The number of walls changes the session

Over 100 m, you swim four lengths in a 25 m pool and two in a 50 m pool. That means more turns, push-offs, and underwaters in short course. Those phases are fast and regularly interrupt surface swimming.

In a 50 m pool, you spend much longer swimming without help from a wall. Rhythm or body-position problems that were being reset at every turn have more time to show up.

The clock does not transfer perfectly

Because walls provide speed, the same repeat can take longer in long course even at a comparable effort. A send-off that works for 10 × 100 m in a 25 m pool may become too tight in a 50 m pool.

Do not preserve the exact clock number just for consistency. Preserve the purpose of the set: amount of recovery, target pace, or effort level. Adjust the send-off when that is what keeps the intended training effect.

Information

Same distance, different rhythm

A 200 m swim contains seven turns in a 25 m pool and three in a 50 m pool. If turns and underwaters are a strength, short course lets you use that skill more often. Long course asks for more uninterrupted surface swimming between walls.

Long course exposes surface efficiency

Without a wall halfway through the 50, you have to hold stroke length, alignment, and breathing rhythm for longer. That makes long course a useful place to see whether technique remains stable after push-off speed has faded.

Short course, on the other hand, gives you many more repetitions of turns and breakouts. It is not less useful or automatically easier. It simply emphasizes a different mix of skills.

Adapt the workout without rewriting it

Most metre-based workouts can keep the same distances. Start by noticing what actually changed: repeat times, available rest, and how the longer sections without walls feel. Adjust send-offs only when needed.

For wall-specific work, a 25 m pool is convenient. For a set where you want to sustain continuous swimming, a 50 m pool gives you a different environment. Training in both when available mostly gives you more information about your swimming.