For years, researchers have known that resistance exercise training –such as weightlifting, in which muscles work against gravity or another force — can be one of the most effective ways to fight the debilitating¹（衰弱的） muscle loss caused by aging. But many older people are unable to get the full benefits of such training because they suffer from conditions such as arthritis²（关节炎） that prevent them from lifting enough weight to stimulate³ muscle growth. And, while younger men and women continue to produce

significant amounts of muscle protein for hours after a resistance exercise workout, seniors receive a much smaller post-workout benefit. Now, though, University of Texas Medical Branch at Galveston researchers have determined⁴ that moderately and temporarily restricting the flow of blood through muscles — a practice adopted by bodybuilders who noticed that it made light weights feel heavier— can be combined with low-level resistance exercise training to produce muscle-mass increases in older men.

"We think that this may be a novel treatment for older people who need to bring their muscle mass back up," said UTMB physical therapy professor Blake Rasmussen, senior author of a paper on the investigation⁵ ("Blood flow restriction⁶ exercise stimulates⁷ mTORC1 signaling and muscle protein synthesis综合，合成 in older men") appearing in the May issue of the Journal of Applied⁸ Physiology⁹. "It could also be used for patients who have had surgery and aren't capable of lifting enough weight to keep their

muscles in shape, or for people who have arthritis or other conditions that make lifting heavy weights a problem."

The UTMB investigators¹⁰ studied changes in the thigh¹¹ muscles of seven older men (average age 70) when they performed four minutes of low-resistance leg extension exercises both with and without inflatable（膨胀的，充气的） cuffs¹³（袖口，护腕） that reduced blood flow out of the muscles. Muscle protein synthesis was measured in each of the men by monitoring changes in a chemical tracer infused into（灌输给） the bloodstream. In addition, a series of biopsies（活组织检查） yielded muscle samples that

were analyzed¹⁴ to track alterations¹⁵（改变，变更） in biochemical pathways critical to muscle growth.

"We saw that when we put the cuffs on, they responded similarly to young people doing traditional high-intensity resistance exercise," said UTMB graduate student Christopher Fry, the lead author of the paper. "The low-intensity exercise produced increases in protein synthesis, and activated¹⁷ two cellular¹⁸ pathways that stimulate protein synthesis and muscle growth in the post-exercise period."

Exactly how restricting blood flow in the muscles generated these effects remains¹⁹ unknown, although Rasmussen and Fry speculated（推测，思索） that either an improved ability to activate¹⁶ Type II muscle fibers²⁰ or a response to the sudden surge of blood into the muscles when the cuffs were released could be responsible. Whatever the mechanism²¹, Rasmussen said, "we think it's an exciting potential new rehabilitation²²（复原） tool."

"You could use this following ACL knee surgery or hip²³ fracture surgery, for example," Rasmussen said. "In the first few weeks after ACL surgery, the joint²⁴ just won't allow you to lift heavy weight. So instead, you could use a really light weight with a restriction cuff¹², which may prevent the muscle loss that you normally see following knee surgery."