Fat reduces strength of muscle tissue, SFU study finds

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Intramuscular fat changes the way muscles work, possibly creating impediments to recovering from obesity.
Photograph by: VINCENZO D’ALTO

High-fat content changes muscle fibres and robs them of strength, according to new research published by researchers at Simon Fraser University.

“Understanding how this fat alters the ability of our muscles to develop force will mark an important step to help maintain mobility and a healthy lifestyle in all Canadians, even if we can’t halt the process completely,” said lead researcher James Wakeling.

Intramuscular fat — which may reside within muscle fibres or accumulate as blobs that bloat and reshape entire muscles — tends to increase in people as they age and in people who become obese.

“Accumulation of intramuscular fat seems to be ubiquitous during aging and for people with obesity,” said Wakeling.

Graduate student Hadi Rahemi stumbled onto the effect while studying the properties of different kinds of muscle fibres and discovered that muscles containing more fat are less powerful.

The fibres in fat-bloated muscles are oriented at different angles because of increased muscle size in obese people and due to muscle shrinkage in the elderly.

When the fibres of the muscle don’t line up with the main direction of force in the muscle, it is robbed of strength, explained Wakeling. In addition, the quality of muscle fibre changes with fat content, which makes them stiffer so more energy is required and muscle force is reduced.

So, our ability to perform everyday tasks declines as fat accumulates in muscles.

With the help of SFU math professor Nilima Nigam, the researchers were able to create mathematical and computational models of five different fat content scenarios, some in which fat was simply added and the amount of muscle fibre remained constant and others where it replaced some muscle tissue.

“I thought that adding fat to muscle would decrease force in proportion to the amount of contractile tissue that was replaced by fat,” said Wakeling. “But the force went down far more than expected.”

The finding suggests that fat content alters the performance and mechanics of the muscle tissue itself, decreasing the force it generates.

“It appears to be working harder against itself or the fat within it,” said Wakeling.


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