What determines a responder or non-responder to an exercise stimulus

What determines a responder or non-responder to an exercise stimulus?
It is well understood that there is variation within individual response to an exercise stimulus, however here is much debate whether the term ‘non-responder’ is appropriate and the supporting evidence for such a concept is according to Hecksteden et al., (2015) somewhat unpredictable, based on inconsistent findings and measurement error.
The degree of response to exercise depends on many factors such as training type, consistency, adherence, duration and intensity, lifestyle, habits, medical issues and of course genetics. These should be considered before labeling an individual as a non-responder, responder or super-responder.
Montero and Lundby, (2017) conducted 6 weeks of cardiorespiratory fitness training on untrained subjects in groups of differing exercise duration 60, 120 and 180 minutes per week. Measuring VO2max and other factors, they found that early non-response results in lower volume groups were eliminated following a second 6 week period with an additional extra hour session per week indicating that getting the duration or dosage right is an important factor.
Ross, de Lannoy and Stotz, (2015) argue that intensity is another equally important factor postulating that low intensity exercise may simply not be enough for obese, sedentary individuals. Their studies focussed on 3 groups differing and increasing in exercise intensity over 24 weeks. Cardiovascular fitness improved in all groups by week 24.
Solomon, (2018) refers to type 2 diabetic individuals who find that exercise does not benefit their control of blood glucose as “non-responders” and appears to support the idea that once factors including any adverse effects to a particular exercise intervention and other individual variability including meal and drug timing are considered then other more suitable exercise interventions should be tried for maximal therapeutic gain.
Timmons et al., 2010 looked at the part played by genetics, accounting for around 50% genetic variance of VO2max in response to endurance training and note that this is not enough to account for total variance. To help compensate in cases of genetic susceptibility, they suggest other protocols such as alternative exercise type, dietary and pharmacology. Ultimately, hard-work, commitment and a positive attitude should be the take-home message with consideration and appropriate management of the aforementioned factors.