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In 2012, the Danish Parliament decided to increase retirement age. Unfortunately, elderly people working in a physically demanding environment may be rendered unable to retain the ability to adequately perform the physical requirements of their jobs, due to age-related decreases in physical performance. Therefore, increasing the retirement age may not necessarily lead to the goal of keeping everybody in the labor market for a longer time. To date, our knowledge about the variations in physical performance of the elderly workforce is limited.
In this cross-sectional study we seek to investigate the effects of aging on physical performance among elderly manual workers.
Approximately 100 Danish manual workers between 50 and 70 years of age will be recruited. The main measurement outcomes include: (1) inflammatory status from blood samples; (2) body composition; (3) lung function; (4) static and dynamic balance; (5) reaction time, precision, and movement variability during a hammering task; (6) handgrip strength, rate of force development, and force tracking; (7) estimated maximal rate of oxygen consumption; and (8) back mobility. Additionally, information regarding working conditions, physical activity levels, and health status will be assessed with a questionnaire.
Data collection is expected to take place between autumn 2017 and spring 2018.
This study will increase the knowledge regarding variations in physical performance in the elderly workforce and may identify potential workplace hazards. Moreover, this study might shed light on the potentially problematic decision to increase retirement age for all Danish citizens.
It is expected that the world’s proportion of elderly people above the age of 60 years will almost double within the next 35 years [
Aging is associated with a gradual loss of muscle mass, strength, and power [
Contrary to the age-related loss of respiratory capacity, skeletal muscle strength is relatively well preserved until the age of 50 years. From this age, the annual decline in strength is approximately 1-2%, whereas muscle power is lost at an even faster rate [
Sarcopenia, also known as the age-related loss of muscle mass, typically starts from the end of the fifth decade of life [
Balance is typically compromised in elderly people. Although postural control is largely related to muscle strength and the ability to produce rapid force, it also requires an integration of the information from the visual, vestibular, and somatosensory systems to generate the appropriate motor response to maintain static and dynamic balance [
To date, we know too little about how physically demanding work affects physical performance and how declining physical performance affects the ability to perform physically demanding work in elderly populations. Specifically, more information is needed about how different work exposures, health statuses, and physical activity levels relate to different measures of physical performance. Although some of the reductions in physical performance might begin as early as the third decade of life, the most pronounced impairments occur starting from the fifth decade. Thus, information regarding the variations in physical performance among elderly manual workers in the last two decades of working life is of importance, so that recommendations related to their work environment can be made. Lastly, chronological age (ie, time since birth) may well be an important risk factor for several adverse outcomes; however, all people age differently. The term
The present paper describes the study protocol for a study that aims to investigate variations in physical performance among elderly Danish manual workers aged 50 to 70 years. Our primary outcomes include handgrip strength, FEV1, and FVC. Secondary outcomes include force steadiness, reaction time, aerobic capacity, motor coordination, balance, body composition, back mobility, and inflammatory status. Tertiary outcomes are self-reported levels of physical activity, health status, and different work exposures. This is the first study to combine measurements of respiratory and musculoskeletal systems in elderly manual workers, and the collected data will therefore increase our knowledge regarding the elderly workforce. The main research questions in the study are:
To what extent does physical performance change in elderly manual workers with physically demanding occupations during the last two decades of working life?
To what extents do work environment and physical activity levels predict respiratory and musculoskeletal function in elderly manual workers?
Based on the available literature, we hypothesize that physical performance is negatively associated with age, and that physical work magnifies this negative relationship when compared to the general population. Thus, we expect work environment and physical activity to be predictive of respiratory and musculoskeletal function in this cohort.
The present study is a cross-sectional investigation which explores the variations in physical performance in elderly (aged 50-70 years) Danish manual workers working in a physically demanding trade. Data collection is expected to take place between autumn 2017 and spring 2018. All tests will be conducted in a research laboratory at Aalborg University, Denmark. Each experimental session is expected to last for approximately 2 hours. The order in which the tests will be conducted is the following: (1) inflammatory status will be measured from venous blood samples; (2) anthropometrics (ie, height, weight) and blood pressure will be measured, followed by an estimation of body composition based on bioelectrical impedance analysis (BIA); (3) lung function will be measured using spirometry; (4) static and dynamic balance will be measured on a force platform during quiet standing and a sit-to-stand motion; (5) reaction time, precision, and movement variability will be measured during a hammering task; (6) handgrip strength, RFD, and force tracking will be measured with a hand dynamometer; (7) estimated VO2max will be measured on a bicycle ergometer; and (8) back mobility (
We aim to include approximately 100 manual workers aged 50-70 years. The study subjects will be recruited from a questionnaire sent out to more than 5000 Danish manual workers as a part of the ALdring og Fysisk Arbejde cohort (ALFA; Aging and Physical Work), which was created from a register-based cohort of all manual workers in Denmark aged 39 years and older in 1999 (n=155,358). Briefly, the questionnaire included 86 items, mostly regarding work and working conditions, but also 23 items regarding health. Lastly, the questionnaire included a question asking if the subject would like to participate in a clinical study of physical performance. Those who respond in the affirmative to this question will be contacted via email. The selection will aim to ensure representability over the age range by recruiting in bins of 5 years from 50 to 70 years. Subjects with musculoskeletal disorders, osteoarthritis, cardiovascular disease, or any other health condition that contradicts physical testing will be excluded from tests they cannot safely perform. Hence, hypertensive subjects will not complete the cycling test, whereas subjects with severe shoulder pain will not complete the hammering test. All participants will be informed about the purpose of the study and will give written informed consent to participate in the clinical examination. The study will be carried out in accordance to the Helsinki declaration and is approved by the ethics committee of region North Jutland (N-20160023).
Test order and estimated time.
Blood will be drawn from the antecubital vein into 6 mL ethylenediamine tetraacetic acid tubes followed by centrifugation and extraction of plasma. Plasma will be used for high sensitivity analysis of C-reactive protein with a latex particle-enhanced immunoturbidimetric assay, and interleukin-6 will be analyzed by an enzyme linked immunosorbent assay.
Body composition will be estimated using a direct segmental multi-frequency bioelectrical impedance machine (InBody 370, Biospace). The apparatus uses three frequencies (5, 50, and 250 kHz) at five body segments (right arm, left arm, trunk, right leg, and left leg), with a test duration of approximately 45 seconds. The main measurement outcomes include fat-free mass, fat mass, and percent body fat. Although not recognized as the
Basal lung function will be measured using a Spirobank II SMART (Medical International Research [MIR], Rome, Italy) spirometer, disposable MIR turbine flowmeters, and MIR winspiroPRO software (version 6.5.0). The main outcomes include FEV1, FVC, and peak expiratory flow, which will be conducted as recommended by The European Respiratory Society [
Static and dynamic balance will be measured during quiet standing and during a sit-to-stand motion on a force platform (AMTI AccuSway, Watertown, MA, USA). Static balance will be assessed during three conditions: first during quiet standing with eyes open; second during quiet standing with eyes closed; and third during quiet standing with eyes open, while counting backwards from 30 in multiples of three (ie, 30, 27, 24, and so on) to increase cognitive load. In each of the above-mentioned conditions the subjects will be asked to stand for 1 minute, which will be repeated three times for each condition, and they will be instructed to stand as quietly as possible [
Reaction time, precision, and movement variability will be measured using a force platform (AMTI AccuSway, Watertown, MA, USA), a computer screen for visualization, and a rubber hammer (
Maximal handgrip strength, RFD, and force tracking will be measured using a digital hand dynamometer (Model G100, Biometrics Ltd, Gwent, UK). The subjects will be seated in a chair with their lower arms resting on an armchair (90-degree angle in the elbow) while holding the dynamometer. The test begins with the subjects generating their maximal force onto the dynamometer and ends when the force starts to decline. Three trials will be performed using the dominant hand. Thereafter, the subjects will perform an endurance trial using their dominant hand, in which they are asked to exert 20% of their maximal force until task failure, which is defined as an inability to maintain the output force within 2% of maximal force around the set value. Maximal grip strength (measured as peak force in Newtons) and RFD (measured as the rate of force rise [change in peak force/change in time] in Newtons per second) will be calculated during the maximal contractions, whereas the standard deviation (absolute variability), coefficient of variation (relative variability), and the sample entropy (structural variability) of the force signal will be computed during the submaximal trial, as described previously [
Illustration of experimental set-up during the hammering task.
The estimated VO2max test will be conducted using a bicycle ergometer (Monark AB, Varberg, Sweden) and a Polar A300 heart rate monitor (Polar Electro Oy). Instructions will be given, as recommended by the Danish Health Authority [
Back mobility will be measured using the fingertip-to-floor (FTF) test. The FTF test is a reliable measure used to assess forward mobility of the spine and pelvis [
The answers to the ALFA questionnaire, which includes questions about general health, work ability, and environment, as well as social and psychological wellbeing, will be used as covariates in this study. To get a current assessment of some of these covariates, a shorter version of the questionnaire will be answered at the time of the clinical examinations. This short questionnaire will include questions about general health, leisure-time physical activity, pain, and work ability (see
All continuous data will be tested for normality using the Shapiro-Wilk test. Appropriate data transformation will be applied if normality is not met. Subject characteristics and descriptive results will be presented as means and standard deviations or standard errors, and percent distribution. Associations between age (dependent variable) and the measured outcomes (independent variables) will be analyzed with univariate linear regression models, whereas multivariate linear regression models will be constructed using backwards elimination (with adjustment for gender in both cases). When available, the measured outcomes will also be compared with normative data assessing the general population in this age group. Pearson’s Chi-square tests will be used to assess the probability of independency between different self-reported work exposures (eg, work experience, seniority, heavy lifts in the workplace) and the measured outcomes (made categorical by dividing outcomes into
Our primary outcomes are handgrip strength, FEV1, and FVC. Based on previous studies, we expect age to be a stronger predictor of handgrip strength compared to FEV1 or FVC; hence, the latter was used to calculate sample size. Considering three predicators (age, height, smoking) describing the primary outcome (FEV1 or FVC) variations with a medium average correlation between each of the predictors and the outcome (rho=0.3), and a low average correlation between the predictors (rho=0.1), the sample size was calculated to be 102 subjects in a multiple regression analysis to obtain 5% type I and 20% type II errors [
Subjects are currently being contracted via telephone and email. It is expected that data collection will be completed by March 2018.
In several jobs, the physical demands for elderly workers are at the same level as for younger workers [
The present study is strengthened by the objective and extensive clinical examination of physical performance employed in a relatively understudied group. One of the limitations of this study includes the use of a cross-sectional design. Specifically, cross-sectional studies investigating alterations in physical performance with increasing age tend to find different changes compared to findings in longitudinal studies. Such discrepancies may stem from several issues, including differences in working conditions, environmental factors, and research methodologies [
Questionnaire.
ALdring og Fysisk Arbejde
bioelectrical impedance analysis
center of pressure
forced expiratory volume in 1 second
fingertip-to-floor
forced vital capacity
Medical International Research
rate of force development
maximal rate of oxygen consumption
The project is funded by Arbejdsmiljøforskningsfonden (project number 20140072843). The funders had no role in the study design, and will not have any role in data collection and analysis, decision to publish, or preparation of the manuscript. We would also like to thank the rest of the ALFA-group, which includes Martin Moesgaard, Kirsten Fonager, Henrik Bøggild, Johan Hviid Andersen, and Claus Dalsgaard Hansen.
ØO and PM had the original idea for the study. PM, ØO, AS, JHB, and KLN conceived the study design. ØO, PM, and JHB obtained the funding. KLN, PM, and AS will be responsible for developing the technical measurements and analyzing the results. KLN wrote the draft of the manuscript before all authors read, critically reviewed, and approved the final version.
None declared.