While examining the effects of the Body Pump workout (an aerobic workout utilizing barbells as resistance), Stanforth et al. (2000) found that subjects worked at an average of29% ofVOzmax and 63% ofHRmax. Subjects burned 265 calories over the 45-60 minute workout. Olson et al. (1991) studied the effects of bench stepping exercise in females and found that the use of two pound hand weights during exercise significantly increased VOz, caloric expenditure, and ratings of perceived exertion (RPE), even when compared to the use of one pound hand weights. They also found that upper body exercise elicited higher HR and lower stroke volume values than leg exercise at the same VOz. These differences relate to a phenomenon called the "pressor response."
Porcari and Curtis (1996) reviewed the pressor response, a concept that results in a disproportionately elevated HR When compared to oxygen consumption during resistance training. The pressor response phenomenon is made up of three key components.
First, this response activates areas o f the brain that control cardiovascular function by attempting to have HR and blood pressures match the number of electrical impulses received by the working muscles. Second, muscular contraction causes compression of the blood vessels that lead to the working muscle, inhibiting fresh blood from reaching the tissue beds while also not allowing waste products to be removed the working areas. This results in HR and blood pressure being regulated by a nervous reflex that doesn't necessarily meet the metabolic needs of the muscle. Third, vasoconstriction also occurs in the non-working muscles in an attempt to redirect blood
to the working muscles. This reduces the heart's stroke volume and increases HR.
RESULTS
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Maxiimal HR and VOz values were compared for the maximal treadmill and kettlebeII VOzmax tests. A significant difference was found value between the VOzmax ofthe treadmill test and the kettlebeII VOzmax test. The treadmill VOzmax was 23% higher than the VOzmax attained during the kettlebeII VOzmax test. No significant difference was found between the maximal HRs attained during either test.
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The main purpose of this study was to determine the energy cost and relative intensity of a typical kettlebell workout. The study also aimed to quantify how the HR and V02 data obtained during the kettlebell snatch workout compared to the guidelines recommended by the ACSM for improving cardiorespiratory endurance. The ACSM (2006) recommends that healthy adults exercise at an intensity of 64% - 94% of HRmax or 40% - 85% of V02max to improve aerobic capacity. The kettlebell snatch workout meets these recommendations, as HR averaged 93% of HRmax and VO2 averaged 78% of V02peak when compared to the kettlebell V02max test (63% of V02max when compared to the maximal treadmill test).
The HR and V02responses during the kettlebell snatch workout indicated a much greater intensity than other studies that incorporated weights or weight training into the workout. However, the one common thread between the studies is a significant difference between % HRmax and % V02max values. During the Body Pump workout (1991), subjects worked at only 29% of V02max, but 63% of HRmax. Similar differences were also seen in studies by Wilmore, et al. (1978) and Garbutt et al. (1994). The subjects in the study by Wilmore et al. (13) worked at 84% of HRmax and only 45% V02max during CWT. The subjects in the study by Garbutt et al. (1994) worked at 69% of HRmax and 50% of VO2max, also performing a CWT workout. The discrepancy between % of HRmax and % of VO2max to varying degrees in all ofthese studies indicates that a pressor response was occurring. Given that the difference between % HRmax and %VO2max was less for the kettlebell snatch workout than in these other studies, it would indicate that the kettlebell snatch workout is more aerobic than the training methods used in other studies. This is likely because a greater muscle mass is active during kettlebell exercise. Larger muscles mean a greater distribution of blood flow.
One primary reason for activation of the pressor response with the kettlebell snatch workout was that even though correct technique for kettlebell snatches does involve the legs, much of the work is actually accomplished using the shoulder muscles. Because ofthe heavy weights used during the workout, the muscles are likely working at a relatively higher percentage of their maximum (% maximal voluntary contraction), thus invoking a high pressor response. A higher HR at any given level ofVO2 is typically seen with arm work compared to leg work.
ACSM recommends an exercise duration of 20-60 minutes exercise in order to produce cardiorespiratory benefits. However, new guidelines published by ACSM and the American Heart Association (2007) state that 20 minutes vigorous aerobic activity is also acceptable in order to promote and maintain physical health. The kettlebell snatch workout falls within these new guidelines, asthekettlebell snatch workout would be considered vigorous exercise.
CONCLUSION
In conclusion, the kettlebell snatch workout meets the ACSM guidelines for improving cardiorespiratory endurance. The 20-minute kettlebell snatch workout also meets ACSM and AHA recommendations for exercise intensity as it is considered vigorous intensity. However, the high HRs reached during the workout indicate the pressor response was activated due to the large volume of work being done with the arms as opposed to the legs.
Energy expenditure during the kettlebell snatch workout averaged 13.6 kcal/min or 272 calories burned during the 20-minute workout. This number is likely an underestimate of total energy expenditure as anaerobic energy expenditure played a significant role. Lactate samples were not taken during the kettlebell snatch workout when lactate levels were likely highest in the blood.
