Fig. 4

The PerStBiRo system’s ability to monitor and identify skill acquisition of hands-free pedaling during training session. Fig. 4a –A sample of about 20 s, note that the 86 years old trainee released his hands from the handlebars (about 94 s of the training session), which was immediately accompanied with upper body instability, i.e., shoulder and head angle instability, during pedaling [purple (α1) and green (α2) line]. Figure 4b – the end of the training session (1100–1120 s of the training session). A sample that represents better upper body stability (i.e., lower amplitudes) during pedaling [purple (α1) and green (α2) lines]