# Biomechanical Effects on Lower Extremities in Human-Robot Collaborative Agricultural Tasks
###### Abstract  
The present study pertaining to a key aspect of human-robot collaborative systems which is usually underestimated, namely occupational health proteolysis. The aim of this investigation was to assess the biomechanical effects of manual symmetric load lifting related to a synergistic agricultural task that utilizes an unmanned ground vehicle to undertake the carriage of loads. Towards that goal, kinetic and kinematic data were collected from the lower extremities of thirteen experienced workers, by testing three different deposit heights (70, 80, 90 cm) corresponding to possible adjustments of the available agricultural robot. Moreover, the muscle activation levels of three lower extremity muscles and one trunk muscle were evaluated via a wireless electromyography system. Overall, the experimental findings revealed that the lower examined load height was associated with larger knee flexion moments and hip extension moments. Nevertheless, this height was related to lower activation mainly of the erectus spinae muscles. Finally, insignificant alterations were observed for the ankle joint as well as the activation levels of the other muscles. Consequently, a height equal to 90 cm is suggested, however, by avoiding extreme lumbar postures. The current results can be exploited for possible ergonomic interventions concerning the optimal deposit height of a robotic platform when a similar case is designed. experienced workers; symmetric load lifting; musculoskeletal disorders; direct measurement methods; kinematic and kinetic data; electromyography; ergonomics; occupational health proteolysis 26 October 2021 8 Decemberactivity, agricultural tasks commonly entail the worker to lift a heavy load by bending forward or laterally, twisting, or/and maintaining a static body posture. A plethora of epidemiological studies have highlighted the strong association between lifting and injuries in the region of the low-back [12; 13]. As a consequence, estimating the spinal loading during lifting has plausibly attracted the interest of ergonomists and clinicians. Indicatively, [PERSON] et al. [14] concluded that load height and mass are significant determinants of low-back load, as lower heights and higher masses are linked with higher loads in the low-back region. [PERSON] et al. [15] explored the lifting stance width, showing that they have an important effect on lifting kinematics, but no significant effect on muscle activation levels of the trunk as well as those of lower extremities. [PERSON] et al. [16] dealt with the effects of lifting speed, deducing that faster lifts are associated with higher sagittal plane moments. Overall, the so-called revised NIOSH (National Institute for Occupational Safety and Health) lifting equation is widely accepted to assess the risks related to back injuries during lifting. In particular, the Recommended Weight Limit (RWL) is provided by:  
\[\text{RWL}=\text{LC}\;(\text{51})\times\text{HM}\times\text{VM}\times\text{ DM}\times\text{AM}\times\text{FM}\times\text{CM} \tag{1}\]  
The basic variables to be considered in the above equation are as follows: (a) The horizontal distance of the load relative to the body (HM), (b) The vertical distance of the load relative to the ground (VM), (c) The vertical distance between the initial and destination lift point (DM), (d) The angle of asymmetry (AM), (e) The frequency and time span of lifting (FM), and (f) The coupling of the worker's grip on the object (CM). Finally, the NIOSH equation utilizes a load constant (LC) equal to 51 pounds, representing the maximal load weight recommended under ideal conditions [17; 18]. Another factor that has to be taken into account is the experience of workers, since experienced workers tend to use different lifting techniques, as for example bending their lumbar region less and more their knees [19] compared to novice ones.