Do Exercise Non-Responders Exist?
Have you invested countless months into working out meticulously tracking your sets, reps, and weights all the while eating plenty of food and getting adequate sleep, yet you still struggle to notice even the slightest bit of progress in terms of performance or physique?
If so, you’ve probably been labeled as a “non-responder” and there are millions more just like you.
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For those of you reading this that have no idea what a non-responder is, you may be more familiar with its other name -- hardgainer.
Essentially, a non-responder is an individual who does not seem to respond (i.e. build muscle and strength) to conventional resistance-training programs.
A number of studies over the years have identified alleged “non-responders” as those subjects who do not seem to demonstrate any significant improvements in strength, power output, or the amount of lean muscle mass they’ve gained from the beginning of an exercise trial until its conclusion. 
However, emerging research disputes the notion of a “non-responder” entirely, suggesting that the term isn’t exactly accurate.
Appearing in Sports Medicine, the new review examines a wide range of studies and begins by discussing the problem with using the terminology of “non-responder”. In short, the idea that someone is completely unresponsive to training is a bit incorrect as it implies that no training methodology whatsoever would benefit an individual. The authors contend that a “non-responder” should be referenced in the literature as an individual who “did not respond” to that given training protocol.
While the difference seems inconsequential, by using the terminology “did not respond” allows for the possibility that said individual could (and very likely) respond to alternative training measures.
Additionally, in refuting the notion of a “non-responder” the authors note that the term “non-responder” itself has no clear-cut definition, meaning it has different implications depending on what variables are measured in a give trial. The authors go on to cite various interpretations of “non-responders” found across exercise studies including: 
- lack of a clinically meaningful change
- lack of a measurable change
- a value above the technical error of the test
- the lowest set percentage of subjects in terms of response
Furthermore, which metrics are used and the number of metrics collected by researchers could also implicate an individual as a non-responder, when in fact they merely may not have improved in that one specific area assessed by the study.
For example, say a given research trial was measuring improvements in VO2 Max. At the end of the trial, 90% of the subjects saw improvements in their VO2 Max, but 10% of the subjects did not.
Does this mean that the subjects gained no improvements in any other measurables of fitness?
No, it doesn’t. It merely means that the 10% did not respond positively to the given training program with respect to VO2 Max. But they very well could have increased lean muscle mass, time-to-exhaustion, etc.
Studies have investigated the inter-individual variability in responses to various training protocols and found some rather interesting things. Published in 2016, a study by Gurd et al recruited 21 healthy men and women and took a baseline measurement of each individual’s VO2 max, heart rate and a host of other physiological parameters. 
Following these baseline measurements, each volunteer completed two different training protocols. One routine was your prototypical endurance-type training, involving riding a stationary bike four times per week for 30-minute bouts at a moderately intense pace. The other training routine involved high-intensity interval training (HIIT), where subjects completed eight 20-second intervals of maximum effort pedaling on a stationary bike interspersed with brief 10-second rest intervals.
Subjects performed each training modality for a period of three weeks, followed by a several month layoff so that they could return to their baseline fitness. The volunteers then performed the other training protocol and again measurements were taken to see what, if any, improvements were derived from the training protocol.
As you would expect, the average “fitness” of the group improved significantly by the end of the study; however, drilling down into the data for each individual, one sees a very different story. Roughly ⅓ of the participants did not respond positively to the endurance training regimen). Likewise, there were individuals who did not respond positively to the high-intensity training protocol either. In fact, there were subjects in both exercise regimes that actually got worse following the training program. 
All of this serves to drive home the point that an individual’s response to a training program is just that individual. Studies tell us what kind of training works well on average for most people over short periods of time. Does that mean the training program published in the latest exercise study is the right one for you?
Maybe, maybe not.
Other research has looked into the non-responder phenomena as well and found that sometimes individuals labeled as non-responders are those who require significantly higher training volumes in order to elicit a statistically significant adaptation.
The 2017 study by Montero et al noted that: 
“In conclusion, individual CRF non‐response to exercise training is abolished by increasing the dose of exercise and primarily a function of hematological adaptations in oxygen‐carrying capacity.
In other words, if all of your friends have gotten great results using 5x5 programs, and you’ve made little to no gains with it, then chances are likely you might need a program with more total training volume.
Going back to the latest review, in the conclusion, the authors state:
“As a result, we might, therefore, be better off stating that people “did not respond” to a particular intervention in a given measure, as opposed to labeling them as “non-responders”, because it seems likely that a different training programme (in terms of intensity, volume, duration, or modality) would elicit a positive response.” 
Essentially, a given person may not respond to one particular training protocol, but that doesn't mean they will not respond to ALL training protocols.
If at the end of the day, you don’t seem to be building muscle or increasing strength with a given program (and you’re doing everything “right” -- diet, sleep, training), then all that means is that you need to tweak the program a bit to suit your body’s needs better.
It doesn’t mean that you won’t respond to any exercise or that you should give up training entirely. Now, you might not have the genetics to be an elite bodybuilder, powerlifter, or strongman, but you can still make impressive gains by customizing your program to generate positive adaptation.
This could involve increasing or decreasing training volume, intensity, or frequency. Or, it could mean using more machine exercises over barbell ones. Whatever you do, don't give up and blame your genetics.
Document, measure, assess, and re-assess. Fine tune things along the way until you develop a program that is both enjoyable and one that generates results.
1) Bouchard, C., & Rankinen, T. (2001). Individual differences in response to regular physical activity. Medicine and Science in Sports and Exercise, 33(6 Suppl), S446-51; discussion S452-3.
2) Ahtiainen JP, Walker S, Peltonen H, et al. Heterogeneity in resistance training-induced muscle strength and mass responses in men and women of different ages. Age (Dordr). 2016;38(1):10.
3) Gurd, B. J., Giles, M. D., Bonafiglia, J. T., Raleigh, J. P., Boyd, J. C., Ma, J. K., … Scribbans, T. D. (2016). Incidence of nonresponse and individual patterns of response following sprint interval training. Applied Physiology, Nutrition, and Metabolism = Physiologie Appliquee, Nutrition et Metabolisme, 41(3), 229–234. https://doi.org/10.1139/apnm-2015-0449
4) Pickering, C., & Kiely, J. (2019). Do Non-Responders to Exercise Exist---and If So, What Should We Do About Them? Sports Medicine, 49(1), 1–7. https://doi.org/10.1007/s40279-018-01041-1
5) Bonafiglia JT, Rotundo MP, Whittall JP, Scribbans TD, Graham RB, Gurd BJ (2016) Inter-Individual Variability in the Adaptive Responses to Endurance and Sprint Interval Training: A Randomized Crossover Study. PLoS ONE 11(12): e0167790. https://doi.org/10.1371/journal.pone.0167790
6) Montero D, Lundby C. Refuting the myth of non-response to exercise training: 'non-responders' do respond to higher dose of training. J Physiol. 2017;595(11):3377-3387.