I would suggest 1/3 of your workouts should have interval training as the main feature. 25s - 50s - 75s - and 100s. After a good warm up swim do them. Just because you are swimming fast you do not have to give up on technique. If you work out 3 X a week at least one work out should be include repeats or if you workout 6 X a week 2 workouts should have repeats included.

Just watch the clock and set your speed for your repeats. When training for the Olympics I did 50s in 28 but made sure my stroke was under control and I held technique.

I've also added some descending and negative split intervals to my workouts and have seen some good results with that.

For example, I'll do 5 x 100, with hundred having a faster 2nd 50 (neg split intervals) and do them on 2:05 (meaning I leave on that time -- I'm not the speediest of swimmers) so I have about 10s of rest between the repeats.

Or I'll do 5 x 100, with each hundred being faster than the last (descending interval) and usually I do them on 2:05 as well -- leaving me about 5 sec of rest on the first (slower) ones, and more rest on the faster ones.

The time on the intervals (2:05 on the example above) changes if I'm having a really on or really off day.

I like 5 X 25s with 10 or 15 sec rest between each 25, rest 30 seconds then repeat the sequence 8 X. Equally paced at a Max Vo2 heart rate. Forget descending times that is a word some coaches use to show how smart they are... thes kind of workout does not make a faster swimmer. It is OK to do descending times during other types of workouts.

I prefer not to do more then 25s, 50s, 75s and sometimes 100s. 400s ??? that is nearly a whole race, not to be confused with a Max V02 workout.

There is an old saying - "You have to train fast to swim fast."

Try doing fartlek training in the pool 10x50 using every other 50 as active recovery so sprint 50 and easy 50, if 50's are to hard start off with 25's on these days start with at least a 800yd warm up my sprint days usually look something like this 800 wu 200 swim 200 pull 200 kick 200 swim. main set 1500 starting off with 100's then 50's and 25's warm down is usually 100 easy free 100 double arm backstroke .

Swimming is all about efficiency, in that respect its a lot like biking, you're trying to maximize your power output while minimizing your drag, but you do need to swim fast in order to be able to preform on race day. I do agree with you that it is worthwhile to at least learn how to do the other 3 strokes. Butterfly and breastroke are good for core strength, and backstroke is good to loosen tight shoulders up, and generally relieve pressure of the shoulder joint.

I love these kind of sets, they make you have to swim faster when you're more fatigued, thus improving efficiency. One of my favorite sets ever was 5 X 800 decending and negative split, so basically i was trying to make every 400 yds faster than the one before it. Something more sane (for those of you not swimming an obscene amount like I am) would be to do 5 X 200 on a fairly challenging interval, just trying to make every 100 faster than the one before it. Ideally your 7th and 8th hundreds should be at your goal race pace, and the last 100 should be about as fast as you can go.

If technique is not a limiter then....

1/2 of your training focus should be on raising MLSS in the pool. This is done through long, hard repetetive, short rest sets... 3x600 with 15-20 secs rest. These hurt. Think 2x20 FTP work on the bike.

1/4 should be focused on raising your VO2... this will help in allowing your MLSS swimming to get faster.

1/4 should be speed... think track work but in the pool. All the good stuff that track work does for you running, short fast stuff in the pool will do for your swimming.

GOOD LUCK!!!!!!!!!

Maximal Lactate Steady State - it may mean this ???
I for one do not want this long hard stuff. I would only do this in about one sixth of my training. But others have other ideas.

Microsoft also uses it as a trainig term.

I know... I need to come up with a "list of terms FAQ" and post it somewhere. : )