## 2 Materials and Methods
### Composite Lifting Index Algorithm  
Each lifting cycle was identified by determining a'start' and a'stop' instant. These time frames were identified using the vertical position of the hands: the'start' and'stop' instants correspond to the minimum and maximum values of the vertical coordinates, respectively, [18] as shown in Figure 2. Since the motion is symmetrical, the identification was carried out only in the right-hand position. Once every cycle was identified, the multipliers of the RNLE for the computation of the \(FILI\) of every cycle were calculated using the data about the position of the optoelectronic system's markers and the IMUs. \[FILI(n)=\frac{L(n)}{LC\cdot HM(n)\cdot VM(n)\cdot DM(n)\cdot AM(n)\cdot CM(n)} \tag{1}\]  
where \(L(n)\) is the load value, manually inserted by the operator; \(LC\) is the load constant equal to 23, as requested by the RNLE [2]. The other multipliers were calculated as presented in [18]; therefore only a brief presentation is given here. \(HM(n)\) is the horizontal multiplier calculated at the beginning of the nth lifting, using the following equation [2]:  
\[HM(n)=\frac{0.25}{H(n)}=\frac{0.25}{Hands_{mp}(n)-Ankle_{mp}(n)} \tag{2}\]  
\(H(n)\) represents the horizontal location (Figure 1B), measured in centimeters, at the beginning of the nth lifting cycle. It was calculated as the distance in the anterior-posterior direction between the midpoint of the left and right third knuckle (\(Hands_{mp}(n)\)) and the midpoint between the ankles (\(Ankle_{mp}(n)\)). This parameter, as well as all the multipliers \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Task**} & \multirow{2}{*}{**Subtask**} & **LC** & **H** & **V** & **VM** & **D** & **A** & **A** & **F** & **FM** & **C** & **CM** & **Load** & **RWL** & **FILI** & **STILI** & **CII** \\  & & **[kg]** & **[cm]** & **WM** & **[cm]** & **WM** & **[cm]** & **[-1]** & **AM** & **[LiHMin]** & **FM** & **C** & **CM** & **Load** & **RWL** & **FILI** & **STILI** & **CII** \\ \hline \multirow{2}{*}{1} & A & 23 & 44.5 & 0.56 & 20 & 0.84 & 50 & 0.91 & 0 & 1 & 3 & 0.88 & Good & 1 & 4 & 8.64 & 0.40 & 0.46 & \multirow{2}{*}{0.50} \\  & B & 23 & 44.5 & 0.56 & 30 & 0.87 & 40 & 0.93 & 0 & 1 & 2 & 0.91 & Good & 1 & 4 & 9.48 & 0.38 & 0.42 & \multirow{2}{*}{0.50} \\ \hline \multirow{2}{*}{2} & C & 23 & 61.5 & 0.41 & 10 & 0.81 & 82 & 0.87 & 0 & 1 & 4 & 0.84 & Good & 1 & 7 & 5.53 & 1.06 & 1.27 & \multirow{2}{*}{1.50} \\  & D & 23 & 56 & 0.45 & 10 & 0.81 & 82 & 0.87 & 0 & 1 & 3 & 0.88 & Good & 1 & 7 & 6.36 & 0.96 & 1.10 & \multirow{2}{*}{1.50} \\ \hline \multirow{3}{*}{3} & E & 23 & 61.5 & 0.41 & 10 & 0.81 & 82 & 0.87 & 0 & 1 & 4 & 0.84 & Good & 1 & 10 & 5.53 & 1.51 & 1.81 & \multirow{2}{*}{1.50} \\  & F & 23 & 58.5 & 0.43 & 10 & 0.81 & 82 & 0.87 & 0 & 1 & 4 & 0.84 & Good & 1 & 10 & 5.81 & 1.44 & 1.72 & \multirow{2}{*}{2.50} \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Lifting task parameters. For each task (1, 2, and 3): the reference values of the load weight (L), the horizontal (H) and vertical (V) locations, the vertical travel distance (D), the asymmetry angle (A), the lifting frequency (F), the hand-to-object object coupling (C), the corresponding reference values of the multipliers obtained from the revised NIOSH lifting equation, recommended weight limit (RWL), single task lifting index (STLI), and composite lifting index (CLI). Figure 1: A representative subject who performed the lifting task (**A**) and a graphical representation of the task and experimental setup (**B**). that needed kinematic data about the hands, we corrected using the XSens kinematic model to obtain the wrist position. In order to determine the precise location of the hands' center, we employed a trigonometric method, which involved adding the distance between the wrist and the third metacarpal from the wrist position (measured for each considered subject) [18].