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Backpack straps can significantly decrease blood flow in the shoulder, arm
The straps of backpacks can significantly increase pressure on the shoulders, potentially obstructing localized blood flow, according to a study presented at the 121st Annual Meeting of the American Physiological Society.
In particular, backpacks carrying even light loads of 26 pounds can decrease upper extremity blood flow in adults, and may cause a loss of fine motor control and increased fatigue, according to a press release from the society.
Timothy Neuschwander, MD, and colleagues at the University of California, San Diego, investigated how backpack straps affected upper extremity blood flow in eight healthy volunteers — six men and two women aged 18 to 30 years.
Backpack straps typically rest on an area of the body where they may compress the axillary vein, which causes abnormally high blood pressure inside the veins and a subsequent decrease of blood flow to the shoulders and arms. Because of this, Neuschwander and colleagues hypothesized that blood flow in the large and small vessels of the upper extremity area would decrease in an individual while wearing a backpack, according to the release.
The researchers measured the right brachial artery of each participant using ultrasound. They also measured index finger pulp microvascular flow using photoplethysmography. Baseline flows were measured immediately before and 10 minutes after each participant wore a 26 pound backpack.
Neuschwander and colleagues found that, after wearing the backpack for 10 minutes, brachial artery blood flow significantly decreased, from 2.66 ± 0.36 mL/sec to 1.52 ± 0.27 mL/sec (P<.05). Index finger microvascular flow also significantly decreased, from 100% to 46% ± 6% (P<.05), according to the release.
The researchers concluded that backpack loads of just 26 pounds decrease upper extremity macrovascular and microvascular blood flows, and may result in a loss of fine motor control and increased fatigue, the release stated.
"We surmise that the mechanism of diminished blood flow is likely due to strap compression of the axillary vein. We think that backpack straps may benefit from a redesign that skirts the vein leading from the upper extremity to the heart," Neuschwander said in the release.
More than 92% of U.S. children carry backpacks, which typically weight about 22% of the child's body weight. Among adults working in certain professions, such as the military, firefighting and mountain rescue, backpacks may equal as much as 60% of total body weight, the release noted.
For more information:
- Neuschwander T, Macias B, Hargens A. Backpack straps decrease upper extremity blood flow. Presented at the 121st Annual Meeting of the American Physiological Society, part of the Experimental Biology 2008 scientific conference. April 5-9, 2008. San Diego.