Twice every second day versus once daily for 3 weeks in trained cyclists: the same two sessions (100-min steady ride + 8 × 5 min) stacked 1-2 h apart raised fat oxidation and oxidative enzymes, compromised the interval session, and improved a 60-min time trial by ~10%
The same as training once a day
Fourteen endurance-trained cyclists/triathletes trained for 3 weeks with the same sessions arranged two ways: alternating a 100-min steady ride and an interval session on consecutive days (High), or doing both on the same day, 1-2 h apart, every second day (Low — the interval session started with reduced muscle glycogen).
Participants
14 endurance-trained cyclists/triathletes, 7 per group.
Protocol
High: daily, alternating a 100-min steady-state aerobic ride with an interval session (8 × 5 min at maximum self-selected effort).
Low: twice every second day — the steady ride, then 1-2 h later the interval session.
3 weeks. Before and after: 60-min steady-state ride (biopsies, substrate oxidation) followed by a 60-min performance trial.
Key Results
Cycling performance improved by approximately 10% in both groups.
Only in Low: resting muscle glycogen (412 → 577 µmol/g dry wt), whole-body fat oxidation during the steady ride (1261 → 1698 µmol/kg/60 min), citrate synthase (45 → 54) and β-HAD (18 → 23) activity, and COX IV protein increased (all P < 0.05).
Mitochondrial DNA and PGC-1α protein were unchanged in both groups.
Authors' conclusion: training twice every second day compromised high-intensity training capacity; the 1-h trial after a 60-min ride improved similarly with either schedule.
Practical Application
Stacking the same work into fewer days changed muscle markers but not the result: in 3 weeks both arrangements improved a 1-h time trial by ~10%, and the stacked schedule cost quality in the interval session. For a performance question, how the week is arranged mattered less than doing the work.
This is not a test of one long ride versus the same time split; it says nothing about events longer than about 2 h.
Limitations
n=7 per group, 3 weeks, randomisation not stated.
The "Low" condition mixes two things — clustering and starting the intervals with low glycogen; the design cannot separate them.
Performance test about 2 h in total; nothing on longer events or durability.
How this entry was checked and changed
Why this level
n=7 per group, 3 weeks, randomisation not reported