For those suffering from mild-to-moderate symptoms of depression or anxiety, exercise is also associated with a reduction of symptoms. Martinsen and colleagues found that a 9-week aerobic training program alongside psychotherapy produced significantly larger reductions in major depressive symptoms compared to psychotherapy alone (Martinsen et al., 1985). With patients who experienced a larger increase in maximum oxygen uptake also experienced a larger reduction of symptoms. In a follow-up study, Martinsen and colleagues found that this could be replicated equally across different exercise modalities, with no difference between those that did aerobic or anaerobic training (Martinsen, Hoffart, and Solberg, 1989). One popular explanation for this is observations of higher levels of plasma β-endorphins after exercise, β-endorphins being a chemical released by the brain that elevates mood and enhances feelings of well-being (Craft and Perna, 2004).