Dr. David Rempel is a Professor of Medicine at the University of CA. He is one of the most important USA researchers in upper extremity cumulative trauma disorders (CTD) in our time. Dr. Rempel’s presentation at ERGOX 2015 focused on the latest research on Carpal Tunnel Syndrome (CTS).
Dr. Rempel discussed “Big Ergo”, a large prospective study spanning from 2001-2011 focusing on the causation of distal upper extremity (UE) CTD including CTS, wrist tendonitis, elbow tendinitis and rotator cuff disorders in a production/manufacturing setting.
The most critical factors in these studies are:
1. The impact of duty cycle or the percentage of time performing pinch or grip forces through an activity, not just considering repetition.
2. Wrist postures of bending and extending did not necessarily increase the risk of CTS, but once force was added, the risk was much higher.
3. If the hand is just moving without any load, it is considered “protective” and is at lower risk for CTS.
4. Pinch forces in excess of 2lbsf or 10lbsf power grip with a medium (50%) to high (90%) duty cycle significantly increases the risk of CTS.
5. Add increasing age and body weight with a stressful job and the risk continues to rise.
6. Other hand activities outside of work and job satisfaction serve to “protect” workers’ from CTS.
The concept is being further developed by the ACGIH in a proposed model, “Fatigue Threshold Limit Value” to determine the maximum force the hand can be active (HAL) before succumbing to fatigue and eventual injury. If we can figure this relationship out, we can really reduce the occurrence of CTS and perhaps CTDs in the workplace!
Bottom line: Be mindful of the time production or manufacturing employees are performing pinch forces combined with repetitive motion. Instead, try and reduce the time force is applied, while also increasing to a power grip to transfer forces throughout the hand.
What are your thoughts on the latest research in Carpal Tunnel Syndrome? Are we closer to knowing “how much is too much?” when it comes to fatigue, hand repetition and force? Does this make you think about changing your operations? Let me know what you think!
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