Beyond aggregate volume-Accelerometer-derived activity phenotypes reveal a decoupling of lean mass and function: A...

Area of Science:

• Gerontology and Exercise Physiology
• Biomedical Data Science
• Kinesiology

Background:

• Lean mass preservation is crucial for muscle strength in aging, but aggregate physical activity metrics fail to capture temporal movement patterns.
• The dissociation between muscle mass and function in older adults necessitates advanced analytical approaches to understand neuromuscular impacts.
• Unsupervised machine learning can identify distinct physical activity phenotypes to clarify their associations with muscle health.

Purpose of the Study:

• To investigate the associations between accelerometer-derived physical activity phenotypes and appendicular lean mass versus grip strength in US adults.
• To compare the explanatory power of phenotype-based models against traditional aggregate volume metrics for muscle mass and function.
• To determine if specific activity patterns, beyond mere volume, are linked to neuromuscular outcomes in aging populations.

Main Methods:

• Utilized National Health and Nutrition Examination Survey (NHANES) 2011-2014 data from US adults.
• Applied K-Means clustering to wrist-accelerometry features (rhythm, fragmentation) to derive activity phenotypes.
• Employed survey-weighted linear regression to assess associations with appendicular lean mass and grip strength, comparing phenotype models with volume-based models using the Akaike information criterion (AIC).

Main Results:

• Identified two phenotypes: high-volume/consolidated (HVC) and low-volume/fragmented (LVF).
• The HVC phenotype was associated with significantly higher appendicular lean mass index, equivalent to five years of age-related decline, but showed no significant advantage in grip strength compared to LVF.
• Phenotype-based models demonstrated statistical equivalence to traditional volume-based models in explaining outcomes (ΔAIC < 1.0).

Conclusions:

• Accumulating high physical activity volume through structured patterns is linked to preserved appendicular lean mass in adults.
• This preservation of lean mass does not necessarily translate to improved grip strength, indicating a dissociation between mass and function.
• Current sarcopenia guidelines focusing solely on aggregate activity volume may be insufficient; integrating targets for sedentary behavior fragmentation is recommended for comprehensive neuromuscular performance.
• Consolidated sedentary behavior may compromise neuromuscular performance despite adequate total movement, highlighting the importance of activity patterns.