Posted: February 17, 2006

Athletics: Aerobic Capacity Training: Maxing the VO2

© 2003 by Ken Mierke

Maximal aerobic capacity or VO2 Max, the amount of oxygen consumed in one minute of maximal aerobic exercise, is widely considered the standard test for aerobic conditioning. Improving VO2 Max is a crucial step in maximizing endurance performance in any event lasting four minutes or longer. The higher an athlete’s VO2 Max, the greater the contribution of the aerobic system to energy production. This translates into greater endurance at any intensity. Each muscle fiber type has both aerobic and anaerobic capabilities. Endurance fibers are mostly aerobic but do have some anaerobic metabolism. Speed-endurance fibers are more balanced. Sprint fibers are mostly anaerobic, but their limited aerobic abilities can still be important in racing. Aerobic capacity workouts improve the aerobic capabilities of the sprint muscle fibers. Stimulating these adaptations requires maintaining an intensity that is high enough to demand recruitment of the sprint fibers, but low enough to enable the athlete to sustain the intensity for a duration that will stimulate aerobic adaptations in those fibers, instead of only anaerobic adaptations.

Aerobic Capacity Intensity To improve aerobic capacity in a well-trained athlete, training should take place at about 95% of VO2 Max. While the results of a VO2 Max test can be useful in pinpointing optimal training pace for aerobic capacity training, research shows that field testing determines optimal intensity very effectively.

Since field testing incorporates psychological as well as physiological variables, and since it is more practical, that method is used most frequently. Perform a time trial of six to eight minutes. Make sure the athlete is well rested before the time trial. Monitor speed or wattage and heart rate during the test. The highest intensity that can be sustained for six minutes produces optimal results for aerobic capacity workouts. We refer to this as six minute time trial pace (TT6) for running or critical power 6 (CP6) for cycling.

The intensity (heart-rate and/or speed) determined by the field test is how fast all aerobic capacity workouts should be conducted. It is not correct to go faster when performing shorter intervals or repetitions and it is not correct that intervals should be performed as fast as possible for this type of training. Training beyond the optimal intensity has no additional benefit to the aerobic system, yet comes at a great cost in terms of the body’s recovery resources. Energy to increase output above 6-minte race pace is derived almost 100% from anaerobic sources and therefore will not increase aerobic capacity. When in doubt, err on the conservative side with aerobic capacity training. It can be a powerful tool, but a little bit goes a long way. The pace determined by your field test could feel too easy for several reasons. You could have improved conditioning or economy since your last test. You could have used less than full effort in the test. Or you could be accustomed to performing workouts too fast for an endurance athlete. Before you increase your interval pace, prove that you need it with a faster field test.

Duration and Work/Rest

To increase aerobic capacity, an athlete needs to spend considerable time performing near maximal oxygen consumption. Raising exercising VO2 involves both an intensity component and a duration component. Even when performing at a very high intensity, it takes one minute and forty seconds to two minutes to elevate oxygen consumption to the levels necessary to optimally increase aerobic capacity. So, performing six sets of two minutes at aerobic capacity pace and twelve minutes near max VO2 are quite different. There are two ways to maintain oxygen consumption near VO2 Max for extended durations in a workout: repeat training and interval training.

Repeat training involves relatively long repetitions with basically full recovery between sets. Since approximately two minutes are required to optimally elevate VO2, repeats need to be considerably longer than two minutes. In a sense, the benefits are only starting at the two minute point, when oxygen consumption has climbed to near maximal levels.

One workout using repetition training would be four repetitions of four minutes each at TT6 pace or CP6 wattage. Obviously this is an extremely taxing workout. Since each repetition yields about two minutes performing near maximal aerobic capacity, this workout will provide about eight minutes near max VO2. This type of workout should be used primarily during late Build and Peak periods. It is also effective in developing lactate tolerance and in preparing an athlete psychologically for the demands of racing. Be conservative with this training because it is extremely costly to the athlete both physically and psychologically.

A second way of maintaining elevated VO2 for extended periods is interval training. Performing shorter repetitions at the same intensity (TT6 or CP6), but minimizing recovery between repetitions leads to increasing VO2 throughout the set. Reducing the recovery causes the athlete to begin each repetition at a higher VO2 than the previous repetition, so that through most of the set the desired near-maximal oxygen consumption is attained much earlier in each repetition. In the example in the previous paragraph, the athlete performed at TT6 pace or CP6 wattage for twenty minutes but only about half of that time was spent near max VO2. An athlete performing a set of short-rest intervals may keep VO2 elevated for a much greater percentage of the set duration.

Be careful not to perform at a higher intensity during shorter intervals. Going above TT6 or CP6 will not increase aerobic gains, but will increase the recovery cost dramatically. The classic aerobic capacity set is five sets of three minutes at TT6 pace or CP6 wattage with a three minute recovery. This is a hard workout that needs to be built up to.

Another very effective aerobic capacity workout is called 30/30s. This workout involves 30 second repetitions at TT6 pace or CP6 wattage with 30 second recoveries between each repetition. This is an extremely efficient workout. The benefits are extremely high and aerobic capacity and high-speed endurance may be increased dramatically, but the cost of the workout (recovery cost and psychological cost) is relatively low since acid doesn’t accumulate to a great degree because of the short repetition duration and the acid can be recycled during the recovery periods.

As repetitions get longer, work-to-rest ratio must increase. Even with a short work repetition, such as 30 seconds, 30 seconds of recovery is not enough time for a huge drop-off in VO2. With a longer, say two minute, repetition duration, a 1:1 work-to-rest is not great enough. I generally limit interval recovery to about a minute between repetitions and consider anything over a minute to be almost full recovery. Even after a hard repetition, oxygen consumption decreases dramatically with significantly more than a minute recovery and the next repetition will require the full two minutes to elevate to near max.

Another effective workout that combines lactate threshold training and aerobic capacity training involves running a segment at LT followed immediately by a segment at TT6 pace or CP6 wattage. This type of workout is effective because oxygen consumption is already considerably elevated at the beginning of the TT6 or CP6 repetition, so the athlete reaches the near-max oxygen consumption much more quickly than when starting from rest or from basic endurance pace.

Begin aerobic capacity training conservatively. It will probably be a significant increase in intensity for most athletes. I recommend starting with short-rest intervals, like 30/30s, for about 8-12 minutes of “on” time and building volume slowly, but consistently. Gradually shift to sets with longer repetitions. Monitor your recovery response carefully because it varies considerably between individuals. Many athletes, even those who tolerate high training volume very well, break down easily with aerobic capacity training.

Ken Mierke, head coach of Fitness Concepts (www.Fitness-Concepts.com) is Director of Training for Joe Friel’s Ultrafit and author of Training for Time Trials (due out 2006) and Training for Triathlon Running. Ken can be contacted at CoachKen@erols.com.