'Muscle power truths' revealed
Scientists have discovered a new truth behind big muscles, turning 50 years of knowledge on its head.
Bulging biceps get their power from a mesh arrangement of cells rather than long ropes, detailed studies reveal.
As muscles flex, tugging filaments fan out in a lattice, say the University of Washington team who made the breakthrough.
This generates force in multiple directions, not just up and down the muscle, Proceedings B journal reports.
And it's not just biceps that use this force - all muscles, including the heart appear to do it.
Prof Thomas Daniel, one of the researchers, said: "This aspect of muscle force generation has flown under the radar for decades and is now becoming a critical feature of our understanding of normal and pathological aspects of muscle."
The basics of how muscle generates power remain the same - filaments of myosin tug on filaments of actin to shorten or contract the muscle.
But myosin doesn't tug in one direction, as previously thought. Instead, it pulls at angles and this gives radial force.
The news will be of interest to bodybuilders who strive to max their muscle power, but could also help doctors treating heart problems.
Co-author Michael Regnier said: "In the heart especially, because the muscle surrounds the chambers that fill with blood, being able to account for forces that are generated in several directions during muscle contraction allows for much more accurate and realistic study of how pressure is generated to eject blood from the heart.
"The radial and long axis forces that are generated may be differentially compromised in cardiac diseases and these new, detailed models allow this to be studied at a molecular level for the first time."