Despite these impressive results with animals, the fitness interventions
with humans, as we have indicated, have produced less reliable
effects on performance in a variety of perceptual, cognitive, and motor
tasks. Clearly, some of the ambiguity in the results obtained in the human
studies could be the result of methodological factors. For example,
studies have employed widely varying age groups. Studies have also
differed with respect to the nature, intensity, and length of the aerobic
fitness manipulations; the type of fitness measures employed; the general
health and fitness level of the participants at the beginning of the
study; subjects’ gender; the tasks used to measure aspects of cognition;
and the nature of the control groups.