Impaired energy production in the cells, poorer blood sugar regulation and poorer heart rate control are consequences of too much high-intensity interval training (HIIT) and can cause both health problems and performance problems for elite athletes. This is shown by a new Swedish study.
When an athlete is to top his form before a competition, one of the most common methods is to enter a hard training camp with very high-intensity interval training and then step down and rest more the week before the competition. Sports researchers call this method of reaching top form for overreaching. However, there is a risk that you train far too hard and have a much longer recovery period, so-called non-functional overreaching. In the long run, it can lead to overtraining.
– Some have argued that non-functional overreaching would be a myth. But now we see for the first time that there is a difference in what happens in the muscles when the training has gone too far, says Filip Larsen, physiology researcher and associate professor at the School of Gymnastics and Sports in Stockholm, who is one of the researchers behind the study.
The researchers have investigated values for blood sugar and lactic acid production as well as the ability to lower and raise the heart rate during a gradually increasing training program with HIIT (high intensity interval training).
Eleven young and healthy subjects had to perform two hard interval sessions on an exercise cycle during the first week of the study. They cycled five sets consisting of four minutes of full speed and three minutes of rest.
The following week, the number of training sessions was increased to three. At the end of week two, one could see clear improvements in, among other things, how many mitochondria, the cells’ energy factories, were formed and how efficient they were in producing muscle energy from nutrition. Week three, the intensity of the training increased even more. The subjects went up to train between five and six times a week and sometimes the time on the rock-hard interval training was also extended.
The values showed that the mitochondrial capacity was now only 60 percent compared with the week before. Blood sugar had higher mountains and deeper valleys, like a diabetic, which among other things has a negative effect on sleep.
We can determine when you cross the line that degrades your values.
Week four the amount of high-intensity training was drastically reduced in order for the subjects to recover. During and after this week, they performed as well or even better than they did during the peak of form week two, but their mitochondria and blood sugar regulation still showed significantly worse values.
After these surprising results, the researchers chose to examine the blood values of several endurance athletes at national team level and it turned out that they also suffered from the same poor blood sugar regulation.
– Now we see that there is actually a difference in what happens in the muscles. We can decide when you go over the limit that impairs your values, which is not good in the long run, says Filip Larsen.
Filip Larsen and his colleagues is now working on and developing a diagnostic test that will be able to warn if it is time to reduce the high-intensity training. If you reach certain values, it’s time to rest. Many of the key values already have simple systems for measuring, such as blood sugar that diabetics measure daily.
– I hope this will be more accessible in the future even for those who only train to stay healthy, says Filip Larsen.
Practicing tabata several times a week and sitting still the rest of the time gives you no solid foundation.
The condition you end up in when the high-intensity interval training gives these negative effects can in the long run lead to overtraining. But according to Filip Larsen, most people who train a lot on a daily basis do not have to worry about it. Two thirds of the population do not even reach the recommended minimum level for physical activity.
– A good measure to know what is too much is if your mood starts to decline. One thing to remember is that you need the low-intensity training as a basis to cope with the high-intensity. Practicing tabata several times a week and sitting still the rest of the time gives you no stable foundation, says Filip Larsen.
– The national ski team’s doctor Per ”Pliggen” Andersson welcomes new results and more research in overtraining and how the body reacts to different forms of training and intensity.
Photo: Carl Sandin / Bildbyrån
Per “Pliggen” Andersson is a national team doctor for the national ski team and works every day with athletes who are always on the edge when it comes to squeezing their bodies.
– It is very welcome when there is new knowledge on this subject because it is one of the biggest issues we deal with in sports and yet we know so little about it, he says.
Per Andersson says that he has worked with several athletes who inexplicably ended up in deep form slumps and that it is medically difficult to pinpoint why.
– They often have diffuse symptoms such as feeling lactic acid much earlier, find it difficult to raise their heart rate and get out. Many describe it as training with the handbrake in. Even if they rest for a week or two, which is a very long time for an elite athlete, they do not get well.
The problem with athletes who either end up in longer form slumps due to too much load or even become overtrained is that you do not get a receipt for it until you see it on the results.
– You do not see that they have ended up in this imbalance with too much load and too little recovery until they start to perform worse a couple of trainings or competitions in a row.
Some people have impaired appetite and depression and sometimes even anxiety.
The national ski team works continuously with standardized physiological tests, such as heart rate and lactic acid measurements to keep track of the athlete’s condition. They also perform health tests that measure the body composition with the distribution of fat and muscle mass. Something that makes it difficult to interpret the results, according to Andersson, is that diet and sleep also need to be weighed.
Per Andersson agrees that the low-intensity training is needed as a basis for coping with the high-intensity interval training. That the mood is usually what is affected first is also consistent with his experience.
– Some have impaired appetite and depression and sometimes even anxiety. I therefore think this sounds like an exciting research result for how we should gain more understanding of how we optimize our training.
The study shows that too much high-intensity interval training leads to health disadvantages and shape dips that last a few weeks longer than expected. But overtraining, which is going a step further, has bigger consequences. An overtrained athlete can hardly be recognized in terms of performance and the recovery takes several months and in the worst case years. Filip Larsen says that the very phenomenon of overtraining, which is so difficult to define, is what he wants to study next.
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