For thousands of years people in Asia have been carrying heavy loads – often more than their own body weight – suspended from a bouncy bamboo pole held over one shoulder.
Now, the Western world is beginning to realise the potential of the technique to dramatically lighten a load by dispersing the weight.
“These remarkable yet simple tools can potentially reduce energetic exertion and lessen sharp forces on the carrier,” says Ryan Schroeder, from Canada’s Calgary University, who was inspired to experiment with the efficiency of load-bearing poles while travelling in Southeast Asia.
Various advantages have been attributed to the technique, but there’s a significant knowledge gap in regards the most energy-efficient way to carry such loads, and the effect of using a rigid pole compared to a bouncing, flexible one.
A new study published in the Journal of Experimental Biology explores this comparison.
Schroeder and colleagues used models to determine energy-minimising solutions for humans carrying loads suspended from flexible poles of various stiffness. They then compared these results with observational data from Vietnamese farmworkers.
Past studies have been largely limited by their exclusive use of inexperienced participants who take time to find the ideal technique for load bearing. The researchers specifically chose to study people who are highly experienced at the task.
Fourteen participants (eight males, six females) were recruited for the study; seven used a pole daily, three weekly, one monthly, and three seasonally.
All were asked to walk along a metre-wide, 20-metre-long path with a steady gait while carrying one of two pole types.
The first was a rigid, season-dried bamboo pole with a full circular diameter. It wasn’t split to make the characteristic flattened carrying pole, so remained it rigid.
The second was the participant’s own personal compliant bamboo pole, prefabricated and well used.
Participants carried loads of 0%, 30% and 50% of their body weights. Wireless inertial measurement units recorded their walking patterns.
Ankle sensors determined step frequency by calculating the time difference between acceleration peaks, while sensors on the lower back and at three points along the pole’s length recorded changes in the centre of mass each step.
The study revealed that carrying weight on a flexible pole, instead of a rigid pole, could save 20% of the bearer’s energy as it makes walking less strenuous.
The bounce of the flexible bamboo pole offsets some of the weight of the load, thereby allowing each stride where the weight of the load is on one foot to be lighter than otherwise.
Applied to this ancient technique, modern technology has reminded us that new does not always equal better.
Ian Connellan is the editor of Cosmos magazine.
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