High Intensity Interval Training was conducted at a European gym called Speedflex, and one of the researchers was a former employee of the company. However, they do seem to have tried to be transparent and the company did not have any input or control over the design.

High-intensity interval training in people with Parkinson’s disease: A randomised, controlled feasibility trial

“No significant improvements in cardiac output, cognitive function or quality of life were seen”

• High-intensity interval training appears to be feasible and acceptable in people with early to mid-stage Parkinson’s disease
• Patient were able to consistently exercise at greater than 85% of their maximal heart rate across the 12 week intervention
• Significant improvements in cardiorespiratory fitness were seen across the intervention period