Robert G. Cutlip

Work, Obesity, and Occupational Safety and Health

There is increasing evidence that obesity and overweight may be related, in part, to adverse work conditions. In particular, the risk of obesity may increase in high-demand, low-control work environments, and for those who work long hours. In addition, obesity may modify the risk for vibration-induced injury and certain occupational musculoskeletal disorders. We hypothesized that obesity may also be a co-risk factor for the development of occupational asthma and cardiovascular disease that and it may modify the workers response to occupational stress, immune response to chemical exposures, and risk of disease from occupational neurotoxins. We developed 5 conceptual models of the interrelationship of work, obesity, and occupational safety and health and highlighted the ethical, legal, and social issues related to fuller consideration of obesitys role in occupational health and safety.

Evaluation of an instrumented walkway for measurement of the kinematic parameters of gait

The purpose of this study was to compare kinematic gait parameters measured with an instrumented walkway system (GAITRite(R)) and a video-based system (peak performance motus 3.1(R)). Subjects walked across a GAITRite mat with embedded pressure sensors. Reflective markers were attached to subjects shoes and video capture was simultaneously performed during each trial. Video data were then digitized manually using peak software. Correlation coefficients for all parameters measured with both systems were high (>/=0.94). Significant differences between systems were found with analysis of variance (ANOVA) for two parameters, step length and stride velocity (P=0.003, 0.0002). The results of this study indicate that the instrumented walkway gave comparable results for temporal parameters but further investigation is needed to evaluate the fidelity of its spatial performance.

National occupational research agenda (NORA) future directions in occupational musculoskeletal disorder health research.

Musculoskeletal disorders are among the most costly health care problems facing society today. The scientific literature has indicated that psychosocial factors, individual factors, workplace physical requirements, and workplace organizational factors have been associated with risk. Since musculoskeletal risk is multi-dimensional, the magnitude of risk attributable to various factors can be of importance to scientists and policy makers in designing countermeasures to reduce injury incidence. Traditionally, the disciplines of biomechanics, physiology, and psychophysics have dominated the body of knowledge that has defined exposure limitations to work. However, recent research has explored the association of psychosocial and work organization factors with musculoskeletal problems. Advances have been made to better quantify the levels of occupational exposure by improved exposure metrics, quantification of three-dimensional loads experienced by certain joints (e.g. the spine), identification of tissue tolerance limits and tissue response to mechanical stresses, and the impact of psychosocial stresses. However, efforts to quantitatively link epidemiological, biomechanical loading, soft tissue tolerance, and psychosocial studies should be pursued to establish a better understanding of the pathways of injury and resultant preventive strategies. Although we are beginning to understand how the major risk factors influence the load-tolerance relationship of human tissue, how these risk factors interact is virtually unexplored. Since the impact of the interactions may be far greater than that of any individual factor, the impact of the interactions between risk factors must be delineated so that work-related risk can be better quantified. Efforts to quantitatively link epidemiological, biomechanical loading, soft tissue tolerance, and psychosocial studies should be pursued to establish a better understanding of the pathways of injury and resultant preventive strategies.

Resistance training increases heat shock protein levels in skeletal muscle of young and old rats

Heat shock proteins (HSP) HSP72, HSC70 and HSP25 protein levels and mRNA levels of HSP72 genes (Hsp72-1, Hsp72-2, Hsp72-3) and HSC70 were examined in tibialis anterior muscles from young and old rats following 4.5 weeks of heavy resistance exercise. Young (3 months) (n=10) and old (30 months) (n=9) rats were subjected to 14 sessions of electrically evoked resistance training using stretch-shortening contractions of the left limb that activated the dorsiflexor muscle group, including the tibialis anterior muscle, while the right side served as the intra-animal control. Muscle wet weight of the left tibialis anterior increased by 15.6% in young animals compared to the untrained right side, while the aged rats demonstrated no significant hypertrophy based on muscle wet weight. There were no differences in mRNA expression between the control and experimental muscles in either the old or the young animals for any of the four genes examined. On the other hand, HSP72 levels as determined by Western blots were significantly (p<0.01) higher (968.8 and 409.1%) in the trained as compared to the contralateral control muscle in young and old animals, respectively. HSP25 expression was increased significantly (p<0.01) by training in muscles of young rats (943.1%) and old rats (420.3%). Moreover, there was no training by age interaction for HSP72, while a significant age and training by age effects were found in muscles for HSP25. There was no change in HSC70 protein expression in response to the training intervention in either age group. SOD-1 enzyme level increased by 66.6% in the trained muscles of the young rats, while this enzyme was 33% lower in trained muscles compared to the untrained control side in old rats. Moreover, a significant (p<0.05) training by age interaction was found for SOD-1 enzyme levels. This study suggests that fast contracting muscles in young and old animals are capable of increasing HSP expression in response to high intensity contractile stress. Furthermore, the data are consistent with the hypothesis that higher levels of oxidative stress in muscles of old animals limit HSP levels and/or function in response to high intensity contractile stress.

Dynamic force responses of skeletal muscle during stretch–shortening cycles

Muscle damage due to stretch–shortening cycles (i.e., cyclic eccentric/concentric muscle actions) is one of the major concerns in sports and occupational related activities. Mechanical responses of whole muscle have been associated with damage in neural motor units, in connective tissues, and the force generation mechanism. The objective of this study was to introduce a new method to quantify the real-time changes in skeletal muscle forces of rats during injurious stretch–shortening cycles. Male Sprague Dawley rats (n=24) were selected for use in this study. The dorsi flexor muscle group was exposed to either 150 stretch–shortening cycles (n=12) or 15 isometric contractions (n=12) in vivo using a dynamometer and electrical stimulation. Muscle damage after exposure to stretch–shortening cycles was verified by the non-recoverable force deficit at 48xa0h and the presence of myofiber necrosis. Variations of the dynamic forces during stretch–shortening cycles were analyzed by decomposing the dynamic force signature into peak force (Fpeak), minimum force (Fmin), average force (Fmean), and cyclic force (Fa). After the 15th set of stretch–shortening cycles, the decrease in the stretch–shortening parameters, Fpeak, Fmin, Fmean, and Fa, was 50% (P<0.0001), 26% (P=0.0055), 68% (P<0.0001), and 50% (P<0.0001), respectively. Our results showed that both isometric contractions and stretch–shortening cycles induce a reduction in the isometric force. However, the force reduction induced by isometric contractions fully recovered after a break of 48xa0h while that induced by stretch–shortening cycles did not. Histopathologic assessment of the tibialis anterior exposed to stretch–shortening cycles showed significant myofiber degeneration and necrosis with associated inflammation, while muscles exposed to isometric contractions showed no myofiber degeneration and necrosis, and limited inflammation. Our results suggest that muscle damage can be identified by the non-recoverable isometric force decrement and also by the variations in the dynamic force signature during stretch–shortening cycles.

Simultaneous determination of the nonlinear-elastic properties of skin and subcutaneous tissue in unconfined compression tests.

Background/aims: The compressive nonlinear‐elastic properties of soft tissues are usually determined using unconfined compression tests. To determine the nonlinear‐elastic behavior of skin and subcutaneous tissue using a conventional approach, the skin and subcutaneous tissue had to be separated before testing. Using such an approach, measurement errors may be increased as a consequence of the reduced specimen dimensions and cumulative experimental errors. In the present study, we propose a novel method to determine the nonlinear‐elastic behaviors of the skin and the subcutaneous tissue simultaneously using specimens of skin/subcutaneous composites.

Proapoptotic factor Bax is increased in satellite cells in the tibialis anterior muscles of old rats.

Aging impairs the ability of muscle to adapt to exercise or injury. The goal of this study was to determine whether age‐related changes in muscle adaptability could be the result of satellite cell apoptosis. Ten days after exposure to an injury protocol, estimates of edema in the exposed tibialis anterior muscles were higher in old (30 months) than young (3 months) rats, and isometric force levels were lower in old rats. Both young and old rats displayed an increase in MyoD labeling in the exposed muscle, indicating that injury induced satellite‐cell activation. However, there were more MyoD‐labeled cells that coexpressed the proapoptotic factor, Bax, in old than in young rats, suggesting that decrements in muscle recovery may be associated with an increase in satellite‐cell apoptosis. Based on these findings we conclude that reducing satellite‐cell apoptosis in aged animals may improve muscle recovery after injury. Muscle Nerve, 2006

Injury and adaptive mechanisms in skeletal muscle.

Work-related musculoskeletal disorders (MSD) are a major concern in the United States. Overexertion and repetitive motion injuries dominate reporting of lost-time MSD incidents. Over the past three decades, there has been much study on contraction-induced skeletal muscle injury. The effect of the biomechanical loading signature that includes velocity, range of motion, the number of repetitions, force, work-rest cycle, and exposure duration has been studied. More recently, the effect of aging on muscle injury susceptibility and regeneration has been studied. This review will focus on contraction-induced skeletal muscle injury, the effects of repetitions, range of motion, work-rest cycles, and aging on injury susceptibility and regenerative and adaptive pathways. The different physiological phenomena responsive to overt muscle injury versus adaptation will be distinguished. The inherent capability of skeletal muscle to adapt to mechanical loading, given the appropriate exposure signature will also be discussed. Finally, we will submit that repeated high-intensity mechanical loading is a desirable means to attenuate the effects of sarcopenia, and may be the most effective and appealing mode of physical activity to counteract the effects often observed with musculo-skeletal dysfunction in the workplace.

A comparison of different postures for scaffold end-frame disassembly.

Overexertion and fall injuries comprise the largest category of nonfatal injuries among scaffold workers. This study was conducted to identify the most favourable scaffold end-frame disassembly techniques and evaluate the associated slip potential by measuring whole-body isometric strength capability and required coefficient of friction (RCOF) to reduce the incidence of injury. Forty-six male construction workers were used to study seven typical postures associated with scaffold end-frame disassembly. An analysis of variance (ANOVA) showed that the isometric forces (334.4-676.3 N) resulting from the seven postures were significantly different (p < 0.05). Three of the disassembly postures resulted in considerable biomechanical stress to workers. The symmetric front-lift method with hand locations at knuckle height would be the most favourable posture; at least 93% of the male construction worker population could handle the end frame with minimum overexertion risk. The static RCOF value resulting from this posture during the disassembly phase was less than 0.2, thus the likelihood of a slip should be low.

Modeling of the muscle/tendon excursions and moment arms in the thumb using the commercial software anybody

A biomechanical model of a thumb would be useful for exploring the mechanical loadings in the musculoskeletal system, which cannot be measured in vivo. The purpose of the current study is to develop a practical kinematic thumb model using the commercial software Anybody (Anybody Technology, Aalborg, Denmark), which includes real CT-scans of the bony sections and realistic tendon/muscle attachments on the bones. The thumb model consists of a trapezium, a metacarpal bone, a proximal and a distal phalanx. These four bony sections are linked via three joints, i.e., IP (interphalangeal), MP (metacarpophalangeal) and CMC (carpometacarpal) joints. Nine muscles were included in the proposed model. The theoretically calculated moment arms of the tendons are compared with the corresponding experimental data by Smutz et al. [1998. Mechanical advantage of the thumb muscles. J. Biomech. 31(6), 565-570]. The predicted muscle moment arms of the majority of the muscle/tendon units agree well with the experimental data in the entire range of motion. Close to the end of the motion range, the predicted moment arms of several muscles (i.e., ADPt and ADPo (transverse and oblique heads of the adductor pollicis, respectively) muscles for CMC abduction/adduction and ADPt and FPB (flexor pollicis brevis) muscle for MP extension/flexion) deviate from the experimental data. The predicted moment potentials for all muscles are consistent with the experimental data. The findings thus suggest that, in a biomechanical model of the thumb, the mechanical functions of muscle-tendon units with small physiological cross-sectional areas (PCSAs) can be well represented using single strings, while those with large PCSAs (flat-wide attachments, e.g., ADPt and ADPo) can be represented by the averaged excursions of two strings. Our results show that the tendons with large PCSAs can be well represented biomechanically using the proposed approach in the major range of motion.