The XMark 5 lb. Black Cast Iron Kettlebell XM-3332-5 improves flexibility and balance while providing a high intensity, strength training workout. Research shows a 20 minute kettlebell workout burns almost 300 calories. Each kettlebell movement engages multiple muscles due to the weight imbalance and the results are a combination of muscle-sculpting and heart-pumping cardio in one high intensity workout. With a higher intensity workout than standard weight training, kettlebell training with the XMark 5 lb.