Jan 29, 2015Altitude Adjustment
Much has been written about the benefits of the live-high, train-low principle. The U.S. Air Force Academy is putting the idea into practice with a special training program.
By Dr. Michael Zupan
Michael Zupan, PhD, is an exercise/aerospace physiologist and Director of the Human Performance Lab at the United States Air Force Academy. He has more than 27 years of expertise in training high school, collegiate, and professional athletes as well as teaching and conducting research. He can be reached at: [email protected].
There are many benefits to being a student-athlete at the United States Air Force Academy (USAFA) in Colorado Springs, Colo. One of them is living at an elevation of 7,200 feet, which allows the athletes to reap the physiological advantages of living and training at moderate altitude.
Of course, you rarely get something for nothing in aerobic training. While many athletes and coaches are aware of the plusses that come from training at moderate altitude, there are also drawbacks, the most significant of which is a decrease in the maximal level of training intensity. To help our athletes reach their full potential, we needed to develop a training system that allows them to obtain the rewards of living at moderate altitude while counteracting some of the negative effects. This kind of balancing act is nothing new for strength coaches, who are used to working athletes hard but not too hard, and ensuring proper recovery while maintaining heavy workloads. However, in our case, finding the right balance for our athletes meant changing the very air they breathe.
The solution we found is still a work in progress, but we’re excited about the results so far. For any school at an elevation of 5,000 feet or above, understanding what we are doing at the USAFA may be helpful.
The performance benefits of training at moderate and high altitudes are well known in athletic circles. Training at altitude started during the lead up to the 1968 Olympic Games in Mexico City, which sits at an elevation of 7,350 feet. At that time, the thought was to train at the same altitude the competition would be held at. However, research and experience have shown it’s more beneficial to do high-intensity training at lower altitudes while also taking advantage of the long-term physiological changes that come from living at moderate altitudes of 5,000 to 10,000 feet.
The positive effects of living above 5,000 feet are varied and include increased red blood cell mass and plasma volume, which allows for greater oxygen delivery to the muscles, and increased production of erythropoietin, which stimulates the production of red blood cells. In addition, altitude training ups mitochondria and aerobic enzyme concentration, which raises aerobic metabolism during exercise. Typically, it takes about 14 to 30 days of training at moderate altitude for these changes to take hold. These benefits result from the body adjusting to the decreased amount of oxygen in the air at higher altitudes. Air is composed of a mixture of several different gases, with nitrogen and oxygen accounting for 78 percent and 21 percent, respectively. This mix remains constant regardless of elevation. What does change–and is relevant to training and performance–is the air pressure. As altitude increases, air pressure decreases, meaning there is less air available for athletes to breathe in, and as a result, less oxygen.
To measure the amount of oxygen in the air, we look at the partial pressure of oxygen (ppO2). Partial pressure describes the density of a specific gas in a given volume of air and is determined by multiplying the percentage of a gas present by the atmospheric pressure. At sea level, the atmospheric pressure is approximately 760 millimeters of mercury (mmHg). This results in a ppO2 of 160 mmHg (760 mmHg X 0.21). However, at the Academy, the atmospheric pressure drops to approximately 590 mmHg, decreasing ppO2 to 124 mmHg (590 mmHg X 0.21). The reduced ppO2 means there is less oxygen available for the athlete to use, creating a drop in red blood cell oxygen saturation. A body’s average resting O2 saturation at sea level is normally 97 to 98 percent. When individuals spend time at altitudes of 5,000 to 10,000 feet, resting O2 saturation falls to 92 to 93 percent. This is important for athletes because O2 saturation also decreases as the intensity of exercise increases. This lower oxygen delivery means the heart must pump a greater volume of blood to the muscles in order to deliver an adequate amount of oxygen to the working tissues. Although this process helps athletes build their overall endurance, it also means they are simply not able to produce the same level of force during high-intensity workouts. Since their maximum efforts are reduced, their training gains are limited compared to athletes working at lower altitudes.
Current research into altitude training suggests that athletes gain the most from a “live high, train low” model, meaning they reside at a moderate or high altitude, but perform high-intensity workouts at lower altitudes. This way they benefit from the body’s adaptations to a lower-oxygen environment while still being able to train at maximum intensity.
Of course, there are several logistical hurdles to “live high, train low,” namely the difficulty of finding locations where athletes can quickly decrease or increase altitude, the cost of moving them from one location to another, and the time required. Instead of bringing our athletes to lower elevations for training sessions, we have addressed these problems at the Air Force Academy by recreating the conditions found at lower altitudes through hyperoxic training in our Human Performance Laboratory.
Hyperoxic training involves creating a training environment with increased oxygen levels. We started using hyperoxic training here in 2011 and have been very pleased with the results. In the hyperoxic environment, our athletes’ tissues can receive about the same amount of O2 as they would when training near sea level. Athletes benefit since they are able to push muscular efforts to the max without being limited by their cardiorespiratory system.
The hyperoxic environment also helps them recover faster between sets. This improved recovery time is crucial since a lot of our hyperoxic workouts utilize interval training, and it’s important that athletes recover quickly for their next set.
The best part is that the athletes don’t need to spend a lot of time in a hyperoxic environment to reap the benefits. Since the biggest drawback of altitude training is a reduction in athletes’ maximum efforts, the differences in oxygen levels only hinder them during high-intensity training. Most athletes at any altitude do high-intensity training only a couple of times a week because of the need to recover after such demanding sessions. By creating a hyperoxic environment for our athletes once or twice a week, they are able to match the high-intensity efforts of their counterparts at lower altitudes. But they only need the hyperoxic environment for their hard days and they can do their easy and moderate days at altitude.
MAKING IT HAPPEN
Here at the USAFA Human Performance Lab, we use a Colorado Altitude Tent (CAT) to create a hyperoxic training environment. Instead of increasing air pressure by pumping more air into a set amount of space–like an airplane does at high altitudes–the Colorado Altitude Tent raises the percentage of oxygen in the tent’s air using six air generators. The units separate the air into nitrogen and oxygen molecules, with each gas being released through different ports. We can simulate various altitudes by pumping different levels of oxygen and nitrogen into the CAT. By pumping more oxygen into the tent, we can increase the percentage of oxygen in the air to 26 percent, raising the ppO2 to 153.4 mmHg. This provides the athletes with the same amount of oxygen they would receive at 850 feet above sea level. For fire safety purposes, the air unit controllers will not allow the oxygen concentration to exceed 26 percent.
We also have two carbon dioxide scrubbers in the tent to limit the buildup of CO2. This keeps the oxygen and nitrogen levels consistent as athletes expel CO2 while exercising. Our tent is a 10’x10′ enclosure that is eight feet high. It’s constructed of an aluminum frame with plastic walls and ceiling and is easy to assemble and disassemble since the walls and ceiling are delivered in panels. In it, we place two cycle ergometers (or rowing machines) and two treadmills–one motorized, one self-powered. This allows us to train up to four athletes at a time. Numerous USAFA teams utilize the hyperoxic CAT environment based on the demands of their sport and desires of their head coach. Most teams do their hyperoxic training during the offseason since the high-intensity work can leave players wiped out and unable to complete a typical in-season sport-specific practice session. Among the teams making the most use of the tent are football (although for now we focus on linemen and running backs because of the large numbers of players involved), ice hockey, basketball, track, wrestling, soccer, swimming, and tennis. We analyze the demands of each sport and develop our hyperoxic training protocols to closely match those specific needs. For endurance athletes, including cross country runners and distance swimmers, we use the motorized treadmill or rowing machines to have them work at steady speed intervals with an increased recovery time. To get the athletes to push past their normal thresholds and tap into the benefits of high-intensity training, we usually set the treadmills one-half to one mile-per-hour faster than their normal running speed outside the hyperoxic tent. When using the rowing machine, we look at the distance they normally row on ergometers in the ambient atmosphere and increase that distance by 10 to 15 percent.
Athletes participating in anaerobic sports requiring short bursts of energy, such as football, tennis, and sprinters in track and swimming, have shorter intervals and complete a high number of total repetitions compared to endurance athletes. They also use greater resistance to better create an “all out” experience. Depending on the demands of their sport, they focus on the upper body or lower body. For upper body training, they use a rowing machine, and for lower body work, the self-powered treadmill, which has an internal braking system that can add up to 150 pounds of resistance to the belt, increasing the load the athlete has to run against. Using this treadmill is very similar to pulling a loaded sled, running with a parachute, or using bungee cords for resistance. The benefit of using the self-powered treadmill is that speed, time, and load (resistance) can be pre-programmed and monitored very closely during the workout.
The resistance on the belt and the length of each interval will vary based on sport requirements. For example, a football lineman will have 30 to 40 pounds of resistance for intervals lasting three to five seconds. A tennis player, meanwhile, will have intervals lasting 20 to 30 seconds with five to seven pounds of resistance. By tailoring the interval-training program to mirror the demands of the athlete’s sport, we increase transfer to the playing field when competing. (See “By the Numbers” below for the loads we use for various sports.)
A printout is given to the athletes and coaches following every workout allowing everyone to track each athlete’s progress. Changes to the protocols can be made as the sport coaches see fit, as long as we deem the protocol practical. Also, as the athletes improve over time, we increase running speed, load, or interval time. LOOKING AHEAD
Our experiences with hyperoxic training at the USAFA have been extremely positive. It has helped our athletes grow bigger, stronger, and faster, and our coaches report improved performance on the playing field.
The one major drawback with our system is the limited number of athletes we can train. Only four athletes can use the tent at one time and each workout session takes about 20 to 30 minutes. This means a team of 20 athletes requires about two hours of tent use. It would be nice to have a larger system so we could train more athletes each day. But for now, we’ll focus on what we have and keep helping our athletes make sure they benefit from living high and training low.