When we exercise, we expect to see improvements in health, fitness, or both. However, substantial research over the past couple of decades has illustrated that the magnitude of training improvements is highly variable between individuals, and a small number of people show no, or perhaps even negative, improvements to an exercise training intervention. These individuals are typically referred to as “non-responders.” Whis phenomenon is not unique to exercise, but new research is finally starting to take a closer look at this topic.
Is Non-Response a Myth?
A recent paper in The Journal of Physiology by Montero & Lundby (2017) throws some new light on these findings. Here, the authors put 78 male subjects through a standardised aerobic training programme for six-weeks, comprised of between one and five training sessions per week of 60-minutes each. The subjects themselves chose which group to participate in. Non-responders to this protocol was defined as those subjects showing no improvements in peak power output greater than the technological error and day-to-day biological variation. Following the first exercise period, non-responders underwent a second 6-week training block with an additional two weekly training sessions. Following this second training block, there were no non-responders, leading the authors to conclude that their study “fundamentally challenges the notion of cardiorespiratory fitness non-response to exercise”, and that their findings “refute the myth of non-response to exercise training.” Michael Joyner and Steve Magnes have both put together great commentary on the article. It has also garnered a lot of attention on social media, with people pointing out that this was, perhaps, obvious, and that of course everyone can respond to exercise.Sometimes change doesn't have to be drastic to transform a non-responder into a responder. @craig100m Click To Tweet
But is exercise non-response a myth as the article proposes? Firstly, it is important to understand how research in this field is typically set up, where a uniform dose of exercise is prescribed to subjects. The HERITAGE study was one of the first to examine inter-individual variation in exercise adaption, looking at improvements following aerobic training. The aerobic training itself was standardised, and was a progression from a heart rate (HR) associated with 55% VO2max for 30 minutes/day to a HR associated with 75% VO2max for 50 minutes/day. This means that each subject had more or less the same internal workload. Following the training protocol, subjects are then assessed within a specific variable, or group of variables. The initial measure in HERITAGE was VO2max; here, the mean improvement was around 19% over twenty weeks. However, some subjects saw much greater improvements than this, as much as 40%. Some, however, saw no improvement, including a small group of people who actually got worse (this is perhaps due to a loss of motivation for the test, as opposed to exercise actually making people worse).
Different training regimens and modalities have been utilised in the research, with different outcome variables assessed. What is usually meant, therefore, by non-response is that the subject did not respond to the specific exercise training programme in the specific variable of choice. The measurement of additional variables tends to illustrate that all individuals show some improvement following exercise. For example, Scharhag-Rosenberger et al. (2012) assessed VO2max, resting HR (rHR), submaximal exercise HR (eHR), and individual anaerobic threshold (IAT) following one-year of endurance training. Four subjects exhibited non-response in terms of VO2max, four in terms of rHR, three in terms of eHR, and one in terms of IAT. Crucially, no individual athlete showed non-response in all four variables, indicating that, at least in this sample, there are no global non-responders to exercise – i.e. every individual improves following exercise, if you measure enough variables.
Placing this into the context of Montero & Lundby’s paper, we can see that non-response is typically present in a specific variable following a uniform training programme. With an increase in variables measured, there is a decrease in non-responders, such that we might reasonably expect that everyone will show improvements to exercise, but these improvements will be varied across many different measures. Montero & Lundby themselves had subjects who did exhibit exercise non-response following the initial exercise intervention, so to call exercise non-response a myth is perhaps a step too far.
All Individuals Are Responders
What is clear from the emerging research is that non-response can be completely mitigated by altering variables associated with training programme design. These include exercise intensity, exercise modality, and frequency. Regarding intensity, Ross et al. (2015) found that increasing the intensity of aerobic exercise from 50% VO2peak to 75% VO2peak eliminated exercise non-response. Karavirta et al. (2011) randomised subjects into four exercise groups; endurance training only, strength training only, concurrent strength and endurance training, and a control group. All groups exhibited large ranges in exercise response, with improvements in VO2peak ranging from -10 to +60% in the endurance trained group, and MVC improvements ranging from -15 to +60% in the strength trained group. But it is the strength and endurance trained group where the crucial data lies; although some subjects saw a negative training response in either VO2peak or MVC, not a single subject saw a negative response in both. In addition, no subject was in the highest quintile of improvement for both VO2peak and MVC. This suggests that a change in exercise modality can also eliminate exercise non-response; individuals tend not to be global non-responders to exercise, merely don’t respond to a specific stimulus. Finally, as Montero & Lundby illustrate, increases in exercise frequency can eliminate non-response.
Transforming Non-Responders Into Responders
In conclusion, when subjected to a standard exercise intervention, a small subgroup of individuals exhibit no improvement in a measured variable. These individuals would commonly be labelled as non-responders. However, by evaluating a greater number of variables, or by manipulating the training programme through alterations in intensity, frequency, or modality, it seems that all individuals can show improvements following exercise. We might, therefore, be better off stating that people “did not respond”, as opposed to labelling them as “non-responders”, because it seems clear that given a different training programme, they would show a positive response.
This is good news, and now means that non-response to an exercise programme is the start of a conversation between patient and practitioner (or athlete and coach) as to how to improve, as opposed to a negative finding. Simply put, if you’re no longer seeing improvements with exercise, change it up by altering exercise intensity, volume, duration, or even type. Coaches likely already know that if they give exactly the same training programme to a group of athletes, there will be a large range in improvements; some will see big improvements, most will see a “normal” improvement, and some will see no improvement. What tends to happen is the coach will then change the training for those athletes who saw a smaller improvement. What this study shows quite nicely is that the change doesn’t have to be huge; it can be as subtle as a change in training frequency or volume, or as previous studies have suggested, a change in intensity. We can therefore view non-response in our athletes as a programming issue, as opposed to a genetic limitation; we just need to find what works for each person and they can maximise the improvements they see from exercise.Non-response can be viewed as a programming issue rather than a genetic limitation. @craig100m Click To Tweet