Muscle as your body's engine, not just for moving

Muscle gets thought of as the thing that lifts the shopping, and that undersells it considerably. Taken together, your skeletal muscles are the largest metabolic organ you have: they burn fuel, store it, generate heat, hold your joints together, keep you upright, and steady your balance.

Which means losing muscle is not simply becoming weaker. It changes how your whole body runs.

After a meal, much of the glucose in your blood is taken up by muscle and stored there for later. Muscle is the largest place it can go.

So the more muscle you keep, the more room there is for that glucose, and the steadier blood sugar tends to be. This is the direct link between strength work and blood sugar control, and it is why the two subjects keep turning up together.

This is the part that has changed how researchers think about it. Contracting muscle releases chemical messengers called myokines, which travel round the body and do a surprising amount: calming inflammation, improving how well insulin works, supporting the brain, and signalling bone to build.

Bone answers back with signals of its own. Muscle and bone are increasingly treated as one connected system rather than two neighbouring ones, which is why the same session pays into both.

Muscle draws on different fuels depending on what you are asking of it. A sudden effort of a few seconds runs on energy already sitting in the cell. A longer, brisker effort mostly burns glucose. At rest and during gentle, sustained activity, fat does most of the work.

Protein is the exception. It is meant for building and repairing muscle, not for burning, and the body only turns to it for fuel when food or protein has been short for a long while. That is worth knowing, because eating too little protein means taking apart the very thing you are trying to keep.

Muscle loss with age has a name, sarcopenia, and so does bone loss, osteoporosis. They very often arrive in the same person, and they feed each other: less muscle means less pull on bone and less signal to stay strong, while weaker bone and poorer balance make people move less, which costs more muscle.

Together they raise the risk of falls, fractures and losing independence far more than either would alone. The cheering news is that the same things address both: regular movement, work against some resistance, and enough protein to build with. This is general guidance on staying strong, not medical advice.