The importance of cardiorespiratory fitness cannot be understated, but currently this is an abundance of literature that investigates traditional aerobic exercise (running, cycling, swimming, etc..) with little focus on potential cardiorespiratory benefits that may come from resistance training. While initially thought to provide no cardiorespiratory benefits due to the long rest periods, there are now more methods being used such as circuit training which may have potential benefits on cardiorespiratory fitness.
Review of major Findings
For traditional resistance training, there does not seem to be substantial contributions to the cardiorespiratory system due to the relatively short work periods and long rest periods, however upon comparison between aerobic and resistance training it has been shown that resistance training increases blood flow when compared to aerobic exercise (2). This would suggest that there may be benefits to cardiorespiratory fitness if training is manipulated accordingly. Ratamess et al. found that mean oxygen consumption (VO2) and ventilation (VE) are inversely related to the rest interval (RI) length, with the greatest VO2 measures seen with RI of less than one minute. When RI was three minutes or greater the benefits of increased oxygen consumption were no longer seen (7). However, with the shortened rest periods, the load had to be lowered each set so that each group (high and moderate intensity) could still hit their goal of 5 and 10 reps per set. This loss of force output would immediately dictate whether to use this method depending on the goal of the session and whether strength or muscular endurance/aerobic capacity are what is being trained.
In a separate study, Alcaraz et al. looked at the relationship of bar speed in the bench press when done in a traditional training protocol and also during a circuit training protocol and the effects that these two training protocols would have on the cardiovascular demands of the individual. What they found was that there was no difference in bar velocity or power despite the circuit training protocol having two lower body exercises substituted for the passive rest period of the traditional training protocol (1). Despite there being no differences in performance, the cardiovascular load was much greater in the circuit training protocol with a higher average heart rate during exercise and rest. This suggests that resistance training circuit protocols can be a viable training method to increase cardiorespiratory fitness.
In another study, Mukaimoto et al. studied the oxygen consumption of three different circuit resistant training (CRT) protocols; a high intensity (80% 1RM) with normal movement, low intensity (50% 1RM) with normal movement, and a low intensity (50% 1RM) with slow movement group. What they found is that the low intensity group with slow movement had a greater total VO2 consumption and energy expenditure, despite a lower average VO2, due primarily to the fact that the total exercising time was much greater than the other two groups. They also found that the blood lactate levels were lower in this group which would suggest that the slow movement training had a greater aerobic component when compared to the same load at normal movement speeds (5). It should be noted that in each of the three groups, the average VO2 for the training session did not reach 50% of VO2Max and thus may not be a suitable stimulus to increase cardiorespiratory function. This may have been due to the fact that all exercises were done on nautilus gym equipment and used only a small amount of muscle groups per exercise. In a study by Gotshalk et al. they investigated the cardiorespiratory responses to a CRT protocol. They found that VO2 was elevated above 50% of maximum indicating that this low intensity (40% 1RM) six exercise circuit could be used to increase cardiorespiratory fitness, possibly as a cross training option or when traditional aerobic exercise isn’t done. A second finding from this paper showed that during resistance exercise, heart rate and VO2 do not increase at the same rate as during aerobic exercise (4), with heart rate reaching above 80% of maximum while VO2 hovers over 50%, thus basing resistance training prescriptions off of heart rate is not a viable option until further research is done. Similarly, Ortego et al. found that there may be gender differences in regard to oxygen consumption during resistance training as they found that women had lower absolute VO2 levels during exercise while having similar heart rate measures (6). This further complicates the issue of prescribing resistance training for increasing cardiorespiratory fitness as sex, and fitness level may be factors that effect if adaptations are possible.
Another factor that may affect oxygen consumption and potential for increases in cardiorespiratory fitness is the exercise type. In a study done by Farrar et al., they measured the oxygen cost of a 12-minute kettlebell swing test. What they found was that average relative VO2 was 65% for the test and heart rate was 87% of maximum (3). At a closer glance, VO2 and HR both rose dramatically within the first minute of exercise and then plateaued for the rest of the 12 minute test after the second minute. These results show that kettlebell swings are a sort of middle ground between traditional aerobic exercise and circuit resistance training. At first glance this shouldn’t make sense, however differences between kettlebell swings and the majority of exercises used in CRT do exist. First, kettlebell swings are full body exercises which is the most obvious difference between exercises selected. Secondly, many exercises selected for CRT protocols have defined concentric-eccentric phases which are typically done in a controlled steady rate. Kettlebell swings however, can be argued as a ballistic exercise which alters the dynamics of the concentric and eccentric muscle actions, which may provide more cardiorespiratory benefits when compared to traditional resistance training and what has commonly been studied in the circuit training protocols.
While there is limited research regarding the cardiorespiratory benefits of resistance training, there is evidence to suggest that circuit resistance training protocls can invoke a cardiorespiratory response which could be greater depending on the speed of contraction and also the amount of rest allowed between exercises and sets. In addition, it seems that dynamic resistance training may provide the most benefits to cardiorespiratory fitness as this shortens the concentric muscle action which would allow for more blood flow to pass through the muscle tissue, however this type of training hasn’t been investigated fully and needs to be looked into more, along with what intensity level (%RM) may elicit the greatest oxygen consumption.
1. Alcaraz, PE., Sanchez-Lorente, J., and Blazevich, AJ. Physical Performance to an Acute Bout of Heavy Resistance Circuit Training Versus Traditional Strength Training. Journal of Strength and Conditioning Research 22: 667-671, 2008.
2. Collier, SR., Kanaley, JA., Carhart, R., Frechette, V., Tobin, MM., Hall, AK., Luckenbaug, AN., and Fernhall, B. Effect of 4 Weeks of Aerobic or Resistance Exercise Training on Arterial Stiffness, Blood Flow and Blood Pressure in pre- and stage-1 hypertensives. Journal of Human Hypertension 22: 678-686, 2008.
3. Farrar, RE., Mayhew, JL., and Koch, AJ. Oxygen Cost of Kettlebell Swings. Journal of Strength and Conditioning Research 24: 1034-1036, 2010.
4. Gotshalk, LA., Berger, RA., and Kraemer, WJ. Cardiovascular Responses to a High-Volume Continuous Circuit Resistance Training Protocol. Journal of Strength and Conditioning Research 18: 760-764, 2004.
5. Mukaimoto, T., and Ohno, M. Effects of Circuit Low-Intensity Resistance Exercise with Slow Movement on Oxygen Consumption During and After Exercise. Journal of Sports Sciences 30: 79-90, 2012.
6. Ortego, AR., Dantzler, DK., Zaloudek, A., Tanner, J., Khan, T., Panwar, R., Hollander, DB., and Kraemer, RR. Effects of Gender on Physiological Responses to Strenuous Circuit Resistance Exercise and Recovery. Journal of Strength and Conditioning Research, 23: 932-938, 2009.
7. Ratamess, NA., Falvo, MJ., Mangine, GT., Hoffman, JR., Faigenbaum. AD., and Kang, J. The Effect of Rest Interval Length on Metabolic Responses to the Bench Press Exercise. Eur J Appl Physiol 100: 1-17, 2007.