Research Update: Show Me the Treadmill!
Jason R. Karp
Your clients all want to make the best use of their workout time. So, how do they do that? For starters, they can choose the right equipment — not all cardio equipment is the same. Here's what the research has found.
Caloric expenditure and intensityThe first consideration when choosing cardio equipment that will allow your clients to maximize caloric expenditure is the amount of muscle mass the equipment uses. Typically, the more muscle engaged in the activity, the more calories your clients will expend — unless the activity is complex or uses both arms and legs, in which case, people may choose a lower-intensity, owing to the increased perception of effort.5 Your clients expend approximately 5 calories for every 1 liter of oxygen consumed (which varies slightly depending on how much fat and carbohydrates are used). Using more muscle mass during exercise also increases energy expenditure after exercise, as the post-exercise metabolic rate (as measured by the excess post-exercise oxygen consumption) has been found to be significantly greater and take longer to return to resting values following lower-body exercise (stationary cycling) than following upper-body exercise (arm cranking) performed at the same relative intensity.6
Weight-bearing activities are associated with a significantly greater caloric expenditure than non-weight-bearing activities,5 even when the two types of exercise are performed at the same level of intensity.1 Among weight-bearing activities, running uses more calories than most everything else, being equaled only by cross-country skiing and sports that require a lot of running, like soccer, squash, handball and racquetball.2,9 However, while these other activities use lots of muscles and expend lots of calories, they also require a high degree of skill, which limits your clients' abilities to perform the activities for long enough or at a high enough intensity to fully realize the aerobic development or energy expenditure benefits. By contrast, running requires little skill, so people are limited only by their fitness level.
A few studies have compared energy expenditure between different modes of exercise. Mier and Feito7 compared energy expenditure on the elliptical trainer between combined arm and leg exercise, and leg-only exercise. They also measured the effects of stride rate and resistance on energy expenditure at two stride rates (110 and 134 strides per minute) and three resistance settings (2, 5 and 8). When using the arms, oxygen consumption, ventilation and rating of perceived exertion (RPE) were all significantly greater than during leg-only exercise. Only heart rate (HR) was similar between combined arm and leg exercise and leg-only exercise. As expected, increases in both stride rate and resistance increased oxygen consumption, ventilation, RPE and HR, with the greatest effect on ventilation and HR occurring as resistance increased from level 5 to 8.
Hagerman, et al.,4 compared metabolic and cardiorespiratory responses in 60 men and 47 women ages 20 to 74 years at similar incremental power outputs during exercise on a rowing machine and stationary cycle. Both men and women were able to produce a higher average maximal power output during cycling than during rowing (207 vs. 195 Watts for men, and 135 vs. 126 Watts for women). However, despite these higher cycling power outputs, ventilation, oxygen consumption and HR were all significantly higher during rowing than during cycling at all similar power outputs, including maximum power output.
Comparing the rates of energy expenditure at RPE values of 11 (fairly light), 13 (somewhat hard) and 15 (hard) on the Borg scale of 6 to 20 between six indoor exercise machines — Airdyne, cross-country skiing simulator, stationary cycle, rowing machine, stair stepper and treadmill — Zeni, et al.,11 found that the treadmill induced a significantly higher rate of energy expenditure at each RPE compared to all of the other exercise equipment. Among the other equipment, the cross-country skiing simulator, rowing machine and stair stepper induced significantly higher rates of energy expenditure than the Airdyne and stationary cycle. The highest HR occurred on the treadmill and the stair stepper, and blood lactate concentration (another marker of exercise intensity) was highest on the stair stepper and rowing machine. The authors concluded that the treadmill is the optimal indoor exercise machine for enhancing energy expenditure when perceived exertion is used to establish exercise intensity.
A second study by the same researchers12 using the same six pieces of exercise equipment also showed that, for a given RPE, the treadmill induces significantly higher HRs compared to exercise on the stationary cycle and rowing machine, while cycling induces the lowest HR. The relationships of blood lactate concentration with RPE were similar among exercise modes except for the cross-country skiing simulator, which induced a lower blood lactate concentration for a given RPE, probably due to the high degree of skill of this exercise, which makes it feel more difficult than what physiological markers would suggest. Using the same RPEs of 11, 13 and 15, Moyna, et al.,8 found that men had the highest energy expenditure at each RPE on the treadmill and cross-country skiing simulator, and women had the highest energy expenditure on the treadmill, skiing simulator and rowing machine. For both men and women, energy expenditure at all RPEs was lowest on the aerobic rider and stationary cycle. Using an RPE of 14, Thomas, et al.,10 also found that oxygen consumption was significantly higher during treadmill running than during stationary skiing, shuffle skiing, stair stepping, stationary cycling and stationary rowing.
Allowing subjects to select their own exercise intensity, as people normally do in the gym, Kravitz, et al.,5 compared oxygen consumption during treadmill running, stationary cycling, cross-country skiing on a NordicTrack and aerobic riding on a HealthRider. Treadmill running produced the greatest total oxygen consumption and caloric expenditure, followed by cross-country skiing, stationary cycling and aerobic riding, despite similar RPEs between exercise modes. Heart rate was similar during treadmill running and cross-country skiing, but was lower during cycling and aerobic riding.
The authors suggest that individuals who can perform weight-bearing exercise will self-select a higher exercise intensity on the treadmill, thus providing themselves with a greater cardiovascular training stimulus and expending more calories compared to other exercise equipment. Given the well-known fact that treadmill running elicits a higher maximum oxygen consumption (VO2max) than cycling in non-specifically trained people,10 exercising at the same relative intensity (percent VO2max) for the two modes of exercise represents a greater oxygen consumption on the treadmill than on the cycle, and, therefore, is a greater calorie-expending workout.
Bone/joint healthWeight-bearing exercise is also good for the bones. Athletes who participate in sports involving running and jumping — soccer, running, basketball, volleyball — have greater bone mineral density compared to non-active people, and even compared to athletes in non-impact sports, such as swimming, cycling, cross-country skiing and rowing. However, along with the benefit to bones comes the greater risk of injury to them, as weight-bearing exercise is more likely to incur bone injuries, such as shin splints (medial tibial stress syndrome) and stress fractures. The major benefit of non-weight-bearing exercises like cycling and swimming is less trauma to the muscles and joints, which allows clients to exercise for longer periods of time and at higher levels of intensity. However, while many people complain that running is hard on their knees, running does not increase the risk of joint injury or osteoarthritis for healthy people, as there is no greater incidence of joint degeneration in people who run compared to people who don't run. Indeed, running may even have a protective effect against joint degeneration.3
Choosing the right cardio equipmentTaking together the research on caloric expenditure and the amount of skill needed to acquire a cardiovascular and caloric benefit, the treadmill would have to be considered the best piece of cardio equipment, followed by the cross-country skiing machine (e.g., NordicTrack), rowing machine, stair stepper and stationary cycle. So, next time one of your clients asks which piece of cardio equipment is best, tell him or her to choose equipment that uses a lot of muscle mass, is weight-bearing and has a low skill level so he or she can get more out of the activity. And, if they choose the treadmill, they'll not only expend more calories and become fit, they may even become as biased as I am.
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Ithaca College Athletics and Events Center