Development and Evaluation of a Hybrid Measurement System to Determine the Kinematics of the Wrist.

Optical Motion Capture Systems (OMCSs) are considered the gold standard for kinematic measurement of human movements. However, in situations such as measuring wrist kinematics during a hairdressing activity, markers can be obscured, resulting in a loss of data. Other measurement methods based on non-optical data can be considered, such as magneto-inertial measurement units (MIMUs). Their accuracy is generally lower than that of an OMCS. In this context, it may be worth considering a hybrid system [MIMU + OMCS] to take advantage of OMCS accuracy while limiting occultation problems. The aim of this work was (1) to propose a methodology for coupling a low-cost MIMU (BNO055) to an OMCS in order to evaluate wrist kinematics, and then (2) to evaluate the accuracy of this hybrid system [MIMU + OMCS] during a simple hairdressing gesture. During hair cutting gestures, the root mean square error compared with the OMCS was 4.53° (1.45°) for flexion/extension, 5.07° (1.30°) for adduction/abduction, and 3.65° (1.19°) for pronation/supination. During combing gestures, they were significantly higher, but remained below 10°. In conclusion, this system allows for maintaining wrist kinematics in case of the loss of hand markers while preserving an acceptable level of precision (<10°) for ergonomic measurement or entertainment purposes.

Do age and work pace affect variability when performing a repetitive light assembly task?

This study examined whether a repetitive light assembly task could be performed according to different movement sequences identified as ways of doing (WoD), and whether the age of the participants or the work pace affected the number of WoDs selected by each participant, or the kinematic parameters for each WoDs. For two work paces, 62 right-handed men in 3 age-groups were asked to fix a handle on a base with 2 nuts without discontinuity for a period of 20 min; no assembly procedure was demonstrated. The WoDs were characterized by a cross tabulation video coding method, and by measuring vertical force applied and the parameters of upper limb kinematics, as well as these measures' approximate entropy (ApEN). Five main different WoDs were used. Although most participants varied their WoD, neither participant age nor work pace affected the number of WoD they used. However, the WoDs differed from each other by the sequence of movements and by the level of ApEn of their kinematic variables without interfering with the production rate. Allowing operators to vary their WoDs when performing repetitive tasks could reduce strain on the locomotor system.

Grasping an object at floor-level: Is movement strategy a matter of age?

Bending down to pick things up off the floor is something that we do every day. This multisegment task can be done in a considerable number of postural configurations because of the large number of degrees of freedom to be controlled when executing it. In this study where volunteers performed a repetitive bending task, multisegment kinematic analysis allowed us to identify seven different bending strategies. Most operators used more than one bending strategy, but no particular strategy-type was found to be specific for a specific age group. However, the number of strategies used by an operator decreased with increasing age. It therefore appears that this factor influences the variability of the strategies used when repeatedly executing a movement involving the lower limbs to collect small objects from floor-level. This decrease in movement variability in senior operators may contribute to their increased risk of developing musculoskeletal disorders.

Age-related changes in grip force and dynamics of hand movement.

The authors investigated whether older adults (n = 16; mean age = 65 years) increased grip force to compensate for load force fluctuations during up and down movements more than young adults did (n = 16; mean age = 24 years) and whether older and young adults exhibited similar adaptation of grip force to alterations in friction associated with changes in object surface texture. As previously reported, older adults used a higher level of grip force than young adults during static holding. Increased grip force was observed in the older group during movement. The increase was appropriate to the lower coefficient of friction estimated for the older group. In both groups, grip force was greater with a smooth than with a rough surface (the latter having the higher coefficient of friction) during static holding and during movement. Moreover, grip force modulation was equally well synchronized with load force fluctuation during movement in the two groups. The authors concluded that changes in organization of grip force with age are well adapted to change in hand-object interface properties. Elevated grip force in older adults does not necessarily signify a fundamental change in synchronizing grip force modulation with load force fluctuation.