Farrar, RE, Mayhew, JL, and Koch, AJ. Oxygen cost of kettlebell swings. J Strength Cond Res 24(4): 1034-1036, 2010-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, V̇o2max = 52.78 ± 6.22 ml·kg−1·min−1) completed a graded exercise test to exhaustion for the determination of V̇o2max. 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 V̇o2, and heart rate (HR) was continuously measured. Percent HRmax and %V̇o2max 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 V̇o2 of 34.31 ± 5.67 ml·kg−1·min−1 and an average HR of 165 ± 13 b·min−1. The average %HRmax (86.8 ± 6.0%) during kettlebell exercise was significantly higher (p < 0.001) than the average %V̇o2max (65.3 ± 9.8%) that was achieved. Continuous kettlebell swings can impart a metabolic challenge of sufficient intensity to increase V̇o2max. Heart rate was substantially higher than V̇o2 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 V̇o2.