Sweetspot Training

Here’s a nice diagram. I’ve said it before but exercise is bad for you, this diagram sort of shows that. I’ll have to clarify what I say of course. Exercise is certainly INITIALLY bad for you. In the diagram it shows that the next day you might only be 80% of what you were (simplistically). So if you do that same exercise day after day after day after day…well…hopefully you get the idea that lots of 80% multiplied together will put you in  a bad place. Worse than where ‘sufferfest’ puts you (that’s a cycling thing).

Yet you can see that with full recovery the athlete is ‘improved’ to 110% after a week or so. Perhaps a long time to wait; but improved nevertheless.

So here is a different take. The inverted ‘U’ or bell shaped curve shows that the ‘best possible’ session (other things being equal – which they aren’t) is the peak in L4. However at that sort of level of training, the physiological strain is starting to ramp up and the duration for which you can perform it is falling rapidly.

So, in fact, the optimal session is somewhere around the L3/L4 boundary – perhaps more likely in L3 than L4. In this diagram it is the circled area. Ah!!! The science of a pretty diagram, who needs pesky numbers and levels of confidence !!

This is looking at percentages of your threshold power (FTP = CP60). Which is the increase in your 60 minute flat out performance (you can think of it as your 60 minute run distance or your FTP if you are a cyclist – they amount to effectively the same thing). For anything/any race over 30 minutes or so threshold power is critically important – basically whichever person’s is the highest should win. It’s very important for 5k too but a few other factors come in there as well. But for ANY triathlon or DUATHLON distance you WILL take more than 30 minutes to complete it, I think (well, actually, I’m pretty positive you’ll take more than 30 minutes!).

If you are looking at measuring improvement in your VO2max then, for most of you, I wouldn’t bother..try measuring it every week for 6 weeks and track the improvement in your VO2max (there will be virtually none). Focus on your FTP. Coincidentally your LTHR is probably one measure which many of you can maintain for an hour or more in a race. ie pretty similar to FTP. You can fairly accurately estimate FTP/LTHR from 20 minute efforts … ie a 5K race or CP20 bike test. Search this site or elsewhere for calculating FTP or LTHR. Anyway, I digress from sweetspot sessions.

So. If you fancy a sweetspot session just have a little sneaky look at this chart and it may well tell you your required effort level using one of the metrics you understand. eg 2x20mins with 5 RI @[RPE7/10, RPE14/20, 85%HRmax, 95% LTHR or 95%FTP and so on]. Do that twice a week; have one long session, have one super fast/short/VO2/interval session, do some weights/plyo/stretch/massage then you WILL improve week-on-week.

Be warned though. You could be getting into dangerous over-training territory. Look in my reviews for a review of BIOFORCEHRV – apps like that can help you fend off the dangers of over-training.

Last Updated on 12 January 2026 by the5krunner

the5krunner

tfk is the founder and author of the5krunner, an independent endurance sports technology publication. With 20 years of hands-on testing of GPS watches and wearables, and competing in triathlons at an international age-group level, tfk provides in-depth expert analysis of fitness technology for serious athletes and endurance sport competitors. ID