Researchers at an Israeli university have found that lifting heavy objects, such as school bags or occupational gear carried by soldiers and firefighters, could damage the nerves that connect the brain and hands.
The damage includes simple irritation to diminished nerve capacity, which limits the muscles' ability to respond to brain's signals, inhibiting movement of the hand.
In practice, this could impact functionality, reducing a worker's ability to operate machinery, compromise a soldiers' shooting response time, or limiting a child's writing or drawing capacity, the Journal of Applied Physiology reports.
Amit Gefen and Yoram Epstein, both professors from the TAU faculties of biomedical engineering and medicine, respectively, with doctoral student Amir Hadid and Nogah Shabshin of the Imaging Institute of the Assuta Medical Centre, have determined that heavy loads on the back could potentially damage soft shoulder tissues.
School bags are a major concern. It cannot be assumed that children's bodies react to shoulder stress in exactly the same way as adults.
Differences in physiology could lead to different consequences, tolerance and damage levels, warns Gefen.
Focusing on soldiers who carry heavy backpacks, the researchers discovered that, in addition to complaining of discomfort or pain in their shoulders, soldiers also reported tickling sensations or numbness in the fingers.
"The backpack load applies tension to these nerves," explained Gefen.
He noted that the resulting damage "leads to a reduction in the conduction velocity - that is, the speed by which electrical signals are transferred through the nerves".