In recent years, kettlebells have re-emerged as a popular training modality for the conditioning of athletes. We sought to quantify the aerobic challenge of one popularly recommended kettlebell workout. Ten college-aged men (age = 20.8 +/- 1.1 years, height = 179 +/- 3 cm, body mass = 77.3 +/- 7.7 kg, Vo2max = 52.78 +/- 6.22 ml.kg.min) completed a graded exercise test to exhaustion for the determination of Vo2max. Two to 7 days later, subjects completed a kettlebell exercise routine consisting of as many 2-handed swings as could be completed in 12 minutes using a 16-kg kettlebell. During this exercise bout, subjects' expired gases were collected and analyzed for the determination of Vo2, and heart rate (HR) was continuously measured. Percent HRmax and Vo2max achieved during the kettlebell exercise were compared with each other using a paired t-test. Subjects completed 265 +/- 68 swings during the 12 minutes and achieved an average Vo2 of 34.31 +/- 5.67 ml.kg.min and an average HR of 165 +/- 13 b.min. The average %HRmax (86.8 +/- 6.0%) during kettlebell exercise was significantly higher (p < 0.001) than the average Vo2max (65.3 +/- 9.8%) that was achieved. Continuous kettlebell swings can impart a metabolic challenge of sufficient intensity to increase Vo2max. Heart rate was substantially higher than Vo2 during kettlebell swings. Kettlebells provide a useful tool with which coaches may improve the cardiorespiratory fitness of their athletes. However, HRs achieved during continuous kettlebell exercise are significantly higher than actual Vo2.