REF-951 · Hickson et al., 1985 · Journal of Applied Physiology, Vol. · Paper · PubMed

Reduced training intensities and loss of aerobic power, endurance, and cardiac growth

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

Twelve subjects cycled and ran 40 min/day, 6 days/wk, for 10 wk, then kept training for 15 more wk at the same frequency and duration but with work rates cut by one-third or by two-thirds. After the first 10 wk VO2max was 11 to 20% higher. Cutting intensity by a third did not hold VO2max, although it remained above pre-training values; cutting it by two-thirds lost more.

Short-term endurance (approximately 5 min) held up in the one-third group but dropped sharply in the two-thirds group. Long-term endurance fell in both. Calculated left ventricular mass had grown approximately 15% with training and went back to control levels in both groups.

The authors conclude that keeping up intensity is essential if reduced training is to preserve the gains in aerobic power and heart size.

Participants

Twelve subjects. Age, sex and prior training status are not given in the abstract.

Protocol

Training: cycling and running, 40 min/day, 6 days/wk, for 10 wk.
Reduced training: an additional 15 wk at a one-third or two-thirds reduction in work rates; frequency and duration the same as in the 10 wk of training.
Outcomes: VO2max (cycling and treadmill), short-term endurance (approximately 5 min), long-term endurance, calculated left ventricular mass from echocardiography.

Key Results

After 10 wk of training, average increases in VO2max were between 11 and 20% (cycling and treadmill running).
One-third reduction in intensity: VO2max not maintained at the 6-day/wk training level, but still higher than pretraining. Two-thirds reduction: VO2max declined to an even greater extent.
Short-term endurance (approximately 5 min): maintained in the one-third reduced group, markedly reduced in the two-thirds reduced group.
Long-term endurance fell 21% with the one-third cut (184-145 min) and 30% with the two-thirds cut (202-141 min).
Calculated left ventricular mass increased approximately 15% after training and returned to control levels after reduced training in both groups.

Practical Application

"In a maintenance period, can I keep the hours and just ride easier?" In twelve subjects who kept training 40 min/day, 6 days/wk for 15 wk but cut the work rate by one-third or two-thirds, VO2max was not maintained and long-term endurance fell by 21% and 30% — unchanged frequency and duration did not protect fitness once intensity dropped. Intensity is the part of the load that has to stay.
This is the counterpart of the maintenance rule: volume and frequency can be trimmed, intensity cannot (REF-587, REF-374). Not from this paper; the base's own practice: the off-season never drops intensity to zero (SYNTH-76).
Even the smaller cut lost long-term endurance (184 to 145 min) while short efforts held. Inference, not tested here: a short hard test after an easy period can look fine while endurance at longer durations has already gone.
Subjects were trained by the study itself over 10 wk; the size of the loss in long-trained athletes may differ.

Limitations

Twelve subjects in two groups; no group continuing at full intensity is described in the abstract.
Subjects' training status before the study, age and sex are not given in the abstract.
PubMed abstract is truncated at 250 words; details beyond it are not used here.
VO2max values after reduced training are not given as numbers in the abstract.
Written from the abstract and record metadata only (full text not read).
How this entry was checked and changed
Why this level

small two-group study of twelve subjects, no non-reduced control described in the abstract; foundational, later summarised in REF-587