  Training helps to maintain and improve sufficient muscle function, body
control, and body coordination. These are important to reduce the risk of
fracture incidents caused by falls, especially for the elderly or people
recovering from injury. Virtual reality training can offer a cost-effective and
individualized training experience. We present an application for the HoloLens
2 to enable musculoskeletal training for elderly and impaired persons to allow
for autonomous training and automatic progress evaluation. We designed a
virtual downhill skiing scenario that is controlled by body movement to
stimulate balance and body control. By adapting the parameters of the ski
slope, we can tailor the intensity of the training to individual users. In this
work, we evaluate whether the movement data of the HoloLens 2 alone is
sufficient to control and predict body movement and joint angles during
musculoskeletal training. We record the movements of 10 healthy volunteers with
external tracking cameras and track a set of body and joint angles of the
participant during training. We estimate correlation coefficients and
systematically analyze whether whole body movement can be derived from the
movement data of the HoloLens 2. No participant reports movement sickness
effects and all were able to quickly interact and control their movement during
skiing. Our results show a high correlation between HoloLens 2 movement data
and the external tracking of the upper body movement and joint angles of the
lower limbs.
