Jem dreams of flying under his own power by pedalling a homemade plane into the air. He sets out to discover why muscles get tired, and to see if he can boost his own using nothing more than beetroot. Meanwhile, Liz explores how hormones and blood sugar affect our energy levels and mood, and Dallas sweats himself to a standstill as he tries to answer the question 'Do we really need to drink eight glasses of water a day?'.
