Objective: The aim of this study was to evaluate the effects of key gap (distance between edges of keys) on computer keyboards on typing speed, percentage error, preference, and usability. Background: In Parts 1 and 2 of this series, a small key pitch (center-to-center distance between keys) was found to reduce productivity and usability, but the findings were confounded by gap. In this study, key gap was varied while holding key pitch constant. Method: Participants ( N = 25) typed on six keyboards, which differed in gap between keys (1, 3, or 5 mm) and pitch (16 or 17 mm; distance between centers of keys), while typing speed, accuracy, usability, and preference were measured. Results: There was no statistical interaction between gap and pitch. Accuracy was better for keyboards with a gap of 5 mm compared to a 1-mm gap ( p = .04). Net typing speed ( p = .02), accuracy ( p = .002), and most usability measures were better for keyboards with a pitch of 17 mm compared to a 16-mm pitch. Conclusions: The study findings support keyboard designs with a gap between keys of 5 mm over 1 mm and a key pitch of 17 mm over 16 mm. Applications: These findings may influence keyboard standards and design, especially the design of small keyboards used with portable devices, such as tablets and laptops.
Introduction Occupational physical activity (OPA), including occupational lifting (OL), seems to increase the risk of cardiovascular disease (CVD). Knowledge about the association between OL and risk of CVD is sparse, but repeated OL is assumed to result in prolonged raised blood pressure and heart rate (HR) eventually augmenting the risk of CVD. To disentangle parts of the mechanisms behind the raised 24-hour ambulatory blood pressure measurement (24h-ABPM), by exposure to OL, this study aimed to explore the acute differences in 24h-ABPM, relative aerobic workload (RAW) and OPA across workdays with and without OL, and secondary to assess the feasibility and rater agreement of direct field observations of the frequency and load of occupational lifting.
Methods This controlled cross-over study investigates associations between moderate to high OL and 24h-ABPM, RAW in per cent of heart rate reserve (%HRR) and level of OPA. This included 2x24h monitoring of 24h-ABPM (Spacelabs 90217), PA (Axivity) and HR (Actiheart), comprising a workday containing OL and a workday without. The frequency and burden of OL were directly observed in field. The data were time synchronized and processed in the Acti4 software. Differences across workdays with and without OL in 24h-ABPM, RAW and OPA were evaluated using repeated 2 × 2 mixed-models among 60 blue-collar workers in Denmark.. Exposure to OL was estimated by direct manual field observation, registering burden and frequency of OL. Interrater reliability tests were performed across 15 participants representing 7 occupational groups. Interclass correlation coefficient (ICC) estimates of total burden lifted and frequency of lifts were calculated, based on a mean-rating (k = 2), absolute-agreement, 2 way mixed-effects model, indicating the raters as fixed effects.
Results OL led to non-significant increases in ABPM during work-time (systolic Δ1.79 mmHg, 95%CI −4.49–8.08, diastolic Δ0.43 mmHg, 95%CI −0.80–1.65), and on 24-hours basis (systolic Δ1.96 mmHg, 95%CI −3.80–7.72, diastolic Δ0.53 mmHg, 95%CI −3.12–4.18), significant increases in RAW during work (Δ7.74 %HRR, 95%CI 3.57–11.91) as well as a raised level of OPA (Δ4156.88 steps, 95%CI 1898.83–6414.93, Δ−0.67 hours of sitting time, 95%CI −1.25–0.10, Δ−0.52 hours of standing time, 95%CI −1.03–0.01, Δ0.48 hours of walking time, 95%CI 0.18–0.78). ICC estimates were 0.998 (95% CI 0.995–0.999) for total burden lifted and 0.992 (95% CI 0.975–0.997) for frequency of lift.
Discussion OL increased both intensity and volume of OPA among blue-collar workers, which supposedly to contributes to an augmented risk of CVD. Although this study finds hazardous acute effects, further investigations are needed to evaluate the long-term effects of OL on ABPM, HR and volume of OPA, also effects of cumulative exposure to OL would be relevant to investigate.
Conclusion OL significantly raised the intensity and volume of OPA. Direct field observation of occupational lifting showed an excellent interrater reliability.
Abstract Ischemic heart disease (IHD) causes mortality and morbidity. High levels of occupational physical activity (OPA) increases IHD risk, and occupational lifting (OL) is suggested as a detrimental OPA exposure. This study investigated the association between accumulated OL throughout working life, and risk for IHD, and potential sex and hypertension differences. Data from Copenhagen Ageing and Midlife Biobank linked to register-based information on incident IHD during 9 years follow-up in the Danish National Patient Registry were included. The outcome was the odds of IHD from baseline (2009–2011) to end of follow-up (2018), among participants without IHD at baseline. Accumulated OL was assessed by linking occupational codes to a Job Exposure Matrix, creating a measure in ton-years (lifting 1,000 kg/day/year). Multivariable logistic regression tested associations between level of accumulated OL and IHD, among the 6,606 included individuals (68% men). During follow-up, 7.3% men and 3.6% women were hospitalized with IHD. Among all participants, the odds for IHD were 47% (OR 1.47, 95% CI 1.05–2.06) higher among those with ≥5 to <10 ton-years, 39% (OR 1.39, 95% CI 1.06–1.83) higher among those with ≥10 to <30 ton-years, and 62% (OR 1.62, 95% CI 1.18–2.22) higher among those with ≥30 ton-years, compared to no accumulated OL. However, these increased odds were in the same direction in the fully-adjusted model but statistically insignificant, ≥5 to <10 ton-years OR 1.28, 95% CI 0.88–1.88; ≥10 to <30 ton-years OR 1.20, 95% CI 0.85–1.69; and ≥30 ton-years OR 1.22, 95% CI 0.81–1.84. No statistically significant interactions, nor any associations, between OL and sex, or hypertension were seen.
