Figure 1.

Diagram illustrating that PD has a long presymptomatic period and that exercise may reduce PD risk, delay the appearance of the symptoms, and slow the disease progression. ? indicates that the illustrated possibilities are suggested by indirect evidence but direct evidence is lacking. The diagram is based on Kish et al. (1988), Hornykiewicz (2001), Braak et al. (2004), Gaig and Tolosa (2009), Hawkes et al. (2010), Savica et al. (2010), Coelho and Ferreira (2012), Burke and O'Malley (2013), Goedert et al. (2013), Kordower et al. (2013), Del Tredici and Braak (2016), Noyce et al. (2016) and Salat et al. (2016). The curves and values are approximate because published data are incomplete and variable. Original illustration of Fu-Ming Zhou.