Depending on whether you're starting out or you're already quite strong, pick a set of dumbbells which are challenging but with which you will be able to complete at least 3/4 sets of 10 reps with.
As you get stronger, increase the weight of the dumbbells.
Remember to warm-up your muscles first and to stretch the muscles worked afterwards. To make this a more challenging and effective workout include some short bursts of cardio either before or after, or in-between the exercises such as skipping or short sprints or jumping squats.
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