Patient care unit (PCU) workers suffer numerous adverse health outcomes that have been related to the physical demands of their work. Musculoskeletal symptoms and injuries in particular are highly prevalent among PCU workers [1, 2]. The 1-year prevalence rate of low back pain in nursing workers has been reported to be approximately 60%.[3, 4] Additionally, the prevalence of musculoskeletal symptoms reported for the previous 12 months among nursing workers ranged between 10% to 15%.[5] Furthermore, in acute care hospitals, back injuries due to sprains or strains have been reported as the most common injuries associated with days away from work. [3, 6] For these injuries, patient handling activities were reported as the main cause.[6, 7]

Patient care unit workers are exposed to physical demands including patient handling tasks such as, lifting, repositioning and manual transferring of patients. These tasks are physically demanding and impose mechanical loads on the back that increase the probability for the development of low back pain and disability.[8-10] Supporting the weight of the torso during simple bending puts large strains on the low back. Furthermore, inclinometer measurements of trunk flexion have been associated with an increased prevalence of low back pain.[11, 12] Punnett et al.[13], found that back disorders were associated with trunk flexion between 20° to 45° (OR=4.9) and flexion greater than 45° (OR= 5.9) among 1335 automobile assembly workers. Physiological studies also demonstrated that these postures increase heart rate and oxygen consumption.[14]

In addition to work-related injuries, scientific literature has reported high rates of cardiovascular diseases and all-cause mortality among workers of physically demanding jobs, including health care workers.[14-16] High physical job demands, often assessed using occupational physical activity (OPA) metrics, have been associated with high energy expenditure, oxygen consumption, and higher risk for CVD disease.[17] Furthermore, high physical activity at work has been associated with a higher risk for ischemic heart disease among nurses. [18]

Trunk flexion and occupational physical activity are parameters that have been largely used to assess and characterize jobs with high physical demands.[11-13, 19-22] Trunk flexion has been usually measured using observational methods, including pen and paper based observation methods, videotaping and computer-aided analysis.[23] As an alternative, the use of wearable sensors has been increasingly accepted because they are less labor-intensive compared to observational methods.[24] Occupational physical activity has also been assessed at a population level using mainly two different methods, questionnaires[25] and direct measurements collected through motion detectors (e.g., accelerometers). Motion detectors provide a more accurate and feasible method for getting detailed information about physical activity levels than questionnaires.[26, 27]

While trunk flexion and OPA both have physiological implications, the relationship between trunk flexion and physical activity while evaluating a physically demanding work environment such as PCU work is not well established.[28] Previous studies have described trunk flexion [29-31] or OPA [32], among nursing home nurses and personal support workers. Only one study[28] analyzed upper arm and trunk postures in registered nurses stratifying by OPA levels. A better understanding of this relation will allow us to comprehend the contribution of trunk flexion at work on OPA levels. An improved understanding of how trunk flexion and physical activity are related may provide a better understanding of the contribution of these two parameters on the occurrence and etiology of disease among PCU workers. These associations will be useful in implementing integrated ergonomic and health intervention to promote health in physically demanding jobs.

In this study, occupational physical activity and trunk flexion were measured during a work shift among PCU workers from two hospitals from Boston, MA. We hypothesized that PCU workers who have larger amounts of trunk flexion will also have greater minutes of moderate and vigorous physical activity during a work shift as indicated through positive and significant correlations.

Complete accelerometer and inclinometer data were collected on 47 of the 50 participants (Table 1) covering 47 single shifts that ranged between 8 and 12 hours in duration distributed between day, evening, and night shifts. Data from three PCU workers were unrecoverable due to instrumentation initialization errors. Participants with successful measurements had a mean age of 42 years (range: 23 – 68 years), were predominantly females with a Female to Male ratio of 7:1. Thirty five participants worked during day shifts (from 7 am to 11 pm) and fifteen in night shifts (from 7 or 11 pm to 7 am).

The goal of this pilot study was to characterize directly measured minutes of physical activity (PA) levels of PCU workers and directly measured metrics of trunk posture during a single shift in order to explore the relation between trunk postures, and minutes of PA. Overall, a wide variability in the distribution of trunk postures measured across the workers was found and resulted in a range of low, medium and high risk for reporting low back pain. However, the amount of moderate and vigorous physical activity for participants was quite small and hence did not vary significantly across these exposure categories. Only 6 minutes of moderate activity or greater were measured during a single shift with no significant correlation with trunk flexion metrics.

These results suggest that within the context of PCU worker, the physical demands of the job while perceived to be moderate to high in terms of the exposure to trunk flexion are actually of low intensity physical activity levels. Trunk flexion was associated at best with lifestyle and light levels of physical activity. Furthermore, the job demands as denoted by the frequency of bends to flexion and extreme flexion may be more associated with fatigue as defined by work physiology than with moderate or vigorous levels of physical activity. In our study the frequencies of trunk flexion to 20° and to 45° were 2.1 and 0.6 bends per minute, respectively. The frequency multiplier within the NIOSH Lifting equation for these rates is based on the psychophysical experiments of Snook and Ciriello [39] and is assumed to be more associated with muscle fatigue rather than challenges to the physiological expenditure. [40] While the scientific literature support that high intensity physical activity at work is detrimental for workers health, these data indicate that the type of activity these workers experience at work is in the range of low intensity physical activity.[41, 42]

The negative correlation between perceived exertion and minutes of sedentary activity within a shift suggests that the perceived exertion of the shift is related to the total time of non-sedentary activity and may hence misclassify self-reported occupational physical activity as moderate or vigorous. In these workers, a large amount of their non-sedentary time is below moderate or vigorous levels of physical activity; however, the same individuals report high levels of moderate and vigorous levels of OPA (presented in Umukoro et al, 2013). PCU workers’ perceived exertion incorporates many of the different physical demands of the job, which may be any non-seated activity such as standing and bending, which are bellow moderate or vigorous levels of physical activity. It also needs to be noted that the perceived exertion for the current shift was not as intense as a typical shift. This issue might affect the total amount of minutes of physical activity at work. However, that will not change the association found between trunk flexion and low levels of physical activity.

We did not measure lifting and the load of lifting in this study but trunk flexion does measure with a high degree of accuracy the load on the low back.[43] Large trunk flexions have been related to an increase in low back loads.[44] Because of this, measuring trunk flexion relative to gravity is often used to quantify back loading in ergonomic workplace evaluation. [19, 45, 46] Measuring trunk flexion is an economical and very feasible method for measuring exposure to bending, an identified risk factor for low back pain. [47, 48]

Physical activity was measured using an accelerometer. This is a validated methodology known to provide reliable exposure estimates, but there are some concerns regarding its limitation for capturing physical activity while adopting static postures (lifting or bending over).[49, 50] This restriction may have led to an underestimation of the physical activity measured at work; however, the frequency of bending as measured through the inclinometer supports the lower level of physical activity measured here. Overall, this pilot study contributes to improving the scientific community’s understanding of the interaction between physical activity levels and physical load in a dynamic and physically demanding work environment such as a hospital setting. Furthermore, we tested associations between total minutes of activity and did not normalize these minutes across the different shift lengths in table 4. We did analyze the data with both absolute and normalized data still observed no significant differences.

The results need to be considered within the limitations of the study methods. First, these results are limited to PCU workers who work under similar circumstances. The small number of workers limited our statistical power in detecting trends and associations. However, we saw some associations between trunk flexion with lifestyle and light physical activity levels. Further studies with a larger sample size and measures per workers during multiple work days are recommended to assess the association between physical loads and physical activity and corroborate our findings.

Overall, PCU workers required to perform a significant number of trunk flexions to 20 ° and 45° during a shift. Even though, these demands can be considered as high, their physical activity related to those are low due to low frequency of the trunk flexion. These findings agree with the results on a previous study that found a small contribution of physical activity at work towards moderate and vigorous levels of physical activity. [32] Interventions aimed in improving PCU workers health need to consider OPA and job demands in order to develop tailored interventions in this working population.