Starting at the top of the range
At 100% of FTP, 64 minutes is roughly what FTP means. Aiming high from the first block leads straight to a failed fourth. Start at 95%, and only go up in the last block if all is well.
CyclingThreshold and sweet spotAdvanced 95 min
Seiler 4 × 16 min threshold session
The Seiler 4x16: four 16-minute blocks at 95–100% of FTP, with just 2 minutes' recovery. 64 minutes at threshold in a 95-minute session. For advanced riders who are already comfortable with a 2 × 20.
Session profile11 blocks
At a glance
- Duration
- 95 min
- Main target
- 95–100%FTP4 Z4 · Threshold
- Time at target
- 64 min
- Estimated load
- 117
- Structure
- 4 × 16′ at 95–100% FTP, 2′ recovery
- Level
- Advanced
- Equipment
- Power meter · Smart trainer
The session in detail
FTP
Time in zone
- Z121 min
- Z210 min
- Z464 min
What the targets mean
| Target | Zone | Time | FTP 200 W | FTP 250 W | FTP 300 W |
|---|---|---|---|---|---|
| 95–100% | 4Threshold | 64 min | 190–200 W | 238–250 W | 285–300 W |
| 50–60% | 1Recovery | 6 min | 100–120 W | 125–150 W | 150–180 W |
Put this session on your bike computer or watch
Wattson works out the targets from your FTP and sends the session to your Garmin, Wahoo, Coros or Suunto.
What this session is for
Four 16-minute blocks adds up to more than an hour at threshold, with breaks so short they're mainly for drinking. The session trains your ability to hold power close to FTP for a long time: less VO₂max, more endurance at threshold, the kind you need for long climbs, time trials and the final hour of a sportive.
It's the longest and least intense session in Stephen Seiler's series (4 × 4, 4 × 8, 4 × 16). In his 2013 study, it produced smaller gains than the 4 × 8 over seven weeks. But a larger study from his group later found that doing a lot of it, within a supervised programme, improved threshold and VO₂max. In short: a good session if you have the time and the base, not a shortcut.
Who it's for
Advanced riders with a solid endurance base and a threshold 2 × 20 that no longer scares them. You also need time: 95 minutes on the bike, plus the recovery afterwards. If you're preparing for a mountain sportive, an Ironman or a long time trial, it looks a lot like your race effort.
When to do it
Once a week at most, in place of another threshold session, with at least one easy day before and after. Avoid the day before a race or long ride, and don't put it in the same week as a heavy VO₂max block. To ease in, start with 3 × 16 minutes, then go to four once the third block stays level with the first.
How to do it
Warm-up
15 min5′ at 45–55% FTP + 5′ at 56–65% FTP + 5′ at 66–75% FTP
15 minutes building from 45 to 75% of FTP, in 5-minute steps. Have two bottles and some food ready: the session lasts over an hour and a half.
Main set
70 min4 × 16′ at 95–100% FTP, 2′ recovery
Four 16-minute blocks at 95–100% of FTP, or 238 to 250 W for an FTP of 250 W, with 2 easy minutes at 50–60% between them. Seiler's principle: the highest level you can hold evenly across all four, which means the bottom of the range to start with. Eat and drink during the recoveries or early in each block. Shift your position slightly now and then without letting the power drop: your back and saddle contact tire before your legs.
Cool-down
10 min10′ at 40–55% FTP
10 very easy minutes at 40–55% of FTP. Eat soon afterwards: over an hour at threshold empties the tank.
How it should feel
The first two blocks are controlled, almost comfortable. The third starts to weigh, the fourth is mostly in your head: nothing is very hard, but everything goes on and on. Sixteen minutes is a long time to stare at a turbo screen. Guide: 7 out of 10 at the start, a good deal more by the end.
Common mistakes
Forgetting to eat and drink
Over an hour at threshold is long enough for a bonk or dehydration to drag the power down. The 2-minute recoveries are there for exactly that.
Stretching the recoveries
The session's value lies in its continuity: 2 minutes, not 5. If you need more, the intensity or number of blocks is too high; drop to 3 × 16 minutes.
Riding it on tired legs
A session this long in an already busy week leaves its mark for days. Put it early in your training week, after an easy day.
When to skip it
Before you start
- A recently measured FTP.
- A solid endurance base and several successful threshold 2 × 20 sessions.
- About 95 minutes free, plus time to recover.
Skip it if
- You're tired, or a race or long ride is planned for the next day.
- You've done a hard VO₂max session in the previous two days.
- You have doubts about your health: get medical advice before long, sustained efforts.
Origin and evidence
Level of evidence
Good evidenceLevel 4 of 5
Seiler et al. (Scand J Med Sci Sports 2013): 35 trained cyclists over 7 weeks; the 4 × 16 group improved less than the 4 × 8 group, around 5% against 11%. As with the 4 × 8, participants rode at the maximum tolerable effort for the session, about 88% of maximum heart rate with lactate close to 5 mmol/L. Another study (Sylta et al., 2017, 63 cyclists) found that accumulating 2 to 3 hours a week of 4 × 16 at maximal effort, within a supervised programme, improved power at the lactate threshold and VO₂peak more than accumulating about 1 hour of 4 × 4. Converting this to 95–100% of FTP is a Wattson approximation, as are the warm-up and cool-down. The 2-minute recovery comes from secondary sources. Bottom line: good evidence.
Sources
- Seiler S. et al., Scand J Med Sci Sports 2013;23(1):74-83
- Sylta Ø. et al., 2017
Frequently asked questions
What power should I ride Seiler 4x16 intervals at?
At 95–100% of FTP: 190 to 200 W for an FTP of 200 W, 238 to 250 W for 250 W, 285 to 300 W for 300 W. Seiler didn't prescribe a percentage: his riders went at the highest level they could hold evenly. Over 64 minutes, that often lands at the bottom of the range, which is fine.
Seiler 4x16 or 4x8: which should I choose?
The 4 × 8 produced bigger gains in the 2013 study and takes half an hour less. The 4 × 16 banks far more time at threshold, which mainly helps long events. A later study from Seiler's group found that doing plenty of it, within a supervised programme, also brought gains. Alternate depending on your goal.
How is the 4x16 different from a 2x20 threshold session?
The intensity is the same, but the 4 × 16 does much more of it: 64 minutes at threshold against 40, with 2-minute recoveries instead of 10. The 2 × 20 is the reference threshold session; the 4 × 16 is the next step, for riders preparing for efforts of more than an hour.
What should I eat during a 4x16?
Whatever sits well with you when riding hard: energy drink, gels or a bar, taken during the recoveries or early in a block. Over an hour at threshold burns through a lot of carbohydrate. Drink regularly, especially on a turbo, where you sweat more with no air moving. Use it to test what you'll take on race day.
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