Continuing on from previous posts, I was interested in whether muscle soreness from flywheel resistance training (FRT) had been documented in clinical populations? A quick scoping of the literature found:
1)   Stroke patients subjected to high-intensity, ECC-overload FRT, comprising less than 2 min of contractile activity twice weekly, showed 100 % adherence and nobody complained of muscle soreness or fatigue at any time - authors’ observations (Fernando-Gonzalo et al. 2016).
2)   Ruffino et al. (2021) compared FRT with traditional heavy slow resistance strength training and found similar pain and function benefits at 12 weeks among people with patellar tendinopathy. They concluded that FRT was another exercise option for managing people with patellar tendinopathy.
Even though there is greater eccentric overload associated with FRT, especially initially after the switch from the concentric contraction, the muscle soreness from FRT does not seem problematic.

References:

Fernandez-Gonzalo, R., Fernandez-Gonzalo, S., Turon, M., Prieto, C., Tesch, P. A., & García-Carreira, M. D. C. (2016). Muscle, functional and cognitive adaptations after flywheel resistance training in stroke patients: a pilot randomized controlled trial. Journal of neuroengineering and rehabilitation, 13(1), 1-11.

Ruffino, D., Malliaras, P., Marchegiani, S., & Campana, V. (2021). Inertial flywheel vs heavy slow resistance training among athletes with patellar tendinopathy: A randomised trial. Physical Therapy in Sport, 52, 30-37.

‍