Built by use

About this video

Bones feel like a fixed, hard frame, and muscles like something you are born with. In fact both are alive, and both change with use: a child who runs and jumps and a grandmother who carries her own shopping are both building something.

Bone is living tissue: bits of old bone are always being removed and replaced with new bone. In childhood and the teenage years much more is added than taken away, and in most people bone mass reaches its highest point by the mid-to-late 20s. How much bone you build by then helps decide how healthy your bones are for the rest of your life; later, bone is lost more quickly and new bone grows more slowly. Bones grow stronger when they carry the body's weight against gravity and take a little force: weight-bearing activity such as brisk walking, running, hopping, skipping and jumping, dancing, climbing stairs and racket sports like badminton.

Muscles grow stronger when they work hard against a weight: your own body (push-ups, squats, climbing), heavy shopping, a stretchy band or weights. The World Health Organization advises this muscle-strengthening activity on at least 2 days a week for adults and 3 for young people. With age muscles slowly get smaller and weaker, but strength exercise slows this down, and it is never too late: a review of 121 trials with about 6,700 older people found strength training made them stronger and better at everyday tasks like bathing or making a meal. For children, the American Academy of Pediatrics says strength training can help if it is well supervised and done with good technique, and well-run programmes have not been shown to harm growth.

Two myths. Sit-ups don't burn belly fat: in one small trial, people did belly exercises 5 days a week for 6 weeks, and their belly muscles got better at the work but their belly fat did not change. And stretching before sport did little to prevent injuries in a review of 25 trials, while strength training cut sports injuries to less than a third. This video explains muscles and bones, from the lesson Strong Muscles and Bones on Knaph.

Transcript

1. 0:00Bones feel fixed, and muscles like something you're born with. In fact, both are alive, and both change with use.
2. 0:07Bone is living tissue. Old bone is always removed and replaced. In childhood and the teenage years, much more is added than taken away. In most people, bone mass peaks by the mid-to-late twenties. Later, bone is lost faster, and new bone grows more slowly. So what you build young matters for life.
3. 0:30Bones grow stronger when they carry your weight against gravity. Walking, running, hopping, skipping, dancing, stairs, badminton.
4. 0:44Muscles grow stronger working hard against a weight. Your own body, heavy shopping, a band, weights. At least two days a week for adults, three for young people. And it's never too late. In over a hundred trials, older people got stronger and better at everyday tasks.
5. 1:04Will weights stop a child growing? Well supervised, with good technique, children can benefit, and good programmes haven't been shown to harm growth.
6. 1:15Do sit-ups burn belly fat? In one trial, six weeks of belly exercises made the muscles better, but the belly fat didn't change.
7. 1:27And to avoid sports injuries, stretching made little difference in a review of twenty-five trials. Strength training cut injuries to less than a third.
8. 1:39Bone and muscle are built by use. Start young, keep going.