[Overactive muscles: it can be more serious than common myalgia or cramp]

Positive muscle phenomena are due to muscle overactivity. Examples are cramp, myalgia, and stiffness. These manifestations have mostly acquired causes, e.g. side-effects of medication, metabolic disorders, vitamin deficiency, excessive caffeine intake or neurogenic disorders. We report on three patients with various positive muscle phenomena, to illustrate the clinical signs that indicate an underlying myopathy. Patient A, a 56-year-old man, was diagnosed with muscle cramp in the context of excessive coffee use and previous lumbosacral radiculopathy. Patient B, a 71-year-old man, was shown to have RYR1-related myopathy. Patient C, a 42-year-old man, suffered from Brody myopathy. We propose for clinicians to look out for a number of 'red flags' that can point to an underlying myopathy, and call for referral to neurology if indicated. Red flags include second wind phenomenon, familial occurrence of similar complaints, marked muscle stiffness, myotonia, muscle weakness, muscle hypertrophy, and myoglobinuria. Establishing a correct diagnosis is important for proper treatment. Certain myopathies call for cardiac or respiratory screening.