bit. You'll also need intuition to know if this is happening. You might schedule another FTP test, or you might manually adjust your FTP. You may also need/want to adjust target power during a workout. If you're using software, you can usually vary the targets by + or - 10%.
If you're working with a coach, you still need to develop intuition as described above! Your coach is not you, and they will need you to tell them if they're prescribing too much or too little.
Here, I argue that many people are better off using the ramp test to test FTP, with caveats. The 20 min test is strenuous; it does help you learn to pace yourself, and it may be better for anaerobically dominant athletes.
Other interval designs
The above are basic interval designs. There are some alternate designs that, if nothing else, provide variety. You can Google search to find samples.
Over/under designs are where you alternate going just below and just above your threshold. If you add just one type of workout to the above, it's this one. They really help your mind and body learn to deal with fatigue. They also mimic demands during group rides or races. People typically say they train your body to clear lactate. The science behind this may be inaccurate. I would generally think of over-unders as a variation on threshold. I use slightly lower total TiZ targets and shorter interval blocks. Related to this, straight-up above-threshold (e.g. ~105% FTP) intervals are also a thing, one design being working up to 4x8 minutes.
One design is as follows. You're building around blocks of 2 mins at 95% FTP, then 1 min at 105% FTP. That's 3 minutes. You could do 3-5 consecutive repeats of those (so you're working with 9, 12, or 15 min chunks), then repeat that a few times (e.g. 3 sets of 9 mins over/unders). I tend to rest for 4 to 5 mins. You can progress by adding blocks, by adding repeats to each block, or by increasing the power during the overs (e.g. 110% over and 90% under), or by increasing the proportion of time over threshold. Just remember that 5% over threshold is harder than you might think.
Hard start workouts have you start with effort above typical VO2max power, e.g. 130-140% FTP, and then settle into a threshold or VO2max block. For example, this GCN video shows a hard start VO2max session attributed to the coach for Matthieu van der Poel. It's a series of blocks of 30s hard start plus 2 mins at VO2max, followed by a very short recovery, for a total of 20 minutes at VO2max or higher. It's also got a long tempo session (2+ hrs) afterward. The presenter, a former pro cyclist, described the intervals as hard. The workout I linked above was a hard start VO2max workout, where I'm targeting the first minute as hard as possible, then going as hard as I think I can for the rest of the block. The theory is that it gets your heart rate ramps up faster than with constant power intervals, so your aerobic system gets to a high workload quickly.
30/15, 30/30, or 40/20 workouts (sometimes called Tabata intervals) can also work for VO2max, although some may feel these are more anaerobic capacity workouts. The first number refers to the interval time (usually as hard as you can sustain) and the second number refers to the recovery time. You might do something like 13 repetitions of 30/15, then rest, then repeat for a total of 3 blocks of 13. I don't think this design is useful for threshold/sweet spot work. These are hard, and you don't want to do them all the time. They can definitely be useful for tuning up for outdoor riding season if you're into harder rides.
Every person's response to a particular interval design may be different from the average. I can't seem to get my heart rate high enough with 30/15s, but hard starts seem to work well. Your experience may be different.
Anaerobic and tempo intervals
I ignored anaerobic power, where you're working harder than VO2max (i.e. you are mainly getting energy from the anaerobic glycolysis pathway, usually 130% FTP or higher). 1-2 minute efforts to break away from a group are mainly anaerobic efforts. 10-30s sprints are totally anaerobic (albeit they use the creatine phosphate pathway for energy). A lot of group rides have sprints that will use this power zone, so you may develop anaerobic power relatively well with just group rides. Otherwise, Google for anaerobic capacity sessions - one example is a 60-90 minute easy ride with maybe 8 full effort, 45-60s sprints.
Tempo intervals (75-85% FTP) may also be worth considering. I think that at least for road cyclists, the received wisdom that tempo is too strenuous to easily recover from and also not hard enough to stimulate good adaptations. However, road races and group rides typically have decisive splits, and being able to do long tempo work won't separate you from the competition. Distance runners do a lot of tempo work, and long solo rides (e.g. brevets) probably spend a lot of time at tempo. You should definitely avoid making your recovery or zone 2 (endurance, long slow distance) rides into tempo workouts, whatever your cycling goals.
Workouts and outdoor riding
Briefly, during riding season, many clubs tend to run 1 or 2 rides in the middle of the week. They tend to have one or two long weekend rides. Your power zone distribution during a club ride will vary, but for a lot of people, you may be spending a lot of time at anaerobic power, not so much at threshold, and then you're at pretty low power when you're drafting. So, not all club rides will be ideal to do threshold training on. There typically aren't enough fast sections where I can get a nice repeated block of VO2max work, either.
I tend to like to do club rides once during the week and both weekend days. Typically I can fit one structured session in, making sure to allow enough recovery before doing it. For example, I might do threshold Tuesday morning, then a Wednesday ride, then recovery rides until Saturday and Sunday. I can sometimes fit a VO2max workout in on Friday. If you ride outdoors twice during the weekday, then don't add any structured sessions (unless you truly want to skip one weekend ride). That said, your own recovery capacity may let you do more, or constrain you to do less.
Keep workouts simple
I've heard coaches say that overly complex workouts aren't often not worth it. The designs above are basic, and maybe boring, but you can find other sources of entertainment, e.g. music, podcasts, TV.
Related to that, if you got into Zwift, it has a lot of training plans. One criticism I've heard of their plans is that some of them have a high workload for beginners. Another criticism is that many of the workouts are poorly targeted, e.g. not long enough spent in the target zone, or doing a mishmash of time in more than one training zone. This might not provide enough stress in each zone to stimulate the appropriate adaptations. However, if you are a beginner, feel free to jump in to a Zwift plan. Also feel free to skip a workout if you feel too fatigued. If you progress to the point where you feel like they aren't giving the training stimulus you need, then refer to my earlier paragraphs.
If you're a beginner, I can suggest trying the 10-12 work FTP builder. They have two hard workouts and 3 easier ones per week. Focusing on the hard workouts, they start you off with tempo riding, then move up to sweet spot. If you're not on Zwift, you can view the workouts here and copy the design. You could do just the two main rides, then skip that plan's endurance rides for other rides of your choice (don't overload yourself). The plan doesn't seem too hard for beginners. The Build Me Up plan may have too much intensity for many people to really benefit, and I'm not sure I recommend it.
I haven't assessed the other plans.
Advanced discussion on VO2max workouts
For VO2max workouts, my understanding from browsing the literature is that to get optimum results, you want to try to get as much time over 90% of VO2max as possible. This means that your aerobic energy system is working very hard, near its maximum output. When you start a VO2max interval, I understand that your body is drawing on anaerobic power, and your aerobic energy system takes maybe a minute to ramp up its output. This is why longer intervals are better. The theory behind hard start or Tabata-style intervals is that because you're working harder than you would in a continuous interval, you should hit 90% of your VO2max quicker, despite the rest periods. Remember that individual response to a workout varies. I personally find that Tabata-type intervals don't get my heart rate high enough, but hard start workouts do. Your own results may vary - in fact, they're likely to vary.
What does 90% of VO2max mean? On the bike, there's no practical way to measure how much oxygen we're consuming - which implies the amount of power the aerobic system is generating. If you browse the forums and the literature, 90% of maximum heart rate is sometimes used as a proxy for being in this state. Keep in mind that the actual heart rate where you hit 90% of VO2max probably varies by person, and our maximum heart rates most definitely vary. If you want to track the amount of time you spend at 90% of maximum HR, you should at minimum do a ramp test to measure your max HR (actually, your actual max HR should be a few bpm higher than your max on the ramp test). Alternatively, when doing longer threshold intervals, your heart rate should trend towards a certain ceiling - for example, I tend to settle around 170 bpm. Your HR in VO2max intervals should exceed this by as much as you can stand. Do not use a formula like 220-age to calculate your max HR - these formulas tell you the average max HR for a given age.
