Motor and Cognitive Exercise in Parkinson's Disease.

Intervention: The exercise program will consist of gait and balance training, lower body strength training and dual task training while treadmill walking. The program will include an individualized and progressive exercise program 3 times x 1 hour a week for 12 weeks with the following exercise modalities: 1. Treadmill training for gait and balance training combined with dual task motor cognitive training. 2. Progressive gait and motor-cognitive balance exercises 3. Progressive resistance training including leg press. The program will be conducted under supervision by a physiotherapist or an exercise physiologist. Usual treatment is permitted during the trial, both pharmacological and non-pharmacological. The treatment is preferably stable during the intervention and follow-up, but necessary changes will be registered. All participants will be examined at baseline, after 12 weeks and again 6 and 12 months after baseline.