Tethered swimming can look strange at first: the swimmer produces maximal effort while barely moving forwards. That is exactly what allows the force generated in the water to be measured directly.
A study published in 2026 tested 21 highly trained swimmers over three consecutive days using 10- and 30-second tethered freestyle tests.
Three values stand out
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Mean force, peak force and impulse showed high repeatability. Interestingly, this reliability remained largely independent of sex, performance level, specialisation and evaluator.
Some fatigue-related variables, such as fatigue index or performance decrement, were less stable.
Not every automatically calculated metric is equally useful
Modern measurement systems often provide a whole list of variables. The temptation is to use all of them to guide training.
But if a metric varies strongly between two identical tests, it may be unsuitable for long-term monitoring – even if it sounds scientifically interesting.
Strength diagnostics in the water
For sprinters, a short tethered test can be an interesting complement to land-based strength tests because the force is produced in the sport-specific movement.
Standardised execution remains essential: the same setup, position, warm-up and, as far as possible, a similar fatigue state.
The real strength of the test is not necessarily comparing one athlete with another. The more interesting comparison is with the athlete's own previous values: after a training block, are they actually producing more usable force in the water – and does that also translate into higher swimming speed?
Interpret fatigue indices cautiously
The fact that some fatigue metrics were less reliable is practically important. They often appear especially attractive because they promise to quantify “fatigue resistance”. But if the measurement fluctuates strongly, it should not drive major training decisions. Robust basic variables are sometimes the better choice.
SCIENTIFIC SOURCE
https://pubmed.ncbi.nlm.nih.gov/41734092/