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The interaction of force and repetition on musculoskeletal and neural tissue responses and sensorimotor behavior in a rat model of work-related musculoskeletal disorders.

Barbe MF, Gallagher S, Massicotte VS, Tytell M, Popoff SN, Barr-Gillespie AE - BMC Musculoskelet Disord (2013)

Bottom Line: In most cases, performance of the HRHF task induced the greatest tissue degenerative changes, while performance of moderate level tasks induced bone adaptation and a suggestion of muscle adaptation.Both high force tasks induced median nerve macrophage infiltration, spinal cord sensitization (increased substance P), grip strength declines and forepaw mechanical allodynia by task week 12.Prolonged performance of HRHF tasks exhibited significantly increased risk for musculoskeletal disorders, while performance of moderate level tasks exhibited adaptation to task demands.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Anatomy and Cell Biology, Temple University School of Medicine, 3500 North Broad St, Philadelphia 19140, PA, USA. mary.barbe@temple.edu.

ABSTRACT

Background: We examined the relationship of musculoskeletal risk factors underlying force and repetition on tissue responses in an operant rat model of repetitive reaching and pulling, and if force x repetition interactions were present, indicative of a fatigue failure process. We examined exposure-dependent changes in biochemical, morphological and sensorimotor responses occurring with repeated performance of a handle-pulling task for 12 weeks at one of four repetition and force levels: 1) low repetition with low force, 2) high repetition with low force, 3) low repetition with high force, and 4) high repetition with high force (HRHF).

Methods: Rats underwent initial training for 4-6 weeks, and then performed one of the tasks for 12 weeks, 2 hours/day, 3 days/week. Reflexive grip strength and sensitivity to touch were assayed as functional outcomes. Flexor digitorum muscles and tendons, forelimb bones, and serum were assayed using ELISA for indicators of inflammation, tissue stress and repair, and bone turnover. Histomorphometry was used to assay macrophage infiltration of tissues, spinal cord substance P changes, and tissue adaptative or degradative changes. MicroCT was used to assay bones for changes in bone quality.

Results: Several force x repetition interactions were observed for: muscle IL-1alpha and bone IL-1beta; serum TNFalpha, IL-1alpha, and IL-1beta; muscle HSP72, a tissue stress and repair protein; histomorphological evidence of tendon and cartilage degradation; serum biomarkers of bone degradation (CTXI) and bone formation (osteocalcin); and morphological evidence of bone adaptation versus resorption. In most cases, performance of the HRHF task induced the greatest tissue degenerative changes, while performance of moderate level tasks induced bone adaptation and a suggestion of muscle adaptation. Both high force tasks induced median nerve macrophage infiltration, spinal cord sensitization (increased substance P), grip strength declines and forepaw mechanical allodynia by task week 12.

Conclusions: Although not consistent in all tissues, we found several significant interactions between the critical musculoskeletal risk factors of force and repetition, consistent with a fatigue failure process in musculoskeletal tissues. Prolonged performance of HRHF tasks exhibited significantly increased risk for musculoskeletal disorders, while performance of moderate level tasks exhibited adaptation to task demands.

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Cartilage responses, assayed using histomorphometry and ELISA, after performance of either a LRLF, HRLF, LRHF and HRHF task for 12 weeks. (A) Summated Mankin score results, a histopathological scoring system used to assay changes in the distal radial articular cartilage. (B) Representative photos of the distal radial articular cartilage showing a pathological loss of Safranin O (pink) staining, tidemark changes (arrows), and presence of a subchondral cyst (asterisk) in a 12-week HRHF rat; changes absent in a FRC rat (left part of panel). This region was used to generate the data shown in panel E. (C) Serum levels of C1,2C, assayed using ELISA. Symbols: aa: p < 0.01, compared to LRLF rats; bb: p < 0.01, compared to HRLF rats; dd: p < 0.01, compared to HRHF rats; **: p < 0.01, compared to food restricted control (FRC) rats (mean FRC values are indicated by dashed line). Mean and SEM are shown. Scale bar = 50 micrometer.
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Figure 8: Cartilage responses, assayed using histomorphometry and ELISA, after performance of either a LRLF, HRLF, LRHF and HRHF task for 12 weeks. (A) Summated Mankin score results, a histopathological scoring system used to assay changes in the distal radial articular cartilage. (B) Representative photos of the distal radial articular cartilage showing a pathological loss of Safranin O (pink) staining, tidemark changes (arrows), and presence of a subchondral cyst (asterisk) in a 12-week HRHF rat; changes absent in a FRC rat (left part of panel). This region was used to generate the data shown in panel E. (C) Serum levels of C1,2C, assayed using ELISA. Symbols: aa: p < 0.01, compared to LRLF rats; bb: p < 0.01, compared to HRLF rats; dd: p < 0.01, compared to HRHF rats; **: p < 0.01, compared to food restricted control (FRC) rats (mean FRC values are indicated by dashed line). Mean and SEM are shown. Scale bar = 50 micrometer.

Mentions: No evidence of cartilage pathology was observed in any of the 0-week trained only rat groups. By week 12, cartilage pathology was evident in HRHF rats (Figure 8). A significant interaction effect was observed for cartilage pathology (the Mankin score; Figure 8A), but a force effect only for serum C1,2C (a general marker of collagen type I and type II degradation) (Figure 8C). Specifically, in the distal radius articular cartilage, histological Mankin scoring showed increased pathology in 12-week HRHF rats (Figure 8A). Figure 8B right panel shows pathological changes in 12-week HRHF rats, including loss of proteoglycan content (reduced Safranin O, pink, staining), an altered tidemark region (arrows), and presence of subchondral cysts (asterisk). These attributes were not observed in FRC rat cartilage (Figure 8B left panel). Serum levels of C1,2C were increased in both 12-week LRHF and HRHF rats, compared to NC, LRLF and HRLF rats (Figure 8C).


The interaction of force and repetition on musculoskeletal and neural tissue responses and sensorimotor behavior in a rat model of work-related musculoskeletal disorders.

Barbe MF, Gallagher S, Massicotte VS, Tytell M, Popoff SN, Barr-Gillespie AE - BMC Musculoskelet Disord (2013)

Cartilage responses, assayed using histomorphometry and ELISA, after performance of either a LRLF, HRLF, LRHF and HRHF task for 12 weeks. (A) Summated Mankin score results, a histopathological scoring system used to assay changes in the distal radial articular cartilage. (B) Representative photos of the distal radial articular cartilage showing a pathological loss of Safranin O (pink) staining, tidemark changes (arrows), and presence of a subchondral cyst (asterisk) in a 12-week HRHF rat; changes absent in a FRC rat (left part of panel). This region was used to generate the data shown in panel E. (C) Serum levels of C1,2C, assayed using ELISA. Symbols: aa: p < 0.01, compared to LRLF rats; bb: p < 0.01, compared to HRLF rats; dd: p < 0.01, compared to HRHF rats; **: p < 0.01, compared to food restricted control (FRC) rats (mean FRC values are indicated by dashed line). Mean and SEM are shown. Scale bar = 50 micrometer.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC3924406&req=5

Figure 8: Cartilage responses, assayed using histomorphometry and ELISA, after performance of either a LRLF, HRLF, LRHF and HRHF task for 12 weeks. (A) Summated Mankin score results, a histopathological scoring system used to assay changes in the distal radial articular cartilage. (B) Representative photos of the distal radial articular cartilage showing a pathological loss of Safranin O (pink) staining, tidemark changes (arrows), and presence of a subchondral cyst (asterisk) in a 12-week HRHF rat; changes absent in a FRC rat (left part of panel). This region was used to generate the data shown in panel E. (C) Serum levels of C1,2C, assayed using ELISA. Symbols: aa: p < 0.01, compared to LRLF rats; bb: p < 0.01, compared to HRLF rats; dd: p < 0.01, compared to HRHF rats; **: p < 0.01, compared to food restricted control (FRC) rats (mean FRC values are indicated by dashed line). Mean and SEM are shown. Scale bar = 50 micrometer.
Mentions: No evidence of cartilage pathology was observed in any of the 0-week trained only rat groups. By week 12, cartilage pathology was evident in HRHF rats (Figure 8). A significant interaction effect was observed for cartilage pathology (the Mankin score; Figure 8A), but a force effect only for serum C1,2C (a general marker of collagen type I and type II degradation) (Figure 8C). Specifically, in the distal radius articular cartilage, histological Mankin scoring showed increased pathology in 12-week HRHF rats (Figure 8A). Figure 8B right panel shows pathological changes in 12-week HRHF rats, including loss of proteoglycan content (reduced Safranin O, pink, staining), an altered tidemark region (arrows), and presence of subchondral cysts (asterisk). These attributes were not observed in FRC rat cartilage (Figure 8B left panel). Serum levels of C1,2C were increased in both 12-week LRHF and HRHF rats, compared to NC, LRLF and HRLF rats (Figure 8C).

Bottom Line: In most cases, performance of the HRHF task induced the greatest tissue degenerative changes, while performance of moderate level tasks induced bone adaptation and a suggestion of muscle adaptation.Both high force tasks induced median nerve macrophage infiltration, spinal cord sensitization (increased substance P), grip strength declines and forepaw mechanical allodynia by task week 12.Prolonged performance of HRHF tasks exhibited significantly increased risk for musculoskeletal disorders, while performance of moderate level tasks exhibited adaptation to task demands.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Anatomy and Cell Biology, Temple University School of Medicine, 3500 North Broad St, Philadelphia 19140, PA, USA. mary.barbe@temple.edu.

ABSTRACT

Background: We examined the relationship of musculoskeletal risk factors underlying force and repetition on tissue responses in an operant rat model of repetitive reaching and pulling, and if force x repetition interactions were present, indicative of a fatigue failure process. We examined exposure-dependent changes in biochemical, morphological and sensorimotor responses occurring with repeated performance of a handle-pulling task for 12 weeks at one of four repetition and force levels: 1) low repetition with low force, 2) high repetition with low force, 3) low repetition with high force, and 4) high repetition with high force (HRHF).

Methods: Rats underwent initial training for 4-6 weeks, and then performed one of the tasks for 12 weeks, 2 hours/day, 3 days/week. Reflexive grip strength and sensitivity to touch were assayed as functional outcomes. Flexor digitorum muscles and tendons, forelimb bones, and serum were assayed using ELISA for indicators of inflammation, tissue stress and repair, and bone turnover. Histomorphometry was used to assay macrophage infiltration of tissues, spinal cord substance P changes, and tissue adaptative or degradative changes. MicroCT was used to assay bones for changes in bone quality.

Results: Several force x repetition interactions were observed for: muscle IL-1alpha and bone IL-1beta; serum TNFalpha, IL-1alpha, and IL-1beta; muscle HSP72, a tissue stress and repair protein; histomorphological evidence of tendon and cartilage degradation; serum biomarkers of bone degradation (CTXI) and bone formation (osteocalcin); and morphological evidence of bone adaptation versus resorption. In most cases, performance of the HRHF task induced the greatest tissue degenerative changes, while performance of moderate level tasks induced bone adaptation and a suggestion of muscle adaptation. Both high force tasks induced median nerve macrophage infiltration, spinal cord sensitization (increased substance P), grip strength declines and forepaw mechanical allodynia by task week 12.

Conclusions: Although not consistent in all tissues, we found several significant interactions between the critical musculoskeletal risk factors of force and repetition, consistent with a fatigue failure process in musculoskeletal tissues. Prolonged performance of HRHF tasks exhibited significantly increased risk for musculoskeletal disorders, while performance of moderate level tasks exhibited adaptation to task demands.

Show MeSH
Related in: MedlinePlus