Aim 1: The "startle paradigm" will be used to investigate the physiological component of fear of PA. The startle paradigm is based on empirical observations that the startle reflex is larger after the priming with unpleasant stimuli and inhibited after the priming with pleasant stimuli. The participants will be primed with various words including those words associated with physical activity that are expected to be unpleasant in patients with high fear of PA. The startle reflex will be triggered by air puffs on the eyes (startle probes) and measured via facial electromyography (EMG). We assume that startle responses primed with PA related words are stronger in patients with high fear of PA compared to the control groups.