WORDS BY Benoit Capostagno

The purpose of all the hours we spend training for a specific event is to improve our performance. Depending on your current level of fitness and experience, improvements could mean finishing in the middle of the pack rather than at the back, winning your age category or stepping on to the top step of the podium at the elite level. Whatever performance means for you, if you put the time in to your training, you want to see results. Understanding the demands of the event will help with formulating realistic goals and designing a structured training programme. Once you know what the event requires, you can design a programme which aims to improve the specific characteristics which have been identified to be crucial for success. This could mean targeting specific weaknesses which need to be improved, while simultaneously maintaining or improving on stronger areas.

Cross Country Marathons (XCM) are mass start events covering a variety of off-road sections with a total distance of at least 60 kilometres and are approximately 3 hours in duration. XCM races are generally longer than XCO races, with course profiles consisting of numerous technical climbs and descents. As a result, the total altitude gain during XCM races tends to be greater than that during XCO races. XCM races have fewer large fluctuations in power output but are still completed at a relatively high intensity (~80 % of maximum heart rate) which means that XCM racing also requires a well-developed oxidative and glycolytic energy system. However, the oxidative energy system has a bigger role to play in XCM racing when compared to XCO events. This often leads to the common misconception that performance in XCM will not benefit from the inclusion of high-intensity interval training (HIT). However, the ability to perform high-intensity efforts could mean the difference between breaking away on the final climb to take the win or making it home to avoid the cut-off in a stage of the Epic.

A brief summary of energy production during exercise

When riding at intensities below your threshold, energy is predominantly supplied through the process of oxidative metabolism, which takes place in the mitochondria, the little power plants within our muscle cells. Oxidative metabolism requires the use oxygen to produce energy from carbohydrates and fat. During longer endurance events, such as marathon mountain biking races, this is the primary process involved in energy production. Oxidative metabolism has a large capacity to produce energy, but it is not immediately activated and once activated, produces energy at a slower rate compared to other energy systems.

By comparison, glycolysis, which also involves breaking down glucose, or its stored form, glycogen, does so without the use of oxygen. Although energy production happens at a far greater rate when compared to oxidative metabolism, the energy yield is far less. Energy required for short intense efforts (< 2 minutes) will predominantly be produced via glycolysis. At high rates of glycolysis, lactate is pumped out of the muscle cells by specialised transporters, which results in an increase in the amount of lactate in your blood. One of the physiological adaptations to high-intensity training is an increase in the number of these ‘lactate transporters’ in our muscle cells, which allows us to clear lactate from the working muscles at a faster rate. Once in our blood, lactate can be transported to other muscles, which are working at a lower intensity, where it can be used to produce energy through oxidative metabolism.

Understanding which energy systems are involved in during a particular activity allows coaches to tailor training programmes that will ensure that the relevant energy systems are appropriately stressed. Creating sessions specific to a particular energy system will improve the functioning of that system and allow for greater energy production. Now that we know what the energy systems involved in energy production are, how do we measure/monitor them?