What Does IM Mean in a Swim Workout?

IM means individual medley: one swimmer swims butterfly, backstroke, breaststroke, then freestyle, in that order. Each takes one-quarter of the distance, so a 100 IM divides into four 25s and a 200 IM into four 50s.

What order do you swim an IM?

Follow butterfly → backstroke → breaststroke → freestyle every time you start a standard IM repeat. USMS defines equal quarters by distance, not by time or effort.

For other abbreviations on the whiteboard, see how to read a swim workout . IM tells you the swimming pattern; the rest and effort still need their own instructions.

How do 100 IM and 200 IM break into lengths?

Divide the total by four, then compare that quarter-distance with your pool length. The following is arithmetic from the USMS equal-quarter definition and its pool-course definitions; yards and metres remain different distances.

IM distance by pool course

Distance instruction	25-yard pool	25-metre pool	50-metre pool
100 IM total	100yd: 4 lengths	100m: 4 lengths	100m: 2 lengths
Each quarter of a 100 IM	25yd: 1 length	25m: 1 length	25m: half a length
200 IM total	200yd: 8 lengths	200m: 8 lengths	200m: 4 lengths
Each quarter of a 200 IM	50yd: 2 lengths	50m: 2 lengths	50m: 1 length

For a 50m pool

Use a clearly rewritten 200 IM if you want every change at a wall.

A 100 IM needs 25m portions, so it does not fit wall-to-wall changes in a 50m pool. Do not silently double a set: agree the extra distance and adjust repeats or rest around the original purpose. Avoid unplanned mid-lane changes in shared lanes.

How do you read an IM set on the board?

Read the repeat count, distance, swimming instruction, then timing. USMS explains that fixed rest starts after finishing a repeat, whereas a send-off sets the time between departures. IM alone does not prescribe speed or rest.

This author-created example is a 400m main set in a 25m pool, not a complete session or a tested progression. Each 100m repeats the whole medley sequence; the next repeat starts with butterfly again. The 30-second rest is an example, not a universal target.

Practice example: four controlled 100m IM repeats

Illustrative main set for swimmers already comfortable with all four strokes · 400m total

4 × 100m Individual medley — TU · Rest 30s between repeats · Each repeat: 25m butterfly, 25m backstroke, 25m breaststroke, 25m freestyle. Swim with controlled technique. Rest at the end of each 100m, not at every stroke change. The rest is illustrative; adjust it to keep the task controlled.

If the board instead specifies a departure time, use the send-off versus rest guide to interpret it. Do not insert extra pauses at every change unless the set calls for a broken medley.

What does reverse IM mean?

Reverse IM, or RIMO, means freestyle → breaststroke → backstroke → butterfly. USMS still assigns one-quarter of the distance to each. It reverses the sequence, rather than asking you to swim backwards or choose any order.

Distinguish a whole IM repeat from separate repeats described as “IM order”. That wording can assign successive repeats to successive strokes rather than dividing each repeat into quarters. Ask which interpretation the coach intends before leaving the wall.

How can you adapt IM when butterfly is not sustainable?

In a non-race workout, decide what the set is practising before changing it. USMS describes drills as work on a particular movement and recommends matching workout design to the intended task. The adaptations below are AquaPlan examples of that principle, not quoted USMS IM prescriptions.

These options change the task; they do not count as an unchanged race IM. In the AquaPlan free workout builder , write the substitute and purpose into the set notes and check pool length before using the session. For sessions to adapt, browse the free swim workout library .

Frequently Asked Questions

What does IM stand for in swimming?

IM stands for individual medley: one swimmer swims butterfly, backstroke, breaststroke, then freestyle, with one-quarter of the total distance assigned to each.

How many lengths is a 100 IM?

In a 25-yard pool it is four lengths totalling 100 yards; in a 25-metre pool it is four lengths totalling 100 metres. Each length uses the next stroke in IM order. In a 50-metre pool, 100 metres is only two lengths, so equal 25-metre portions do not align with the walls.

What is reverse IM order?

Reverse IM, also written RIMO, is freestyle, breaststroke, backstroke, then butterfly. The USMS glossary assigns one-quarter of the total distance to each, just as in regular IM.

Can I replace butterfly in a practice IM?

For a non-race workout, agree a labelled adaptation with the coach or session plan. A familiar butterfly drill or single-arm fly can keep a butterfly focus; freestyle can keep the distance and intended effort but removes that part of medley practice. None is an unchanged full-stroke IM.

Sources and editorial process

Sources checked October 19, 2026. The USMS glossary supplies IM, reverse-IM and pool-course definitions; its adult-training guide supplies workout notation and task-led drill principles. Length counts are arithmetic; the practice set and substitutions are illustrative editorial examples.

Limitations: this is a practice-notation explainer, not a current competition-rule guide or a personalised training plan. No first-hand testing is claimed. Race turn requirements and legal finishes need the applicable event rules; drill substitutions are for clearly labelled non-race practice.

Automated editorial check (daily-ai-v1): this article was authored using AI and checked through an automated editorial process. No human expert review is claimed.

Article publisher

Published and maintained by AquaPlan. The article above identifies its evidence sources and automated editorial process; no human expert review is claimed.