TABLE 1.
Muscle mass, strength, and function outcomes with protein or free amino acid interventions during experimental disuse1
| Study | Model and duration | Age, y | Nutrition intervention | Muscle mass | Strength and function | Effect |
|---|---|---|---|---|---|---|
| Holloway et al. 2019 (57) | 7 d leg immobilization | Young adults | ∼66.8 g/d of proprietary amino acid–containing formulation on top of 1.0 g · kg−1 · d−1 dietary protein | 2.4% ↓ volume and 3.1% ↓ CSA of quadriceps in control group, no change with intervention | Similar reductions in peak leg isometric torque | Yes |
| Arentson-Lantz et al. 2019 (58) | 7 d bed rest | ∼69 | Mixed macronutrient diet vs. isoenergetic, whey-augmented, higher-protein-quality diet | 1035 vs. −680 ± 138 g ↓ leg lean mass, control vs. intervention, (P = 0.08) | 20% ↓ knee extensor peak torque both groups | Yes |
| Backx et al. 2018 (61) | 7 d leg immobilization | ∼22 | 7.5 g leucine/d (2.5 g leucine/meal) | 6% ↓ quadriceps CSA both groups | 9% ↓ leg extension 1-RM both groups | No |
| Mitchell et al. 2018 (59) | 14 d leg immobilization | ∼50 | 20 g/d high-quality dairy protein with morning meal | 4.1% ↓ thigh muscle CSA both groups | 24.7% ↓ knee extension torque both groups | No |
| English et al. 2016 (6) | 14 d bed rest | ∼52 | 13.2 g leucine/d (4.4 g leucine/meal) | 1.5 kg ↓ whole-body lean mass after 7 d in control group and no change with intervention; similar decrease after 14 d | 15% vs. 7% ↓ knee extensor peak torque, 14% vs. 2% ↓ knee extensor endurance, 9% vs. 1% ↓ muscle quality, control vs. intervention, (P < 0.05) | Yes |
| Dirks et al. 2014 (60) | 5 d leg immobilization | ∼69 | 20 g/d leucine-enriched whey protein supplement directly after breakfast and before sleep | Similar reductions in quadriceps CSA | Similar reductions in leg extension 1-RM | No |
| Deutz et al. 2013 (56) | 10 d bed rest | ∼67 | 1.5 g Ca-HMB, 4 g maltodextrin, 200 mg calcium, and sweetener twice daily | 2.05 kg ↓ whole-body lean mass in control group, no change with intervention | No change in isokinetic knee extensor strength in either group | Yes |
| Ferrando et al. 2010 (5) | 10 d bed rest | ∼69 | 15 g EAAs 3 times/d | Similar reductions in total and leg lean mass | 51% vs. 13% ↑floor transfer time, control vs. intervention, (P < 0.05) | Yes |
| Trappe et al. 2007 (62) | 60 d bed rest | ∼32 | 1.0 vs. 1.6 g protein · kg−1 · d−1 (3.6 g leucine, 1.8 g valine, 1.8 g isoleucine supplement per day) | 21% vs. 24% ↓ quadriceps muscle volume, control vs. intervention, (P < 0.05) | Similar reductions in supine squat strength | No |
| Paddon-Jones et al. 2004 (55) | 28 d bed rest | ∼37 | 16.5 g EAAs plus 30 g sucrose 3 times/d | 0.4 kg ↓ leg lean mass in control group, no change with intervention | 17.8 vs. 8.8 kg ↓ single-leg, leg extension 1-RM, control vs. intervention, (P < 0.05) | Yes |
1
CSA, cross-sectional area; EAA, essential amino acid; HMB, β-hydroxy-β-methylbutyrate; 1-RM, 1-repetition maximum. ↑ indicates increase and ↓ indicates decrease.