REF-1220 · Hickson et al., 1982 · Journal of Applied Physiology · Paper · PubMed

Can I shorten my sessions and keep my fitness?

In 13 study-trained subjects, cutting 40-min sessions to 26 or 13 min at the same intensity, 6 days a week, kept VO2max for 15 weeks; 2-h endurance fell 10% at 13 min. Abstract only.

Blimited evidenceMeasured on non-athletes and recreational people

Hickson and colleagues asked whether gains in maximal oxygen uptake, endurance and heart size can be kept when training sessions are shortened. Thirteen subjects bicycled and ran 40 min a day, 6 days a week, for 10 weeks, then trained either 26 or 13 min a day for another 15 weeks, with intensity and frequency kept as in the last 3 weeks of training.

The 10 weeks raised VO2max by 10-20% in bicycle and treadmill tests, and calculated left ventricular mass by 15-20%. Through the 15 reduced weeks VO2max stayed at the trained level in both groups, short-term endurance (about 5 min) was kept, and left ventricular mass stayed elevated.

Long-term endurance (2 h or more) was unchanged in the 26-min group but fell significantly in the 13-min group (139 to 123 min, given as 10%).

The authors conclude that almost all of the gains can be kept with up to a two-thirds cut in session length, and that the trained state is not regulated uniformly: VO2max and short endurance held while long endurance fell with the larger cut.

Our reading: with its companion papers on intensity (REF-951) and frequency (REF-1219) this is the evidence under the base's maintenance rule that volume and frequency can be trimmed but intensity cannot (REF-951, REF-587) — but it was measured in people trained for 10 weeks, and the one thing that gave way was long endurance.

Protocol

Participants: n = 13; age, sex, body size and training status before the study are not given in the abstract.
Training phase: bicycling and running, 40 min a day, 6 days a week, for 10 weeks. The intensity, the split between the two modes and the session content are not given in the abstract.
Reduced phase: 15 weeks at 26 min a day (about a one-third cut) or 13 min a day (about a two-thirds cut); intensity and frequency as in the last 3 weeks of the training phase. Group sizes and how subjects were allocated are not given in the abstract.
Outcomes: VO2max in bicycle and treadmill tests; short-term endurance (approximately 5 min); long-term endurance (2 h or more; the test work rate is not given in the abstract); calculated left ventricular mass (method not given in the abstract).
Comparator: each group against its own trained values; no group continuing at 40 min a day is described in the abstract.
Funding and conflicts: not stated in the abstract.

Key Results

OutcomeAfter 10 weeks of trainingAfter 15 weeks at 26 min/dayAfter 15 weeks at 13 min/day
VO2max (bicycle and treadmill)+10 to 20%stayed at the trained levelstayed at the trained level
Short-term endurance (about 5 min)change not given in the abstractmaintainedmaintained
Long-term endurance (2 h or more)change not given in the abstractunchangedfell significantly, 139 to 123 min ("10%")
Calculated left ventricular mass+15 to 20%stayed elevatedstayed elevated
A number that does not add up: 139 to 123 min is a fall of 11.5% (our arithmetic), reported in the abstract as 10%.
Typo in the abstract: "26 of 13 min/day" reads as "26 or 13 min/day", consistent with the rest of the abstract.
Not in the abstract: group sizes, the VO2max values themselves, the variability of any result and the between-group statistics.

Mechanisms

Measured: calculated left ventricular mass, raised 15-20% by training, stayed elevated on 13 min a day at the same intensity — the central, cardiac adaptation held on a third of the session length.
Authors' interpretation: "all aspects of the endurance-trained state may not be regulated uniformly in reduced training": VO2max and short-term endurance held in both groups, while long-term endurance fell in the 13-min group.
Inference: VO2max and a 5-min effort lean mostly on the heart's capacity and on the intensity stimulus, both kept here; 2-h endurance also depends on muscle oxidative capacity and fuel use, which may need more minutes of work to hold. No muscle measure is reported in the abstract, so this is our explanation, not a finding.
Inference: set beside REF-951 (same frequency and duration with work rates cut by one-third or two-thirds: VO2max not kept, heart size back to control, long endurance −21% and −30%), intensity is the element that protects VO2max and heart size, while long endurance needed both: it fell when intensity was cut at full session length (REF-951) and when session length was cut by two-thirds at full intensity (this study).

Practical Application

Can I shorten my sessions and keep my fitness? In 13 study-trained subjects, cutting 40-min sessions to 26 or 13 min at the same intensity, 6 days a week, kept VO2max for 15 weeks; 2-h endurance fell 10% at 13 min. Abstract only.
In a maintenance phase, trim minutes, not intensity (B, from the abstract, study-trained subjects): with frequency and intensity held, session length could fall by a third without measurable loss over 15 weeks, and by two-thirds with loss only in the longest test. The counterpart is REF-951: keeping the minutes and cutting the intensity lost VO2max.
Long-event athletes should not cut length too far. Endurance of 2 h or more held at 26 min a day but fell at 13 min; a marathoner, gran-fondo or Ironman athlete running a block aimed at something else should keep some longer sessions (our reading; how long and how often was not tested).The review entry REF-587 summarises endurance as held with volume cut 33-66% (to 13-26 min a session) when intensity is kept; that is true here for VO2max and the 5-min test, not for 2-h endurance at the two-thirds cut.
A short test can hide a long loss (inference, also from [REF-951]): VO2max and the 5-min test held while 2-h endurance fell, so after a maintenance phase check the event's own duration, not only a ramp test.
Transfer limits: subjects trained 10 weeks by the study, 6 days a week; long-trained athletes have more to lose and were not tested. Maintenance on fewer days a week is a different question (REF-1219). Practical maintenance rules for the season are in SYNTH-76.

Limitations

Abstract only. The APS full text could not be fetched (a bot check blocked the download); OpenAlex and Semantic Scholar list no open copy. Group sizes, subject characteristics, the intensity of training and the test protocols are not given in the abstract.
Small groups, no full-training control. Thirteen subjects in two groups; no group continuing 40 min a day is described, so "maintained" means "no significant change from the trained value" in a small group — no evidence of a loss, not proof of none.
Study-trained subjects. Ten weeks of training created the trained state; how athletes with years of training respond to shorter sessions is not shown.
Frequency held at 6 days a week. A 13-min session six times a week is a different pattern from the two or three sessions a week most maintenance plans use.
Arithmetic. The long-endurance fall, 139 to 123 min, is 11.5% of the group means against the 10% stated; the 10% may be a mean of individual changes, which the abstract does not say.
Funding and conflicts: not stated in the abstract.
How this entry was checked and changed
Why this level

(from the abstract) — two small groups whose sizes and allocation are not given in the abstract, no group continuing the full 40 min a day is described, and the subjects were trained by the study itself; the full text (APS, normally free after 12 months) could not be fetched (publisher bot check), so only the abstract was read