Age-Related Changes in Cognitive and Physical Performance

Abstract

Dr. Boley’s considerations on peak of cognitive and physical performance across the lifespan (1) remain of high relevance for gerontologists today, 75 years after its initial publication on the Journal of Gerontological Medical Science. Upon reviewing the literature of that time, Dr. Boley suggests three facts. First, human performance appears to peak at around age 30 for several higher-level cognitive tasks, including philosophy, science, music; second, human performance peaks at a similar age for physical function tasks requiring central nervous system input, such as golf, bowling or other sports requiring precision, strategizing, and high-level coordination. He also finds a variation in the levels of performance after the peak is reached; specifically, levels tend to remain higher for cognitive tasks and decline rapidly for physical tasks. He illustrates this point with a very simple yet compelling graph plotting performance in these two domains, against chronological age ranging from about 10–90 years (Figure 1, edited). In its elegant simplicity, Dr. Boley’s graph invites a reflection on our current understanding of age-related changes in physical and cognitive function and the implications for interventions. The solid line represents performance in cognitive tasks; the broken line represents performance of physical function tasks requiring neuromuscular coordination. The two lines indicate distinct yet similar age-related patterns of performance of cognitive and complex motor tasks. Both are remarkably similar to that of cerebral white matter volume (2): an increase in early years, with a peak around age 30–40, and a decline thereafter. Such temporal co-occurrence of white matter remodeling and performance, yet unexplored at the time of Dr. Boley’s publication, suggests a causal link between the two; it also suggests there may be shared central nervous system (CNS) resources that govern both cognitive and physical performance. Indeed, Dr. Boley points out some physical tasks require more cognitive inputs than others, and this fact is used to explain the similarity in temporal trends of performance across the two domains. However, I was surprised to see no overt reference to a direct correlation between the two domains. In other words, a relation between cognitive and physical function appears implicitly understood, but it is not explicitly tested. The relation between CNS resources, cognitive, and physical performance has been explicitly tested in some fields of study, most remarkably Sport Medicine Physiology, generating novel strategies to promote physical performance (3). Substantial evidence exists that the CNS influences physical performance, either directly via sensori-motor networks’ involvement, or indirectly, by dampening the perception of fatigue (3). For example, sharpened attention and heightened motivation can serve to ignore common discomforting signs during exercise, such as rising temperatures, increasing heart-beat, or pain. The earliest scientific report of such intimate link between cognitive and physical functioning is probably from 120 years ago by Mosso (4), indeed an exercise physiologist. What is the approach of Gerontological research to this topic today? Is it closer to a dualistic brain-body approach or to an integrated understanding of human performance? Certainly, there has been a surge in excellent work on age-related changes in CNS and mobility in the past decade or so; this journal has dedicated much attention to this topic (5–9). Similar to the field of Sport Medicine, there are promising indications of translation of such evidence into novel therapeutic approaches. For example, interventions targeting cognitive function appear to also improve physical function and viceversa (10). However, evidence is primarily for small trials or for selected groups of older adults. Intervention trials for the most part remain organized into silos with one primary outcome examined in isolation from others. There remains the need to systematically include both cognitive and motor domains in such trials; not only as outcomes, but also, and perhaps more importantly, as factors that could influence response to the intervention. For example, the effects of physical function interventions (eg, strength training or physical activity programs) may be higher in those with higher cognitive function, because these individuals may be more likely to understand the exercises and carry them out on their own. Similarly, successful cognitive interventions may require adequate physical abilities to ensure higher participation (eg, attendance to session). A second feature of this graph that is of interest is the distance in years between the age of peak performance and the typical average age of our gerontological studies’ populations. Is it useful to hold our focus on peak performance, given that our studies begin 40 or 50 years later? Should our focus instead shift toward the plateaus following the peaks? Intervention strategies in older age aim to maintain performance as high as possible for as long as possible, to delay rapid decline; in other words interventions already focus on the plateau following the peaks. Yet, such efforts also show modest results. There has been a renewed advocacy toward life-course approaches to study age-related changes in performance, requiring observations to begin much earlier in life (11), potentially examining even the times preceding the occurrence of the peaks of performance. Such studies must account for the factors influencing performance, including but not only sex, gender, ethnicity, education, psychosocial factors, medical conditions, genetics and epigenetics. Of note, Dr. Boley’s report, focusing on men, reflects the thinking of a time when most data were available in selected sex (male), and ethnicity (white) groups, without a clear reference to other contributors of performance. Much ground has been covered in gerontological research on the risk and protective factors of performance. In conclusion, Dr. Boley’s report from 1946 is a reminder of the importance of conducting a careful observation of the multifaceted nature of human performance, beginning as early as possible in life, using an integrated approach linking cognitive and physical function domains, and accounting for complex contributing factors.

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