Introduction

Nurses' health impairment affects their quality of life and compromises patient safety [ 1 ]. The nursing profession requires performing heavy workloads, lifting and transferring patients from beds, working in awkward postures, and spending substantial time standing or walking on concrete and hard surfaces [ 2 - 4 ]. Musculoskeletal disorders and fatigue—linked to overexertion, slips, trips, and falls—have been reported among nurses, placing the profession among the high- risk jobs for nonfatal workplace injuries [ 5 ]. Previous studies have demonstrated that fatigue can increase postural sway after repetitive lifting among male and female workers [ 6 ].

In this regard, some researchers have examined the association between working at night and postural balance impairments to evaluate whether fatigue- related night work and sleepiness can affect the postural balance of shift workers . For example, FV Narciso et al. (2016) reported that working continuously for 12 hours at night and the consequent drowsiness could negatively affect postural balance and psychomotor performance in shift workers [ 10 ].

According to estimates, nurses walk 4–5 miles [ 11 ]— approximately 9,000 steps—during a 12-hour shift [ 12 ]. Despite this, there remains a gap in understanding the association between shift work and gait biomechanics. It is crucial to examine the effect of night work on walking biomechanics, as most falls occur during walking, and gait evaluation can be considered an effective functional approach for predicting falls to ensure the safety of both nurses and patients [ 13 ].

Evidence suggests that working outside the typical 9:00 am–5:00 pm period, such as rotating shifts and night work, results in circadian rhythm misalignment, disrupting the synchrony between the body’s internal clock and the external environment, leading to sleep disorders [ 1 , 14 ]. This disruption causes performance impairment, daytime sleepiness, health deterioration, physical and psychological distress, decreased alertness and vigilance [ 15 , 16 ], interruption of workers’ recovery from fatigue [ 17 ], and poor dietary habits [ 18 ]. More specifically, there is a link between disrupted sleep and skeletal muscle health, which is essential for human movement, substrate storage, and plays a significant role in energy and protein metabolism in night workers [ 19 ].

Although no study has directly investigated skeletal muscle health in shift workers, Aisbett et al. suggested that artificial light exposure, sleep patterns, and eating habits could impact skeletal muscle function and health [ 19 ]. Considering that the nursing profession is physically demanding—ranking second only to industrial work [ 20 ]—it is assumed that the cumulative effects of fatigue, sleepiness, and impaired skeletal muscle function might influence nurses' physical activity.

To our knowledge, this is the first study to examine differences in biomechanical gait parameters between nurses working night versus day shifts. Therefore, the main purpose of this research was to assess the gait and dynamic stability of nurses. In the present study, we hypothesized that gait kinematics and dynamic stability would differ significantly between the two groups of night and day shift workers.

Methods

This cross-sectional study was approved by the Human Research Ethics Committee of Shiraz University of Medical Sciences (Ethics code: IR.SUMS.REC.1397.336). Convenience sampling was employed to select participants who met the inclusion criteria. All participants provided written informed consent after receiving a detailed explanation of the study procedures. Participants were female nurses working in the postsurgical orthopedic wards of Namazi and Chamran hospitals. The sample comprised 16 nurses working 12-hour night shifts from 8 p.m. to 8 a.m. (with at least 3 years of night shift experience) and 15 nurses working day shifts from 8 a.m. to 2 p.m.

Participants completed two questionnaires: the Morningness-Eveningness Stability Scale improved (MESSI) questionnaire and the Nordic Musculoskeletal Questionnaire to assess chronotype and ensure sample homogeneity [ 21 , 22 ]. All participants were morning chronotypes with no history of musculoskeletal disorders. Exclusion criteria included regular physical exercise, pregnancy, sleep pattern disorders, visual or vestibular dysfunction, brain-related diseases, use of prostheses, neuromuscular diseases (e.g., Parkinson’s disease, multiple sclerosis), sleeping for more than one hour during the shift, alcohol consumption during the day before measurements, and any special medical conditions.

Participants were evaluated immediately after their respective shifts. Testing occurred between 8–9 a.m. for night-shift nurses and 2–3 p.m. for day-shift nurses. A Qualisys motion analysis system (Proreflex, Qualisys Track Manager® Ltd., Gothenburg, Sweden), consisting of eight high-speed cameras and Qualisys Track Manager software, was used to record walking kinematics and determine marker locations, respectively. Data were collected at a frequency of 120 Hz. Forty-three markers (19 mm in diameter) were placed bilaterally on anatomical landmarks, including the anterior superior iliac spine (ASIS), posterior superior iliac spine (PSIS), iliac crests, acromion processes, medial and lateral sides of the knee joints, greater trochanters, first and fifth metatarsal heads, medial and lateral malleoli, second toe tip, and heels. Additionally, four cluster markers were attached to the anterolateral surfaces of the legs and thighs using extensible Velcro straps, and one marker was placed on the top of the head.

Participants walked along a flat pathway, and three acceptable walking trials at a comfortable self-selected speed were recorded for each participant. Only trials in which the participant’s dominant foot landed on the force plate were used for further analysis. Data filtering was performed using a Butterworth low-pass filter with a cutoff frequency of 10 Hz. Gait cycle phases were determined using heel strike and toe-off data.

Data were imported into OpenSim software to build a musculoskeletal model with 23 degrees of freedom and 76 scaled muscles for each subject (Figure 1). To evaluate dynamic stability, force plate data were recorded using a Kistler force plate (Kistler Instrument®, Winterthur, Switzerland). Dynamic stability was assessed via center of mass (COM) movement in the mediolateral and vertical directions, which were normalized to the base of support and leg length of each subject, respectively.

Figure 1. Scaled Subject-Specific Musculoskeletal Model

The gait spatiotemporal parameters (stride length, cadence, and walking velocity), kinematics of the ankle, knee, and hip joints, as well as the pelvic and trunk segments during the stance phase of gait, and dynamic stability measurements were obtained from a subject-specific musculoskeletal model developed for each participant. The normality of the data distribution was assessed using the Shapiro-Wilk test. Group differences in all mentioned parameters were analyzed using independent-sample t-tests. All statistical analyses were performed using IBM® SPSS version 21.0 (IBM Corp., Armonk, NY, USA), with a significance level set at 0.05.

Results

Demographic characteristics of the participants are summarized in Table 1. No significant differences were observed between the groups regarding demographic data. The mean walking speed of nurses working the day shift was 1.14 ± 0.13 m/s, compared to 1.16 ± 0.16 m/s for those working the night shift (p = 0.33) (Table 3). There were no significant differences in the mean values of spatiotemporal gait parameters between nurses working day and night shifts.

Regarding joint kinematics, although the range of pelvic and lumbar rotations increased after the night shift compared to the day shift, this difference was not statistically significant (p > 0.05). The mean values of the range of motion (ROM) for other joints in both day and night shift groups are presented in Table 2. Overall, no significant differences were found between the mean values of these parameters in day versus night shifts (p > 0.05).

Dynamic stability was also evaluated in this study and was assessed by tracking the movement of the center of mass (COM) in the vertical and mediolateral directions. The excursions of COM motion in the vertical and mediolateral directions were normalized to leg length and base of support, respectively. The results of dynamic stability are presented in Table 3. According to the data, the mean COM excursion in the vertical direction was 4.77 ± 0.8% of leg length for the day shift group and 4.36 ± 0.89% for the night shift group. COM movement in the mediolateral direction was significantly different between the two groups.

Discussion

It seems that those working night shifts may face greater challenges in regulating their activities, which not only affects their job performance but may also increase the incidence of physical and psychological health problems [ 23 ]. However, it is not yet well understood whether working at night influences gait characteristics. Moreover, it remains unclear whether night shift work impairs dynamic stability, potentially leading to an increased risk of falls. Therefore, this study aimed to compare the kinematic parameters and dynamic stability of nurses working day and night shifts.

It has been shown that fatigue resulting from working both day and night shifts may lead to impaired postural balance performance [ 5 ], which can reduce motor control and increase the range of motion, potentially affecting gait [ 24 ]. However, our findings do not align with these results, as we found no significant differences in the ranges of motion of the pelvic, hip, knee, and ankle joints between nurses working day and night shifts. Considering findings from previous studies reporting a strong relationship between range of motion (ROM) and walking speed [ 25 ], the results of the current study did not support this relationship, as we found no significant differences in gait velocity or ROM between the two groups. This might be due to the working conditions of night shift nurses, who may have sufficient time to rest [ 26 ]. Although we asked participants to avoid taking naps, we could not fully control this factor. Previous research has reported that napping can be considered a strategy to attenuate the adverse effects of night shift work and may contribute to improved working conditions, performance, and safety [ 27 ].

Although several studies have explored the effect of working at night on postural balance and stability among night workers , there is a paucity of knowledge about how night shifts affect the spatiotemporal gait parameters of nurses, which could, in turn, impact their performance and patient safety [ 29 ]. Previous studies have demonstrated that acute sleep deprivation may deteriorate postural stability and performance, leading to increased postural sway due to decreased vigilance, alertness, and an inability to maintain a stable position [ 10 ]. Because increased postural sway strongly affects walking patterns, we investigated whether there were differences in gait biomechanics between night and day shift workers. However, we found no significant differences in most of the spatiotemporal parameters, except for the center of mass (COM) movement in the mediolateral direction, which is more closely related to dynamic stability. Although we observed significant differences in mediolateral COM movement, no significant differences were found in gait kinematic variables between the two groups. This finding suggests that mediolateral fluctuations of COM do not affect joint range of motion or gait biomechanics, and thus no adaptive strategy is required [ 25 ]. Therefore, based on the results of our study, it can be concluded that there is no substantial difference in the gait patterns of night and day shift nurses, indicating no increased risk of falling while walking.

It has been noted that nursing roles vary depending on the unit in which they work—such as medical, surgical, operating theatre, mental health, pediatric, or emergency units—and these differing responsibilities may impose distinct physical activity demands. Consequently, the workload of nurses may differ based on the unit and associated duties. In the present study, we were unable to recruit nurses working in the same unit but on different shifts, which may have influenced the comparability of workload between the day and night shift groups [ 29 ].

One of the possible limitations of this study is that, although we collected data immediately after the nurses’ shifts ended, it would have been more accurate to take measurements multiple times during their shifts. Previous research has suggested that the difficulty of tests, such as unipedal versus bipedal protocols, could influence the assessment of fatigue-related impairments in postural balance [ 30 ]. Therefore, future studies should be designed to examine postural balance variables under dual-task conditions. Additionally, we suggest that more conclusive results could be achieved by investigating the effects of prolonged sleep deprivation on muscle function at the molecular level, as well as its impact on locomotion, in future research.

Conclusion

This study is the first to investigate gait kinematic variations in nurses working both night and day shifts. Given that nursing is a physically demanding profession and that movement impairments in nurses can directly affect patient safety, it is essential to understand how sleeplessness and fatigue influence gait kinematics. Based on our findings, we concluded that there are no significant differences in spatiotemporal gait parameters, vertical indicators of dynamic stability, or joint range of motion between day and night shift nurses. These results suggest that working night shifts does not alter the biomechanical gait patterns of nurses.

Acknowledgement

The authors sincerely thank all participants for their valuable contribution to this study.

Author’s Contributions

MTK and MR reviewed the literature and conceived the study. MTK, FY, and MR were involved in protocol development, obtaining ethical approval, participant recruitment, and data analysis. FY and MR drafted the initial version of the manuscript. All authors reviewed and approved the final manuscript.

Funding

This research was supported by a grant from the Vice Chancellor of Research, Shiraz University of Medical Sciences, Shiraz, Iran (Grant Number: 11-13910).

Conflict of Interest

The authors declare no conflict of interest.

References

1. Giorgi F, Mattei A, Notarnicola I, Petrucci C, Lancia L. Can sleep quality and burnout affect the job performance of shift‐ work nurses? A hospital cross‐sectional study. Journal of advanced nursing. 2018; 74(3):698-708.
2. Thompson BJ, Stock MS, Banuelas VK. Effects of accumulating work shifts on performance-based fatigue using multiple strength measurements in day and night shift nurses and aides. Human factors. 2017; 59(3):346-56.
3. Anap D, Iyer C, Rao K. Work related musculoskeletal disorders among hospital nurses in rural Maharashtra, India: a multi centre survey. Int J Res Med Sci. 2013; 1(2):101-7.
4. Stolt M, Miikkola M, Suhonen R, Leino-Kilpi H. Nurses’ perceptions of their foot health: implications for occupational health care. Workplace health & safety. 2018; 66(3):136-43.
5. Thompson BJ, Stock MS, Banuelas VK, Akalonu CC. The impact of a rigorous multiple work shift schedule and day versus night shift work on reaction time and balance performance in female nurses: a repeated measures study. Journal of occupational and environmental medicine. 2016; 58(7):737-43.
6. Bannon HM, Hakansson NA, Jakobsen MD, Sundstrup E, Jorgensen MJ. The effects of a fatiguing lifting task on postural sway among males and females. Human movement science. 2018; 59:193-200.
7. Ma J, Yao Y, Ma R, Li J-Q, Wang T, Li X, et al. Effects of sleep deprivation on human postural control, subjective fatigue assessment and psychomotor performance. Journal of international medical research. 2009; 37(5):1311-20.
8. Rodgers C, Paterson D, Cunningham D, Noble E, Pettigrew F, Myles W, et al. Sleep deprivation: effects on work capacity, self- paced walking, contractile properties and perceived exertion. Sleep. 1995; 18(1):30-8.
9. Siu K-C, Huang C-K, Beacom M, Bista S, Rautiainen R. The association of sleep loss and balance stability in farmers. Journal of agromedicine. 2015; 20(3):327-31.
10. Narciso FV, Barela JA, Aguiar SA, Carvalho AN, Tufik S, de Mello MT. Effects of shift work on the postural and psychomotor performance of night workers. PLoS One. 2016; 11(4):e0151609.
11. STOlT M, SuHONeN R, Virolainen P, Leino-Kilpi H. Lower extremity musculoskeletal disorders in nurses: A narrative literature review. Scandinavian journal of public health. 2016; 44(1):106-15.
12. Welton JM, Decker M, Adam J, Zone-Smith L. How far do nurses walk? Medsurg Nursing. 2006; 15(4):213-7.
13. Papa EV, Garg H, Dibble LE. Acute effects of muscle fatigue on anticipatory and reactive postural control in older individuals: a systematic review of the evidence. Journal of Geriatric Physical Therapy. 2015; 38(1):40-8.
14. Merchaoui I, Bouzgarrou L, Mnasri A, Mghanem M, Akrout M, Malchaire J, et al. Influence of shift work on the physical work capacity of Tunisian nurses: a cross-sectional study in two university hospitals. Pan African Medical Journal. 2017; 26(1):1-10.
15. Lim YC, Hoe VC, Darus A, Bhoo-Pathy N. Association between night-shift work, sleep quality and metabolic syndrome. Occupational and environmental medicine. 2018; 75(10):716-23.
16. Shariat A, Tamrin SBM, Daneshjoo A, Sadeghi H. The adverse health effects of shift work in relation to risk of illness/disease: A review. Acta Medica Bulgarica. 2015; 42(1):63-72.
17. Liu Q, Shi J, Duan P, Liu B, Li T, Wang C, et al. Is shift work associated with a higher risk of overweight or obesity? A systematic review of observational studies with meta-analysis. International journal of epidemiology. 2018; 47(6):1956-71.
18. Flahr H, Brown WJ, Kolbe-Alexander TL. A systematic review of physical activity-based interventions in shift workers. Preventive medicine reports. 2018; 10:323-31.
19. Aisbett B, Condo D, Zacharewicz E, Lamon S. The impact of shiftwork on skeletal muscle health. Nutrients. 2017; 9(3):248.
20. Choobineh A, Rajaeefard A, Neghab M. Association between perceived demands and musculoskeletal disorders among hospital nurses of Shiraz University of Medical Sciences: a questionnaire survey. International Journal of Occupational Safety and Ergonomics. 2006; 12(4):409-16.
21. Weidenauer C, Täuber L, Huber S, Rimkus K, Randler C. Measuring circadian preference in adolescence with the Morningness-Eveningness Stability Scale improved (MESSi). Biological Rhythm Research. 2019;1-13.
22. Palmer K, Smith G, Kellingray S, Cooper C. Repeatability and validity of an upper limb and neck discomfort questionnaire: the utility of the standardized Nordic questionnaire. Occupational medicine. 1999; 49(3):171-5.
23. Abate H, Letta S, Worku T, Tesfaye D, Amare E, Mechal A. Shiftwork sleep disorder and associated factors among nurses working at public hospitals in Harari Regional state and Dire Dawa Administration, Eastern Ethiopia: a cross-sectional study. BMC nursing. 2023; 22(1)
24. Kesler RM, Bradley FF, Deetjen GS, Angelini MJ, Petrucci MN, Rosengren KS, et al. Impact of SCBA size and fatigue from different firefighting work cycles on firefighter gait. Ergonomics. 2018; 61(9):1208-15.
25. Hallemans A, Ortibus E, Meire F, Aerts P. Low vision affects dynamic stability of gait. Gait & posture. 2010; 32(4):547-51.
26. Ruggiero JS, Redeker NS. Effects of napping on sleepiness and sleep-related performance deficits in night-shift workers: a systematic review. Biological research for nursing. 2014; 16(2):134-42.
27. Takeyama H, Kubo T, Itani T. The nighttime nap strategies for improving night shift work in workplace. Industrial health. 2005; 43(1):24-9.
28. Robillard R, Prince F, Boissonneault M, Filipini D, Carrier J. Effects of increased homeostatic sleep pressure on postural control and their modulation by attentional resources. Clinical Neurophysiology. 2011; 122(9):1771-8.
29. Chappel SE, Verswijveren SJ, Aisbett B, Considine J, Ridgers ND. Nurses’ occupational physical activity levels: A systematic review. International journal of nursing studies. 2017; 73:52-62.
30. Nussbaum MA. Postural stability is compromised by fatiguing overhead work. AIHA journal : a journal for the science of occupational and environmental health and safety. 2003; 64(1):56-61.