Physiological Workload of Chainsaw Felling and Processing Workers in Uneven-aged Mixed Stands Opterećenje radnika tokom sječe i izrade motornom pilom u raznodobnim mješovitim sastojinama

Forest harvesting in Bosnia and Herzegovina is done by chainsaws in felling and processing phase, and cable skidders in skidding phase in most cases. The aim of study was to determine physiological workload of chainsaw operator in felling and processing of wood assortments on the basis of the measurement of a heart rate. The research was carried out in mixed uneven-aged stands of Silver fir ( Abies alb a L.), European beech ( Fagus sylvatic a L.) and Norway spruce ( Picea abies (L.) Karst.) managed by two Cantonal Public Enterprise in Bosnia and Herzegovina. Heart rate was measured using Garmin Forerunner 35 GPS Running Watch with Wrist-ba sed Heart Rate ( Garmin Ltd., United States ) with continuous data logging and storage of heart rate readings. Felling and processing works were recorded with action camera during whole working day. Time study was performed based on made videos. The average working heart rate (effective time and delays) was 117 bpm (beats per minute) for subject A and 113 bpm for subject B. The results of Kruskal-Wallis test showed signi ficant differences for average heart rate in relation to time study element. The average heart rate reserve (%HRR) was 47.15% for subject A and 50.00% for subject B. The study results showed that heart rate reserve of chainsaw operator during tree felling and processing exceeded value of 40% which corresponds to heavy work and may have negative impacts on the health of the workers.


INTRODUCTION -Uvod
The forests in Bosnia and Herzegovina are mostly uneven-aged with natural regeneration. Forest harvesting is done by chainsaws in felling and processing phase, and cable skidders in skidding phase in most cases (Sokolović & Musić, 2009;Halilović et al., 2013;Marčeta et al., 2014;Halilović et al., 2015).
Works in forestry have specific characteristics that distinguish them from other industry sectors, which are manifested through the subject of work and working conditions (Kulušić, 2000;Lipoglavšek & Staudt, 2005). The forestry workers are exposed to above-average physiological workload for almost entire working lifetime (Vondra, 1995;Martinić, 2006) due to a significant share of manual work, work with machines with proven harmful effects and constantly changing outdoor working conditions. All these factors make the work site of a forest worker one of the most dangerous, with a high probability of injury during working lifetime or suffering from occupational diseases, which shortens working and life expectancy (Šporčić et al., 2015;Eroglu et al., 2015a).
The negative effects of works in the forestry to worker's health and safety are especially expressed in forest harvesting. This study is based on the phase of felling and processing of wood assortments due to partial mechanization of works, ie the use of motor-manual means of work (chainsaws) which causes significant physiological workload. Tree felling is a physically demanding and dangerous job (Grzywiński, 2015;Bačić et al., 2020) which involves training, use of protective equipment and continuous attention (Melemez & Tunay, 2010). It may have negative impacts on the health of the forest workers and increase the prevalence of work-related musculoskeletal disorders (Arman et al., 2021). The most share of forced working postures occurs during tree felling with a chainsaw (Grzywiński, 2015).
Ergonomic research conducted in forestry for decades (Tomanić, 1995) aims to humanize work by improving the characteristics of means of work, as well as determining the organization of work in which workers are exposed to the least physiological load.
The physiological stress of workers in forestry can be established on the basis of the measurement of a constant heart rate (Robek &Medved, 2006;Grzywiński et al., 2017). Maximum heart rate (HRmax) is a standard indicator of the highest acceptable individual exertion in work physiology. Variations in the heart rate during work are directly proportionate to the intensity and duration of work, the more intense and longer is the work, the higher is the heart rate . Determining the physiological workload on the basis of heart rate is a very suitable method for research in the forestry due to its practicality (Martinić, 1995;Grzywiński et al., 2017). Researchers used heart rate measuring for determination of physiological workload of forestry workers in previous studies (Kirk & Sullman, 2001;Yovi et al., 2006;Stampfer et al., 2010;Silayo et al., 2010;Melemez & Tunay, 2010;Ҫalişkan & Ҫağlar, 2010;Ottaviani et al., 2011;Spinelli et al., 2014;Huber & Stampfer, 2015;Eroglu et al., 2015b;Ottaviani Aalmo et al., 2016, Bačić et al., 2018Borz et al., 2019;Spinelli et al., 2020;Arman et al., 2021).
Physiological workload (%HRR) of workers during harvesting operation was 40.9% according to Eroglu et al. (2015b). Based on a review of the available literature, Martinić (1995) states that the average heart rate of workers during felling and processing of wood by chainsaw is 108-116 bpm. Ҫalişkan & Ҫağlar (2010) determined that average working heart rate of chainsaw operator during felling in spruce forest was 122.8 bpm, while the pre-work resting heart rate was 70.5 bpm. The average physical workload (%HRR) rate was 44.79%. Huber & Stumpfer (2015) found the relative heart rate (%HRR) during felling in spruce dominated stands range from 23.43% to 35.26% and the highest physiological workloads during the felling task. According to Leszczyński & Stańczykiewicz (2015) the maximum heart rate (HRmax) of chainsaw operator 29 years old, 170 cm high and 76 kg weight was 191 bpm, while heart rate at rest (HRrest) was 69 bpm during tree felling and processing in late thinning of coniferous stands. The relative heart rate (%HRR) in same research was 39.05% for effective work time. Melemez & Tunay (2010) established the following: average working heart rate of chainsaw operator 115 bpm, average heart rate reserve 42% and resting heart rate 73 bpm. According to Cheţa et al. (2018) average heart rate during felling and processing in old hybrid poplar dominated stand ranges from 93.5 to 132.1 bpm, and %HRR ranges from 21.76 to 57.49%. The highest physical strain to the worker was reported during technical delay, and the lowest during work preparation. Arman et al. (2021) cited that the mean mean level of physical workload during clearcut operations in the pine plantation was 43.54% of the relative heart rate (HRR) which corresponds to heavy work. Silayo et al. (2010) calculated percentage of heart rate increase during work compared to resting heart rate and found that the physical workload was 65% heart rate increase for chainsaw operator. Resting heart rate of chainsaw operator 32 years old was 55 bpm (Huber & Stumpfer, 2015). Grzywiński et al. (2017) found that a working posture influence the level of physiological workload of a chainsaw operator. Higher heart rate values were found during standing bent forward body postures compared to squatting and half-kneeling.
The aim of the study was to determine physiological workload of chainsaw operator in felling and processing of wood assortments because similar researches were not conducted in Bosnia and Herzegovina.

Heart rate measurements -Mjerenja otkucaja srca
Two male workers were chosen in order to measure the psysiological workload during tree felling and processing (table 2). The workers were considered representative of the felling worker population in enterprises in terms of age, skill and productivity. Subject A felled and processed trees in one compartment in the area of SF and subject B in three compartments in the area of ZDF.
Heart rate was measured to assess the level of physiological workload, using a Garmin Forerunner 35 GPS Running Watch with Wrist-based Heart Rate (Garmin Ltd., United States) with continuous data logging and storage of heart rate readings (figure 2). The measurements were performed during whole working day including delays for 17 days in March and April 2019. Felling and processing works were recorded with action camera during whole working day. Time study was performed based on made videos. Heart rate monitor was placed on workers left hand so it did not interfere with work acitivites. Recorded heart rate data was downloaded via Garmin Connect users interface and sorted out in MS Excel 2016. Statistical analyses were carried out using the Statgraphics Centurion XVI software. After checking for normality (Shapiro-Wilk W test) and homogeneity of variance (Levene's test), the Kruskal-Wallis non-parametric multiple-comparison test was used to test the effect of the factor "time study element" on the average heart rate. The working day was divided into: a) effective time  Relative heart rate was calculated as follows (Vitalis, 1987): where %HRR is relative heart rate at work (%), HR work is average heart rate during work (bpm), HR rest is resting heart rate (bpm), HR max is the maximum heart rate (bpm), bpm is a abbrevation for beats per minute.
Maximum heart rate (HR max ) was calculated as follows: HR max = 220 -age (Rodahl, 1989). The minimum measured heart rate value during working day was taken as the resting heart rate (HR rest ).

Very low <75
Low

RESULTS -Rezultati
The average working heart rates for time study elements range from 104 to 128 bpm for subject A and 91 to 131 bpm for subject B. The average working heart rate (effective time and delays) is 117 bpm for subject A and 113 bpm for subject B (table 5). The results of Kruskal-Wallis test showed significant differences for average heart rate in relation to time study element (table 5).
The minimum heart rate was recorded during the preparatory-final time for both subjects and maximum during the moving to the landing site for subject A and dealing with hung up trees for subject B (table 5).
Heart rate reserve exceeded value of 40% -a permissible value as described by Potočnik &Poje (2017) for all work tasks of effective time and delays expect preparatory-final time and personal delay for subject A and preparatory-final time for subject B. Moving to landing site caused the highest heart rate reserve (56.10%) for subject A and dealing with hung up trees for subject B (63.63%). Workers during moving to landing site work task walk on difficult terrain carrying chainsaw, fuel and tools which causes physical strain. Also, dealing with hung up trees cause significant physical strain because of characteristics of work task and workers posture. The heart rate reserve for the whole study time was estimated at 47.15% for subject A and 50.00 for subject B (table 5) indicating a high physiological strain.
Physiological workload for most time study element was moderate according to Apud et al. (1989) expect moving to landing site for subject A and dealing with hung up trees for subject B where it was high and preparatory-final time for subject B where it was low (figure 3). Delimbing and processing 123b 120b Dealing with hung up trees -131a Preparatory-final time 104d 91f Technical delay 110c 110d Personal delay 107c,d 105e Moving to landing site 128a 121b Kruskal-Wallis p 0.0000 0.0000 Different letters show significant differences among time study elements according to the Kruskal-Wallis test

DISCUSSION -Diskusija
The average working heart rate for subject A (117 bpm) and subject B (113 bpm) from this study were similar to result (115 bpm) cited by Melemez & Tunay (2010) and Arman et al. (2021) for clear cut in the pine plantation (116.08 bpm). The determined average working heart rate for subject B is within the interval 108 -116 bpm cited by Martinić (1995) for workers in felling and processing phase, while average working heart rate for subject A is slightly greater. Ҫalişkan & Ҫağlar (2010) found higher value of the average working heart rate of chainsaw operator during felling in spruce forest (122.8 bpm), and Cheţa et al. (2018) smaller during felling and processing in old hybrid poplar dominated stand (107.1 bpm).
The maximum heart rate values were measured during the moving to the landing site for subject A (128 bpm) and dealing with hung up trees for subject B (131 bpm), while Arman et al. (2021) found the the highest mean heart rates during the tree processing (117.7 bpm), back cut (115.6 bpm), and undercut (114.8 bpm).  (2015) found the highest values of relative heart rate for felling task in spruce dominated stands. According to Cheţa et al. (2018) the highest physical strain to the worker was reported during technical delay. The lowest physiological workloads were measured during the preparatory-final time for both subjects. According to Cheţa et al. (2018) the lowest physical strain to the worker was reported during work preparation which corresponds to the results of this study.

CONCLUSIONS -Zaključak
This study aim to determine physiological workload of chainsaw operator during felling and processing of wood assortments in mixed uneven-aged stands in Bosnia and Herzegovina. The study results showed that heart rate reserve of chainsaw operator during tree felling and processing exceeded value of 40% which corresponds to heavy work and may have negative impacts on the health of the workers and increase the prevalence of work-related musculoskeletal disorders. Considering a slightly higher heart rate reserve (%HRR) of the chainsaw operator compared to results of other research it is necessary to consider measures that would lead to its reduction including the training of workers, changes in the organization of work and continuous medical examination of workers with the aim of determining ability to perform felling and processing works.
The presented results contribute to establishing physiological workload of chainsaw operator during felling and processing in Bosnia and Herzegovina.