Raising FTP on 8 Hours a Week: Threshold, Sweet Spot or VO2max Intervals?

Every training app and coaching forum has a view on the fastest way to raise FTP. Sweet spot fans point to the volume of work you can do just below threshold. Threshold purists say you should train at the intensity you want to improve. VO2max advocates argue that raising the ceiling lifts everything beneath it. And short, sharp interval formats like 30/15s have their own following.

For a professional, the choice matters less: there's time for all of it. For an age-group triathlete with about 8 hours a week across three sports, the bike may get three or four of those hours, and one or two of them can be hard. This article asks what the evidence says about which intensity to put in those slots, who that evidence comes from, and what it means for a triathlete's week.

What the studies actually measure

FTP is a coaching concept, usually estimated from a 20-minute test. Research rarely measures it directly. Instead, trials report:

• Threshold markers, such as power at a blood lactate of 4 mmol/L, ventilatory thresholds, maximal lactate steady state or critical power.
• Time trials of fixed distance or duration, often 20 to 40 minutes.
• VO2max and peak power from incremental tests.

These are related to FTP but not identical. TriForward's "Is FTP Dead?" covers how FTP relates to critical power and other thresholds. In this article, "threshold power" means whichever of these markers a study used.

The three contenders

The labels below are coaching terms, and the boundaries between them are fuzzy:

• Threshold intervals: efforts of roughly 8 to 20 minutes at or close to FTP.
• Sweet spot: longer efforts slightly below threshold, often described as about 88 to 94% of FTP. It's a coaching and training-platform term, not a research category.
• VO2max intervals: efforts of roughly 3 to 8 minutes near maximal aerobic power, or short-interval formats such as 30 seconds on, 15 seconds off.

Sprint intervals of 30 seconds all-out are a fourth option, covered in TriForward's "Do 30-Second Sprints Belong in a Triathlete's Week?".

The cycling network meta-analysis

A 2024 exploratory systematic review and network meta-analysis by Bernardo Norte, James Steele and James Wright, published in the International Journal of Strength and Conditioning, pooled trials of interval training in endurance-trained cyclists.

• 14 studies and 302 cyclists, with VO2max ranging from about 47 to 73 ml/kg/min. Mean ages ranged from 21 to 43.
• Short interventions: on average 5.8 weeks, with 2.3 interval sessions a week.
• Comparisons: high-intensity intervals (roughly 1 to 8 minutes, including longer submaximal efforts up to 16 minutes), sprint intervals (20 to 30 seconds all-out) and low- to moderate-intensity continuous training.

The main findings:

• Intervals beat steady riding, modestly. The overall effect was small (standardised mean difference 0.33).
• Threshold outcomes improved a little more (0.46), but the confidence interval crossed zero, so it's uncertain.
• No interval type was clearly best. Most comparisons between interval lengths were trivial to small and imprecise.
• Longer programmes didn't produce clearly bigger effects within the 2- to 12-week range studied.

The authors concluded that both high-intensity and sprint intervals are effective and that the best prescription can't be explained by interval type or duration alone. They were candid about the limits: the review was exploratory and not pre-registered, it began as an undergraduate dissertation, and most estimates were imprecise. Sex wasn't reported for the pool as a whole, but the included studies that did report it were mostly or entirely male.

Programming variables across 29 studies

A 2021 systematic review and meta-analysis by Michael Rosenblat and colleagues in Sports Medicine asked which programming variables predicted time-trial improvement. It included 29 studies with 67 training groups: 400 men and 91 women, with an average age of 25 and a mix of inactive, active and trained participants, across cycling, running and other sports.

Key findings:

• Training status mattered most. Trained athletes improved time trials by about 2%, while less-trained people improved by up to 6%.
• For high-intensity intervals, the length of each effort mattered more than the intensity.
• There was a dose-response with the number of sessions, the number of weeks and the total work done.
• Exceeding a minimum effective dose may not add further benefit, the authors concluded, and the best dose differs between high-intensity and sprint intervals.

Inference: for a trained triathlete, a realistic target from a block of interval training is a gain of a few per cent, not a transformation. And getting the sessions done consistently over weeks may matter more than choosing the "right" intensity.

Evidence from elite athletes

A 2025 meta-analysis by Hans-Peter Wiesinger, Thomas Stöggl, Will Hopkins and colleagues in Frontiers in Physiology looked at 34 studies in highly trained and elite athletes, including cyclists, runners, triathletes and duathletes, skiers and rowers, as well as team-sport athletes. It grouped interval training into six types, from long aerobic intervals to all-out sprints.

• Adding interval training to conventional training improved most measures by 1.1 to 2.3%.
• The more aerobic types of interval training raised VO2max by about 2.6%.
• The largest effect, 12.6%, was seen in female endurance athletes after 6 weeks of traditional long intervals, although data from women were scarce.
• The effect of interval type was unclear for most measures, as were the effects of sex, programme length and training phase.

These are elite athletes, so the absolute numbers may underestimate what a less-trained age-grouper can gain. But the pattern matches the cycling meta-analysis: intervals help, and the evidence doesn't clearly separate the types.

The short-interval trial

Individual trials can show bigger differences. A 2015 trial by Bent Rønnestad and colleagues in the Scandinavian Journal of Medicine & Science in Sports is often cited, and it's relevant because of the riders' training volume.

• Participants: 16 trained to well-trained male cyclists completed the study (9 short-interval, 7 long-interval), average age 33. Before the study they trained about 8 to 10 hours a week.
• Short intervals: three series of 13 × 30 seconds hard, 15 seconds easy, with 3 minutes between series.
• Long intervals: 4 × 5 minutes at the highest sustainable power, with 2.5 minutes' recovery.
• Both groups did two sessions a week for 10 weeks, matched for effort and total work time (about 20 minutes per session), with the rest of their training at low intensity.

Results:

• Power at 4 mmol/L lactate: +12% after short intervals, +5% after long intervals. The difference between groups wasn't statistically significant.
• 40-minute all-out power: +12% versus +4%, a difference that approached significance.
• VO2max: +8.7% versus +2.6%, a significant difference.
• Average across five power tests: +10.0% versus +3.1%, significant.

The groups were tiny and the study only included men. It shows that a well-designed short-interval format can raise threshold-related power substantially in riders on a moderate training volume. It doesn't show that short intervals beat everything else: the meta-analyses, which include this trial, don't find a consistent winner.

Where threshold-heavy training fell short

A 2014 trial by Stöggl and Sperlich in Frontiers in Physiology compared four ways of distributing intensity over 9 weeks in 48 well-trained endurance athletes (41 completed), including runners, cyclists, cross-country skiers and a few triathletes, averaging 31 years old and training 10 to 20 hours a week. The paper didn't report the number of men and women.

• A threshold group spent about 54% of training at threshold intensity.
• A polarised group spent about 68% at low intensity and 26% at high intensity, with only 6% at threshold.
• A high-intensity group and a high-volume group made up the other two.

The polarised group improved VO2peak by 11.7% and power or speed at 4 mmol/L lactate by 8.1%. The high-intensity group also improved. The threshold group's VO2peak didn't improve significantly, and neither did its peak power or speed (+1.8%) or its power or speed at 4 mmol/L (+1.4%). It also had the most dropouts.

This doesn't mean threshold work is useless. It means that making threshold the bulk of your training, in athletes already training many hours, did less than a mix of easy and hard. Inference: a programme built mostly on sweet spot and threshold work sits closer to this trial's threshold group than to its polarised one, which is a reason for caution, though not proof.

Why different intensities can end up in the same place

A 2017 review by MacInnis and Gibala in The Journal of Physiology summarised how interval intensity shapes adaptation. Both near-maximal interval training and all-out sprint training produce the classic endurance adaptations, including a higher VO2max and more mitochondria in muscle. At the whole-body level, harder intervals generally raised VO2max more than moderate continuous training when the volume of work was matched, while sprint training matched moderate training despite far less total work. The authors noted that how intensity, duration and frequency interact is still largely unexplored.

Inference: threshold power depends on several things at once, including VO2max, the fraction of it you can sustain and muscle metabolism. Different interval types push on these in different proportions, which may be why they so often end up with similar gains in trials.

The sweet spot gap

No controlled trial of "sweet spot" training was found for this article. Its popularity comes from coaching experience and training platforms, and the argument is reasonable: you can accumulate a lot of time near threshold with less fatigue than true threshold or VO2max work. That might suit a time-crunched rider. But it's an argument, not a tested result. If sweet spot works well for you, there's no evidence that you need to abandon it; there's also no evidence that it's superior.

Populations and sex split

• The cycling network meta-analysis included 302 trained cyclists; sex wasn't reported for the pool as a whole, and the included studies that reported it were mostly men.
• The programming review included 400 men and 91 women, many of them not endurance-trained.
• The elite review had few data from women.
• The short-interval trial included only men.
• The intensity-distribution trial included men and women, but didn't report the split.

None studied age-group triathletes training across three sports, and most were short: 4 to 12 weeks. Inference: the evidence is reasonable for "intervals help trained endurance athletes" and weak for "this specific interval type is best for a 45-year-old triathlete".

Fitting it into 8 hours

Here's one way to apply the evidence, which is inference rather than a tested plan:

1. Two hard bike sessions a week at most. The trials used about two. For a triathlete, a hard run session may already take one of your weekly "hard" slots, so one or two on the bike is realistic.
2. Keep the rest easy. In the trials, interval sessions sat on top of mostly low-intensity training. TriForward's "Double Threshold, Single Reality" discusses intensity balance in a multisport week.
3. Rotate interval types across blocks. Since no type clearly wins, a block of 4 to 8 weeks with VO2max or short-interval work, followed by a block with longer threshold efforts, covers the bases.
4. Count the sessions you complete, not the ones you plan. The dose-response in the programming review was with sessions, weeks and total work.
5. Retest occasionally. A gain of around 2% is easy to miss with a noisy test; TriForward's "Your Durability Test Is Mostly Noise" explains why small changes can disappear in testing error.

For long-course athletes, raising threshold power is only part of the job. TriForward's "How Long Does the Long Ride Actually Need to Be?" covers the endurance side.

A triathlon scenario

The following example is illustrative, not drawn from a study. A 39-year-old training for an Olympic-distance race has 8 hours a week: three swims, three runs and three rides. Two rides are 3 × 15 minutes of sweet spot, and the third is a long ride. Their FTP hasn't moved in a year.

Based on the evidence above, they might:

• Swap one sweet spot session for VO2max or short-interval work for a 6- to 8-week block.
• Keep the other as a threshold session, with longer efforts close to FTP.
• Make sure the long ride and other sessions stay genuinely easy, so the two hard rides can be hard.
• Check their running intensity, since three hard sessions across sports may be one too many.

Common mistakes

• Doing every ride at sweet spot. It can leave you moderately tired all the time, without truly easy or truly hard days.
• Changing the plan every two weeks. The trials ran 4 to 12 weeks; adaptations take time to show.
• Expecting big jumps. About 2% in trained athletes is a realistic gain.
• Ignoring the run. A hard brick or run interval session is part of the same weekly load.
• Choosing intervals you won't complete. A session you consistently cut short delivers less work than a slightly easier one you finish.

What we don't know

• Whether sweet spot is as good as, or better than, other intensities. It hasn't been tested in a controlled trial.
• The best intensity for triathletes, who also run and swim.
• How women and older athletes respond, given how few are in the trials.
• What happens over a full season, since most trials last weeks, not months.

References

• Norte B, Steele J, Wright J. Physiological and performance adaptations to interval training in endurance-trained cyclists: an exploratory systematic review and meta-analysis. International Journal of Strength and Conditioning, 2024;4(1). doi:10.47206/ijsc.v4i1.271
• Rosenblat MA, Lin E, da Costa BR, Thomas SG. Programming interval training to optimize time-trial performance: a systematic review and meta-analysis. Sports Medicine, 2021;51(8):1687–1714. doi:10.1007/s40279-021-01457-2
• Wiesinger HP, Stöggl TL, Haller N, Blumkaitis J, Strepp T, Kilzer F, Schmuttermair A, Hopkins WG. Meta-analyses of the effects of high-intensity interval training in elite athletes, part I: mean effects on various performance measures. Frontiers in Physiology, 2025;15:1486526. doi:10.3389/fphys.2024.1486526
• Rønnestad BR, Hansen J, Vegge G, Tønnessen E, Slettaløkken G. 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(2):143–151. doi:10.1111/sms.12165
• MacInnis MJ, Gibala MJ. Physiological adaptations to interval training and the role of exercise intensity. The Journal of Physiology, 2017;595(9):2915–2930. doi:10.1113/JP273196
• Stöggl T, Sperlich B. Polarized training has greater impact on key endurance variables than threshold, high intensity, or high volume training. Frontiers in Physiology, 2014;5:33. doi:10.3389/fphys.2014.00033