Ladder training consists of metric distances that increase or decrease in length over the course of a given set. I have long been a fan of ladder training, and incorporate it into every workout to develop and maintain endurance, and to keep things interesting (ladder training has a funny way of tricking you into covering more distance when you'd rather throw in the towel).
The most basic ladder "set" can be outlined as a group of metric distances as follows: 500, 400, 300, 200, 100 meters. The total distance is 1,500-meters, or one mile.
This is a great set to try if you're new to the concept of ladder training, or if you are trying to get in shape for your first one-mile or more ocean swim. Take 20 seconds rest after the 500, 15 seconds rest after the 400, 10 seconds rest after the 300, and five seconds rest after the 200.
Your goal should be to increase your average speed with each shorter distance. What you are conditioning your body to do here is "negative split," a race strategy where the back half of your race is faster than the first half. Negative splitting is a sure sign of a swimmer's endurance ability, and is a favored technique by elite swimmers in longer races.
If you incorporate the above set into your daily swim regimen, you will notice your endurance increase over the course of a few weeks. As this happens, you may want to pay attention to your average per 100-meter time and see if you can lower it to make the set more challenging.
For example, if your usual 500 takes you six minutes and you work your way down to a 1:10 for your 100, attempt a 500 at 5:50 (which is 5x100's holding a 1:10 pace) and stay consistently faster as you proceed down the ladder. This way, you are building upon your previous training (thus a 100 of "1:10" becomes the building block of a new ladder set where your first 500 is made up of five "1:10" 100's).
But don't stop there. Just because you've bettered your performance on this ladder, it does not mean your work is finished. One way to double your endurance capacity is to return "up" the ladder you just completed by swimming 100, 200, 300, 400, 500.
Use the same rest-interval ratio (five seconds, 10 seconds, 15 seconds, 20 seconds) and attempt to duplicate your times from the first ladder. You are doubling your distance and asking your body to swim just as fast.
At first, you will find your last 400 and 500 to be interminable and painful, but soon this two-mile down-and-up ladder set will have you hooked on the challenging and dynamic workout technique known as ladder training.
The possibilities after this are endless. You can create your own ladder sets by starting out with a 1,000, 900, 800, 700, etc. if you are preparing for a multi-mile marathon swim. Or you can do mini-ladders, like a 100, 75, 50, 25, several times through to develop your sprinting or middle-distance stamina. You can also do ladder sets within ladder sets, such as 5x100's, 4x200's, 3x300's, 2x400's, 1x500.
As you can see, one nice thing about ladders is that they keep things interesting. Swimmers, especially those who compete in distance events, have few choices when it comes to developing endurance; they can swim thousands of meters for hours on end (known as "garbage yardage" by the more cynical of our group) or they can endure torturous sets that challenge the mind with their endless monotony (80x100's @ 1:30 holding the same time for each one).
I think swimming long distances and completing repetitive sets have their place in a swimmer's training log since they ingrain endurance mentality into an athlete's mind. However, it is important to stay motivated during a workout, or else you may not finish it or just go through the motions.
Ladder training sugar coats the pill by always promising a shorter set once you finish the current one (after that 500, you have a shorter 400, then an even shorter 300, you eventually see the light at the end of the tunnel.
On days that you feel tired and unmotivated, ladder training can have a vigorous effect on your psyche and your will to stay in the pool and complete a challenging workout.
Alex Kostich was an All-American swimmer at Stanford and is an open-water masters swimming champion.