Repeat The Same Training?

I started keeping a handwritten training log (pictured below) after I started running when I turned 13. Back then there were no apps to keep such records for you. I will record how far I ran, time taken, how I felt, what shoes I used etc. 

I found it useful so I can look back on what at training I did when taking part in a similar event. Say my key interval workout for a 1500m track race I won previously was 8x200m with 30 seconds rest. I would replicate those sessions along with deciding if I could handle more. Back then, I was a teenager and was able to run personal bests in all my events every year.

I assume that when I responded well to a training program once, I'll respond similarly or better the next time. However, a recent study suggested otherwise.

A group of researchers had subjects do the same 8 week endurance training program twice, but separated by a period of detraining that had to return to baseline. 42 out of the 53 recruited completed the study.

Each 8 week period had 24 supervised 45 minute interval cycling sessions at modrate to maximal intensity. Identical training instructions were applied such that the same training program was repeatedly prescribed to the same individuals. Exercise intensity was individually prescribed relative to performance and adjusted every second week to mainatin a comparable training stimulus across periods.

Results show very poor reproducibility of adaptation. One athlete increased VO2 max by about 600mL min⁻¹ after the first training period. However, there was no improvement at all after the second training period. Yes you read correctly, zero improvement.

Same athlete, same program, but very different outcome. I asked a few coaches whom I treat if this was similar to the athletes they coach. They told me they see it all the time. Training response varies.

The training may be the same but the variations in external factors such as sleep, diet, work stress, travel and illness etc contributes to the variability in individual training adaptations.

That's what the researchers concluded too. The substantial within-individual fluctuations were largely consistent between training periods and they suggest that this  within-individual fluctuations does not reliably reflect their capacity to adapt to the same training stimulus in the future.

So low stress plus good training leads to adaptation while high stress plus the same training may lead to very different outcomes.

Take away message? Do not assume that because a program worked once, it will work the same way the next time. Monitor the state of your own life stresses and modify accordingly.

Reference

OddenIV, Hamarsland H, Odden TU et al (2026). Limited Reproducibility Of Individual Physiological Adaptations To Repeated Endurance Exercise Training. J App Phy. DOI: 10.1152/japplphysiol.00154.2026