Tonight in health watch:Looking for a more efficient way to work out?A centuries old weight is getting a big lift in gyms around the country.Janet Choi reports.Shoshana Rudnick has been taking this class for two years.. and she says it's working.Shoshana says, 'I have much more definition in my arms, and my legs and I just feel like I'm more toned and I'm much more lean.'She says that's because she is using this weight - called a kettlebell.It looks like a cannonball with a handle.Although they seem like the latest fitness trend, these weights were actually developed by Russian bodybuilders 300 years ago.Lorna Kleidman - a world champion kettlebell athlete - says there is a reason this shape works better than traditional weights.Kleidman says, 'By adding a handle to the weight you're adding an additional joint to your arm. Whether doing rotational movements or swings it takes a little bit more of your body, a little bit more muscle groups and a little bit more of your heart pumping.'A new study shows kettlebell action can burn 20 calories per minute.Experts say that means a powerful workout in a short amount of time.Lorna Kleidman says, 'You know you don't have to do this work out for an hour .. or do your weightwork and then do your cardio there's no such thing.'Kleidman says the combination of strength, balance and cardio is great for anybody at any level.Gail Bauchman says, 'I mean this is just an hour twice a week and you get the results.'Lisa Schaub says, 'I saw amazing results immediately but they continue. I'm getting stronger, I'm getting leaner.'And the lift students get from those results - is why they stick with it.