# Heart Rate Index as a Measure of Physical Workload in Chainsaw Operations
## 3 Results
### Influence of Working Positions on Work Performance  
Figure 8 presents ergonomic and non-ergonomic working positions in motor-manual tree processing. It contains a line and working phases of cutting, chopping, and manual handling, which are the main parts of motor-manual tree processing and can cause an overload of the musculoskeletal system. It is evident that the weight of the load affects whether the working position is ergonomic or not and whether we exceed the set parameters. It turned out that when working with the heaviest tool (AC--MS 500i/90 cm 9.3 kg), the worker's body is burdened in non-ergonomic positions for the longest time. The presented results document that working with a chainsaw includes ergonomic and non-ergonomic activities. The worker should know which are ergonomic positions (as explained in Section 2.4) and the critical load level concerning non-ergonomic positions. From the point of view of health and safety at work, it is important to plan an appropriate distribution of work and rest periods between individual tasks. To work with motor-manual tree processing tools, it would be appropriate to develop a recommendation that takes into account both the working position and the physical load during the work activity, as well as the load caused by the work tool itself. The results of this study highlight important implications for worker fatigue and productivity, particularly through the lens of time distributions observed in physiological responses. The heart rate (HR) data reveal how different tasks and tools, for example, \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Saw Type** & **Type** & **Preparation** & **Cutting** & **Chopping** & \begin{tabular}{c} **Manual** \\ **Handling** \\ \end{tabular} & **Other** & **Break** & \
\begin{tabular}{c} **Task** \\ **Preparation** \\ **Time** \\ \end{tabular} &
\begin{tabular}{c} **Total** \\ **Time** \\ \end{tabular} \\ \hline MS 500i/90 cm 9.3 kg & AC & 0:01:05 & 0:24:02 & 0:00:42 & 0:03:55 & 0:01:42 & 0:01:10 & 0:07:34 & 0:40:10 \\ \hline MS 500i/50 cm 7.5 kg & BC & 0:00:25 & 0:11:48 & 0:00:00 & 0:00:42 & 0:00:33 & 0:03:57 & 0:31:02 & 0:48:27 \\ \hline MS 362/50 cm 7.1 kg & BD & 0:01:05 & 0:22:21 & 0:00:00 & 0:00:45 & 0:00:00 & 0:03:31 & 1:15:21 & 1:43:03 \\ \hline Total time & & 0:02:35 & 0:58:11 & 0:00:42 & 0:05:22 & 0:02:15 & 0:08:38 & 1:53:57 & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Time working cycle and combinations of saws. Figure 7: Heart Rate Workload Index and a saw type. the use of the different saw types, influence fatigue accumulation, providing actionable insights for optimizing forestry workflows and ensuring worker safety. Time distributions of HR data showed prolonged periods of elevated cardiovascular strain during tasks involving heavy equipment operation, such as chainsaw use and tree felling. These periods correspond to peak physical effort, which, if sustained without adequate recovery, can lead to cumulative fatigue. Fatigue not only impairs productivity but also increases the risk of errors and injuries, particularly in hazardous environments like forestry. Tasks requiring precision, such as trimming or sorting logs, showed lower HR variability, suggesting a lower physical demand but potentially greater mental fatigue due to the need for sustained focus. The implications for productivity are twofold. First, the data underscore the need for strategic task rotation to balance physical and mental demands throughout a work shift. For example, alternating between high-intensity tasks, like tree felling, and lower-intensity tasks, such as log sorting, could help reduce overall fatigue. Second, incorporating regular recovery periods, guided by HR thresholds, can mitigate the risk of overexertion and maintain consistent productivity over time. As for inter-device reliability, the analysis of HR data from multiple devices revealed some discrepancies in readings, particularly during periods of intense hand motion or extensive force to keep working tools in.