Reliability of Peak Treadmill Exercise Tests in Mild Alzheimer Disease

Abstract

The prevalence of Alzheimer disease (AD) doubles every 5 years after the age of 65, reaching nearly 50% after age 85 (Evans et al., 1989). This, along with an unprecedented growth in the elderly population, is leading to dramatic increases in the incidence of AD. Thus, effective strategies for promoting healthy brain aging and preventing AD are increasingly important. One strategy that appears promising in promoting healthy brain aging is exercise and physical activity. Evidence is accumulating that endurance exercise is beneficial to brain health (Laurin, Verreault, Lindsay, MacPherson, & Rockwood, 2001), and increased cardiorespiratory fitness is associated with increased brain volume in subjects with very mild to mild AD (Burns et al., 2008).

While enhancing cardiorespiratory fitness may be a strategy for preventing cognitive decline in AD, there is limited information available on the validity and reliability of cardiorespiratory fitness measures in this population. The gold standard measure of cardiorespiratory fitness is maximum oxygen consumption (VO2max) (Frankin, 2001), the highest rate of oxygen uptake attainable during maximal or exhaustive exercise (American College of Sports Medicine, 2005). If the subject becomes exhausted and ends the test prior to reaching the physiologic VO2max, the end of the test is called peak oxygen consumption (VO2peak). It is unknown if advanced age and cognitive difficulties in people with AD would limit their ability to fully participate in a standard graded exercise test to reliably assess VO2max or VO2peak.

Treadmill exercise testing has been found to be reliable in subjects with traumatic brain injury and mental retardation, although these subjects were very young (Fernhall, Millar, Tymeson, & Burkett, 1990; Mossberg & Greene, 2005). Traumatic brain injury and mental retardation are different disease processes than AD and would be expected to result in static rather than progressive cognitive symptoms. With AD, memory is impaired as is the ability to follow commands, however patients in the earliest stages of AD would be expected to respond to prompting and reminders to follow testing procedures. To our knowledge, no studies have assessed the reliability of peak treadmill exercise testing in subjects with AD. In our previous research on patients with very mild to mild AD (Burns, et al., 2008), we have found them to be capable of ambulating on a treadmill and completing peak treadmill exercise testing with 3 participants out of 74 (126 total peak exercise tests) identified as having EKG changes during testing. All 3 participants had negative follow-up testing in cardiology. The purpose of this study was to investigate the reliability of a graded peak treadmill exercise test in elderly people with early AD.