We all know that exercise is good for us. The lists of benefits that exercise can give us is as wide as it is varied; it lowers our risk of obesity, metabolic syndrome, and cardiovascular disease. It provides a mental health benefit. It reduces our chances of having low bone mineral density. It’s an important part of the healthy aging process, with exercise allowing for a maintenance of muscle strength as we grow older, making us less likely to suffer from falls, and keeping us mobile and active for much longer.
It’s clear, therefore, that exercise is a good thing. But what if exercise wasn’t so good for us? What if, instead of lowering our risks of various disease states, exercise instead increased it? This is known as an adverse response, and, recently, a growing body of evidence suggests that it is a real and replicated phenomena.
The dangers of exercise
A paper published in 2012 attempted to discover just how common these adverse effects are. By pooling data from a number of exercise intervention studies, the authors explored an adverse response (defined as a worsening of health biomarkers more than two times the standard technical error of the test) for four traits:
- systolic blood pressure (a marker for hypertension);
- plasma triglycerides;
- fasting insulin;
- and HDL-cholesterol (markers for cardiovascular and metabolic diseases).
On average around 10% of subjects had an adverse response in at least one of these markers following training, with roughly 7% seeing an adverse response in two or more factors. Other studies have found similar results, such as this one from 2014, and this from 2015. Potentially one of the drivers of this, as ever, is genetic variation between individuals, with changes in genes related to catecholamine sensitivity associated with fat gain following aerobic training.
Exercise vs. training
So far, all of this research has been conducted on sedentary, and typically unhealthy, subjects, but it’s easy to see how this might apply to athletes undergoing training.
On the one hand, athletes also often face more severe adverse responses in several areas. Injury and non-functional overreaching/overtraining are two adverse responses encountered more often by athletes. Both of these are typically symptoms of mismanagement of training load, and so eliminating, or at significantly reducing, these types of adverse responses should be achievable.
But adverse responses in traditional measures are also possible with athletes. Give a group of approximately 20 athletes roughly the same training program, and you would expect a variation in training response – some would undoubtedly improve, whilst others, especially in more experienced athlete groups, may stay the same, or even show some form of regression. This regression could be down to a number of drivers; perhaps the workload is too high, inducing increased amounts of fatigue. Perhaps the training the athletes were doing wasn’t suited to their individual make up, as a study I was involved in that was published in 2016 showed. Perhaps the time-course of adaptations in some individuals takes longer than others, and so if we artificially create an end-point, it appears that they haven’t responded to training adequately – but if we gave them more time, they might have. Returning to the studies showing adverse responses to exercise in sedentary subjects, we could speculate that a longer time spent training would eliminate this adverse response, which might only be temporary.
Weighing the good and the bad
A further point to consider, particularly from a public health perspective, is that we’re at risk of creating a false dichotomy here, making exercise either completely good or completely bad. Instead, exercise might have some negative effects for some people, but these appear to be in very specific, single (or, in some cases, double) markers. This is in contrast to the improvements these individuals may well be seeing in tens or even hundreds of other aspects. So, whilst this adverse response to exercise might increase an individual’s fasting insulin – increasing their risk of type-II diabetes – it could simultaneously be reducing their body fat, which lowers their overall risk of type-II diabetes. Alongside this, that individual could be gaining improvements via a reduction in stress, perhaps making them less likely to binge eat, and an increase in muscle mass, which will also enhance metabolic control. The totality of exercise, in this case, is therefore overwhelmingly positive.
But the flip side is also true; whilst athletes tend to be (but aren’t always) more healthy than the general population, thanks in part to all the exercise they do, they could undo all this good work by having a single measure negatively affected by exercise, if the effect of that marker is large. For example, athletes may experience numerous positive health effects from exercise, but as soon as they veer into overtraining, which has a multitude of quite serious negative health consequences, they run the risk of undoing all these improvements. Similarly, a severe injury can also have very large negative consequences for the athlete, leading them to miss competitions, harming them financially, and possibly increasing their levels of stress or depressive feelings.
In summary, both exercise (for the general population) and training (for athletes) are overwhelmingly positive. For the general population, the myriad of positive health benefits across a broad array of markers and metrics that exercise brings likely outweigh the few negative responses to exercise. For athletes, negative responses to training are more severe, and in the case of overtraining and injury may serve to undo many of the positive outcomes of training. Further evidence, were it needed, that adequate progressions and training loads are important pieces of the puzzle when it comes to allowing athletes to compete successfully.