Furthermore, multicomponent interventions with aer- obic exercise as a component showed differing effects.One study reported improved cognition as measured by the French Rapid Evaluation of Cognitive Function scale (n = 38) [21], but other studies demonstrated no changes on the Boston Naming Test (n = 27) or the Hopkins Verbal Learning Test (n = 11) .
Together, the above findings indicate that aerobic exer- cise could either maintain or improve cognition in persons with AD, which are very positive findings given that progressively worsening cognition marks the course of AD. Nonetheless, aerobic exercise studies in AD are few and have been limited by such factors as small sample sizes, variable comparator groups, inconsistent cognitive measures, variable domains of cognition as a main out- come, and application of multicomponent interventions that masked the true effect of aerobic exercise. The comparability of those findings is further limited due to the varied doses of aerobic exercise. The doses rarely met the weekly 150-minute moderate-intensity level of exertion that has been recommended for older adults or the 6-month duration considered sufficient for producing cognitive gains in non-AD samples. The prescribed exercise frequency ranged from 1 to 5 times a week, session duration from 20 to 40 minutes, intensity from very low to moderate, and program duration from
5 weeks to 4 years across the studies. In addition, there was substantial discrepancy between prescribed and delivered exercise doses. Methods for ensuring exercise delivery are often unreported, while the retention and adherence rates ranged from 59 to
92% and 10 to 90%, respectively. It is likely that a dose–response relationship between exer- cise and cognition exists, but remains unknown due to unclear exercise adherence and treatment fidelity