Intervention practices in musculoskeletal disorder prevention: a critical literature review.

Musculoskeletal disorders (MSDs) affect much of the workforce and remain a major form of occupational ill health. With a view to improving the efficacy of interventions, this review examined preventative actions relating to these disorders. A detailed analysis grid was used to classify the information contained in the 47 reviewed articles whose common aspect was to report actions carried out in the workplace that led to the implementation of changes to prevent MSDs. The analysis identified and characterized three major categories of intervention processes in MSD prevention: the complete type (n=17), the shortened type (n=16), and the turnkey type (n=14). These three groups of intervention processes were differentiated by their approaches and their contexts of application. The result was important differences in the changes implemented. Because of the variability in intervention processes and possible impacts on MSD prevention, a proposal to "delimit" these processes so as to improve their effectiveness is presented.

Participatory ergonomic processes to reduce musculoskeletal disorders: summary of a Québec experience.

This article critically reviews 11 participatory ergonomic interventions carried out in Québec by the Occupational Health and Safety Research Institute (IRSST). In the introduction, the characteristics of the approach used are situated in relation to the literature on this subject. Based on the "Ergo team" formula, the approach aims to provide company personnel with the skills to analyze and correct hazardous workstations in relation to musculoskeletal disorders (MSD), using an analysis process that the researchers developed. Although isolated workstations were corrected, the process aims for more general impacts on the company. In the 11 interventions, 40 work situations were analyzed, and in 31 cases, changes were implemented to reduce MSD risks. The most common changes dealt with the tools/equipment (77.4% and physical layouts (84%); changes involving work methods (29% and work organization (12.9%) were less common. The difficulties encountered in the interventions are summarized, and the possible impacts of the interventions on the organization and psychosocial factors are discussed. The authors then address the limitations of the paper and the factors that should be considered in evaluating such a participatory process. The authors conclude that the participatory process was successful in implementing changes in companies and that other studies are necessary for a better understanding of the process and its impacts.

Sex differences in lifting strategies during a repetitive palletizing task.

Forty-five manual material handlers (15 females, 15 expert males and 15 novice males) performed series of box transfers under conditions similar to those of large distribution centers. The objective of the study was to verify whether sex differences in joint motions and in back loading variables (L5/S1 moments) exist during multiple box transfers. The task consisted in transferring 24 15-kg boxes from one pallet to another (4 layers of boxes; 6 boxes/layer: 3 in the front row, 3 in the back) at a self-determined pace and then at an imposed pace of 9 lifts/min. Full-body 3D kinematic data were collected as well as external foot forces. A dynamic 3D linked segment model was used to estimate the net moments at L5/S1. The results show that the peak L5/S1 moment during lifting for females was significantly lower than for males, but once normalized to body size the difference disappeared. In general, the female workers were very close to the posture adopted by the novice males at the instant of the peak resultant moment. However, females were closer to the box than the male workers. One major sex difference was seen when lifting from the ground, with the use of interjoint coordination analyses. Female workers showed a sequential motion initiated by the knees, followed by the hip and the back, while expert males showed a more synchronized motion. The lifting strategy of females likely stretches lumbar spine passive tissues, which in turn put them at greater risk of back injuries. As observed in our previous studies, these differences between expert males, novice males and females are especially notable when the box is lifted from the ground.

Functional origin of rate-induced changes in atrioventricular nodal conduction time of premature beats in the rabbit.

The characteristics and origin of the rate-induced changes in atrioventricular nodal conduction time of premature beats (A2H2 intervals) were studied in isolated rabbit heart preparations. Increasing the basic driving rate during a periodic premature stimulation prolonged (a net inhibitory effect) and shortened (a net facilitatory effect) significantly (p less than 0.01, n = 17) the A2H2 intervals associated with long and short recovery times (H1A2 intervals), respectively. The origin of these responses was sought for by analyzing interactions between facilitation and fatigue. When the fatigue developed at a fast basic rate was estimated from changes in conduction time of basic beats and subtracted from the corresponding A2H2 intervals, the calculated A2H2 intervals showed enhanced facilitation but no fatigue. When independently obtained fatigue and facilitation effects were added to the control A2H2 intervals for corresponding H1A2 intervals, resulting A2H2 intervals correlated strongly with the ones observed at the equivalent fast basic rate (r = 0.99, p less than 0.001). Moreover, changes in the A2H2 intervals of premature beats tested with constant coupling intervals during 5-min fast rates were biphasic, confirming the overlapping and competition between facilitation and fatigue effects. Hence, rate-induced deviations of premature nodal conduction time from that predicted by changes in recovery time are consistent and result from the interaction between the overlapping effects produced by two independent, antagonist, and dynamically distinct nodal properties (facilitation and fatigue).

Selective functional characteristics of rate-induced fatigue in rabbit atrioventricular node.

The slowly developing rate-induced prolongation in atrioventricular nodal conduction time, termed "fatigue," was selectively studied using specifically designed stimulation protocols in isolated rabbit heart preparations. A nodal recovery curve (A2H2 versus H1A2 intervals; nodal conduction time of each premature beat plotted against corresponding recovery time) was obtained before and after a stable and nearly maximum fatigue had been reached by driving the atrium for 5 minutes at a fast rate close to the upper limit of 1:1 nodal conduction. The fatigue uniformly prolonged all A2H2 intervals (12.3 +/- 1.3 msec) and systematically increased the minimum H1A2 interval at which complete nodal block occurred (24.8 +/- 4.0 msec) (p less than 0.01, n = 6). To study the rate and time dependence of fatigue, nodal conduction times were obtained during three rapid 5-minute pacings corresponding to 50%, 75%, and 100% shortening of the pacing interval in the 1:1 nodal conduction range. The respective maximum fatigue-induced increases in conduction time were 5.4 +/- 1.8, 9.0 +/- 2.7, and 12.5 +/- 2.1 msec (p less than 0.01, n = 6). However, the pacing interval had no significant effect on the time required to reach either 50% (17.1 +/- 3.5 seconds) or 90% (92.6 +/- 15.4 seconds) of the fatigue observed after 5 minutes of fast rate. At the termination of any rapid stimulation, the fatigue effect dissipated with a time course that was inverse but symmetrical to that of its induction. These findings support the existence of an independent, slow, nodal memory process by which the conduction time changes according to past events with a long time constant.

Training in handling: an evaluative study.

Training programmes in handling have been one of the most used means of preventing work-related backache. The effectiveness of these programmes has not yet been demonstrated however, since they have rarely been evaluated. The purpose of this study was precisely to assess one of these programmes in the hospital sector which specifically dealt with the handling of patients. A field study was conducted and handling methods used by 32 trained orderlies were characterized using an observational grid developed and validated specifically to describe patient handling operations. The extent to which these orderlies used the handling methods taught was determined, and the observed deviations from these methods were characterized and interpreted. The results show that the handling principles taught (working with a straight back using the legs) were not frequently used in the workplace. Furthermore, the use of training was closely related to the type of handling carried out. In handling operations in which the effort includes a horizontal component (mainly those carried out in bed) the training was hardly used, while in vertical handling operations the taught principles were more frequently used. These results suggest that actual training is not well adapted to the handling of patients, particularly to horizontal handling carried out in the bed. Two main deficiencies in the actual programmes are pointed out. First, it is shown that, for reasons of physical constraints, training could not always be applied; second, the rationale of the taught principles could also be questioned, particularly the emphasis given to the use of the legs.

Electrogenesis of freshly explanted spontaneously active clusters of neonatal rat ventricle cells.

Spontaneously active explanted rat ventricle cells show 4 to 7 h after explantation fast rising TTX sensitive action potentials but 24 h after explantation, electrogenesis is determined by slow rising. Mn sensitive action potentials. Because 4 to 7 h after explantation the electrical properties of the cells resemble more those of the tissue they were derived from than of cells 24 h after explantation, we conclude that the occurrence of slow rising action potentials is not directly related to the method of tissue disintegration but develops gradually after explantation.