## 2 Materials and Methods  
### Experimentation Setup  
The experimental tests were carried out in a farm in the region of Volos, in central Greece. The study involved 20 participants (13 male, 7 female), whose average age, height, and weight were 30.95 years (SD \(\approx\) 4.85), 1.75 m (SD \(\approx\) 0.08), and 75.40 kg (SD \(\approx\) 17.20), respectively, where SD corresponds to the standard deviation. The participants' demographics are summarized in Table 1. To be eligible for inclusion in the present investigation, all subjects should have not had any history of surgeries or sustained any musculoskeletal injury during the last year that could influence their performance. All participants, prior to any experimental procedure, had to complete an informed consent form that was approved by the Institutional Ethical Committee.  
Following informed consent, each participant had to perform a specific activity. In particular, they have to walk an unobstructed distance of 3.5 m, lift a crate, and carry it to their point of departure, where they have to place it on an immovable agricultural robot. This task can be divided in six continuous sequential sub-activities, namely:  
1. Standing still until the signal is given to start;
2. Walking a distance of 3.5 m without carrying any crate;
3. Bending down to approach the crate;
4. Lifting the crate from the ground to an upright position;
5. Walking back the distance of 3.5 m with carrying the crate;
6. Placing the crate onto the robot.  
For the purpose of the present study, two UGVs were utilized (Husky and Thorvald), which are usually used in outdoor environments (Figure 1) [42; 43]. The two available UGVs correspond to a deposit height of the crate equal to 40 cm (Husky) and 80 cm (Thorvald). Furthermore, the crate was either empty (tare weight equal to 1.5 kg) or full with weight plates with a total mass (crate and plates) approximately equal to 20% of each participant's mass, similarly to [44; 45]. The mass of the available weight plates was 1 and 2.5 kg for the purpose of easily adjusting the required mass to be lifted and carried. An open plastic crate, commonly used in agriculture, was used with handles on both sides at 28 cm height above its base. The dimensions of the crate were 31 \(\times\) 53 \(\times\) 35 cm (height \(\times\) width \(\times\) depth). Consequently, each participant carried out four sub-cases:  
1. Empty crate--Husky;
2. Crate full of the required weight--Husky;
3. Empty crate--Thorvald;
4. Crate full of the required weight--Thorvald.  
Each sub-case was performed three times in a randomized order and at each participant's own pace, which stands for 12 efforts for each subject. Finally, all participants were instructed to carry out a five-minute warm-up in order to avoid possible injuries. The inclusion of different subjects, as per genre, age, weight, height, and loading heights on  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Variable** & **Mean \(\pm\) Standard Deviation** \\ \hline Age & 30.95 years \(\pm\) 4.85 \\ Height & 1.75 m \(\pm\) 0.08 \\ Mass & 75.40 kg \(\pm\) 17.20 \\ \hline Gender & 13 males, 7 females \\ \hline \hline \end{tabular}
\end{table}
Table 1: Participants’ demographics.  
Figure 1: The available agricultural robots that were used in the present analysis, namely **(a)** Husky and **(b)** Thorvald robots.  
robots, was targeted toward a large variability on the collected data, so the trained model was able to identify the activities conducted under a broad range of conditions.