New science shows that it's not just how much muscle you have that's important--it's what's inside it that matters most. Metabolically active muscle--the kind that's devoid of harmful fat and teeming with mitochondria, the metabolism-boosting powerhouses within cells--has a profound influence on everything from your weight to your energy levels to your risks of diabetes and heart disease. Even your chances of surviving a hospital stay or beating cancer are affected by the health of your muscle.
As the years go by and we spend more time sitting and less time moving, our muscle loses its zing. Mitochondria slowly decline in number and vigor, while fat starts to seep in. Health and vitality start to decline, leading to weight gain, exhaustion from everyday activities, and greater likelihood of lifestyle disease.
It turns out that the wealth of our mitochondria and the leanness of our muscle is bound to how much we move. When muscles need energy, they call on the mitochondria to turn glucose and fat into ATP, cellular energy. If we stay away from the gym too long, the body notices that it doesn't need as many mitochondria, and their numbers start to dwindle. Over time, this decreases our energy and capacity to burn fat.