To get the most out of a gym session, fitness class or a run, do it at the time of day that best suits your own natural internal body clock, say health researchers. Early risers or "larks" should exercise in the morning for maximum benefit, while night owls should train in the evening, they suggest. Synchronising exercise in this way could boost heart gains, especially for people already at higher risk of heart disease, according to a new study published in the journal Open Heart . Volunteers