A modicum of exercise...

this is the minimum amount of exercise required to keep the body's battery charged up. Look at the will power to force movement as an alternator to allow adequate charge production to enhance the battery. This charge can be used for physical or mental output. To run too much energy through the musculature of the body (too much physical exercise) is to excessively discharge potential electrical flow which can be used to build up the charge on the brain; whereas, if not enough physical movement can be produced, the circulation of the cerebrospinal fluid to maintain a strong charge on the body's battery becomes more challenging. Enough physical yoga can perform this function adequately and efficiently. Then this mental power, derived from increased electrical charge in the brain area, can be used to concentrate with, which is the first step to advancing one's Self in meditation.