REF-1218 · Hickson et al., 1981 · Medicine & Science in Sports & Exercise · Paper · PubMed

How long does the same workload keep raising my VO2max?

About 3 weeks here: VO2max rose, flattened until the work rate was raised, then rose for 3 weeks again. Nine people, probably untrained, no control.

Blimited evidenceMeasured on non-athletes and recreational people

Hickson, Hagberg, Ehsani and Holloszy followed nine subjects through 9 weeks of training for 40 min a day, 6 days a week. For the first 4 weeks the training work rates were held constant; they were then raised to a higher level and held constant for another 5 weeks.

In both periods VO2max increased for the first 3 weeks and then stayed the same; the half-times of the increase were 10.3 and 10.8 days. VO2max rose 23% over the 9 weeks. The falls in heart rate and blood lactate during a standard submaximal test also happened within the first 2 to 3 weeks of each period.

The authors conclude that the systems limiting VO2max adapt quickly (half-time under 11 days) and that, unless the training stimulus is increased, a high-intensity daily programme gives no further rise in VO2max and no further fall in submaximal lactate or heart rate after 3 weeks.

Our reading: the clearest early evidence that a constant stimulus plateaus within weeks and that raising it restarts the response — the physiological case for progression inside a block; it is one small uncontrolled group, probably untrained, and its 3-week figure does not transfer as a number to trained athletes.

Protocol

Participants: nine subjects; the record's MeSH terms list men and women (numbers not given); age and prior training status not given in the abstract.
Training: 40 min a day, 6 days a week, for 9 weeks; the abstract calls it "a high intensity daily exercise program". The exercise mode and how intensity was set are not given in the abstract.
Period 1 (weeks 1-4): training work rates kept constant.
Period 2 (weeks 5-9): work rates increased to a higher level and kept constant.
Measurements: VO2max repeatedly during training (the sampling interval is not given in the abstract), and heart rate and blood lactate during a standard submaximal exercise test.
Analysis: half-time (t1/2) of the VO2max increase in each period; no control group.
Funding: US Public Health Service grants (NIH; record's grant list) and non-US-government support (record's publication types); conflicts not stated.

Key Results

PeriodWork rateVO2max responseHalf-time of the riseSubmaximal heart rate and lactate
Weeks 1-4constantrose for the first 3 weeks, then constant10.3 daysfell within the first 2-3 weeks
Weeks 5-9raised, then constantrose for the first 3 weeks, then constant10.8 daysfell within the first 2-3 weeks
Whole 9 weeks+23%
Not given in the abstract: VO2max values, the size of each period's rise, the work rates, the step between periods, individual responses and the timing of the tests.
Authors' conclusion: "unless the training stimulus is increased, a high intensity daily exercise program does not result in a further increase in VO2max or further decreases in the blood lactate or heart rate responses to submaximal exercise after 3 wk."

Mechanisms

Measured: the central (VO2max) and submaximal (heart rate, lactate) responses followed the same time course: a rise or fall over 2-3 weeks after each change of load, then a plateau.
Authors' interpretation: the adaptation of the systems that limit VO2max is rapid, with a half-time of less than 11 days; the response is matched to the stimulus and stops when the stimulus stops rising.
Inference: a half-time of about 10 days means, on the exponential model a half-time implies, about three-quarters of the attainable rise for a given load by 3 weeks and about 85% by 4 weeks (our arithmetic).The abstract's "increased for the first 3 wk and then remained constant" is slightly stronger than that model predicts; the remaining rise was presumably within the test's noise. Either way, most of the response to a load comes in its first 3-4 weeks.That is consistent with the base's house default of 3-6-week blocks with a retest (SYNTH-33, SYNTH-42) and with REF-005's runners, whose second month at a higher frequency added nothing (REF-005).
Inference: in trained athletes the attainable rise per step is smaller and the step itself must be larger relative to what they already do; the plateau may come at a different time, and output at threshold or durability may keep moving after VO2max has flattened. This study measured none of that.

Practical Application

How long does the same workload keep raising my VO2max? About 3 weeks here: VO2max rose, flattened until the work rate was raised, then rose for 3 weeks again. Nine people, probably untrained, no control.
Progress inside the block: the same sessions at the same power or pace stop paying within weeks; raise the work (power, pace, reps or duration) every week or two, or change the stimulus, rather than repeating an unchanged week for two months (direction from this study; "every week or two" is our practice, not a figure in SYNTH-33, whose rule is to add work before intensity).
Read a plateau as information, not failure: a marker that stops moving after ~3-4 weeks of an unchanged load is what this study predicts; the response is to change the load, not to conclude the athlete cannot improve (SYNTH-42 reading the block).
Expect most of a block's VO2max change early: with a half-time of about 10 days, a retest after 3-4 weeks captures about three-quarters or more of the response to that load (inference from the half-time; measured in probably untrained people).
Do not transfer the number to a trained athlete: the 3-week plateau and the 23% gain are a beginner's timetable; in trained athletes, VO2max moves less and more slowly (REF-465: lower fitness gains more from any training; REF-1003: world-class cyclists' VO2max flat over five seasons).

Limitations

Uncontrolled: one group of nine; season, learning effects on the test and measurement drift are not separated from training.
Probably untrained: prior training status is not given in the abstract; the size of the gain points to a low starting fitness (inference).
Heavy programme: 40 min a day, 6 days a week at "high intensity"; the plateau is for that load and may differ for lighter or more varied training.
Two fixed steps only: the study cannot say whether a smaller weekly progression avoids the plateau or how large a step restarts the rise.
Plateau vs half-time: "constant after 3 weeks" sits a little uneasily with a 10-day half-time, which predicts about a quarter of the rise still to come at 3 weeks (our arithmetic); the abstract gives no values to check.
Abstract gaps: exercise mode, intensities, test frequency, VO2max values, sexes and ages.
Written from the abstract and record metadata (full text not read).
How this entry was checked and changed
Why this level

uncontrolled pre-post with repeated measures, n = 9; read from the abstract (closed access, 1981; no open copy via Europe PMC or OpenAlex). No control group, one laboratory; prior training status, age, sex split, exercise mode, intensity and test frequency are not given in the abstract