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Tension in stretching fibres triggers muscle-building proteins to add new sarcomeres inside existing ones

31 August 2025

Tiny Gains

Building muscle doesn’t just happen in the gym, where damage or hypertrophy recruits new muscle fibres to bulging biceps. During development, each of our muscle fibres must grow longer as the bones they’re attached to move further apart. But how? Here researchers use a combination of advanced microscopy and image analysis tool to spot patterns of stretchy regions called sarcomeres, highlighted between blue dots along these muscle fibres from fruit flies (Drosophila). The team discover that tension in the stretching fibres triggers muscle-building proteins to add new sarcomeres inside existing ones – a bit like tying elastic loom bands in the middle of a chain together to make a bracelet longer (although ~10,000 times smaller). Fruit flies share many of our genes, so these insights will help us to understand how our musculoskeletal system develops, ready to cope with press ups in later life.

Written by John Ankers

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BPoD stands for Biomedical Picture of the Day. Managed by the MRC Laboratory of Medical Sciences until Jul 2023, it is now run independently by a dedicated team of scientists and writers. The website aims to engage everyone, young and old, in the wonders of biology, and its influence on medicine. The ever-growing archive of more than 4000 research images documents over a decade of progress. Explore the collection and see what you discover. Images are kindly provided for inclusion on this website through the generosity of scientists across the globe.

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