Some more research has recently been done on the application of interval-training techniques to cycling, for the benefit of PwPs [1].

For this trial they chose twelve 30-minute sessions, each session including a 5-minute warm up and a 5-minute cool down. For each of the 20 minutes in the middle of each session, participants were asked to pedal as fast as they could for 15 seconds and then pedal at a comfortable pace for 45 seconds. A stationary recumbent bicycle was used and the resistance was set to the lowest level. Significant improvements were recorded for each of the motor-related tests performed (e.g. 10-meter walk, timed-up-and-go, etc.).

The authors acknowledge that there is now a need for a separate study to compare the benefits of interval-training techniques with those of steady-cadence cycling.

[1] Mehmet Uygur , Maria Bellumori & Christopher A Knight (2017): Effects of a low-resistance, interval bicycling intervention in Parkinson’s Disease, Physiotherapy and Practice, DOI: 10.1080/09593985.2017.1359868

Effects of a low-resistance, interval bicycling intervention in Parkinson's Disease. - PubMed - NCBI

(abstract only - the rest is behind a paywall)