How are calories burnt when performing a bicycle crunch?

Patient: Hi, when performing a bicycle crunch is it the movement of the legs in general, or the crunching up of the legs as close to the chest as possible, or the crunching up of the as high to the chin that determines the calories burnt. Which one of these three actions determines the calories burnt when performing a bicycle crunch.Also is it the crunching up as high of the leg to the chin or the crunching up as close to the chest of the leg that burns calories and builds the quadricep muscle in the legs. And, when does contraction occur in the legs during a bicycle crunch. Finally, is the leg contracted at a longer length when crunched as high to the chest as possible compared to when it is only slightly moved/ crunched during a bicycle crunch, and do small leg movements during the bicycle crunch result in the same amount of calories burnt or less calories burnt compared to bigger/ longer movements of the leg during a bicycle crunch. Thankyou for your help and kind regards,Kelly.

Doctor: Hello,Thank you for your medical query at AskTheDoctor.comI understand your concern.Crunching of the legs as high as the chest in a repeated movement is what burns calories. Crunching up to the level of the chin starts involving accessory muscles, and not just the rectus muscles.It is like when we do weight training, we should always pick weight where we are comfortable and do more repetitions. Pulling up to the chin does contract the muscles more, however, there is an increased risk of injury and muscle spasm. So pulling up to the level of the chest is recommended. This done properly burns most calories.The moment you start pulling the leg, contraction in the quadriceps muscles occurs.I will say when small movements are done repeatedly it burns more calories. It contracts way more when it is pulled up to the chest too. Bigger longer movements take more time, slowing down the flow and also increases fatigue.Hope this was helpful,Feel free to follow-up,Regards.