Last night's viewing - Usain Bolt: the Fastest Man Alive, BBC1; Britain's Secret Treasures, ITV1

A few days ago, Martina Navratilova revealed something that, I suspect, could apply to many sports superstars: as a gifted tennis player who spent her teen and twentysomething years eating what she should, avoiding alcohol and training religiously, a certain kind of arrested development took place, and she found herself having to tackle a displaced adolescence later in life.

Usain Bolt: the Fastest Man Alive, an hour-long documentary on the Jamaican sprinter's dazzling career (from record-breaking achievements to multiple gold medals), turned out to be both a study of his sporting genius and more subtly, a display of the arrested development that Navratilova talked about.

The archive footage began with a 14-year-old Bolt displaying a rare natural potential that blossomed into extraordinary feats on the track. The footage showed such serious-minded focus, such invincibility and such long stretches dividing him from the other runners that he looked like a God competing with mere mortals.

But off the track, he was more of a boy. We learned that he shares his Kingston house with friends; he loves his PlayStation; his best friend is his personal assistant. With his young, puckish face stuck on a 6ft 5in, 220-pound frame, he was shown doing what looked like water aerobics with mates. When the interviewer asked about girlfriends, he looked evasive and said he liked to be free; quizzed about the stress of constant travel and media attention, he shrugged and said he had got used to it. In his most rebellious moments, he joked about being at Burger King to his coach and – even! – stayed up in a bar one night, singing to Bob Marley's "Three Little Birds".

For all his extravagant talent and training (there were clips of him running while dragging a weighted harness, War Horse-style), he seemed to have the child star's syndrome, with his singular focus and juvenile charm. At points, he resembled Tom Hanks's character in Big, the film about a boy stuck in a man's body.

His father said he had wanted to become a cricketer before he was persuaded otherwise. He proudly went on to question how his child had turned out to be so fast. But if we wanted an explanation or answer, we weren't given it. Bolt took us through his technique (head down, drive the body forward, straight up and raise knees, look left to right, confirm lead and glide to finish), but the impenetrable affability refused to let us go any deeper or understand intention.

It was on the odd losing streak that chinks began to appear. The one major blip in his career was a false start that disqualified him from the World Championships final in South Korea in August 2011. His training buddy and fellow Jamaican, Yohan Blake, won the race, and it was in his aftermath comments to camera that we got a hint of what lurked beneath the carefree surface. He said he felt happy for his friend, but his face showed a very controlled irritation at not winning. Bolt was beaten by Blake this month at the Olympic trials in Jamaica and the astonished media promptly renamed the lightning Bolt "Beatable Bolt". It will be fascinating to watch what happens on the track in London and also to – hopefully – see a sequel to this documentary in future years.

Britain's Secret Treasures was essentially an archaeology programme dressed up in a Top 50 countdown format. Michael Buerk and Bettany Hughes presented, him sombre, her smiley, while John McCarthy talked us through the discovery of a slave shackle and Saul David waxed lyrical about an ancient toy canon, but the format gave the programme a superficiality and "amazing finds" were discussed too briefly and in sound bites. The one exception came at the end when a man was reunited with his grandfather's war medal and, gulping back tears, learned of the "continued gallantry" that his unassuming granddad had never talked about.