Two weeks of reduced activity decreases leg lean mass and induces "anabolic resistance" of myofibrillar protein synthesis in healthy elderly.
Level 4 - case-series / case-control
Single-arm prospective pre-post intervention study without a separate control group
PubMed 23589526 · doi:10.1210/jc.2013-1502
What was done
Ten healthy older adults (age 72 ± 1 y) underwent 14 days of reduced daily step count. Before and after the intervention, body composition, physical function, muscle strength, and insulin sensitivity were measured. Fasted, postabsorptive, and postprandial myofibrillar protein synthesis (MPS) rates were quantified using primed constant infusions of L-[ring-(13)C6]phenylalanine with serial muscle biopsies.
What was found
Daily step count decreased by ~76% to 1413 ± 110 steps/day. This intervention resulted in: - Leg fat-free mass reduction of ~3.9% (P < .001). - Postabsorptive insulin resistance increase of ~12% and postprandial insulin sensitivity reduction of ~43% (P < .005). - Increases in TNF-α (~12%) and C-reactive protein (~25%) (P < .05). - Postprandial MPS reduction of ~26% (P = .028), with no change in postabsorptive MPS rates.
Why it matters
It demonstrates that brief periods of reduced daily ambulation induce anabolic resistance and rapid muscle loss in healthy elderly adults, alongside metabolic and inflammatory declines.
Limits
The study is limited by a very small sample size (n = 10) and an uncontrolled, single-arm design. Long-term recovery or reversibility after resuming baseline activity was not reported in the abstract.
Cited by
- supports Abrupt step reduction induces anabolic resistance in older individuals.