Try running or jumping with a backpack, and the physics of force become obvious as the load slams into your shoulders and back.
Now, an expert in fish muscle physics has developed a spring-mounted backpack – for people – that doesn’t bounce with each step. That reduces the calorie cost of carrying a load and cuts the “peak forces” that normally pound the spine.
The spring-loaded packs promise to cut down on injuries to backpackers everywhere, from schoolchildren to rescue workers, Lawrence Rome and his colleagues report in the current issue of Nature.
“There are hundreds of millions of backpacks in the world, and everybody suffers the same problems,” Rome said. “It’s clear our backpack would help.”
Normally, an internal frame backpack bobs up and down 2 to 3 inches with every step, requiring a carrier’s energy to lift it up, and creating extra force at the bottom of the downswing, said Rome, a biophysicist at the University of Pennsylvania in Philadelphia.
But Rome’s new pack uses the same principle that helps Asian merchants run with heavy wares on flexible bamboo poles.
In the new backpack, stretchy cords attach the load to a sliding frame. That cuts the energy required to carry the load so significantly that a person could carry 60 pounds in a springy pack for the same energy required to carry just 48 pounds in a normal pack, the scientists calculated.
Moreover, a conventional 60- pound pack creates 100 pounds of “peak force,” even when the bearer is only walking, Rome said.
Because the new pack’s springs let it remain at essentially the same distance from the ground, even as its bearer moves up and down with each stride, “the peak force doesn’t go above 70,” Rome said.
The pounding of a heavy pack definitely slows down mountain rescue workers, said Joe Ben Slivka of the Summit County Rescue Group.
“When you’re operating at 13,000 feet or higher, every ounce counts, every step counts, every calorie counts,” Slivka said.
The new pack’s design is impressive, Slivka said. “I’d be interested in testing it with our very heavy loads.”
Summit rescuers carry 50- to 75-pound packs during missions that take a serious toll on their backs, he said. After most missions, rescue workers seek the help of masseuses or chiropractors to de-knot their backs, Slivka said.
“Now, from a kid perspective, I also can see where it would be huge,” Slivka added.
International studies show that heavy backpacks create back strain and sometimes injury in children, Rome said.
He said that his prototype pack weighs about 13 pounds more than a conventional backpack.
“But we made no effort to lighten it,” he said. “That’s just not what you do in the universe of a biology laboratory.”
Luke Boldman, an industrial designer with Golden-based Mountainsmith, said he’d heard about the spring-loading technology but isn’t yet convinced it’s more than a gimmick.
It would be costly to produce, Boldman said, and with so many other potential innovations out there, it’s not likely Mountainsmith will jump to develop springy packs.
“Maybe our customer base is more conservative,” he said, “but they’re not out to spend an extra $300 on a newfangled innovation.”
Besides, Boldman said, many people are very comfortable with today’s internal frame systems.
“Most backpackers are inclined to suffer a little anyway,” he said, “being in the backcountry.”
Staff writer Katy Human can be reached at 303-954-1910 or khuman@denverpost.com.
