I swam Friday with my sister Pegeen (while visiting her in Dayton OH). She started on her usual routine — nonstop laps – which she does in part, because she’s improved her efficiency and enjoys being able to swim farther. But also because – never having swum competitively — she doesn’t know what else to do.

I did what, as a long-time competitor seems most natural — a brief warmup followed by interval repeats. I invited Pegeen to join me, suggesting we swim 8 repeats on an interval of 1 minute, 40 seconds — 100-yard repeats for me and 75s for her. I quickly explained how to keep track of time: "When swimming any interval ending in :40 (40, 1:40, 2:40, etc.) divide the face of the clock into thirds and begin successive repeats on :00, :40, :20, :00 and so on." And to keep track of number of repeats, remember that each repeat which begins on :20, will be a multiple of 3 (3rd, 6th, 9th repeat, etc.) And so we started.

On her first 75, she forgot to stop after three laps. On another she stopped after 50. So Pegeen’s first insight into the difference between lap and interval swimming came quickly: You need to pay attention.

After we finished the set, she related a second: "Wow, I swam faster."

That made me realize how many interval training benefits most lap swimmers might never realize. As we drove home, I listed several reasons why those who swim purely for self-improvement and fitness could benefit from training more like competitive swimmers – trading some of their nonstop laps for shorter repeats on a timed interval.

1) It promotes attention. The simple fact of needing to keep track of what lap you’re on, how many repeats remain in the set, and when you should start the next repeat promotes more constant engagement than when you just swim laps. I.E. You’re training yourself to activate more brain cells while moving muscles. At first you may find yourself – as Pegeen did – challenged to use all of those brain cells simply to stop and start when you should. But, before long you’ll be able to do that with less "processing power" liberating brainpower for stroke counting, focal points or, say, varying your breathing pattern.

2) You swim faster. If you normally swim 1500 yards nonstop (60 lengths) and shift to 20 x 75 (20 sets of 3 lengths) your average speed should increase significantly – without even trying. Swimming faster without swimming harder is satisfying, healthful and good for your swimming. The first time you replace a straight 1500 with 20 x 75 (or 15 x 100 or 10 x 150 or 5 x 300 or 3 x 500) you’ll probably finish feeling as if you’ve both swum faster and in a more "dynamic" way. You may also feel more energized, rather than more fatigued. That’s the training effect at work, which brings us to…

3) You increase the training effect. Swimming faster always involves increasing propulsive forces relative to resistive forces (or drag). Doing so naturally activates more muscle and demands more of your circulatory and respiratory systems, all of which promote the anti-aging effects of exercise. Isn’t it nice to gain all that upside without even increasing the lap count or needing more time (well maybe a little more) for your workout.

FYI, here’s what I did during our brief swim:
8 x 100 on 1:40
8 x 50 on 1:00
Though the sets are quite basic, I made several conscious choices during them:

1) 1:40 interval for 100s. In recent years I’ve still been able to swim 100-yard intervals at or under those I did in college, on a few occasions as low as 1:15. But, in the last year or so I’ve begun to feel aging starting to slacken my pace and shorter intervals have come to feel more like a survival exercise. I find that allowing a bit more recovery during repeat sets, helps me maintain a slightly faster pace, without excessive effort and therefore with less fatigue. I swim a bit faster — and feel fresher afterward — than on tighter intervals. On this set I was aiming to maintain a pace near 1:20 per 100. Working for 80 seconds and resting for 20 – a 4:1 ratio of work to rest – is still highly aerobic.

2) Increased my stroke count by one on each length. On each 100 I took 12+13+14+15 SPL (Strokes Per Length). I swam the first length at an SPL that required exacting efficiency, but allowed myself one added stroke on each subsequent length. This is a simple way to maintain or even increase pace throughout the repeat – a valuable exercise for anyone who likes to race in distance events.

3) Increased my breathing frequency on each length. On each 100, I breathed every 3 strokes on the 1st 25, breathed 2 right, 2 left (2R2L) on the 2nd 25, breathed 3R3L on the 3rd 25 and every cycle to my left on the 4th 25. Increasing breathing frequency helped me feel as if I gained energy, contributing to my ability to increase pace.

4) Finished with a set of 50s. On the 100s I averaged just over 40 seconds per 50. On the 50s, I increase my pace to just 38 to 39 seconds per 50 yet swam them in a slightly lower average stroke count (12+14). Faster pace in fewer strokes definitely reflects an increase in propulsive forces. And indeed, during my set of 50s I did concentrate on feeling more muscle activation, especially in my core.