I am an Ironman triathlete and an exercise physiologist. I have two questions for you:
1) Id like your comments on the best method to measure cardiorespiratory variables so I can establish training guidelines for running and cycling. Do you think that cardiorespiratory variables measured during a treadmill test can be used to establish a heart-rate orientated training program for a cyclist and visa-versa?
2) What is the more important indicator of aerobic capacity, VO2 max or percentage of VO2 max, that an athlete can sustain during exercise?
Thanks,
Tina Cross
Salt Lake City, Utah
Dear Tina,
Ill address your queries in order:
1) Maximal oxygen uptake/consumption (VO2 max) is generally accepted to be the best indicator of endurance performance capacity. Consequently, this variable is frequently used to determine training intensities in numerous endurance sports.
VO2 max is assumed to be highly dependent upon the mode of testing, with the highest values normally attained during treadmill running. Therefore, to optimize the effectiveness of a training program, training activities need some specificity with regard to mode, duration and intensity.
Training effects also appear to be specific to the mode of training used by an athlete; therefore, differences between testing modes vary with training. Due to this specific adaptation, runners are generally tested on a treadmill and cyclists are tested on a cycle ergometer.
Triathletes, however, engage in three aerobic modes of exercise, each using different muscle groups. Consequently, to take into account testing mode specificity, triathletes are usually tested with three different trial types to monitor their training program.
It has been suggested, however, that a cross-training effect develops when a high volume of training is performed regularly with different modes of exercise. If this effect is real, then it may be possible to monitor various training activities with a single indicator of work intensity and avoid multiple testing sessions.
Numerous studies have shown that heart rate (HR) and oxygen consumption (VO2) are strongly correlated in cycling, as well as in running. Since the availability of HR monitors has increased, HR is now the variable of choice in controlling work intensity during training.
It has also been suggested that in trained endurance athletes, HR values would be similar in different exercise modalities when exercise intensities are equivalent. Comparisons between exercise tests or between laboratory and field tests have been conducted since the dawn of exercise physiology and have been the topic of numerous publications. Such comparisons generally used similar protocols or those that generated similar physiological responses.
Nagel et al. (Med Sci Sports Exerc; 3:149-154, 1971), for example, compared the VO2 requirements of gradual treadmill, cycle ergometer and step-device tests at seven different workloads. Even though the protocols of that study were very similar from one test mode to another, the VO2 results presented once per minute showed small but significant differences between tests.
These results, along with those from similar studies, have revealed that adaptation in an exercise test appears to be specific to the mode of testing.
In my experience with testing elite triathletes, HR does vary with the mode of exercise chosen. In particular, HR at the anaerobic threshold (AT), and not at maximum HR, differs between running and cycling. These athletes tend to have an AT of approximately five to eight beats per minute higher when running as compared to cycling.
Therefore, my advice is to test yourself and your athletes in a sports-specific exercise test. This will allow you to analyze cardiopulmonary variables for a sport-specific HR orientated training program.
2) This is a question I would like to expand on in a future Speedlab column. Saltin and colleagues (Res Quart Exerc Sport; 67: 1-10) showed that black runners were able to run substantially faster at all distances beyond 5K despite VO2 max values that were the same as those of white middle-distance runners.
These researchers suggested that the black runners were able to sustain a substantially higher proportion of their VO2 max when racing. Thus, the crucial finding was that the black distance runners had superior fatigue resistance, not a higher VO2 max.
Interestingly, physiologists have known for at least two decades that the percentage of VO2 max that athletes can sustain during exercise is an important predictor of performance (Costill et al; Med Sci Sports Exerc; 5: 248-52, 1973). Yet we have perhaps failed to emphasize that this is likely to be a more important determinant of performance in prolonged exercise than VO2 max alone.
Furthermore, it has not been fully appreciated that the percentage of VO2 max sustained during exercise is a measure of the athletes resistance to fatigue.
More support for this explanation can be surmised from the fact that these athletes ran at 100 percent or greater of their VO2 max in race distances of 1 to 2k. Yet it is not at those distances that the Kenyans dominance is most apparent. If the Kenyans success was due to their unusually high VO2 max values, one would expect Kenyans also to be dominant at race distances of 800 meters to the mile, which is not the case.
In addition, it has been suggested that improvement in running economy is perhaps the most likely response to training, especially among those who are already well-trained. This adaptation allows the better-trained athlete to run faster at the same oxygen consumption than the less-trained athlete.