Translational Control of Anabolic Resistance in Aging Muscle
Phase: NA
Conditions: Physical Inactivity
Sponsor: University of Utah

Translational Control of Anabolic Resistance in Aging Muscle 
 
NCT03839628 
 
July 24, 2018 
 
 
 

Study Protocol 
 
Objectives 
This is an interventional study enrolling older individuals aged 60-85y to observe 
changes during physical inactivity. This study is investigating the relation between short-
term physical inactivity and the impact of muscle health and function. 
 
Experimental Design and Methodology 
Subject Characteristics. Older adults were recruited from the Salt Lake City area via 
local advertisements and Center on Aging registry. To determine eligible older adult 
volunteers, an initial screening visit occurred which included a medical history, a 
physical exam, blood tests to determine liver and kidney function (to exclude 
cardiovascular, liver and respiratory disease, uncontrolled hypo/hyperthyroidism and 
hypertension, history of deep vein thrombosis) and an oral glucose tolerance test 
(OGTT) and HbA1c to exclude those with pre-diabetes. Subjects had normal glucose 
regulation as determined from HbA1c. Participants read and signed the informed 
consent (IRB_00084354) and the study was reviewed and approved by the University of 
Utah Institutional Review Board and conformed to the Declaration of Helsinki and Title 
45, US code of Federal Regulations, Part 46, “Protection of Human Subjects”.  
Lean Mass and Muscle Function Tests. Lean mass assessment via dual-energy X-ray 
absorptiometry (DXA), and knee extensor isometric strength was determined. These 
tests will occur within one week before the reduced activity experiment (below) and will 
be repeated similarly after completing the reduced activity period.  
Leucine Anabolic Resistance Experiment and Muscle Biopsies. On a separate day 
subjects were admitted to the University of Utah clinical research center (CCTS) the 
evening before the anabolic resistance experiment and were provided a standardized 
meal (65% CHO, 20% fat, 15% protein) at dinner prepared by the University of Utah 
CCTS Metabolic Kitchen (dietician). The next morning, after an overnight fast (10h) and 
placement of an intravenous antecubital catheter, subjects underwent a muscle biopsy 
procedure. After the biopsy, subjects consumed a 500mL of low-caloric flavored water 
mixed with 2.5g of crystalline L-Leucine (Leu). We and others have shown that this dose 
of leucine in older adults is effective to elicit an acute anabolic response (mTORC1, 
protein synthesis) to ingestion, yet demonstrate anabolic resistance when repeated after 
bed rest or 14d of reduced activity. Additional biopsies occurred at 1 and 3h after 
consumption of the drink, representing key time points to capture peak and late leucine 
protein anabolic responses. Biopsies occurred on the same leg and out of separate 
incisions. Blood sampling for amino acid and insulin concentrations occurred at baseline 
and every 20min following leucine ingestion. Muscle tissue was immediately washed 
with saline and dissected of visible non-muscle tissue, flash-frozen in liquid nitrogen for 
later analysis. A remaining portion of non-frozen tissue was used for histochemical 
analysis for fiber CSA determination. After the reduced activity period (below), 
participants repeated the anabolic resistance experiment as detailed above except the 
biopsies occurred on the opposite leg.  

Reduced Physical Experiment.  After completion of the first leucine anabolic resistance 
experiment, subjects adhered to 14-days of reduced physical activity. The goal was to 
have the participant drop their physical activity levels by 75% of their normal activity 
levels (e.g., 8,000 to 2,000 steps) as determined by a hip-placed pedometer that the 
participant will be able to see and record. Reduced physical activity is effective to elicit 
protein-induced anabolic resistance by 25-50% as well as reduce muscle size and 
strength and glucose tolerance. Participants were encouraged to maintain their normal 
habitual diet during the reduced activity. On Day 14, after an overnight stay and fast, a 
second leucine anabolic resistance experiment coupled with muscle biopsies was 
repeated as detailed above.  Lean mass, strength, power and OGTT measurements 
were re-assessed 24h later.