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It is said that crunches for 1 hour at moderate speed ( say 20/ minute ) can burn close to 400-500 calories.
If you do bicycle crunches at a speed of 50 per minute for 3 minutes ( 150 ), it will help you burn close to 80-100 calories.
This is a great way of strengthening your core, however, try to limit it to 30-40 per minute, otherwise the muscles can go in a state of spasm.
Hope this was helpful,
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