1 Introduction

According to the monthly follow-up of the accidental sickness benefits (benefits paid to insured persons who have suffered accidents at work or were affected by occupational diseases), granted under ICD-10 Codes (M00-M99: diseases of the musculoskeletal system and connective tissue), represented by code B-91, indicates that from January to December 2016, benefits were designed for an average of 8,378 workers per month. Totaling 100,528 benefits in a single year. The amount spent only with insured persons who suffered occupational accidents or illnesses, paid by INSS (National Social Security Institute), exceeded the 100 million reais mark.

In that same year, the companies paid to the justice of Brazil more than 3 billion reais in labor lawsuits. And for the claimants (employees who filed labor lawsuits), 22 billion reais.

It is assumed that many of these occupational characteristics disorders develop when the duration of recovery time between successive operational activities or periods of work is insufficient (Colombini et al. 2014).

This type of disturbance is common in high-cadence production line. The cadence of work would be a quantitative aspect, referring to the speed of the movements that are repeated in a unit of time. Therefore, high-speed production line is equivalent to a high-speed work. (Ministry of Health: Repetitive strain injuries and work-related musculoskeletal disorders, 2001)

If there are a large number of hours with muscle contractions intense pains may arise, requiring relaxation to restore blood circulation. A rest period should be provided so that the circulation has time to remove metabolic products accumulated within the muscles (ITIRO IDIA 2005).

In all the functions of the human body can be verified the rhythmic exchange between energy expenditures and force replacement, or in a simple way, between work and rest. The pause of work is therefore an indispensable physiological condition in the interest of maintaining production capacity (Grandjean 1998).

It can be defined as a recovery or pause period in which there is a substantial inactivity of one or more myotendine groups previously involved in the execution of work actions (Colombini et al. 2014).

According to sub-item 17.6.3 of NR 17 (Regulatory Norm that aims to establish parameters that allow the adaptation of working conditions to the psychophysiological characteristics of the workers, in order to provide maximum comfort, safety and efficient performance), on the work organization, this subitem says that to prevent psychic overload, static or dynamic muscular neck, shoulders, back, upper limbs and lower limbs industries should provide respite for rest.

In case of repetitive work it is advisable to have a recovery period every 60 min with a ratio of 5 (work): 1 (recovery); it results that the ideal distribution relation of repetitive work is 50 min of repetitive work and 10 min of recovery (Colombini et al. 2014).

The measurement of heart rate has been used by several authors to estimate the physical workload of workers in different types of work (Sullman et al. 2007).

The evaluation of physical workload was the first parameter treated by the physiology of work and remains a central issue for most workers in the world (Fiedler et al. 2008). Heart rate (HR) is an important indicator for assessing the workload, due to the innumerable knowledge acquired in human physiology and the great ease of recording the data (Edholm 1968).

For continuous work over an 8-h work day, HR should not increase continuously, and after the end of work the HR should return to normal resting values after about 15 min. HR also should decrease after recovery (pause). The maximum HR limit should occur when the mean pulse rate reaches 30 bpm (women) and 35 bpm (men) above the resting pulse. In relatively light work the pulse rate rises rapidly and remains at a height corresponding to the intensity of the work and remains constant throughout the duration of the workload. When the work ends, within a few minutes the pulse rate returns to the initial levels (Grandejean 2001).

When heavy work is done, the heart rate rises steadily while it is performed, until work is stopped or the person is in a state of exhaustion that forces them to stop.

The activities related to the type of compensatory gymnastics or pause gymnastics, interrupt the tasks of the work place, being in the middle of the day or peak of fatigue. It prevents postural addictions from activities of daily living (ADLs) and from practical life activities (PBLs). In addition to breaking the monotony of work, it is used to compensate for some overloaded structures (LIMA, 2003, apud Carvalho and Mesquita 2006).

For Couto (1995), during a workday of eight hours the heart rate should not exceed 110 bpm, because above this limit there is indication of fatigue. Souza and Minette (2002) say that as fatigue increases, work rhythm, reasoning and attention are reduced, making the worker less productive and more susceptible to errors, incidents and accidents.

Thus, this study has the objective of evaluating the effects of the pause through the heart rate of the volunteers, calculating the energy expenditure and classifying the physical workload.

2 Methods

The study was carried out in a pharmaceutical company of cosmetic products, in a production line of high cadence with sampling of 10 volunteers, with average age of 34,8 years (±5,65), being 30% of the male sample and divided into control and experimental groups. The control and experimental group had 80% of the sedentary sample, but the experimental group had 20% of the population with systemic arterial hypertension and 60% had a habit of alcoholism once a week. In both groups there is no smoker. The choice of the line was for convenience and indication of the company. The chosen line was the hydroalcoholic packaging sector, which is characterized by the mechanical packaging of the bottles, and manually empty bottles of the cardboard boxes are placed in the jars on the mats, after the mechanical containers are placed: valve, cache, finishing of the packaging, packaging of the product and placing the product ready in cardboard boxes, having several units in a box, then going through 11 points of manual intervention with 70 technical actions per minute, with static postures standing and sitting.

The routine of the volunteers involves a preparatory gymnastics before the work day and a 5-min break with part-time postural gymnastics, within an 8-h workday, with an hour apart for an extra-day lunch. The control group performed work gymnastics and the experimental group had the gymnastics replaced by compensatory gymnastics working only the lower limbs, in order to completely rest the upper limbs.

The physical workload or cardiovascular load was calculated with the HR collected through a pulse oximeter, PalmSAT 2500a, 7.4 oz, with two operating buttons of the NONIN MEDICAL, INC. Battery. The HR values were collected by the factory’s physiotherapists, who wrote down a standard table at three times of the day: entrance (before pre-gym), pre-pause and post-pause. The methodology of Apud (1997) was used to calculate the cardiovascular load (CCV) of the work, corresponding to the percentage of HR during the work in relation to the maximum usable HR, through the following equation:

$$ CCV\, = \,FCT - FCR \, \times \, 100/FCM - FCR $$

On what:

CCV = cardiovascular load;

FCT = working heart rate;

FCM = maximum heart rate (220 - age); and

FCR = resting heart rate.

The CCV calculation used the FCR as the FC collected at the entrance of the production line and the FCT was the pre-pause. The HRC should be measured in the same position as the person working (RIO, PIRES, 2001). The FCR of the experimental group was 93.15 bpm (±11.9) and the control group was 88.9 bpm (±6.3). In order to carry out continuous work without health risks, the CCV, according to Apud (1997), should not exceed 40% in a work shift of 8 h, and the CCV was higher than this value, it is calculated the heart rate limit (FCL). According to Minette et al. (2007), the breaks are necessary to avoid the work overload when physical loads are detected.

The table proposed by Apud (1997) was used to classify the physical workload, in which the FCT is taken into account for this classification (Table 1).

Table 1. Classification of physical workload and heart rate
Full size table

The plant was contacted by SESMT (Specialized Service of Safety Engineering and Occupational Medicine) and then three meetings were scheduled with the company’s board of directors. The first one was for presentation of the theme, the second for clarification and delivery of the terms of acceptance of the company and free and informed consent of the employees, and the third for training of physiotherapists who collected the data. The company’s physical therapists gave the employees the free and informed consent form, assuring all their rights in relation to the study and with a form on habits of life and personal data, filled by the volunteers themselves. In addition to the meetings held in the factory, two more visits were made, to collect the terms and to collect the material with the data of the heart rate.

The data analysis was performed in a descriptive way, tabulating the data in Microsoft Office Excell® in order to identify and characterize the sample and the cardiovascular responses related to HR values. To determine the homogeneity of the groups, the Shapiro-Wilk test was used. Significance was set at p < 0.05.

3 Results and Discussion

The sample consisted of 10 volunteers, with a mean age of 34.8 years (±5.65), with 70% of the female sample divided equally between the control and experimental groups.

According to the normality test of Shapiro-Wilk, the values of the samples are normal, since p < 0.05. Regarding the results, it was statistically shown that the post-pause heart rate of the experimental group was effective, since p < 0.05, whereas the result of the control group was not statistically significant, since p > 0.05, demonstrating that gymnastics labor with total pause of MMSS is better than full-body workout with the objective of decreasing the HR in high-speed production line of MMSS. Regarding CCV, the experimental group had a CCV of 463% lower than the control group, but not statistically significant (p > 0.05), due to the small number of samples.

The CCV calculation indicated that on average the CCV of the experimental group was 10% and the control group of 2%, that is, no group reached 40% of the maximum load, indicating that the time of 5 min of pause already implemented in the company is effective for normalizing cardiovascular load.

The study by Carvalho (2012), who also evaluated the CCV and the pause, entitled “Ergonomic conditions of workers in chicken broiler sheds during the heating phase”, analyzed the CCV to evaluate the need for pause and concluded that in this population the CCV was 50% and that the worker then needed 25 min rest for every 35 min worked, calculated using the formula Tr = [Ht x (FCT-FCL)] ÷ (FCT-FCR), where Tr of the pause and Ht - working time (in minutes), being used only when the CCV exceeds 40%.

Also, the study of Carmo (2010), “Ergonomic evaluation of the gel application operation in two forest companies”, the CCV required for the manual planting operation with gel application was 41.0% in A and 40, 0% in B, concluding that every 60 min of the daily workday the worker should work 58 min and rest for another 2 min. Both studies had CCV above 40%, which according to Apud (1997) indicates physiological overload. These data show us the possible relation of CCV and the pause with regard to cardiovascular overload, indicating that the hourly pause regime is necessary when the CCV is equal to or greater than 40%.

The data of the mean working heart rate presented in Fig. 1, from both groups, allows to classify the workload of this production line as light, since it is within the range of 75 bpm to 100 bpm proposed by Apud (1997), however, classification by the OCRA checklist, described by Colombini et al. (2014) as an instrument for the mapping (identification and estimation) of biomechanical overload risk of the upper limbs, is classified in the violet area, where the exposure indexes are equal to or higher than 22.6, showing high risks. That is, in the general state of the worker there is no cardiovascular overload, but the upper limbs are exposed to repetitive strain injury through the analysis that the industry performed 6 months earlier through the Check List OCRA, in which it was classified as risk).

Fig. 1.
figure 1

Heart rate in the control group and in the experimental group, evaluated at the worker’s entrance, before the pause and after the pause.

Full size image

As the heart rate of the control group and the experimental group decreased after the pause, as shown also in Fig. 1, it indicates that the 5-min pause is effective for reducing energy expenditure, since there is no increase in cardiac output. According to Lemura and Von Duvillard (2006), as the demand for strength increases, intermediate and fast-contracting fibers are recruited by the central nervous system, increasing energy expenditure and provoking fatigue more quickly, evidenced by an increase in cardiac output (HR × systolic volume) to meet the demands of increased blood flow in the active muscles.

A study recently published by Souza et al. (2015) conducted research to compare HR changes in different work shifts. Regarding the parameters of HR variability, the study found that this population working in other shifts has the autonomic cardiovascular system with less favorable regulation (greater sympathetic modulation and lower parasympathetic modulation) compared to the control group (day shift workers), increasing HR during work, these changes, which are associated with a higher risk of cardiovascular disease. As our study evaluated second shift workers, we can emphasize the importance of breaks for these workers, and the need for further studies in this area for greater understanding.

4 Conclusion

This study demonstrated that the pause presented satisfactory results for the energetic recovery and cardiovascular stabilization of the volunteers, both with the work gymnastics already offered by the company and compensatory work gymnastics, since the volunteers do not have CCV above 40%. However, the experimental group with total rest of upper limbs with compensatory labor gymnastics during the 5 min presented an important reduction, indicating that in the same pause period, it is possible to reduce still more the energetic expenditure, being an alternative favorable to the higher income of the collaborator.

The data provided by the CCV, classification of Apud (1997) and Check List OCRA, showed us that more studies are necessary in this area, showing that the fact that there is no physiological, cardiac overload and less fatigue propensity, the upper limbs can be exposed to injury by repetitiveness in the same way. Another factor to consider is the need for a larger sample due to the expressive values ​​of CCV.