Swim 100m Repeat Timer

The 100 metre repeat is swimming's workhorse set. Ten of them on a fixed send-off is a complete aerobic session, and the same structure at a faster send-off with fewer repeats becomes threshold or race-pace work. The distance is long enough to establish rhythm and short enough to repeat many times.

Ten repeats is the conventional set length because it produces a round total — a kilometre — and enough repetitions for pacing errors to show up. Sets of five are too short to expose a bad early pace; sets of twenty are a different, longer session with different recovery cost.

Rest-based and send-off sets are different sessions

A set written as '10 × 100 with 15 seconds rest' gives constant recovery regardless of speed. A set on a send-off gives shrinking recovery as you tire. They feel entirely different by the eighth repeat.

Rest-based sets are more forgiving and better for technique work or for swimmers new to structured sets. Send-off sets are better for training pacing discipline, because they punish going out fast in a way that rest-based sets do not.

Descending and negative-split variants

A descending set asks each repeat to be faster than the last, which forces a conservative start and rewards control. It is one of the most useful set structures in swimming and one of the hardest to execute honestly.

Negative splitting within each 100 — second fifty faster than the first — trains the same discipline at a smaller scale and is a good place to start.

Stroke count is data

Counting strokes per length alongside the time turns a repeat set into a technique session. A repeat swum at the same time with fewer strokes is a real improvement; the same time with more strokes usually means the pace was bought with effort rather than efficiency.

Watching stroke count rise across a set is also the clearest early signal that technique is degrading, well before the times start to slip.

Typical send-offs for a 10 × 100 aerobic set. Adjust from your own repeatable pace rather than from a target you have not held.

100m repeat sets by ability
Level	100m pace	Aerobic send-off	Threshold send-off
Competitive	1:05–1:15	1:25	1:20
Strong club	1:15–1:25	1:35	1:30
Solid masters	1:25–1:40	1:50	1:45
Improving	1:40–1:55	2:05	2:00
Developing	1:55–2:15	2:30	2:20

Rest-based sets give constant recovery; send-off sets shrink it as you tire. They are different sessions, not different notations.
Counting strokes per length alongside time turns a repeat set into a technique session — rising stroke count is the earliest sign of fatigue.

Source: Set structures and send-off conventions are established swim coaching practice rather than a published standard

Sources

Set structures and send-off conventions are established swim coaching practice rather than a published standard , TheTimerLab — accessed 2026-07-28

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❓ Frequently Asked Questions

Why are 100m repeats so common in swimming?

The distance is long enough to establish rhythm and short enough to repeat many times, and ten of them makes a round kilometre. It works as aerobic, threshold or race-pace work depending only on the send-off.

What is the difference between rest-based and send-off sets?

Rest-based gives constant recovery regardless of speed; send-off gives shrinking recovery as you tire. By the eighth repeat they feel like entirely different sessions.

Which should I use?

Rest-based sets are more forgiving and suit technique work or swimmers new to structured sets. Send-off sets train pacing discipline because they punish going out fast.

What is a descending set?

Each repeat faster than the last. It forces a conservative start and rewards control, and it is one of the most useful and hardest-to-execute-honestly structures in swimming.

Why count strokes?

Because it separates efficiency from effort. The same time with fewer strokes is a real improvement; the same time with more strokes means you bought the pace with effort. Rising stroke count is the earliest sign technique is degrading.

How many repeats should a set have?

Ten is conventional because it is enough repetitions for pacing errors to show. Five is too short to expose a bad early pace; twenty is a different session with a different recovery cost.