Is there any scientific evidence that the relation between training effort (measured as the amount of time spent training for the purpose of this question) and training result (increase in strength, increase in lean mass or increase in endurance depending on your goal) in resistance training is at least partially linear? Linear here means that a doubling/halving of effort would result in approximately a doubling/halving of result. I know that the relation is not linear at the high end (i.e. high effort and high result) without consuming "performance enhancing" substances due to the relation leveling off (i.e. the result approaching some threshold that is hard to overcome even with the highest effort), but the relation could still be linear at the low end or somewhere in between.
I'm only interested in actual evidence, not assumptions or speculation. If there is no evidence, that's fine - don't make it up. To be even more specific, let's assume both effort and result are averaged over relatively short timespans like weeks or months, not years or a whole lifetime. Averaging over shorter timespans probably makes no sense due to the result being too small to be measured with certainty, and averaging over years or more might contaminate the data with the results of unrelated influences like aging, injuries, long pauses, etc. . Some statistical noise is fine - if the evidence indicates a roughly linear relation, I would be interested. Ah, and of course I assume that the candidates are eating adequately to support their results - it is obvious that without adequate protein intake, no amount of effort will produce measurable results. And to clear up one final possibility of misunderstanding: I'm talking about marginal efforts & results to borrow a term from economics. What counts is added effort and added result; whatever happened before you start measuring or after measuring ends is irrelevant.