Trends in industry are leaning toward stereotyped jobs with low workloads. Physical variation is an intervention to reduce fatigue and potentially musculoskeletal disorders in such jobs. Controlled laboratory studies have provided some insight into the effectiveness of physical variation, but very few have been devoted to force variation without muscular rest as a component. This study was undertaken to determine multiple physiological responses to five isometric elbow extension protocols with the same mean amplitude (15% maximum voluntary contraction, MVC), cycle time (6 s), and duty cycle (50 %). Sustained (15 %Sus) and intermittent contractions including zero force (0-30 %Int) differed significantly in 19 of 27 response variables. Contractions varying by half the mean force (7.5-22.5 %Int) led to 8 and 7 measured responses that were significantly different from 0-30 %Int and 15 %Sus, respectively. A sinusoidal condition (0-30 %Sine) resulted in 2 variables that were significantly different from 0-30 %Int, and 16 different from 15 %Sus. Finally, ten response variables suggested that varying forces with 1 % as the lower contraction level was significantly less fatiguing than 15 %Sus, while no responses were significantly different from 0-30 %Int. Sustained contractions led to decreased twitch force 24-h post-exercise, whereas recovery was complete within 60 min after intermittent contractions. This suggests that time-varying force may be a useful intervention to reduce local fatigue in workers performing low-load tasks, and also that rest per se did not seem to cause any extraordinary effects beyond those predictable from the force variation amplitude.

ObjectivesJob exposure matrices (JEMs) can be constructed from expert-rated assessments, direct measurement and self-reports. This paper describes the construction of a general population JEM based on self-reported physical exposures, its ability to create homogeneous exposure groups (HEG) and the use of different exposure metrics to express job-level estimates.MethodsThe JEM was constructed from physical exposure data obtained from the Cohorte des consultants des Centres d’examens de santé (CONSTANCES). Using data from 35 526 eligible participants, the JEM consisted of 27 physical risk factors from 407 job codes. We determined whether the JEM created HEG by performing non-parametric multivariate analysis of variance (NPMANOVA). We compared three exposure metrics (mean, bias-corrected mean, median) by calculating within-job and between-job variances, and by residual plots between each metric and individual reported exposure.ResultsNPMANOVA showed significantly higher between-job than within-job variance among the 27 risk factors (F(253,21964)=61.33, p<0.0001, r2=41.1%). The bias-corrected mean produced more favourable HEG as we observed higher between-job variance and more explained variance than either means or medians. When compared with individual reported exposures, the bias-corrected mean led to near-zero mean differences and lower variance than other exposure metrics.ConclusionsCONSTANCES JEM using self-reported data yielded HEGs, and can thus classify individual participants based on job title. The bias-corrected mean metric may better reflect the shape of the underlying exposure distribution. This JEM opens new possibilities for using unbiased exposure estimates to study the effects of workplace physical exposures on a variety of health conditions within a large general population study.

ObjectivesJob exposure matrices (JEMs) are increasingly used to estimate physical workplace exposures. We conducted a cross-national comparison of exposure estimates from two general population JEMs to aid the interpretation of exposure–outcome associations across countries and to explore the feasibility of cross-national application of JEMs to provide workplace physical exposure estimates.MethodsWe compared physical exposure estimates from two general population JEMs created from the FrenchCohorte des consultants des Centres d’examens de santé study (27 exposure variables) and the American Occupational Information Network database (21 exposure variables). These exposure variables were related to physical demands or ergonomic risk factors for musculoskeletal disorders. We used a crosswalk to match French Profession et Catégorie Sociale job codes with American Standard Occupational Classification job codes and calculated Spearman’s correlations and Cohen’s kappa values for exposure variable pairs between these French and American JEMs. We defined a priori 50 matched French and American JEM variable pairs that measured similar exposures.ResultsAll variable pairs measuring similar physical exposures demonstrated positive correlations. Among the 50 matched pairs, 33 showed high correlation (ρ≥0.70) and 46 showed at least moderate agreement (κ≥0.41). Exposures expected to be mutually exclusive (manual work vs office work) showed strongly negative correlations.ConclusionsFrench and American general population physical exposure JEMs were related, sharing moderate to high association and moderate to substantial agreement between the majority of variable pairs measuring similar exposures. These findings will inform cross-national comparisons of study results and support some uses of general population JEMs outside their countries of origin.

A B S T R A C TIncorporating touchscreen interaction into cockpit flight systems offers several potential advantages to aircraft manufacturers, airlines, and pilots. However, vibration and turbulence are challenges to reliable interaction. We examine the design space for braced touch interaction, which allows users to mechanically stabilise selections by bracing multiple fingers on the touchscreen before completing selection. Our goal is to enable fast and accurate target selection during high levels of vibration, without impeding interaction performance when vibration is absent. Three variant methods of braced touch are evaluated, using doubletap, dwell, or a force threshold in combination with heuristic selection criteria to discriminate intentional selection from concurrent braced contacts. We carried out an experiment to test the performance of these methods in both abstract selection tasks and more realistic flight tasks. The study results confirm that bracing improves performance during vibration, and show that doubletap was the best of the tested methods.

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