TABLE 3.

Summary of future directions for protein-based countermeasures against muscle disuse atrophy¹

• Identify intracellular mechanisms mediating disuse-induced impairments in postabsorptive MPS (i.e., mTOR-independent signaling)

• Perform more frequent muscle biopsies after feeding under disuse conditions to elucidate changes in intracellular signaling underlying anabolic resistance

• Examine intracellular signaling underlying disuse atrophy with concomitant changes in inflammation and hormonal profiles similar to postinjury conditions; assess MPB using stable isotope methodology during short-term disuse (<14 d)

• Execute basic mechanistic studies to determine optimal protein-based countermeasures for overcoming anabolic resistance

• Investigate efficacy of different protein or free amino acid interventions in multiple groups (i.e., young vs. old, short vs. long duration, immobilization vs. bed rest)

• Evaluate potentially protective combination of light-load resistance exercise (i.e., ∼16% 1-RM) and protein or free amino acid supplementation during disuse conditions

• Determine whether NMES at frequencies, durations, or intensities specific to rehabilitation protocols used in clinical practice modulates postabsorptive or postprandial MPS during disuse

• Undertake translational research implementing findings from mechanistic studies to postinjury disuse conditions (i.e., after orthopedic surgery)

¹MPB, muscle protein breakdown; MPS, muscle protein synthesis; mTOR, mammalian target of rapamycin; NMES, neuromuscular electrical stimulation; 1-RM, 1-repetition maximum.