Just like with progressing movement difficulty in point # 1, you can increase difficulty by changing the work / rest ratio. (ashotofadrenaline.net)
And in 2009, The U.S. National Library of Medicine conclusively stated that Bifidobacterium infantis «showed significant improvement in the composite score for abdominal pain / discomfort, bloating / distention, and / or bowel movement difficulty compared with placebo.» (cheflynda.com)
Non-motor («invisible symptoms») of PD are common, and may affect everyday life more than the more obvious movement difficulties. (parkinson.org)