Effects of prolonged load carriage on angular jerk of frontal and sagittal knee motion.
Samantha M Krammer, Micah D Drew, Tyler N Brown
PMID 33373876WHAT IT FOUND
Carrying 15 or 30 kg while walking made knee motion less smooth, especially side-to-side.
After 60 minutes, side-to-side motion became more abrupt. This was a lab study in 18 healthy adults, not people with knee injury.
Key findings
01Compared with no load, 30 kg increased peak and cost of sagittal knee jerk, while 15 kg increased only jerk cost.
02Body borne load significantly increased peak and cost of angular jerk for frontal plane knee motion.
03During the 60-minute walk, frontal plane jerk cost increased at minute 60 compared with minutes 0 and 15, and at minute 45 compared with minute 0; peak jerk did not change significantly.
STILL TO COME
How it was doneWhat they foundWhat it means for PTs
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What it does not show
The participants were healthy community adults, not service members or patients, so the findings may not apply to people already at risk for knee injury. The study measured knee motion smoothness, not pain, injury, or osteoarthritis, so it cannot show that these changes cause harm. Only 18 participants were studied, and they were all able to carry 34 kg. Participants did not need prior load carriage experience, so experienced carriers may respond differently. The authors did not analyse sex differences, although they note females may have different knee biomechanics. The authors did not measure trunk posture, which they note may also change with load. The jerk calculation may include compounded error from repeated derivatives.
Declared interests
The article lists NIH extramural research support and states no conflicts of interest.
The easy way to misread this
Do not conclude that carrying 15 or 30 kg causes knee injury or osteoarthritis. The study measured knee motion smoothness in 18 healthy adults during a walking task, and it did not follow anyone for injury.