Interrelationships Between Skeletal Muscle Adaptations and Performance as Studied by Detraining and Retraining
Participants
n = 6: well-trained runners (abstract)
Context: classic work on the kinetics of adaptation loss and recovery; the authors describe the subjects as "near their upper limit of adaptation"
Protocol
Phase 1 (Baseline): testing in the trained state — VO2max, an intense submaximal performance run, muscle biopsy (SDH, LDH)
Phase 2 (Detraining): 15 days of detraining
Phase 3 (Retraining): 15 days of retraining
Measures: VO2max, maximal and peak heart rate, performance time in the intense submaximal run, blood lactate after the tests, muscle enzyme activities (SDH, LDH), muscle fibre areas (3 subjects)
Key Findings
| Parameter | Detraining (15 d) | Retraining (15 d) | p |
|---|---|---|---|
| VO2max | –4% | increased by a similar amount | <0.05 |
| SDH (succinate dehydrogenase) | –24% | no significant increase | <0.05 / NS |
| LDH (lactate dehydrogenase) | –13% | no significant increase | <0.05 / NS |
| Performance time, intense submaximal run | –25% | still 9% below the initial level | <0.05 |
| Maximal heart rate | +4 beats/min | –7 beats/min | <0.05 |
| Peak heart rate during the performance run | +9 beats/min | –9 beats/min | <0.05 |
| Blood lactate after VO2max test and performance run | ~20% lower | ~20% lower (still) | <0.05 |
| Muscle fibre areas (3 subjects) | tended to be larger | tended to be larger | — |
Mechanisms
VO2max vs enzyme dissociation (abstract data): VO2max was back to about baseline after 15 days of retraining, but SDH and LDH activities did not recover in that time, and performance remained 9% down — the authors conclude that a longer retraining period is needed for muscle to re-adapt to its original trained state.
Inference, not tested here: the faster recovery of VO2max than of muscle enzyme activity and endurance performance is consistent with central (cardiovascular) adaptations returning before peripheral (mitochondrial) ones; the paper did not measure stroke volume or plasma volume.
The higher maximal and peak heart rates after detraining are in the data; their cause is not.
Practical Application
In n=6 well-trained runners, 15 days of detraining cut VO2max 4%, SDH 24%, LDH 13% and performance time in an intense submaximal run 25%, and raised maximal and peak heart rate by 4 and 9 beats/min; 15 days of retraining restored VO2max but not the enzyme activities, and performance was still 9% below baseline — even a short break costs a highly adapted athlete measurable capacity, and two weeks of retraining are not enough to buy it back. Asymmetry: lost in 15 days, not regained in 15 days.
VO2max recovers before muscle endurance does — after a break, do not read a normal VO2max-type effort as full recovery of the aerobic muscle; the enzyme and endurance side lags.
Not from this paper; the base's own practice: keep some stimulus through illness or travel breaks where possible, rebuild progressively after a forced break of more than a week, and re-introduce hard sessions after a period of aerobic work rather than immediately — the specific day counts and load percentages are house rules, not this study's data.
Limitations
n=6, single group, no control; 1979 methods.
Fibre-area data from 3 subjects only, trends not tests.
Runners "near their upper limit of adaptation" — the magnitude of loss in less trained athletes is not addressed.
How this entry was checked and changed
Content correction 2026-09-27
Sport "running, swimming, sprint" -> running. Tier 4-5 Elite -> Tier 2-3 (abstract: well-trained runners).
"Submaximal HR +9 / −9" -> abstract: peak heart rate during the performance run. Blood lactate ~20% lower after both phases added.
"Plasma volume loss 7-14 days", "recovery likely 4-6 weeks", "8-12 weeks", "August Krogh Institute" -> not in the abstract; deleted.
Rule block (">10 days", "30 min Z1", "7 days minimal loss", "3-5 day reduced load", ">30 days", "50% → 70% → 90%", "1-2 weeks aerobic") -> house rules, not this study; relabelled as the base's own practice without numbers.
Cross-reference descriptions checked against the cited entries' current content; wrong years, wrong entries and claims the cited entry does not make were corrected.