Influence of shift work on the physical work capacity of Tunisian nurses: a cross-sectional study in two university hospitals

Influence of shift work on the physical work capacity of Tunisian nurses: a cross-sectional study in two university hospitals

Irtyah Merchaoui^1,&, Lamia Bouzgarrou¹, Ahlem Mnasri¹, Mounir Mghanem¹, Mohamed Akrout¹, Jacques Malchaire², Neila Chaari¹

 

¹School of Medicine, Occupational Health & Ergonomics Department, University of Monastir, Tunisia, ²Catholic university of Louvain, Rue rosier bois 75, 1331 Rosières, Belgium

 

 

^&Corresponding author
Irtyah Merchaoui, School of Medicine, Occupational Health & Ergonomics Department, University of Monastir, 5019-Monastir, Tunisia

 

 

 

 

Rotating shift work is defined as work schedule in which groups of workers rotate through set periods throughout the day [1, 2]. About 20% of European countries workforce and 15.2 million Americans are concerned with this pattern [3]. In developing countries, about 15-30% of the workforce are involved in shift work [2, 3]. In Tunisia, it is estimated that about one fifth of the population is working with a rotating shift. According to Griffiths, the proportion of workers who work in shift schedule is increasing more and more [4]. All over the world, Health care providers are bound to work shift-work to cater for the needs of the sick people and are consequently exposed to the disruption of the synchronous relationship between the body´s internal clock and the environment. Many authors have reported that night shift has physical and psychological effects [5, 6]. Night work disrupts the body circadian rhythmicity, sleep alertness and performance [7-9]. It may also have long term health outcomes such as obesity, type 2 diabetes and cardiovascular diseases [7-14]. Night work can also have negative impacts on emotional health, family and social life, drug use and job-related stress. This is particularly damaging for women with family responsibilities (pregnancy and child raising) [3, 6]. For all night workers, and especially nurses, these physical and psychological effects have consequences at the workplace, such as decreased alertness and reduced job performance that could endanger the lives of the patients [15]. The aim of the present study is to determine the influence of rotating shift work on physical working capacity of Tunisian nurses and to design recommendations to managers so that they implement effective preventive measures of premature physical decline to avoid long term health outcomes.

 

 

Study design: a cross-sectional study was conducted to assess the effect of rotating shift work on the physical capacity of nurses.

 

Setting: this study lasted 15 months (from October 2012 to December 2013) and was conducted at the university hospitals of Monastir and Mahdia in Tunisia. Data collection was performed using a questionnaire administered by 4 trained interviewers who did move into different departments to collect data and perform physical tests on nurses.

 

Participants: the sample consisted of 293 nurses, representative of 1181 nurses and nursing assistants. The participants were recruited by stratified random sampling according to gender and departments. All were fully informed of the objectives and the protocol of the study, of the confidentiality of their participation and their data and their right to refuse to participate and to withdraw at any moment. They were requested to sign a written consent to participate.

 

Variables: in our study, rotating shift time work was defined as working in a rotating shift, and day time work was defined as working exclusively during the morning time. The main outcome measures were: Work ability index (WAI): in clinical occupational health and research, this is usually used to assess work ability during health examinations and surveys [16-18]. The first section collects demographic dataand the second one consists of 7 items. WAI is calculated by summing up the points for each item. The total WAI score ranges from 7–49 points, and the scores are categorized into 4 classes: poor (7–27), moderate (28–36), good (37–43) and excellent (44–49). Perceived physical (PPL) and mental (MPL) workloads: assessed through a simple question classifying the workload as heavy or light. Physical (PAD) and domestic (DAD) activity duration: assessed in hours per week. The body mass index (BMI): Expressed in kg/m², it evaluates the degree of obesity and consequently allows the assessment of the associated health risks.

 

Physical Capacity: The physical ability was evaluated by a battery of physical tests: The Grip Strength Test: is a measure of the maximum grip force (MGF) using a JAMAR dynamometer (Patterson, Nottinghamshire, United Kingdom). The MGF, expressed in kg, is correlated to the age and the global muscle force of the person [19-21]; The muscle force of the lower limbs: assessed through the 30s sit-to-stand test where the number of stands a person can complete in 30 seconds is recorded using a folding chair without arms [22]; The one leg test (OLT): consists in measuring the efficiency of postural control on one leg without support on a flat surface. Although many studies have examined the use of the OLT, none has demonstrated conclusively whether it can be used as a practical marker of premature aging or of work capacity evaluation [23]; Joint flexibility: is assessed through two types of tests: The thumb- C7 distance and Fingertip-to-Floor test (FTF). The thumb- C7 distance is usually used to determine the degree of flexibility of the shoulder to perform the internal rotation: It measures the distance between the C7 spinous process and the ipsilateral thumb while the hand is behind the same side shoulder [24]. The Fingertip-to-Floor test (FTF) measures the distance between the fingers and the floor when the patient is standing up and trying to touch his toes without bending the knees [25].These two parameters were measured in centimeters; Saltsa tests: are used for screening musculoskeletal disorders (MSDs) of the upper limbs. They can diagnose 12 types of specific MSDs and a general syndrome involving non-specific MSDs but constituting an early indicator of MSDs. These tests were established by the Swedish National Institute for Working Life (NIWL) in 1997 as a research program on working life issues in a European perspective [26,27].The total Saltsa score represents the total number of joint disorders in the upper limb; Pulmonary endurance: the peak expiratory flow is measured with a peak flow meter which is a handy, easy-to-use tool to assess air flow limitation. It can be an important aid in both the diagnosis and monitoring of asthma. The literature has reported that this flow is correlated to gender, height and age. In fact, during ageing, there is a progressive decline in respiratory function, because of a loss of respiratory muscle strength, increased stiffness of the chest wall and reduced elastic recoil of the lung and diffusion capacity [28]. In our study we used the rate Z pick flow defined as the pick flow ? divided by the height, to assess pulmonary endurance.

 

Data measurement: the first approach was to compare the two groups’ variables of daytime and rotating shift time nurses and give a physical assessment. The second approach was to divide the groups of shift schedule and day time nurses according to job seniority to find out differences within these sub-groups.

 

Statistical methods: the data were analyzed using the SPSS 21 software. Descriptive statistics were used to describe the population characteristics by calculating the frequencies and the percentages for categorical variables on the one hand, and the means, standard deviations and extent of extreme values for quantitative variables on the other hand. The chi-square test was used to check whether the associations found presented a statistical significance (p< 0.05). The Student t-test was used to compare group means. The cross-tabulation analysis was used to analyze categorical data.

 

 

First step: according to work schedules

 

Our survey sample of 293 was representative of 1181 nurses and nursing assistants with 111 day time nurses, and 182 rotating shift time working nurses. Sex ratio was about 1.061. In our sample, as shown in Table 1, the mean age was about 44.26 years for the participating nurses working in daytime schedule and about 41.65 years for those working in shift time schedule. The analysis of socio-demographic factors revealed that job seniority was associated with work schedules (p=0.026). Actually, nurses working in day time schedule seem to be more experienced than those of rotating shift schedule (mean range for job seniority equal to 20.62 years and 17.12 years respectively). The perceived physical and mental workloads were significantly associated with work schedules (p=0.02 and 0.01 respectively) (Table 1). The mean WAI score was about 40 ± 6.28. According to the WAI categorical classification, most of the participants had a good or excellent work capacity (75%).The independent-sample t showed no significant association between work schedule and work capacity (p >0.05) (Table 1). Concerning the physical capacity tests, the Grip strength test (p=0.001) and the pulmonary endurance (p=0.05) were the only physical tests to show an association with the rhythm of work. In fact, nurses working in shift times seemed to have better muscle force and better pulmonary endurance than those working in day time schedule (Table 1).

 

Second step: according to Job seniority within each schedule group: the comparison between nurses within the shift schedule group based on job seniority showed that over-ten-years of seniority nurses in both schedule groups were more likely to have weight gain (p= 0.001). The workability index was significantly decreased with job seniority within the shift schedule work group (p=0.01) (Table 2). Otherwise, Peak flow test (p=0,014), salsa test, one leg test (p=0.001), muscle force of lower limb test (p=0.001) finger to floor test(p=0.001) and the thumb-C7 distance (p=0.045) were significantly better within the group with less than 10 years job seniority (Table 2). Concerning the influence of job seniority on different variables within the day time group , it seems that the over-ten-year group in day time work had a significantly more time to perform physical activity (p=0.034). they were also more likely to have weight gain (p=0.001) .T-tests were used to analyse the relationship between seniority within the day time group and the different capacity physical tests and showed that the lower limb test (p=0.0001) ,the one leg test (p=0.003), the thumb-C7 test (p=0.001), finger to floor test (p=0.022) and Saltsa test (p=0.0001) were better in the less-than-ten-year group in the day time group (Table 2).

 

 

The purpose of our study was to examine if and how work ability and physical capacities were associated with rotating shift work among Tunisian nurses. Taken together, the study findings suggest that mental and physical loads were heavily perceived in shift healthcare workers (p=0.01; p=0.02) and that the maximum grip force was the only physical variable significantly influenced by the rhythm of work. In fact, maximum grip force was stronger in rotating shift work nurses (p=0.0001). These were the only effects of rotating shift work on nurses’ physical capacity of work. As for the question of seniority subgroups in each kind of work schedule, the Body Mass Index increased with seniority in both schedules. All the physical tests, except the grip strength test and the Peak Flow, were better in less-than-ten-year groups in shift and day time schedules. Finally, Peak Flow was significantly better in less-than-ten-year seniority in the shift work group. Mental and physical workloads were significantly perceived by shift-schedule nurses. The events giving rise to such a perception are probably in relationship with the lack of staff during shift work whereas shift work nurses have exactly the same work conditions and strain as day time nurses.

These results are in accordance withthose observed in earlier studies which concluded that inadequate and atypical schedules may impact health [29-31].This may result in a reduced quantity and quality of sleep, a decline in cognitive and physical performance and an associated increased risk for errors and accidents and interference with the nurse´s family and social commitments [31]. Moreover, the disruption of circadian rhythm and the shift work conditions (such as lightening, temperature and the reduction of in the number of available workforce and services) influence the perception of one´s work capacity [29]. All these negative consequences may be perceived by a worker as a mental and physical job strain reducing his capacity to perform his work. Contrary to expectations, this study did not prove any significant association between work schedules and work ability index.

These findings corroborate those of CAMERINO stating that Work schedule is not related to changes in WAI [32]. These findings could be explained by the “napping phenomenon”. In fact, while performing data collection, we noticed that most of the rotating shift nurses had a nap during shifts and shared the work tasks together. Besides, a fixed work shift team is a helpful concept to cope with shift work because relationships between coworkers would be stronger and it would be easier to communicate and understand each other and to perform better work tasks. In the literature, napping is even recommended in some studies to help nurses cope with shift work and to make it less stressful [33]. For night shift nursing, Da SILVA found that napping during the 12-hour night shift results in less sleepiness at work and less need for recovery after work [34]. But, despite the absence of association between the WAI and work schedule in our study, we could prove that a less than 10 years job seniority was a predictor of a better work ability index within the shift schedule group (p=0.01). This finding corroborates the shift-schedule-seniority effects and consequently aging effects on workability index, agreeing with the findings of other studies [16,35].

It is obvious that work capacity is a dynamic process that changes greatly according to several reasons, apart from ageing, throughout an individual´s work life. In fact, it is well known that shift work could interfere with the circadian sleep/wake cycle resulting in excessive sleepiness and fatigue interfering with performance and health [15]. Previous cross sectional studies specifically related to nursing profession and health care personnel showed that work capacity as assessed by the Work Ability Index (WAI) decreased with age in shift schedules and found a significant association between sleep problems and WAI [36]. No significant differences were found in muscle performance tests apart from the grip strength test which was the unique muscular physical capacity test to be significantly improved by rotating shift work (p=0.0001). The versatility of tasks requiring hand force and dexterity, while there is added to a lack of staff during shifts, might be a possible explanation for this [37]. However, this result has not previously been described. BAMBAEICHI, did not bring any proof of the influence of time of the day and partial sleep deprivation on muscle strength in eumenorrheic females [38]. Furthermore, grip strength has been used as a predictor of functional limitations for upper body limbs and even as all-cause mortality predictor in healthy population [39,40].

Concerning joint flexibility, the Chi-square test did not show any significant differences between shift time and day time schedules in the thumb-C7 distance test or the finger to floor test. However, these tests seem to worsen according to seniority in shift work (p=0.001 / 0.001) or day time work (p=0.001/0.0001). This finding suggests that the breakdown of joint flexibility in our population is due to seniority at work and thus to age and not to shift schedules. This is consistent with earlier observations which showed that age-related changes that occur in the cartilage matrix can contribute to the decrease of joint flexibility in elderly and to the development of osteoarthritis [41,42]. Moreover we couldn’t prove any statistical link between rotating shift schedule and Saltsa test. However, this test was significantly linked to seniority within day time work (p=0.0001) group and shift time work (p=0.001) group. Consequently, Saltsa tests regrouping all the physical tests screening for musculoskeletal joint disorders in the upper limb had a significant relationship with seniority and thus were age-related. In the literature, nurses working in shift schedule reported especially low back and neck pain compared to daytime nurses who reported upper extremities pain and were at great risk of sustaining an occupational musculoskeletal injury [43, 44]. The risk of low back pain could be explained by the highly physically demanding postures and tasks required in shift schedule such as patient transfers. The long exposure to this physical postural risk could lead to MSD among shift nurses [44]. Interestingly, no reference was made to seniority in the literature for the physical tests while cognitive decline is well documented.

Concerning pulmonary performance, there was no significant relation between its index and nurses’ work schedule. However, our findings suggest that an over 10- year - exposure to shift work within the shift work group affects pulmonary performance. This could be related to aging because of the significance of age distribution between both groups. The concept of lung physiological aging has been well documented in the literature [16]. Several limitations are to be considered with respect to this study: in order to avoid any linguistic misunderstanding, 4 trained interviewers did explain questionnaires in Tunisian dialect. Moreover, the study was a cross-sectional one in design but a longitudinal study would be more appropriate to achieve higher levels of evidence of nurses´ work capacity progression during their professional career. Moreover, given the length of the questionnaire and the tests and the lack of time for some nurses, some of responses were qualified as rushed (especially for nurses of the emergency and intensive care units) and we had to set up further appointments to perform the survey as requested.

 

 

The findings of our study have a number of practical implications. In fact, the recommendations should be focused on implementing effective preventive measures in hospitals to encourage health promotion of nurses and other healthcare workers. Most studies rely heavily on the general scientific literature in the field of shift work assuming that it is associated with health problems. Since there is no ideal shift, the focus of the literature has been on improving the design of the existing shift systems and on reducing as much as possible shift schedule and quick change from night to day work [45-48]. This suggests that hospital managers and Heads of Departments should be aware of the necessity of avoiding shift schedule for over-10-year-seniority and giving nurses the freedom of choice regarding shifts [30]. This can be one possible implication of our results regarding the fact that work capacity will be worse after 10 years of seniority. Consequently, it would be better to automatically change nurses from shift work to day time work starting from this limit. On the other hand, recovery time and rest breaks or naps must also be considered, supported and legally implemented. This issue is widely cited in the literature. In fact, effective napping strategies are highly required such as planning and ensuring shift nurses take a rest or 20 minute-naps, creating a nap room that is quiet, safe, clean and close to units, including timers to alert nurses at the end of the nap period [45, 47]. Personal measures are also required such as physical exercise, healthy and balanced meals and avoiding smoking. Nurses of both schedules should be aware of these, and occupational health physicians have many opportunities to emphasize on these personnel-related measures in every occupational check-up. This may reduce the negative impact of shift work and improve tolerance to this work pattern. Occupational health may also reduce nurse fatigue by developing a fatigue risk management program including Primary, Secondary and Tertiary interventions. The literature also highlights some techniques and therapies used to deal with the circadian disturbance such as bright light and blue light which have not been yet experimented in our hospitals [48]. Taken together, these results suggest that there is a need for further clarification of the consequences of the rotating shift system in the clinical environment and the adoption of a shift system with fewer physical health implications through further longitudinal studies.

 

 

The authors declare no competing interests.

 

 

All the authors contributed substantially to the study conception and design. IM, LB, JM and NC conducted the conception of the project, the analysis and interpretation of data.AM and MM recruited the participants. IM drafted the work and JM and MA revised it critically for important intellectual content. All authors gave final approval of the version to be published and agreed to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All authors have read and agreed to the final version of this manuscript and have equally contributed to its content and to the management of the case.

 

 

The authors would like thank Sir Moncef Rassas and Sir Adel Rdissi for proof-reading the article.

 

 

Table 1: socio-professional characteristics, physical and cognitive tests of the sample according to work schedule

Table 2: socio-professional characteristics and physical tests of the sample according to job seniority within each schedule group

 

 

1. Berger AM, Hobbs BB. Impact of shift work on the health and safety of nurses and patients. Clin J Oncol Nurs. 2006 Aug; 10(4): 465-71. PubMed | Google Scholar


2. Harrington JM. Health effects of shift work and extended hours of work. Occup Environ Med. 2001; 58: 68-72. PubMed | Google Scholar


3. Wang Y, Gu F, Deng M et al. Rotating shift work and menstrual characteristics in a cohort of Chinese nurses. BMC Women's Health. 2016; 16: 24. PubMed | Google Scholar


4. Griffiths P, Dall'Ora C, Simon M and al. Nurses’ shift length and overtime working in 12 European countries: the association with perceived quality of care and patient safety. Med Care. 2014 Nov; 52(11): 975-81. PubMed | Google Scholar


5. Claire CC. Negative impacts of shiftwork and long work hours. Rehabil Nurs. 2014 Jan-Feb; 39(1): 16-25. PubMed | Google Scholar


6. Matheson A, O’Brien L, Reid J-A. The impact of shiftwork on health: a literature review. Journal of Clinical Nursing. déc 2014; 23(23 24): 3309 20. PubMed | Google Scholar


7. Korompeli A, Muurlink O, Tzavara C et al. Influence of Shiftwork on Greek Nursing Personnel. Saf Health Work. 2014 Jun; 5(2): 73-9. PubMed | Google Scholar


8. Ardekani ZZ, Kakooei H, Ayattollahi SM et al.Prevalence of mental disorders among shift work hospital nurses in Shiraz, Iran. Pak J Biol Sci. 2008 Jun 15; 11(12): 1605-9. PubMed | Google Scholar


9. Von Treuer K, Fuller-Tyszkiewicz M, Little G. The impact of shift work and organizational work climate on health outcomes in nurses. Journal of Occupational Health Psychology. 2014; 19(4): 453 61. PubMed | Google Scholar


10. Griep RH, Bastos LS, Fonseca Mde J et al. Years worked at night and body mass index among registered nurses from eighteen public hospitals in Rio de Janeiro, Brazil. BMC Health Serv Res. 2014; 14: 603. Google Scholar


11. Kim MJ, Son KH, Park HY et al. Association between shift work and obesity among female nurses: Korean Nurses’ Survey. BMC Public Health. 2013 Dec 20; 13: 1204. PubMed | Google Scholar


12. Buss J. Associations between obesity and stress and shift work among nurses. Workplace Health Saf. 2012 Oct; 60(10): 453-8. PubMed | Google Scholar


13. Jermendy G, Nádas J, Hegyi I et al. Assessment of cardio metabolic risk among shift workers in Hungary. Health Qual Life Outcomes. 2012 Feb 1; 10: 18. PubMed | Google Scholar


14. Vetter C, Devore EE, Wegrzyn LR et al. Association between rotating night shift work and risk of coronary heart disease among women. JAMA. 2016; 315(16): 1726-1734. PubMed | Google Scholar


15. Burch JB, Tom J, Zhai Y et al. Shiftwork impacts and adaptation among health care workers. Occup Med (Lond). 2009 May; 59(3): 159-66. PubMed | Google Scholar


16. Mehrdad R, Mazloumi A, Arshi S et al. Work ability index among health care personnel in a university hospital in Tehran, Iran. Work. 2016 Mar 9; 53(4): 851-7. PubMed | Google Scholar


17. Ilmarinen J, Tuomi K and Seitsamo J. New dimensions of work ability. International Congress Series. June 2005; 1280: 3-7. Google Scholar


18. De Zwart BCH, Frings-Dresen MHW, Van Duivenbooden JC. Test–retest reliability of the Work Ability Index questionnaire. Occup Med (Lond). 2002 Jun; 52(4): 177-81. PubMed | Google Scholar


19. Roberts HC, Denison HJ, Martin HJ et al. A review of the measurement of grip strength in clinical and epidemiological studies: towards a standardized approach. Age Ageing. 2011 Jul; 40(4): 423-9. PubMed | Google Scholar


20. Mathiowetz V. Comparison of Rolyan and Jamar dynamometers for measuring grip strength. Occup Ther Int. 2002; 9(3): 201-9. PubMed | Google Scholar


21. Miller MC, Nair M, Baratz ME. A device for assessment of hand and wrist coronal plane strength. Journal of Biomechanical Engineering. 2005;127(6): 998-1000. PubMed | Google Scholar


22. Mayorga-Vega D, Merino-Marban R, Viciana J. Criterion-related validity of sit-and-reach tests for estimating hamstring and lumbar extensibility: A meta-analysis. J Sports Sci Med. 2014 Jan 20; 13(1): 1-14. PubMed | Google Scholar


23. Morioka S, Fukumoto T, Hiyamizu M et al. Changes in the equilibrium of standing on one leg at various life stages. Curr Gerontol Geriatr Res. 2012; 2012: 516283. PubMed | Google Scholar


24. Han SH, Oh KS, Han KJ, Jo J et al. Accuracy of measuring tape and vertebral-level methods to determine shoulder internal rotation. Clin Orthop Relat Res. 2012 Feb; 470(2): 562-6. PubMed | Google Scholar


25. Batti'e MC, Bigos SJ, Sheehy A et al. Spinal flexibility and individual factors that influence it. Phys Ther. 1987 May; 67(5): 653-8. PubMed | Google Scholar


26. Moreira RF, Sato TO, Foltran FA et al. Prevalence of musculoskeletal symptoms in hospital nurse technicians and licensed practical nurses: associations with demographic factors. Braz J Phys Ther. 2014 Jul-Aug; 18(4): 323-33. PubMed | Google Scholar


27. Jellad A, Lajil H, Boudokhan S et al. Musculoskeletal disorders among Tunisian hospital staff: prevalence and risk factors. The Egyptian Rheumatologist. 2013; 35(2): 59-63. Google Scholar


28. Boezen HM, Schouten JP, Postma DS et al. Distribution of peak expiratory flow variability by age, gender and smoking habits in a random population sample aged 20-70 yrs. Eur Respir J. 1994 Oct; 7(10): 1814-20. PubMed | Google Scholar


29. Härmä M. Work hours in relation to work stress, recovery and health. Scand J Work Environ Health. 2006 Dec; 32(6): 502-14. PubMed | Google Scholar


30. Galatsch M, Li J, Derycke H et al. Effects of requested, forced and denied shift schedule change on work ability and health of nurses in Europe-Results from the European NEXT-Study. BMC Public Health. 2013 Dec 5; 13: 1137. PubMed | Google Scholar


31. Palhares Vde C, Corrente JE, Matsubara BB. Association between sleep quality and quality of life in nursing professionals working rotating shifts. Rev Saude Publica. 2014 Aug; 48(4): 594-601. PubMed | Google Scholar


32. Camerino D, Conway PM, Sartori S et al. Factors affecting work ability in day and shift-working nurses. Chronobiology International. 2008; 25(2&3): 425–442. PubMed | Google Scholar


33. Takeyama H, Tomohide K, Itani T. The nighttime nap strategies for improving night shift work in workplace. Ind Health. 2005 Jan; 43(1): 24-9. PubMed | Google Scholar


34. Da Silva BFN, Fischer FM, Rotenberg L et al. Effects of naps at work on the sleepiness of 12-hour night shift nursing personnel. Sleep Science. 2009; 2(1): 24-29. Google Scholar


35. Fischer FM, Da Silva Borges FN, Rotenberg L et al. Work ability of health care shift workers: what matters?. Chronobiology International. 2006; 23(6): 1165-1179. PubMed | Google Scholar


36. Knutsson A. Health disorders of shift workers. Occup Med (Lond). 2003 Mar; 53(2): 103-8. PubMed | Google Scholar


37. Merchaoui I, Bouzgarrou L, Amri C et al.Determinants of Grip Strength in Tunisian Nurses: A Bicentric Study. Recent Pat Inflamm Allergy Drug Discov. 2016; 10(1): 54-60. PubMed | Google Scholar


38. Bambaeichi E, Reill T, Cabl NT et al. The influence of time of day and partial sleep loss on muscle strength in eumenorrheic females. Ergonomics. 2005 Sep 15-Nov 15; 48(11-14): 1499-511. PubMed | Google Scholar


39. Metter EJ, Talbot LA, Schrager M et al. Skeletal Muscle Strength as a Predictor of All-Cause, Mortality in Healthy Men. Journal of Gerontology: Biological sciences in the Public Domain. 2002; 57A(10): B359–B365. PubMed | Google Scholar


40. Kuh D, Bassey EJ, Butterworth S et al. Grip strength, postural control, and functional leg power in a representative cohort of British men and women: associations with physical activity, health status, and socioeconomic conditions. J Gerontol A Biol Sci Med Sci. 2005 Feb; 60(2): 224-31. PubMed | Google Scholar


41. Loeser RF. Age-related changes in the musculoskeletal system and the development of osteoarthritis. Clin Geriatr Med. 2010 Aug; 26(3): 371-86. PubMed | Google Scholar


42. Li Y, Wei X, Zhou J et al. The age-related changes in cartilage and osteoarthritis. Biomed Res Int. 2013; 2013: 916530. PubMed | Google Scholar


43. Attarchi M, Raeisi S, Namvar M et al. Association between shift working and musculoskeletal symptoms among nursing personnel. Iran J Nurs Midwifery Res. 2014 May; 19(3): 309-14. PubMed | Google Scholar


44. D'Agostin F, Negro C. Musculoskeletal disorders and work-related injuries among hospital day-and shift workers. Med Lav. 2014 Jul 16; 105(5): 346-56. PubMed | Google Scholar


45. Takahashi M, Iwakiri K, Sotoyama M. Musculoskeletal pain and night-shift naps in nursing home care workers. Occup Med (Lond). 2009 May; 59(3): 197-200. PubMed | Google Scholar


46. Richter HD, Acker J, Sxholz F et al. Health Promotion and Work: Prevention of Shift work in Compagnies. EPMA J. 2010 Dec; 1(4): 611-618. PubMed | Google Scholar


47. Fallis WM, Mc Millan DE, Edwards MP. Napping during night shift: practices, preferences, and perceptions of critical care and emergency department nurses. Crit Care Nurse. 2011 Apr; 31(2): e1-11. PubMed | Google Scholar


48. Zamanian Z, Kakooki H, Ayatollahi SMT et al. Effect of bright light on shift work nurses in hospitals. Pak J Biol Sci. 2010; 13(9): 431-436. PubMed | Google Scholar