Preparing To Race At Altitude: Ultra X Mexico 2019

Written By Marina Ranger

Marina Ranger is a GB Age Group Triathlete, ultra runner, and all-round endurance challenge enthusiast. In 2016, she ran 500km in 5 days to raise money for the Pink Ribbon Foundation. Marina has also completed several Ultra X events, including winning the inaugural Ultra X Mexico in 2019.

2 December 2019


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Marina Ranger (First female finisher at Ultra X Mexico 2019) writes about her experience at The Altitude Centre in preparing for the race.

I knew when signing up for Ultra X Mexico it would be the toughest multi-stage ultra I have done to date. Mexico was my sixth; and I knew my next one had to be a step up from the rest, something that would seriously challenge me and force me to break new boundaries.

Much of Mexico was unknown territory for me, namely the altitude and elevation. The race started at 2,300m above sea level and over the course of 250km, we had to climb 12,000m. While I have experience in single stage mountain ultras, Mexico is doing this every day, for five consecutive days, which is something I have never put my body through. Given this, I knew I had to adapt my training to focus on the conditions I had the least experience and confidence in, appreciating these would be the variables that would be the largest factor in affecting my running ability.

Replicating the conditions of a race is an approach I take in training for any race. Living in London provides barriers to both training with elevation and altitude as it is at sea level and pancake flat. However, we are lucky enough in this day and age to have everything at the tip of our fingers, including an altitude chamber where people train to experience a harder workout as they are essentially starved of oxygen.

This chamber is in the Altitude Centre by Bank tube station and is a huge factor behind why I had the race of a lifetime finishing as first lady in Ultra X Mexico’s first edition of the race. The Altitude Centre is a training room/chamber that has reduced oxygen levels to replicate an altitude of 2,700m above sea level with treadmills, bikes, mats and a couple of rowing machines.

At sea level, oxygen content is 20.9% and at 2,700m above sea level this reduces to 15% oxygen. At altitude, given the lower oxygen levels, your body has to work harder to deliver oxygen to the muscles, because there is less of it. Your body’s ability to deliver oxygen to the muscles at altitude can be measured through your blood oxygen saturation levels (spO2). spO2 can be considered as the percentage of your red blood cells that are saturated with oxygen. As you exercise, spO2 generally falls as you begin to utilise more oxygen and even more so when at altitude.

Before I started training at the Altitude Centre, I had an altitude test to be used for a comparison against the same test at the end of the programme. The test consisted of base line health checks including; resting heart rate, blood pressure, breathing reflex and lung function followed by a treadmill set (below) at sea level and then at 2,700m above sea level. During the treadmill set they measure your heart rate and spO2 levels at each interval and compare the two to see how your body reacts to being at altitude.

Treadmill ramp test set:
2 mins @ 1% incline
2 mins @ 2% incline
2 mins @ 3% incline
2 mins @ 4% incline
2 mins @ 5% incline
2 mins @ 6% incline
Total time: 12 mins
Speed for both tests: 10.5km/hr (this can increase/decrease depending on individual ability)

My results indicated I was average at adapting to the lower oxygen levels. My spO2 levels decreased by 14%! Additionally, my heart rate was on average 7 beats faster per minute at altitude, with the largest difference being 12 beats per minute faster. Based on these findings, I knew the intermittent hypoxic exposure of training at altitude would help align my physiology with what it was at sea level and hence improve my performance in Mexico.

I signed up to their 6-week programme, which includes 15 sessions and 5 pod sessions (I will explain what these are later). This worked out at 2 sessions per week up until the last few weeks before the race where I increased this to 3 in addition to the 5 pod sessions.

They hold classes so the majority of my sessions were spin or run classes inside the chamber, which was great for motivation. The classes have been designed by the sports scientists at the centre and are a variety of high intensity sets to improve VO2 Max. They’ve got watt bikes, which is a huge winner for me. I can’t stand spin classes without meters and hence any gauge of how far you’ve gone or how your power compares to your last session! The readings get uploaded to their online portal at the end of each session so you can really see how you’re performing and improving week on week.

Each class I did was different so it never became comfortable and always pushed me enough to feel super satisfied at the end of each class. Plus, the instructors are really fantastic; great energy, so friendly and push you the perfect amount to keep breaking those barriers. In addition to the classes, I did a few self-made sessions on the treadmill at incline. These treadmills go up to 20% incline!! Couldn’t have been more perfect for my hill training!

The pod sessions require no exercise as you simply sit down for an hour with a mask on and off your face in 5-minute intervals for one hour. This technique is called Intermittent Hypoxic Exposure where you breathe in short bursts of mountain air, alternated with normal air to help you adapt to low oxygen levels even quicker. Each subsequent session is at a higher altitude than the last. My first session started at 3,500m and by the fifth I was at 5,438m. They go up to over 8,000m but there was no need for me to go much further as the race was only at 2,500m.

Throughout the six weeks I felt I was getting noticeably fitter as my pace was dropping for the same rate of perceived exertion. For example, on a steady 10km run, my pace was 30 seconds faster per km. I’ve genuinely never had such quick and significant improvements in my running speed in all my seven years of running. At the end of my programme, the week before I flew to Mexico, I repeated the same health tests and treadmill ramp test that I did before I started training at the Altitude Centre. Not only did it feel better but my results significantly improved!

Most impressively, my heart rate only increased by 1 beat per minute on average throughout the whole test. That indicated that I would be better at dealing with the added physical demands of altitude in Mexico. A lower heart rate also improves efficiency, meaning I could sustain my energy for longer. My blood oxygen saturation (spO2) levels also improved, indicating my body had more oxygen to work with at altitude and was therefore better at getting oxygen to the blood at altitude. The below table explains the difference in my treadmill ramp test results between the initial test at the start of my 6 week programme and the test just before I left for Mexico.

Pre / Post Test Results Comparison
Heart rate (average difference between sea level and altitude)7 bpm1 bpm-5 bpm
Heart rate (maximum difference between sea level and altitude)12 bpm3 bpm-9 bpm
Blood oxygen saturation (average difference between sea level and altitude)-14%-10%4%
Blood oxygen saturation (maximum difference between sea level and altitude)-15%-10%5%

While I am a sucker for hard data, beyond figures, I value ‘feel’ just as importantly, so despite the positive results, I hate to get complacent and always leave an element of doubt in the back of my mind as a buffer in case on race day I don’t feel on good form. Luckily, I didn’t end up needing this buffer as I felt really strong and able to perform at a high standard against my initial expectations and also the rest of the field.

I felt fully confident in my ability to get through the race and in good time soon into day one, so I knew early on I would be in for a good week of racing. This confidence boost enabled me to enjoy the experience even more because even without having reached the finish line, I felt a sense of self-satisfaction in knowing I had prepared well in my training.

And it was just as well I felt this good because it was relentlessly brutal. Every day brought a new challenge, whether that be the technical trails, heat, endless climbing, loose rock, thin air or steep and dangerous descents. It is the first multi stage race out of the six I’ve done where I’ve stood on the start line each day in pain from the day before. It’s also the most varied race I have done, with almost all of the varying factors bringing their own element of a personal battle to the experience.

It’s a beast of a race and in my opinion needs substantial preparation for. Obviously, the result of a race can’t be put down to one element, it is a combination of many. However, as I mentioned at the beginning, I truly believe that having this exposure to training at altitude was a major reason why I had such a good race and hence an even more incredible experience running in Ultra X Mexico.  


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