Visual feedback and age affect upper limb reaching accuracy and kinematics in immersive virtual reality among healthy adults.

This cross-sectional study aimed to evaluate the effect of visual feedback, age and movement repetition on the upper limb (UL) accuracy and kinematics during a reaching task in immersive virtual reality (VR). Fifty-one healthy participants were asked to perform 25 trials of a reaching task in immersive VR with and without visual feedback of their hand. They were instructed to place, as accurately and as fast as possible, a controller held in their non-dominant hand in the centre of a virtual red cube of 3 cm side length. For each trial, the end-point error (distance between the tip of the controller and the centre of the cube), a coefficient of linearity (CL), the movement time (MT), and the spectral arc length of the velocity signal (SPARC), which is a movement smoothness index, were calculated. Multivariate analyses of variance were conducted to assess the influence of visual feedback, age and trial repetition on the average end-point error, SPARC, CL and MT, and their time course throughout the 25 trials. Providing visual feedback of the hand reduced average end-point error ( P  < 0.001) and MT ( P  = 0.044), improved SPARC ( P  < 0.001) but did not affect CL ( P  = 0.07). Younger participants obtained a lower mean end-point error ( P  = 0.037), a higher SPARC ( P  = 0.021) and CL ( P  = 0.013). MT was not affected by age ( P  = 0.671). Trial repetition increased SPARC ( P  < 0.001) and CL ( P  < 0.001), and reduced MT ( P  = 0.001) but did not affect end-point error ( P  = 0.608). In conclusion, the results of this study demonstrated that providing visual feedback of the hand and being younger improves UL accuracy and movement smoothness in immersive VR. UL kinematics but not accuracy can be improved with more trial repetitions. These findings could guide the future development of protocols in clinical rehabilitation and research.