# Metabolic Energy Consumption during Green Area Management
## 3 Results  
Concerning the evolution of the volume of oxygen consumed (VO\({}_{2}\)), considering workers of group I during the use of grass cutting blade, it was on average 25.56 \(\pm\) 0.57 IO\({}_{2}\)h\({}^{-1}\). Dividing this consumption into the three monitoring phases, during the preliminary phase, i.e., the phase of low initial activity, this value averaged 22.25 \(\pm\) 1.56 IO\({}_{2}\)h\({}^{-1}\), reaching 29.64 \(\pm\) 1.28 IO\({}_{2}\)h\({}^{-1}\) during the full working phase. In the resting phase, the value was 15.42 \(\pm\) 1.02 IO\({}_{2}\)h\({}^{-1}\). Carbon dioxide production rate (VCO\({}_{2}\)) was averaged at 18.62 ICO\({}_{2}\)h\({}^{-1}\), with values, respectively, of 18.3 \(\pm\) 0.52 ICO\({}_{2}\)h\({}^{-1}\), 24.96 \(\pm\) 1.45 ICO\({}_{2}\)h\({}^{-1}\) and 13.5 \(\pm\) 1.05 ICO\({}_{2}\)h\({}^{-1}\) for the three different monitoring phases. The maximum consumption of O\({}_{2}\) was 51.34 IO\({}_{2}\)h\({}^{-1}\) while that of CO\({}_{2}\) production was 39.66 ICO\({}_{2}\)h\({}^{-1}\). As shown in Figure 3, showing the average VO\({}_{2}\) and VCO\({}_{2}\) values of group I while using the cutting blade, there is a peak in oxygen consumption in the preliminary period (red line), which coincides with the start of work, and then tends to stabilise as work becomes fully operational. During the full work phase, consumption rises again, increasing the time during which the body is engaged in the operative phase. As the end of work approaches, consumption tends to stabilise downwards, indicating that the operator is preparing himself for the end of work. Referring to VO\({}_{2}\) consumption (mL/s), Figure 4 shows the difference between the groups, with II group recording the highest O\({}_{2}\) consumption (912 \(\pm\) 12) respect groups I (300 \(\pm\) 5) and III (687 \(\pm\) 7). With regard to the type of blade mounted on the brush cutter, the shredder blade (611 \(\pm\) 8) and brush knife (601 \(\pm\) 8) are more suitable for the work performed than the grass-cutting blade (828 \(\pm\) 16), recording a significantly lower O\({}_{2}\) consumption (Figure 5). This indicates that the first type of blade is not the most suitable for the type of turf present, thus increasing the number of actions required to remove weeds. The maximum level of work (or O\({}_{2}\) consumption) that can be achieved without metabolic lactic acid production is referred to as the respiratory quotient RQ, expressed as in Equation (1) when it takes a value equal to 1. Figure 6 shows the trend of VO\({}_{2}\) and VCO\({}_{2}\) as a function of time for worker groups during the use of the blades. In all the cases analysed, this value is around 0.95. This indicates that the work is carried out without lactic acid production in the aerobic zone. Figure 3: Average values of VO\({}_{2}\) and VCO\({}_{2}\) by group I with grass-cutting blade during the test. The red vertical line delimits the preliminary period, while the green and blue lines delimit the full-working and rest periods respectively. In the Y-axis the workers' group is listed. The average heart rate (HR) was 113 \(\pm\) 12 beats per minute (bpm), with a maximum of 149 \(\pm\) 7 bpm. The tests showed that heart rates were similar during the preliminary and rest periods of the trials but increased during the full work phase (Figure 7). The difference between the groups' heart rates is an average difference of \(\pm\)25 bpm. This is a rather low difference for field trials considering that, according to ISO 8996:200, the variation between recorded observations can be up to 20%. Figure 4: VO\({}_{2}\) consumed by worker groups on average during the trial period (mean \(\pm\) standard error). In the X-axis the workers’ group is listed. Data marked with different non-capital letters are significantly different by [PERSON]’s test (\(p<0.05\)). Figure 5: VO\({}_{2}\) consumed on average during the trial period using the different cutting blades (mean \(\pm\) standard error).