Sports Science Monthly – May 2017

This month we take a look at new research on how genetic variations might affect psychological skills, the differences between physiological and biomechanical training load monitoring, synthetic tendons, and practical issues in sports nutrition. To start off with, however, we dive into the interplay between energy intake and overtraining syndrome.

As always, the full Sports Science Monthly is available exclusively to HMMR Plus Members. The first topic below is free to everyone, but sign up now to read about all the research. To get an idea of what Sports Science Monthly is all about, the April 2016 edition is available in its entirety for free.

This Month’s Topics

Energy Intake During Intense Training Blocks

→ Quick Summary: Most athletes consume too few calories during intense training, and this can limit performance significantly.

I’ve written previously for HMMR Media about my experiences with overtraining, in which one of the key triggers was trying to decrease my body fat to levels which were perhaps too low for me to achieve. I’m typically of the opinion that professional athletes tend to eat too few calories to support their training; the mindset is often “how little can I eat and still perform,” and opposed to “how much can I eat without putting on weight.” My opinion is based on a number of experiences I’ve had – I’m currently working with an elite team-sport national team where the players are so concerned about putting on weight that they really do under eat. It’s a great example of how social factors, including body image expectations, can interact with sporting needs and demands to culminate in underperformance, and also a reminder to practitioners that these social factors need to be considered (and perhaps gently changed) when working with athletes of different cultures.

When we exercise, our body utilises energy from a variety of different sources, primarily carbohydrates (either recently ingested or stored as muscle glycogen) and fat (usually in the form of body fat). These fuel sources enable us to continue to perform. The brain has a system by which it can monitor the levels of our fuel sources, and alter exercise intensity accordingly. For example, rinsing your mouth with a carbohydrate drink improves exercise performance, even if the carbohydrate is not then ingested. This indicates that there are receptors in the mouth that sense this carbohydrate, and signal to the brain that more is coming (even if it isn’t), allowing exercise to continue. Energy is also important post-exercise, both in terms of adaptation and recovery. Availability of fuel sources post-exercise can alter the adaptive mechanisms of exercise, and playing around with the availability of carbohydrates can subtly change the adaption signals occurring within the body. Similarly, availability of different forms of energy can impact recovery from exercise. In addition, energy availability can alter a host of different other performance factors; lack of energy can lead to the development of the female athlete triad, which can increase the risk of stress fractures. Too little energy intake can also increase the risk of immune dysfunction, increasing the prevalence of illnesses, which can significantly impact training and competition performance.

It’s safe to say that energy intake is important in athletes. And yet, as I’ve already mentioned, athletes, even (and perhaps especially) elite ones tend to under consume energy during training. A paper published recently in PloS One examined this in a group of elite Australian rowers during a four week training block. Both before and after this training block, the athletes underwent a battery of tests. One of these determined resting metabolic rate, which significantly decreased over the course of the training block. The average decrease was by 2 calories per kilogram of fat free mass, which doesn’t sound like much – but an elite male rower could have 80kg+ of fat free mass, meaning that he would be using 160 calories per day less at the end of the training block than at the start. Again, this absolute value isn’t all the great, but what it signifies is more important; it illustrates that the rowers’ metabolic rate is slowing down, which in turn means a number of vital processes linked to health and adaptation are likely to be occurring at sub-optimal rates. In addition to this, the athletes lost an average of 2.2kg of fat mass over the four-week period – again indicating that caloric intake wasn’t sufficient (these athletes were not looking to reduce body fat). Finally, the four-week training block lead to a decrease in 5km time trial performance, and an increase in mood disturbances.

It’s difficult, of course, to say for sure that the decrease in metabolic rate, as caused by insufficient energy intake, was the cause of the decreased performance and increased mood disturbance; it may well be that hard training itself causes this. The likelihood is that it’s a mixture of the two, and that sufficient energy intake would at least reduce the size of the performance decrement seen. The potential mechanism proposed for this loss of metabolic rate is due to hormonal changes, primarily in leptin, occurring in an attempt to preserve body mass (i.e. prevent weight loss).

Most athletes consume too few calories during intense training & this can limit performance. Share on X

So what does this all mean? Some of this is obvious: exercise training uses energy, which is good if you’re trying to lose fat. The flip side of this, which is especially important in elite athletes, is that hard training can require an increase in energy intake in order to prevent a decrease in resting metabolic rate. The athletes in this study were rowers, consuming close to 3500 calories per day, and this still was likely insufficient; this shows just how much energy elite athletes can require. This obviously then has practical effects in terms of the food you actually eat; it will be hard to get this amount of energy from fruits and vegetables, for example, so higher energy foods are likely to be required. This can be in the form of fat, which has a very high energy density (9kcal per gram), but also tends to be highly satiating, meaning that the athlete might feel full before they can consume sufficient energy. Carbohydrates therefore represent another option, and the research suggests that carbohydrate intake should be periodised over a training year in endurance athletes in order to maximise adaptations across a broad range of pathways.

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