REF-934 · Costill et al., 1991 · Medicine & Science in Sports & Exercise, Vol. · Paper · PubMed

Adaptations to swimming training: influence of training volume

Blimited evidenceMeasured on highly trained athletesWritten before October 2026, being re-checked

To assess what a period of increased training volume contributes to swimming performance, two matched groups of collegiate male swimmers were studied before and during 25 wk of training.

Both trained together once a day for about 1.5 h for the first 4 wk; for the following 6 wk one group (LONG) trained twice a day, 1.5 h in the morning and 1.5 h in the afternoon, while the other (SHORT) continued once a day; for the final 14 wk both again trained once a day.

Swimming power, endurance and performance improved significantly over the season with no differences between the groups. During the 6 wk of doubled training the LONG group's sprinting velocity declined, whereas the SHORT group's sprinting performance increased significantly.

Participants

Two matched groups of collegiate male swimmers; group sizes are not given in the abstract.

Protocol

25 wk season. First 4 wk: both groups one session per day, approximately 1.5 h.d-1.
Following 6 wk (abstract: "weeks 5-11"): LONG = two sessions per day (1.5 h morning + 1.5 h afternoon); SHORT = one afternoon session with the LONG group.
Final 14 wk: both groups together, one session per day (1.5 h.d-1).
Outcomes: swimming power, endurance, sprinting velocity and performance; MEDLINE indexing lists blood cortisol, testosterone, creatine kinase and muscle enzymes.

Key Results

Significant improvements in swimming power, endurance and performance across the 25 wk in both groups; no differences between the groups.
During the 6 wk of increased training: LONG — a decline in sprinting velocity; SHORT — a significant increase in sprinting performance.
Both groups showed little change in swimming endurance and power after the first 8 wk of training, though performances improved significantly after each taper period.
The abstract gives no magnitudes.

Practical Application

In collegiate male swimmers, 6 wk of two 1.5 h sessions per day did not improve swimming power, endurance or performance beyond one 1.5 h session per day, and sprinting velocity declined during the doubled block while it rose in the once-a-day group. To "will doubling my swim volume make me faster?": not in this study — for swimmers already training daily, the extra session bought nothing measurable and cost sprint speed while it lasted.
Gains came after tapers: both groups changed little in endurance and power after the first 8 wk, yet performances improved significantly after each taper period.
Inference, not tested here: for a triathlete on two or three swims a week the question is different — this study compared one daily session with two, not few weekly sessions with more.
Not from this paper; the base's own practice: the swim framework SYNTH-74 prefers frequent, shorter swims to rare long ones; that rule is practice and is not what this study tested.

Limitations

Group sizes, training distances and effect magnitudes are not in the abstract.
Matched groups; randomisation is not stated.
Collegiate male swimmers training daily in 1991; pool-sprint and middle-distance context, not triathlon or open water.
The volume difference lasted 6 wk only, inside a season that was otherwise identical.
Written from the abstract and record metadata only (full text not read).
How this entry was checked and changed
Why this level

matched-group training study without stated randomisation; sample size not given in the abstract