## 2 Material and Methods
### Pilot Tests to Identify the Critical Tasks  
First, brainstorming among the authors (experts) and three people who usually carry out operations on a ladder (furniture, curtain, and air conditioning assembly workers) was conducted to identify the most frequent and critical actions in terms of ergonomics and discomfort. Given the heterogeneity of the group, experts, and non-experts, a first list of operations, both domestic and non-domestic, which require a ladder to be carried out has been drawn up. Some examples were window washing, painting, cleaning the internal roof of the house room, screwing the plasterboard, changing a light bulb, and picking up and moving objects. Then, starting from these activities, a list of the movements to be carried out for each of them was drawn up. For example, to clean windows it needs to make repetitive vertical movements with just one arm; to screw in a light bulb, make a rotating movement with one hand; to clean a top it needs to make repetitive horizontal movements with just one arm. After the identification of the movements, a pre-experimental phase was carried out on a sample of 15 users. Each participant was asked to perform each movement twice, once standing and once using a ladder. Informed consent was obtained. The sample consisted of 8 men and 7 women, aged between 24 and 32. The height varied from 165 cm (female participant) to 180 cm (male participant), no specific inclusion Criteria have been applied, but the subject does not have disabilities and has to be able to work on a ladder (no height-related dizziness has to be recorded in the subject history). The tests were carried out randomly and at the end of each test, the participant had to assign a score of perceived discomfort on a scale from 1 to 10. The tests were necessary to be able to select the movements that reported a significant difference if performed from the ground or on the ladder. The authors chose 4 operations: the operations that, in the re-experimental phase, presented a difference of at least two points between the two setups for 80% of the sample.  
The identified tasks were:  
1. Top screwing: representative of all those operations that require the arms to be raised, with possibly the handling of a tool needed to carry out the operation, and a force exertion in the vertical direction. This group includes operations such as: screwing at the top of a ceiling, drilling at the top, painting the ceiling, changing a light bulb, etc. (Figure 1a).
2. Frontal screwing: representative of all those operations that require the arms to be maintained horizontally to carry out the operation, with possibly the handling of a tool needed to carry out the operation far from the body's center of gravity and force-exertion in the horizontal direction. This group includes operations such as frontal screwing, frontal drilling, wall painting, fixing of a frame, etc. (Figure 1b).
3. Object picking from bottom forward: representative of all those operations that require a forward bend with a vertical applied load, for example, to pose or take an object positioned in front of the ladder, in a lowered position (Figure 1c).
4. Object picking from the bottom sideways: representative of all those operations that require a downward bending and a twist of the torso with a vertical applied load, for example, to pose or take an object positioned laterally on the ladder, in a lowered position (Figure 1d).