Table 3 Summary of usability protocol with supervisors’ observations and participants’ feedback

Functionality and interaction with the system

− Good and stable connection of laptop (with system software) to TV^a

− Technical issues (as system crashes or frozen pictures on the screen)^a,b

− Simple set up^b

− Unstable (Bluetooth) connection of IMUs to the system^a,b

− Easy usable game composition^b

− Navigation via laptop keyboard instead by IMUs (as cursors)^a

− Inaccurate evaluation of movements by IMUs (evaluation algorithms)^a

IMUs

− Comfortable to wear (participants did not notice them during training)^b

− Suboptimal material of IMU cover (cover expanded after heating up while charging)^a

− Suboptimal material of IMU fixation strap (difficult to clean the Velcro fixation, material sticks to some clothes)^a,b

− Difficulties to attach the IMUs with the Velcro fixation (especially at wrists)^a,b

Design

− Exciting game story of travelling around Europe to different cities^b

− No variation in music^b

− Pleasant music^b

− No explanation about feedback system (colour code, performance score)^b

− Helpful cues (arrows) to prepare the next movement^b

− Virtual instructor guiding through exercises^b

− Helpful indication of number of exercise repetitions^b

Training principles

− Visual feedback with colour code (green, orange, red) during exercising^b

− No specific feedback regarding exercise execution and single body part movements^a,b

− Performance score as feedback after exercising^b

− Training load and progression determined by supervisors (no automatic progression)^a

− Low variability in exercises^a,b

− Training load even in high levels not exhausting^1,2

Exercises

− Clear structure of exercise levels^b

− No proper introduction of exercises (just start copying the movements of the virtual instructor)^a,b

− Complex exercises with additional arm movements provide more fun than simple (boring) movements^b

− Only frontal view of exercises (side view missing)^b

− No further information about exercise (e.g. muscles involved)^b

Emotions

− General enjoyment and fun^a,b

− Frustrated and displeased by technical issues and inaccurate evaluation of movements^a,b

− Increased motivation through virtual instructor (better than train alone)^b

− Missing challenge due to easy exercises^a,b

− Happy when seeing a progress or achieving higher performance score^a,b

− Bored of low training variability^a,b