The Secrets of Peak Performance I : Carbohydrate Fueling
The last few weeks have been pretty hectic what with the excellent Elite performance show at Excel and exposure to an established electrolyte product which I am currently testing during the unusual, albeit welcome mini-heatwave we are experiencing here in the south-east. As my client base is predominantly pure-play cyclists I will also be using it during my attendance at this years UCI public qualifying Italian session for the World Champs road race at the GF Charly Gaul in Trento, 19th July. I hope to be reporting on the benefits of Eletewater in the coming weeks….
Prior to that outcome, I expect to put together a rather complete picture of the elements of performance cycling important to getting the most out of training and competition. Fueling (Hydration and Nutrition), Recovery and Adaptation (different modalities, hypoxia, ergogenic supplements), Concurrent training (Strength & Endurance, and the role of protein), Power; Understanding cycling performance- what you might not know.
In this first post on ‘The secrets of peak performance’ I would like to kick off with carbohydrate fuelling, as we are deep into the peak period for endurance events and competition. This will hopefully be a critical topic for most of you.
Much of contemporary personalised nutrition advice is at best, an educated guess. I have previously posted a few times about the abundance of fad diets favouring high carb/ low fat or low carb/ high fat. However, here I wanted to put into context some of the practical advice, more firmly established through evidence and currently applied at high level competition.
Firstly, it is interesting to note that there is little certainty with regard to nutritional mapping and particular bias of individuals towards carbohydrate or fat metabolism whether at rest or exercising. What can be done through indirect calorimetry is to determine metabolic dependence towards % carb/fat at particular intensities through the respiration exchange ratios (RER) from volumes of O2:CO2 (basically a mathematical guess) which is confused by the fact that composition of fuelling changes over time for any one intensity, and by other metabolic substrates such as amino acids and ketones. which are also used for fuel. Therefore oxygen exchange studies are usually very lengthy repeat assessments. Complicated isotopic carbohydrate labelling have struggled to demonstrate clear difference in preferential metabolism. Fat(max) oxidation assessments through ventilatory rates maybe useful as a crude training tool. Don’t forget that there is an intensity at a lower percentage fat oxidation which is sustainable for a longer duration, ultimately using more calories from fat, and usually falls around the first aerobic lactate threshold turning point on a lactate power profile.
What is known, is that the majority of the ‘average’ population (95%, to 2 standard errors) are mixed substrate oxidisers although little overlap exists between the infinite combinations of expression in the metabolic pathways which exist between people. Much in the same way that we sweat at different rates, but with many more differences in organs, blood vessel network and mechanisms responsible for whole body metabolism. It gets complex.
So as suggested before in a previous post, the main aim for nutritional strategies should be about getting the fundamentals right (basic macronutrition, meal timing and calorie amounts) and then using some trial and error in composition to influence performance and adaptations. I will talk about protein intake again when discussing concurrent training at adaptation, but right now I will focus on carbohydrate availability as a training and racing modality. This should also include emphasis on training the gut, in respect to gastric emptying of high or low particle size (osmolality) carbohydrates at high concentration (10-30% weight/volume solutions).
So the main question that is being asked in the world of sports performance, and in particular cycling…is, should athletes restrict carbohydrates (train low) or load up on carbohydrates (train high)??
Individually, muscle glycogen storage is very different, yet trainable. Glycogen stores determine maximal work rates over time, and serve as a limiting factor to exercise duration.
As a brief overview of glycogen distribution in the body:
Blood 5 g (systemic)
Liver 88-160 g (systemic)
Muscle 570 g (localised, used specifically)
Supplementing carbohydrate over a prolonged duration of exercise results in metabolic marker increases such as exogenous carbohydrate rates of oxidation, but very little evidence of performance benefits.
This article by Asker Jeukendrup, one of the most well respected researchers in the field of applied sports nutrition, covers the topic in a bit more detail.
He has also published a book, Sport Nutrition, An introduction to energy production and performance, 2010. May be more suitable for those wanting to explore deeper into the science.
Simply, glucose which is more easily absorbed than maltodextrin, may be consumed up to 60 g/hr, but will evoke a greater insulin response at sub-threshold rates of exercise when fuelling has a large fat oxidation reliance. I have written about the benefits of delayed release carbohydrates (such as the modified corn starches) to improve rates of fat oxidation by reducing the insulin response. At higher intensity this insulinogenic response should become more mute as exogenous carbohydrate is taken up directly by the muscles after the first pass effect through the liver. Therefore providing some differentiation between training and racing nutritional strategies.
Addition of fructose through the alternative transporter…increases carbohydrate absorption by a further 50% (90g/hr, an additional 30g/hr), where isotopically labelled 13C-glucose shows that increased oxidation is dictated by increased metabolic availability.
Hence what this means is that a further 50% of carbohydrate is available when required. Such as during long distance sub-maximal intensity events.
Jeukendrup goes on to address these issues further here.
In fact, carbohydrate oxidation rates of greater than 1.5 g/min have been measured after about 120-180min of moderately intensive exercise in well-trained individuals. The equivalent of 90-120g/hr of carbohydrate after this initial time period.
The table below highlights the timescale for optimal fuelling between glucose alone and glucose/fructose mix:
Optimal fueling or restriction?
Fuelling at these rates can be somewhat of a challenge, where ingesting 90g/hr of mixed carbohydrate may feel quite unnatural and hence the need to train the gut for optimal performance under these conditions as gastric emptying is impeded by: High intensity exercise >70% VO2max, Dehydration and Hyperthermia.
So experimenting with new fuelling strategies or carbohydrate blends should be practiced well in advance of competition.
The final question I will raise is whether there are performance benefits to restricted carbohydrate availability compared to optimal fuelling rates shown above?
Evidence for benefits to ‘training low’ has come from the observations that restricted CHO increases training adaptations and more efficient muscular function through evoking greater mitochondrial biogenesis.
Specifically, energy deprivation can result in-
- Increased upregulation of transporter markers AMPK/ PGC-1alpha.
- Increased volume of mitochondria – efficiency.
- Increased fatty acid oxidation at higher intensities.
However, in current literature there is no real evidence for any negative or positive performance gain – even though many biochemical markers were positive. This serves as an ambiguous message as there is no certainty in what is an effective method for carbohydrate restricted training. Even so, this mode of training is thought to be beneficial in recovery and adaptation through muscle hypertrophy and muscle protein synthesis (MPS) through cell signalling cascades in the muscle cells, discussed in: The Secrets of Peak Performance V- Recovery and Adaptation.
Train Low and Race High
Training high – improves gut absorption and carbohydrate availability and hence exogenous (externally ingested) oxidation rates – but does this translate into an increased performance over durations > 2.5hr.
This does not allow for restrictive adaptations as seen in some low carbohydrate situations – which may limit subsequent performances and longer term development. In fact, carbohydrate restriction is thought to be responsible for improved muscle glycogen in some situations, and hence may explain performance benefits.
Ultimately optimal carbohydrate fuelling (external) could be more beneficial to gain greater training adaptations of training the gut than to utilise more muscle glycogen???
It is not known what is the best compromise.
Possibly, it may be that a combination of Training High episodically, to train for optimal fuelling, interspersed with Training Low to promote restricted carbohydrate adaptations and Racing High (in terms of carbohydrate availability) may be the best of both worlds!!
There are few robust principals which determine any individuals optimal fuelling strategy either for training or competing. Sound guidelines to what should be well considered strategies have appeared from the scientific literature over recent years, now exist. These should be applied in a practical and personalised approach, determined by the performance goals. Then further fine-tuning can occur to maximise the gains that can be achieved personally.