“A boy with Herculean appearance”

An 11-year-old boy presented with stiffness of his gait since early childhood. Stiffness was noted upon initiating movement leading to falls and frequent toe walking; symptoms would improve after a few minutes with movement. Family history was negative. Physical examination revealed generalized muscular hypertrophy (Figure) and mild proximal and distal muscle weakness. There was grip myotonia (delayed relaxation after contraction) (Video; available at www.jpeds.com) and percussion myotonia of different muscles.

source https://www.jpeds.com/article/S0022-3476(21)01246-4/fulltext?rss=yes