Research into the Use of Exercise to Slow Aging is Not as Simple as One Might Think
One might naively think that studying the effects of exercise on human aging is fairly straightforward. This isn't the case, as illustrated by the authors of this commentary. Very little is simple when it comes to making use of existing epidemiological data, or trying to construct studies that shed light on the question of how exactly exercise interacts with aging. It seems very clear that exercise is a good thing, and that most of us should be undertaking more of it, but once down in the weeds, at the detail level, it is all too easy to find large gaps in present knowledge and contradictory or poorly designed studies.
Preserving functional health and quality-of-life in old age is a major goal and global challenge in public health. The high rate of sedentary behavior that is characteristic of the older adult population exacerbates impairments of physiological and structural systems that are typically seen in the aging process. Achieving an understanding of the profound influence of physical activity on all aspects of health in old age is the driving force behind the emergence of "physical activity in old age" as a growing area of research. Accumulated evidence implies that being physically active and exercising is far superior to other optimal aging facilitators. Yet this area of research faces numerous constraints and obstacles.
Compared to other age groups, old age is typified by increased heterogeneity, which complicates research and renders practice harder to conduct. This heterogeneity is typical of physical performance as well as cognitive and behavioral performance. With respect to physcial activity (PA) in old age, a reductionist approach is often adopted. For example, PA programs may be developed to affect specific types of performance (e.g., muscle strength, aerobic endurance, and balance), by manipulating parts of an intact physiological movement system. However, one typical manifestation of aging is a heterogenous decline in these physiological systems. In healthy organs, these systems communicate with one another to maintain homeostasis; yet aging causes the breakdown of different physiological systems, which in turn may affect other more intact physiological systems, thereby interfering with this homeostasis. As such, this individual pattern of aging could imply the need for critically rethinking PA training principles for aging populations.
Due to the large heterogeneity of evaluation methods and PA interventions, standardized guidelines are lacking for assessing the benefits of PA programs for specific groups of older adults. While the literature presents numerous reports that employed specific criteria for assessing physical fitness, the PA programs that were used for such interventions are not always clearly described. Moreover, in addition to the lack of standardized assessment tools and intervention details, research studies fall short in providing guidelines for the standardized reporting of PA protocols - in terms of the type of PA, intensity, number of repetitions, and more. With exercise and other types of PA, there is clearly no "one-size-fits-all," especially in the diverse aged population. Yet, research on older populations is typically biased towards healthy and relatively young older adults, with certain groups of older individuals frequently being excluded from research on aging - especially in studies with PA interventions.
Despite evidence on the benefits of PA in advanced age, public health initiatives often fail to examine clinically relevant effects of PA on physical and cognitive health. For example, it has been hypothesized that the highly controlled environments in which some PA research is conducted limit its replicability in real-world community settings. While the efficacy of the PA intervention may perhaps be more clearly demonstrated in laboratory settings, there is a dearth of research that indicates its effectiveness when conducted in real-world conditions as well. In addition, the effect of PA in clinical populations may vary, based on the stage of the disease, the nature of a concomitant medical treatment, and the patients' current lifestyle.