The Deadlift is one of the best exercises for your lower back, your glutes, and your hamstrings. It works all three muscles at once, and you'll find that it can help you build that core strength that is lacking.
The beauty of using the kettlebell is that you can focus on improving your form--something harder to do with a barbell. Make sure to keep that back straight, and you'll shred those core muscles like a superstar!
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Stand with your legs spread at shoulder width, and keep your knees slightly bent. The kettlebell should be on the floor between your feet.
Grip the kettlebell with both hands, and begin to pull up. As you lift, thrust your hips forward, keep your shoulders back, and keep your eyes looking forward. Feel your core tighten--particularly your lower back and glutes--and stand perfectly straight.
As you dip forward to lower the weight, keep your spine straight, don't move your shoulders, and let your lower back and glutes do the work.
Reps as desired