Benefits of interval training for Triathletes

Performing your main sets on intervals:

  • rewards employing efficient technique
  • forces more even pacing
  • helps you remember your times during and after the set
  • turns a maximal effort swim into a game of “try to make the interval”
  • creates more swim volume at or faster than threshold pace than the equivalent length continuous swim

Let’s go into a little more detail on interval training.  First you must understand that swimming intervals work differently than bike or run intervals.  A bike and run interval will typically be a prescribed duration for the workload, and a prescribed duration for rest and the rest duration is typically 30 seconds or longer.  In the sport of swimming the prescribed interval is the amount of time a swimmer has to swim the prescribed distance AND rest before leaving the wall again to start the next interval.  By tying the workload (a fixed distance) to a fixed time (the interval) the swimmer is rewarded for swimming efficiently with more rest.  Swimming hard is also a way to get more rest but the harder efforts also create more fatigue and require more recovery time.  Swimming JUST fast enough to make the interval is also a viable technique to make the set and is sometimes required when the interval is extremely hard.  Rarely would this technique be employed if the interval is easy.

Case 1: A set of 100s on intervals

Assume a swimmer has a threshold pace of 1:42 / 100 yards.  I test threshold pace by having a swimmer swim a fixed distance that takes somewhere between 15 and 20 minutes all-out .  I always perform the test by distance regardless of the swimmer’s ability because the faster they swim the sooner the test is over.  Whatever the pace held on that test is their threshold pace and the biggest priority of a triathlete in the pool should be to push threshold pace down over time.

This swimmer is going to do a set of 10x 100s at threshold pace rounded up to the nearest 5 or 0 and plus 5 seconds, 8x 100s at threshold pace rounded up to the nearest 5 or 0, and 5x 100s at threshold pace rounded down to the nearest 5 or 0.  So that’s 1:42 rounded up to 1:45 and plus 5 seconds giving an interval of 1:50 for the 10x 100s, 1:42 rounded up to 1:45 for the 8x 100s, and 1:42 rounded down to 1:40 for the 5x 100s.  Again this is NOT the target pace.  This is the amount of time the swimmer has to swim each 100 and rest before starting the next 100.

10x 100s on a 1:50

The swimmer starts the set on the top (the 60) and swims nice and smooth on the 1st 100 and swims a 1:38 without too much effort.  The 1st 100 is typically easy even when the interval is hard.  The swimmer has “earned” 12 seconds of rest before he has to push off for the 2nd 100.

On the 2nd 100 he swims what feels just as easy as the first 100 but he’s carrying fatigue from the first 100 and swims a 1:42 – right at his threshold pace.  He has earned 8 seconds of rest before he has to go again.

On the 3rd 100 he swims a 1:44 and gets 6 seconds of rest.  You could now consider this swimmer “in the set” where his freshness early in the set is gone and now he’s functioning more aerobically.

On the 4th 100 he swims a 1:42 and gets 8 seconds of rest – he’s back at his threshold pace at least.

On the 5th 100 he remembers to really tighten up his streamlines off each wall and swims a 1:41 at the same intensity as the 4th 100.  He has earned 9 seconds rest.  His decision to work on technique has earned him more rest and he gets immediate feedback from that decision.

On the 6th and 7th 100 he focuses on fully exhaling before he breathes to his left side because a coach told him he had a hitch in his stroke when he breathed left and if he could eliminate that hitch he would have a slightly higher stroke tempo without feeling like he’s forcing the tempo higher.  That change allowed him to get back to 1:39s on numbers 6 and 7 – 3 seconds faster than his threshold pace and getting 11 seconds of rest.

On the 8th and 9th he continues to hold 1:39s because he feels that is the optimal ratio of effort to rest.  He could swim faster and get more rest or slow down and reduce intensity but get less rest.  1:39 feels good for now but they are getting increasingly difficult even though he feels he is targeting the same intensity.

On number 10 with no number 11 to do he uses up the rest of his anaerobic capacity and swims a 1:36 besting the interval by 14 seconds and his threshold pace by 6 seconds and then spends the next 30 to 60 seconds at the wall catching his breath.  He could have also choose to swim easier on the last 100 to just make the interval and end the set nice and easy.  Typically a coach won’t want to see a swimmer slow down near the end of a set, but if there are still more hard sets to do it might be an acceptable choice.


8x 100s on a 1:45

Now let’s take that same swimmer and give him 8x 100s on an interval that is just his threshold pace rounded up to 1:45 per 100.  Again, this is not his target pace.  He now has 1:45 to complete each 100 and rest instead of 1:50 per 100.  If he were to swim the exact same paces as the previous set he’d get less rest between each 100 and less rest makes the set harder.  He can also choose to swim a little faster and get a little more rest, but swimming faster either takes more effort or better technique (or both).  With the interval as fast as it already is it’s going to be hard to earn more rest without employing the best technique he knows.

He leaves on the top and swims a 1:37 without much effort just like last time but only gets 8 seconds of rest because the interval is faster.

On number 2 he’s still “fresh enough” and swims a 1:39 and gets 6 seconds of rest.

On number 3 fatigue is setting in and he swims a 1:41 – still faster than his threshold pace but it felt harder than threshold pace because he’s dealing with the fatigue of the first two 100s.

On number 4 and 5 he holds steady at a 1:42 for each only getting 3 seconds of rest.  We call these “touch-and-goes” when you just perform a slow open turn at the wall and never actually put your foot down.

On numbers 6 and 7 he’s in a groove and makes sure to keep his head down because he has a bad habit of swimming with his head too high and gets pace back down to 1:41 – one second faster than his threshold pace and getting 4 seconds of rest.

On number 8 he really goes for it and swims a 1:39 besting the interval by 6 seconds and his threshold pace by 3 seconds.  It’s not as fast as the 1:36 on his last 100 from his previous set, but he went into this 100 with more fatigue so the 1:39 is comparatively good given the faster interval of the set.


5x 100s on a 1:40

Now the set is 5x 100s at threshold pace rounded DOWN so now his interval is 1:40 – that’s faster than his threshold pace.  Imagine bike intervals at above your FTP power and how long you can typically sustain those intervals – it’s not very long.

On number 1 he feels the seriousness of the set and has a fast start at a 1:35 and gets 5 seconds of rest.

On number 2 he’s tired already and swims a 1:38 getting 2 seconds of rest.  This is a fast touch-and-go

On number 3 he swims right at 1:40 pretty much getting no rest and just glancing at the clock during an open turn.

On number 4 he swims a 1:42 and technically misses the interval by 2 seconds but keeps going because there’s only one left.

On number 5 he swims right at 1:40 again but he left 2 seconds late from the last interval so technically he misses the set overall by 2 seconds even though he did swim 1:40 for the last interval.  That 1:40 was the last 100 of the day and was an absolute maximal effort even though it was slower than the 1:36 and 1:39 he did on his last 100s earlier in the practice.  Sounds like a big failure right?  Nope, because he just swam a 500 at faster than his threshold pace.  He had to fight tooth and nail to do it and it was the hardest set he’s done all week, but the point is that he got it done and the next time he does a threshold test he’s likely going to be faster.

Case 2: continuous swims

Now, let’s pretend the set was a 1000 continuous at Threshold pace + 2 seconds, an 800 at threshold pace, and a 500 all-out.

If our swimmer was a former year round swimmer and the pool has a suitable pace clock mounted in the correct position on the side of the pool he might be able to glance at the clock while swimming and know his pace during the set (elite swimmers do this).  Given that our swimmer has a threshold pace of 1:42 he is probably not a former year round swimmer, AND given that he’s training for triathlon he’s far less likely to be swimming in a pool with a pace clock in the right place or a pace clock at all.  You might be thinking, “I have a watch that tells me my pace as I swim” well I guess it’s better than nothing, but having to stop and glance at the watch that is on your wrist (which you need for swimming) is not ideal.  As a general rule a swimmer will NEVER stop mid-set and so stopping to check pace would be unheard of.  Basically what I’m saying is please do not stop and look at your watch every hundred or two to check your pace.  You won’t be doing this in a race anyway (at least you shouldn’t be).  Intervals will help you build your sense of pace and you’ll have no need to check your watch anyway.


1000 continuous at threshold + 2 seconds per 100

He starts his 1000 trying to target Threshold pace +2 seconds per 100.  MOST of the triathletes I have coached will take a continuous swim out a bit too fast and finish a bit too slow.  They felt like they kept the effort the same the whole way but their pace slowed over the course of the swim.  This is not ideal pacing.  Imagine when you do bike intervals by power or run intervals by pace.  You ramp up to the target power or pace and hold it there as your HR slowly climbs and then levels off.  An inexperienced swimmer is more likely to shoot HR up to a plateau quickly and then let pace fall as HR holds steady.  A set performed on intervals does not allow this to happen because if the swimmer starts fast they will be forced to wait at the wall for the interval to come around again.  Intervals help force even pacing.

He finishes the 1000 and swims a 17:22 which is right on the 1:44 pace he was targeting.  The only bad news is he positive split the 1000 with his first 500 being a 8:32, and the second 500 8:50.  A slower finish is not desired because swimming well while fatigued is primarily what makes you better both from a fitness standpoint and a technique standpoint.  It’s not as hard to swim slower when you are tired.


800 continuous at threshold pace

The 800 goes similarly to the 1000 except instead of at his threshold pace he’s one second slower than his threshold target.  It’s a small mistake, but had he known his pace throughout the course of the 800 he might have been able to correct that and swim right at his threshold pace.  He still positive split it but not as badly as the 1000.  He swam 13:46 splitting it 6:50 for the first 400 and 6:56 for the second 400 at an average pace of 1:43.


500 continuous all-out

The 500 is all-out and this is where it gets tougher to predict a time.  If he was having a good day maybe he could have averaged 1:40s for the 500 swimming an 8:20.  If he was having a not so good day and just averaged his threshold pace that could be an 8:30 for the 500.  MOST of the triathletes I’ve coached would be doing well to match their threshold pace on a 500 all-out at the end of practice.  If they were having a good day perhaps they could best it by a little.


Comparison and Conclusion

Rewards employing efficient technique.  Let’s say during that 1000 he remembers the same technique advice as he did in the 10x 100s.  Tighter streamlines off the wall and fully exhale before breathing left.  If he begins correcting these things during the 1000 how does he know if those corrections are actually making him faster?  Also, let’s assume they ARE making him faster.  Does he get an immediate reward for swimming faster?  His average pace at the end of the 1000 should be faster had he not made those changes, but he won’t know for certain if his pace was a result of the intensity he was swimming or the technique he was employing.  The technique improvements made during the 10x 100s give an immediate reward (more rest) between each 100.

Forces more even pacing.  Many triathletes over-pace the first half of any long continuous swim and then slow down mid swim to the finish.  In the set of 5x 100s he takes out his first 100 in a 1:35 but is then forced to rest for 5 seconds.  If the same swimmer took out his 500 in a 1:35 and then rested zero seconds before the 2nd 100 his 2nd 100 is going to be slower than the 2nd 100 of the 5x 100s.  5 seconds is still more than 0 and while short, it SHOULD have a tangible effect on the swimmers subsequent 100s.  Basically the interval helps smooth out uneven pacing.  Eventually these pacing mistakes will go away because the intervals will teach him not to do it.  If he only did continuous swims and checked 100 splits afterwards learning to pace correctly would likely take longer because the feedback comes later instead of during the set.

Remembering times.  The set of intervals is going to make the swimmer MUCH more likely to remember how he paced each set.  It’s easier than you think to remember your splits from a set of 100 repeats because those times were important to you during the set because they dictated how much rest you got.  If he had done the continuous swims he won’t have access to his 100 splits during the swim (unless he knows how to read the deck clock during the swim) and he’s far less likely to go and look at his data after the fact (assuming the watch picked up the splits correctly – please don’t manually take 100 splits during the swim.  You need your hands for swimming and streamlining).  Even if he looks at his splits after the fact it will be too late.  During the main set is the best time to internalize and learn from those splits.  After the workout it’s too late.

“Try to make the interval” game.  I find that most athletes enjoy the challenge and the “game” of trying to make that extremely tough interval instead of the same length continuous swim all-out.  During the 5x 100s there are 5 chances to be rewarded during the set.  The reward is making the interval and getting rest even if it’s a little 2 seconds slow touch-and-go.  With the 500 all-out there is only once chance for a reward and that’s at the end of the 500 when you check your time or average pace.  I’m no psychologist but I’m pretty sure there’s something to be said about incremental rewards during a difficult activity over one large reward at the end.  Both the 5x 100s and 500 all-out have a big reward at the end anyway – you’re done.  Only the intervals reward you along the way.  If the interval is too fast or the swimmer is too tired those 5 rewards could be turned into 5 punishments but ultimately if the athlete is on an appropriate interval these instances should be rare.  The worst that can happen is the 5x 100s just turns into a 500 continuous anyway.

Swim volume at faster than threshold pace.  The overall workload of the two different workouts is similar.  The interval workout had a faster overall pace for the time spent swimming than the continuous swim.  This swimmer CURRENTLY has a threshold pace of 1:42, but would like to be at 1:30 in a year’s time.  Time spent swimming FASTER than your current threshold pace is more productive than time spent swimming at or slower than your threshold pace.  As a swimmer swims faster the technique changes more than it does with running and certainly with cycling.  You might be thinking that a swimmer “can’t just choose to swim faster than threshold all the time” and that’s true – we don’t have unlimited energy.  If the main sets involve a lot of faster than threshold swimming the swimmer should go slower elsewhere in practice like warmup, drill sets, and cool down.  Frequently a swimmer will swim too hard during these parts of the workout and not hard enough during the main set.  A triathletes priority should be to improve threshold pace above all else.  Most triathletes have decent endurance but poor swim technique (even a 1:25 threshold pace triathlete swimmer has comparatively poor technique to a 1:05 threshold pace former collegiate swimmer).  A triathlete will get much more “bang for buck” focusing on swimming faster and putting off swim endurance until race day approaches.  Even then, because the swim in a race is sub-maximal it doesn’t take an incredible amount of swim specific fitness to complete an Olympic to Iron-distance swim.  I would rather have a former swimmer who is completely out of shape swim the swim leg of my triathlon relay over a non-swimmer who is otherwise in excellent shape.


A note about continuous swims

Now, don’t think all intervals are 100 in length.  You can do intervals of any length from 25s up to 1000s.  In college I remember doing sets of 4x 1500s and 6x 1000s on intervals, but then we also did wacky stuff like 160x 25s on intervals as well.  There is still a need to swim longer distances continuously to prepare for the specific workload of the races a triathlete is doing but not as much as you might think.  Those long continuous swims are best saved for open water anyway where the swim is truly continuous (no walls).  More often than not I will watch a swimmer who has fast turns (flip turns or open turns) slow those turns down on a long continuous swim in the pool.  A continuous swim in the pool needs to have fast turns the whole way through to best simulate open water swimming.  The main benefit of a continuous swim is building muscular endurance of the lats, shoulders, and arms and not overall endurance improvement.  You COULD use long continuous swims to improve overall endurance, but that time would probably be better spent cycling or running (and most triathletes would prefer that anyway).  Another important time to do a long continuous swim is while getting used to a wetsuit (preferably in cold open water because swimming in a warm pool in a wetsuit is not a good idea).  If it’s a full sleeve wetsuit it will change the muscular load on the arms slightly.  Extension becomes harder as the wetsuit material stretches, but the power phase of the stroke becomes slightly easier as the wetsuit material contracts.


My main event in college was the 1,650 (1500m) and we only swam those lengths continuously maybe once a month and sometimes not at all during practice because we would swim those distances on the weekends at dual meets.  Everything else we did was broken up into intervals.  When I was racing triathlons from 2008 to 2011 I did not a single open water swim during that time while still having the fastest swim at almost every race.  I was already good at swimming and I had all the swim specific muscular endurance I needed to swim a 1500 or 1.2 miles at ~80% threshold intensity.  If I was going to do a 1500m or 5k open water race at 100% or 95% threshold intensity I would have needed substantially more swim specific muscular endurance, but it was never needed for triathlon.  The interval based training we did in college will work for triathletes too and I know this from my on deck coaching experience.  It will take some effort to learn how to read the clock or at least set up your watch in a way that’s conducive to doing intervals, but I’m sure you can do it.