Researchers publishing in Aging Cell have shown a relationship between mitochondrial dysfunction and mobility decline in older adults.
A changing longitudinal study
Since 1958, a team of researchers from the National Institute on Aging Intramural Research program has been conducting the Baltimore Longitudinal Study of Aging (BLSA). The BLSA, which has been used for other research, continuously enrolls volunteers free of chronic conditions from a variety of age groups.
The organization conducts visits every one to four years, depending on age. Participants younger than 60 were seen every four years, participants between 60 and 79 were seen every two years, and participants who were at least 80 were seen every year.
Major revisions were made in 2003 to the BLSA study to add phenotypic measurements and molecular biomarkers. Due to the longitudinal nature of the study, changes in technology have occurred during its duration, and Dr. Luigi Ferruci and colleagues explain that extensive efforts have been made over time to control for these changes in analysis.
Linking oxidative capacity to mobility
A new analysis has been published from the BLSA study  using data collected between 2013 and 2019. The researchers examined 380 participants who were at least 60 years old and cognitively normal, had good posture and walking speed, and were free from strokes and Parkinson’s disease. The participants also had to be mobile enough, according to specific measurements, to qualify.
To determine muscular oxidative capacity (the ability to use oxygen) after exercise, the researchers measured the recovery rate of phosphocreatine (kPCr). A higher oxidative capacity represents more favorable muscle health, and a primary function of phosphocreatine is to maintain adenosine triphosphate (ATP) levels after muscle use.
Gait speed, a predictor of functional decline and mobility, was measured in four different scenarios at two different times. This study used multiple speed scenarios based on a prior study that measured fitness in older adults , including usual and rapid speeds during a 2.5-minute walk and a 6-minute walk. Another scenario included a 400-meter walk.
Muscular oxidative capacity is correlated with age
Lower levels of kPCr was associated with a higher body mass index (BMI) and lower muscle strength. Women had lower kPCr scores than men, and black participants had lower kPCr than white participants.
When the investigators ran analysis at one specific time point (cross-sectionally), a lower kPCr was significantly associated with a slower 6-minute walk at usual gait speed, a slower 2.5-minute walk at usual gait speed, and a slower 400-meter walk. There was no association observed between kPCr and the 6-minute rapid gait speed.
When the investigators ran a longitudinal analysis, a lower kPCr at the start of the study was significantly associated with a larger decline in all the walking scenarios. These analyses were adjusted for baseline sex, age, phosphocreatine depletion during exercise, and BMI over time.
The investigators ran additional analyses after adjusting for the covariates of longitudinal thigh muscle strength, baseline thigh muscle strength, total lean mass, and total fat mass. This data can be seen in their supplementary data tables, and many of these results further support their conclusions.
Collectively, these results suggest that worse mitochondrial function, as shown by a lower kPCr, contributes to mobility decline. Additional studies are needed to verify these results.
Future research is needed to examine the loss of muscle fibers. Such loss, specifically of type II muscle fibers, can lead to sarcopenia . It is known that excess sedentary time decreases mitochondrial density and surface area of muscle fibers. Taking the results of this study into account along with exercise physiology research, there is data to support the idea that aerobic and resistance exercise increase muscular oxidative capacity and thus ameliorate age-related muscle decline.
 Tian, Q., Mitchell, B. A., Zampino, M., Fishbein, K. W., Spencer, R. G., & Ferrucci, L. (2022). Muscle mitochondrial energetics predicts mobility decline in well-functioning older adults: The baltimore longitudinal study of aging. Aging cell, e13552. Advance online publication. https://doi.org/10.1111/acel.13552
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