Using passive or active back-support exoskeletons during a repetitive lifting task: influence on cardiorespiratory parameters.

The objective of this laboratory study was to assess the cardiorespiratory consequences related to the use of different back-support exoskeletons during a repetitive lifting task. Fourteen women and thirteen men performed a dynamic stoop lifting task involving full flexion/extension of the trunk in the sagittal plane. This task was repeated for 5 min with a 10 kg load to handle. Four conditions were tested: with a passive exoskeleton (P-EXO), with two active exoskeletons (A-EXO1 and A-EXO2), as well as without exoskeleton (FREE). The oxygen consumption rate and cardiac costs were measured continuously. Results showed a significantly lower (p < 0.05) oxygen consumption rate for all exoskeletons as compared to FREE (12.6 ± 2.2 ml/kg/min). The values were also significantly lower (p < 0.001) for A-EXO1 (9.1 ± 1.8 ml/kg/min) compared to A-EXO2 (11.0 ± 1.8 ml/kg/min) and P-EXO (11.8 ± 2.4 ml/kg/min). Compared to FREE (59.7 ± 12.9 bpm), the cardiac cost was significantly reduced (p < 0.001) only for A-EXO1 (45.1 ± 11.5 bpm). Several factors can explain these differences on the cardiorespiratory parameters observed between exoskeletons: the technology used (passive vs active), the torque provided by the assistive device, the weight of the system, but also the level of anthropomorphism (related to the number of joints used by the exoskeleton). Our results also highlighted the lack of interaction between the exoskeleton and sex. Thereby, the three back-support exoskeletons tested appeared to reduce the overall physical workload associated with a repetitive lifting task both for men and women.

Evaluation of two upper-limb exoskeletons during overhead work: influence of exoskeleton design and load on muscular adaptations and balance regulation.

PURPOSE: Overhead works (OHW) are identified as a major risk factor for shoulder musculoskeletal disorders. The use of upper-limb exoskeletons (EXOUL) is emerging to address these challenges. This research tested the influence of EXOUL design and load on the upper-limb and postural muscles activity, and on the balance control, during OHW. METHODS: This study compared two passive EXOUL, notably differing by the level of assistive torque delivered. Both EXOUL was examined in two load conditions (2 vs. 8 kg). Twenty-nine volunteers performed a static OHW for each condition. RESULTS: Both EXOUL led to similar reductions in shoulder flexor muscle activity (12.3 ± 7.8% of RMSREF), compared to without equipment (29.0 ± 14.2% RMSREF). Both EXOUL resulted in a reduction in the activity of shoulder (3.6 ± 3.2% RMSREF) and wrist (2.4 ± 1.7% RMSREF) extensor muscles (4.9 ± 3.9 and 5.9 ± 6.1% RMSREF, respectively). The use of EXOUL led to reductions in back muscle activity, depending on the exoskeleton design (in % RMSREF, 12.9 ± 9.4 for EXO1, 22.8 ± 12.6 for EXO2 and 32.0 ± 18.4 without equipment). Wearing EXOUL induced changes in balance regulation, depending on both exoskeleton design and load condition. CONCLUSION: The increase of assistive torque was not associated with an increase in EXOUL performance. However, the exoskeleton design (mass, balance, and assistive torque) has to be suitable for the load handled during static OHW to optimize the effects of using an EXOUL on the postural muscles.

Temporal leeway: can it help to reduce biomechanical load for older workers performing repetitive light assembly tasks?

Current industrial production systems allow assembly of customised products which include additional elements distinguishing them from a reference model. This customisation can result in significant additional time constraints which compel workers to complete their tasks faster, which may pose problems for older workers. The objective of this laboratory study was to investigate the impact of restrictive or flexible pacing during assembly of customised products among groups of younger and older participants. The data gathered were used to analyse cycle-time, assembly performance, muscular load, and kinematic adaptations. The flexible pacing condition was found to improve production performance, increasing customised assembly cycle-time and reducing biomechanical load, for both young and older participants. However, as the task required fine manual dexterity, older participants were subjected to a higher biomechanical load, even in the flexible pacing scenario. These results should encourage assembly-line designers to allow flexible time constraints as much as possible and to be particularly attentive to the needs of older workers.

Ergonomic assessment of the surgeon's physical workload during standard and robotic assisted laparoscopic procedures.

BACKGROUND: Standard laparoscopy is responsible for musculoskeletal problems because of surgeons anti-ergonomic positions. Robot-assisted laparoscopy seems to reduce these musculoskeletal disorders thanks to the surgeons seated position. The objective of this study is to evaluate the muscular strain and cognitive stress induced by these two techniques during real operations conducted on the pig. METHODS: Electromyographic activities, heart rate, physical and mental workloads (NASA Tlx and Borg CR-10) were recorded. RESULTS: Physical workload and perception of the effort invested was significantly greater during the standard laparoscopies (p<0.05). Mental stress was however identical for the two techniques. In Standard Laparoscopic group, greater physical activity was found for trapezius and dorso-lumbar muscles, and significant appearance of fatigue of the trapezius muscles should also be noted. Finally, heart rate during standard laparoscopy was increased (92.1 ± 1.6 bpm vs 83.7 ± 1.8, p<0,01), confirming greater physical expenditure. CONCLUSIONS: Robot-assisted laparoscopy is a less physically stressful surgical technique than standard laparoscopy.