###### Abstract  
This study aimed to quantify musculoskeletal symptoms/pain and characterize the physical demands at work and outside of work among precast concrete workers. Direct heart rate (HR) measurements and self-reported activity levels were used to estimate the physical demands. A total of 27 precast construction workers participated in a survey, and 21 wore a HR monitor smart watch for seven days. The HR data were parsed in minutes associated with occupational and nonoccupational physical activity. Correlation analysis and multivariate regression models were conducted to assess the associations between direct measured physical activity with self-reported physical activity, body mass index (BMI), years of work, smoking, and Borg ratings of perceived exertion (RPE). Approximately half of the participants experienced musculoskeletal symptoms in the last seven days and moderate functional limitations in carrying out activities of daily living (ADLs). The regression model revealed a positive relationship between direct measured moderate occupational physical activity (OPA) and the Borg RPE. Furthermore, an inverse association was found with BMI, smoking status, and years of work. The workers accrued a median of 415 min of moderate OPA per week. The findings showed a high amount of moderate OPA minutes per week and musculoskeletal issues among the precast concrete workers. musculoskeletalel disorders; acute and chronic pain; survey questionnaire; workloads; construction industry; physical activity; heart rate; wearable electronic devices +
Footnote †: journal: _Sci. Leisure time and occupational physical activity have contrasting health effects. While leisure time physical activity reduces cardiovascular mortality [14], OPA increases the cardiovascular disease mortality risk [15; 16]. This contradictory effect is known as the \"physical activity paradox\". The differences in the frequency, intensity, duration, and recovery time seem to explain this [16; 17]. These opposing effects require addressing OPA in physically demanding jobs to protect and promote workers' health. Construction workers seem to be exposed to a significant amount of OPA levels that might have a negative impact on their health [18; 19]. For example, [PERSON] and [PERSON] (2017) tested a wristband-type wearable heart rate sensor to continuously measure workers' physical demands during construction work and concluded that automated and continuous physical demand measurement can be enabled at the construction field [19]. Construction workers with musculoskeletal disorders have reported pain in different anatomical regions [9; 20; 21]. Musculoskeletal pain has been identified as an important burden for this working population that is aggravated by the physical characteristic of the job [5; 6]. Work-related musculoskeletal disorders and pain have been identified as the main source of interference with normal work activities in the construction sector [7]. Furthermore, WMSDs have been identified as the leading cause of occupational disability in construction workers [22]. Hence, integrated interventions aiming at reducing the impact of the job's physical demands on construction workers' health are mandatory. Assessing physical activity levels at work as a proxy of physical demands is essential to designing tailored interventions addressing physical demands. Previous studies have collected information on physical activity based on self-reports, whereas other studies lack sufficient and accurate direct measurements [23; 24]. Musculoskeletal pain is also an essential factor that needs to be accounted for during an intervention. Pain limits workers' ability to participate in work, social, and self-care activities. Significant pain also impairs quality of life [25]. The appropriate assessment of the physical demands and the presence of musculoskeletal pain in this working population is essential to help design effective interventions aiming at reducing the impact of the physical demands on the musculoskeletal system.