Ergonomic task reduction prevents bone osteopenia in a rat model of upper extremity overuse

Abstract

We evaluated the effectiveness of ergonomic workload reduction of switching rats from a high repetition high force (HRHF) lever pulling task to a reduced force and reach rate task for preventing task-induced osteopenic changes in distal forelimb bones. Distal radius and ulna trabecular structure was examined in young adult rats performing one of three handle-pulling tasks for 12 wk: 1) HRHF, 2) low repetition low force (LRLF); or 3) HRHF for 4 wk and than LRLF thereafter (HRHF-to-LRLF). Results were compared to age-matched controls rats. Distal forelimb bones of 12-wk HRHF rats showed increased trabecular resorption and decreased volume, as control rats. HRHF-to-LRLF rats had similar trabecular bone quality as control rats; and decreased bone resorption (decreased trabecular bone volume and serum CTX1), increased bone formation (increased mineral apposition, bone formation rate, and serum osteocalcin), and decreased osteoclasts and inflammatory cytokines, than HRHF rats. Thus, an ergonomic intervention of HRHF-to-LRLF prevented loss of trabecular bone volume occurring with prolonged performance of a repetitive upper extremity task. These findings support the idea of reduced workload as an effective approach to management of work-related musculoskeletal disorders, and begin to define reach rate and load level boundaries for such interventions.

Prolonged performance of a high repetition low force task induces bone adaptation in young adult rats, but loss in mature rats

“…The reduced radial bone quality in the mature rats indicates that prolonged performance of even moderate demand upper extremity, hand intensive task may increase the risk of fracture or osteopenia, matching results from human subjects showing reduced bone mass in females with heavy or one-sided hand workloads [17–19], and decreased bone mineral density in distal forearm bones of subjects with carpal tunnel syndrome [22, 23]. Our findings of increased bone inflammatory cytokines and osteoclast activity in the mature HRLF rat bones, combined with recent findings of reduced cytokines and preservation of bone volume after anti-inflammatory treatments [29, 92], supports an underlying inflammatory mechanism that should be considered in future intervention studies on animal and human subjects with WMSDs.…”

“…We have previously shown in this model that anti-inflammatory doses of ibuprofen, provided as a secondary intervention, reduced TNF-alpha and IL-1beta levels, and prevented loss of bone volume in young adult rats performing a high repetition high force task for 12 weeks [29]. An ergonomic task reduction intervention in which young adult rats were moved from a high repetitive high force task in week 4, to a low repetition low force task for another 8 weeks, also reduced inflammatory cytokine levels and lead to enhanced bone formation [92]. These two studies support an underlying bone inflammatory cytokine mechanism in this model that was further enhanced by aging in rats involved in performing this repetitive loading task for 12 weeks.…”

Forced Treadmill Running Reduces Systemic Inflammation Yet Worsens Upper Limb Discomfort in a rat model of Work-Related Musculoskeletal Disorders

“…Twenty-nine female Sprague-Dawley rats were procured at 4-7 months of age from Charles Rivers (King of Prussia, Pennsylvania), housed and handled until reaching young adulthood (3 months of age at the onset of the experiment). Female rats were used exclusively because: 1) higher incidences of work-related musculoskeletal disorders occur in human females than males [43][44][45], 2) sex is a potential confounder, and 3) results can be compared with those from our previous interventional studies using female rats [12,41,42,[46][47][48]. Animals were housed individually in standard rat cages (ventilated and with hardwood chip rodent bedding) with free access to water in an AAALAC-accredited animal facility with a 12-hour light: 12-hour dark cycle.…”

Forced treadmill running reduces systemic inflammation yet worsens upper limb discomfort in a rat model of work-related musculoskeletal disorders

“…Twenty-nine female Sprague-Dawley rats were procured at 4-7 months of age from Charles Rivers (King of Prussia, Pennsylvania), housed and handled until reaching young adulthood (3 months of age at the onset of the experiment). Female rats were used exclusively because: 1) higher incidences of work-related musculoskeletal disorders occur in human females than males [43][44][45], 2) sex is a potential confounder, and 3) results can be compared with those from our previous interventional studies using female rats [12,41,42,[46][47][48]. Animals were housed individually in standard rat cages (ventilated and with hardwood chip rodent bedding) with free access to water in an AAALAC-accredited animal facility with a 12-h light: 12h dark cycle.…”

“…Maximum grip strength of the limbs used to reach was reported for all rats after food restriction, at the end of task week 10 for the 10-wk HRHF and 10-wk HRHF+TM rats, at the end of the 6 week treadmill regimen for the TRthen-TM rats, and at matched time points for FRC rats. The "up-down" von Frey testing method was used for forepaw and hindpaw mechanical sensitivity testing of all rats, bilaterally, as previously described [38] and as we have previously used [12,[46][47][48]. Monofilaments (North Coast Medical, Morgan Hill, CA) of different diameters were used to elicit a forepaw withdrawal reflex.…”