Muscle tissue makes up 30 to 40 percent of body weight, and this film argues it works less like plumbing and more like a gland. Wilhelm Bloch of the German Sport University Cologne explains myokines, the messenger substances muscles release during activity that reach the brain, liver, heart, and intestines, and shows early research into how these compounds affect the growth and movement of cancer cells. Alice Kindich, who has metastatic breast cancer, describes nine months of weight training in a companion study and the improvement in her quality of life since starting. Ingo Froböse, also from Cologne, makes the case for strength training in old age as a defense against sarcopenia, the degenerative loss of skeletal muscle. The film also follows 33-year-old Leonie Poppe over six weeks of training, documenting the physical and mental changes she experiences. Between the lab explanations and personal cases, the film builds a picture of muscle as an organ with its own chemistry, one that influences ageing and disease well beyond simple strength.