Attention-Deficit/ Hyperactivity Disorder (ADHD) is a neurobehavioral condition characterized by inattentive, hyperactive and impulsive behavior. Over the last years it has been suggested that children with ADHD could benefit from physical exercise close in time before situations that requires concentration and attention, e.g. in school settings. The empirical support for this claim is lacking. The theoretical focus in this paper is on the arousal theories of ADHD, the Dynamic Developmental Theory (DDT) and the Dual-Process theory. The arousal theories explain the behavior seen in children with ADHD as due to an underactivation or underarousal. These theories predict an effect of physical exercise. On the other hand, the DDT and the Dual-Process theory do not predict an effect of physical exercise. The aim of this study was to investigate whether physical exercise has positive effects on behavioral symptoms seen in children with ADHD. This was tested using Spontaneously Hypertensive Rats (SHR), a common and validated animal model in ADHD. The test group had free access to a running wheel in the home cage before tested on an operant conditioning task, the control group did not have this access. The results of the study did not reveal any significant effect of physical exercise. If these data can be generalized to children with ADHD, the practical implications are that behavioral symptoms are not reduced by physical exercise in children with ADHD. The data do not yield support to theories suggesting changed arousal as a causative factor in ADHD. Instead, the data support the effect of reinforcement in the control of behavior.