What's Cool In Road Cycling

Toolbox: Timing Arrival at Altitude

The hot trend in elite athletics the past decade has been the use of altitude training and hypoxic tents to improve aerobic capacity and performance. The converse question is also intriguing – if you are competing at altitude, when is the best time to arrive at altitude?

Altitude History
The bulk of altitude physiology research in sport science has focused on using altitude training or hypoxic (low oxygen) exposure as an ergogenic tool. The real watershed event that sparked all this research happened the year I was born, way back in 1968. That year, the Summer Olympics took place at Mexico City, at 2240 m above sea level.

Back in the 1960s, very little was known about how the body responds to altitude or reduced pressures and oxygen content. In the beginnings of manned space flight, scientists weren’t even sure whether humans could survive, let alone function, in a space capsule. This led the original Mercury and Soviet flights to be almost automatic joyrides for the astronauts, with everything controlled on the ground. Similarly, very little was known about how athletes would fare in the rarefied atmosphere in Mexico City, spurring a great deal of initial and groundbreaking work in the field.

Basic Altitude Physiology
First, a reminder, air at altitude has the exact same composition (20.93% oxygen) as at sea level. The difference is in the lower total atmospheric pressure, such that each litre of air we breathe in has fewer molecules of oxygen. This is what generally causes aerobic capacity to decrease at altitude – we may still suck in 100 L, but there’s less oxygen getting into our lungs and bloodstream.

The flip side of this is the advantage of having fewer molecules hanging about in the air – lower wind resistance – the holy grail of aerodynamics. The allure of having a significant reduction in wind resistance is the reason why many world record attempts, including Eddy Merckx’s classic 1974 hour record (Mexico City) and Chris Hoy’s recent attempt on the Kilo record, are located at altitude. In Hoy’s case, the altitude in Bolivia was about 3500 m, a rather “astronomical” location!

When to Get High?
The tricky question when competing at altitude, especially for athletes living in lower elevations, comes down to this – should I get to altitude as long as possible beforehand to acclimatize, and possibly suffer the consequences of lower training capacity and fitness, or should I attempt a “commando mission” approach and arrive at altitude as close to competition time as possible?

The timing of arrival at altitude was the question posed by a 2001 study in the prestigious journal Medicine and Science in Sports and Exercise by researchers from South Africa and Australia. In this study, fifteen young (16 years on average) male rugby players were tested on a variety of tests at sea level, and then transported up to a test centre at 1700 m altitude, where they underwent testing again at 6h, 18h, and 47h after ascent. The study therefore also provided information on the time course of performance upon the first few days of altitude exposure.

Basic Methodology:
• All subjects were sea-level residents with no altitude experience for at least 3 months before testing.

• The controls performed in the study are pretty good. Subjects were thoroughly familiarized with the testing, then performed two complete tests at sea level to obtain baseline data. Lab temperatures were controlled and consistent at both sea-level and altitude (21oC). No other activity was performed by the subjects to remove confounding effects of training or fatigue.

• The circadian rhythm effects were controlled by the timing of ascent and testing, with the timing of ascent simulating typical arrival times for a 3 pm competition. For example, the 6h trial simulated arriving at altitude at 9 am for a 3 pm event, and the 47 h trial simulating arrival at 10 pm two nights before the event.

• Tests conducted were chosen to be easy and quick to enable mass testing of a large number of athletes. This included: a) a Shuttle Run test to determine maximal aerobic capacity, b) a 5 min submaximal cycling test at a set (100-200 W) workload intended to push heart rates up to near max, and 3) a repeated pushup test (23 done at a rate of 1 every 2 s). Hematocrit and hemoglobin was also measured at each test. The tests can be criticized for being pretty “tame,” but we are talking about young boys here and also trying to run fifteen subjects through quickly and simply.

Study Results
• For this study population, the testing was NOT too easy, with a fair number of subjects unable to complete the workload at altitude.

• Heart rates were significantly higher during the submaximal cycle test at 6h compared with sea level (182 vs 177 beats per min), but returned to “normal” at 18 and 47 h (177 and 176, respectively). Only five subjects could complete the full 5 min at the 6h trial compared to nine at sea level.

• The same pattern in heart rates were found for the four trials with the shuttle run aerobic capacity test. The tolerance time for the shuttle test was 37% shorter at 6h compared to sea level. While it improved with the 18 and 47h test, they both remained lower than at sea level.

• No changes were observed in either hemoglobin or hematocrit with any of the four tests.

Current practice or advice given to athletes to date suggests that a commando mission approach may be a good method for avoiding the problems with initial exposure to altitude. The results of this study leads to the exact opposite conclusion, namely that athletes should try to arrive as early as possible to the competition altitude to give their bodies time to acclimatize to the hypoxia. Fortunately, even if logistics preclude early travel, the popularity of hypoxic tents among elite athletes is making adaptation easier to achieve. Specifically, athletes can set their hypoxic exposure to match what would be expected at the competition venue, performing a “live high train low” program to maintain maximal fitness. In addition, testing can be performed at the competition altitude to determine when the athlete is truly “ready.”

However, this “remote” acclimatization still carries some problems, namely the potential problems from jet lag if you adapt at home and then have to cross many time zones to compete.

Finally, as a closing note, a similar question is now being asked by athletes in preparation for the Beijing Olympics, with its threat of rampant air pollution. Go early and acclimatize, or get in and get out? The thought of sitting at home deliberately breathing in pollutants to get adapted is not terribly appealing!

Weston, AR, G. MacKenzie, M.A. Tufts, and M. Mars. Optimal time of arrival for performance at moderate altitude (1700 m). Med Sci Sports Exerc 33: 298-302.

About Stephen:
Stephen Cheung is a Canada Research Chair in Kinesiology at Brock University, with a research specialization in the effects of thermal stress on human physiology and performance. He can be reached for comments at [email protected].

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