Table 1.
Characteristics of included trials reporting bed-rest-induced changes in muscle mass and size and muscle function
| Study (Ref.) | Average Characteristics of Included Participants (n, Sex, Age, Height, Mass) | Bed Rest Modality, Bed Rest Duration, Days Between Baseline and Post Measurement | Assessment Method (Parameter and Units) | Relative Change at the End of Bed Rest |
|
|---|---|---|---|---|---|
| Atrophy of the knee extensor muscles | Knee extension strength | ||||
| Mulder et al. (33) | Healthy adults, n = 10 (0 women), age 30 ± 6 yr, height 179 ± 5 cm, mass 78 ± 5 kg | 6° Head-down tilt bed rest, 5 days, 5 days | 1.5T MRI (m. quadriceps femoris CSA in mm2); MVIC at a 90° knee angle | –2.2 % | –8.6 % |
| Rittweger et al. (34) | Healthy adults, n = 12 (0 women), age 34 ± 7 yr, height 179 ± 7 cm, mass 76 ± 6 kg | 6° Head-down tilt bed rest, 5 days, 5 days | MVIC at a 90° knee angle | NA | –4.1 % |
| Dirks et al. (12) | Healthy adults, n = 10 (0 women), age 23 ± 1 yr, height 181 ± 2 cm, mass 75 ± 2 kg | Horizontal bed rest, 7 days, 7 days | Computed tomography (knee extensors: m. quadriceps femoris CSA in mm2) | –3.0 % | NA |
| Dirks et al. (35) | Healthy adults, n = 10 (0 women), age 27 ± 1 yr, height 181 ± 3 cm, mass 78 ± 5 kg | Horizontal bed rest, 7 days, 7 days | Computed tomography (knee extensors: m. quadriceps femoris CSA in mm2) | –1.1% | NA |
| Ferrando et al. (36) | Healthy young adults, n = 5 (0 women), age 23 ± 3 yr | Horizontal bed rest, 7 days, 7 days | 0.6T MRI (thigh volume in cm3 | –3.0 % | NA |
| McDonnell et al. (37) | Healthy adults, n = 11 (0 women), age 24 ± 2 yr, height 180 ± 7 cm, mass 73 ± 12 kg | Horizontal bed rest, 10 days, 10 days | Computed tomography (knee extensors: m. quadriceps femoris CSA in mm2); MVIC at 60 °knee flexion | –3.6 % | –14.5 % |
| Bamman et al. (38) | Healthy adults, n = 8 (0 women), age 30 ± 2 yr, mass 178 ± 2 cm, mass 72 ± 4 kg | 6° Head-down tilt bed rest, 14 days, 14 days | MVIC at a 60° rad of knee flexion | NA | –14.5 % |
| Pisot et al. (10)a | Healthy young adults, n = 7 (0 women), age 23 ± 3 yr, height 177 ± 7 cm, mass 75 ± 9 kg | Horizontal bed rest, 14 days, 14 days | 1.5T MRI (m. quadriceps femoris volume in cm3); MVIC at a 110° knee angle with hip fixed at 90° | –6.1 % | –9.8 % |
| Akima et al. (22) | Healthy adults n = 4 (0 women), age 20 ± 2 yr, height 171 ± 5 cm, mass 67 ± 11 kg | 6° Head-down tilt bed rest, 20 days, 21 days | 1.0T MRI (knee extensors: m. quadriceps femorisb; volume in cm3 and CSA in cm2); MVIC at a 90° rad of knee flexion | –7.5 % | –16.8 % |
| Akima et al. (39) | Healthy adults, n = 6 (0 women), age 23 ± 3 yr, height 170 ± 8 cm, mass 67 ± 14 kg | 6° Head-down tilt bed rest, 20 days, 20-23 days | 0.2T MRI (knee extensors: m. quadriceps femoris; volume in cm3) | –10.3 % | NA |
| Kawakami et al. (19) | Healthy adults, n = 5 (0 women) | 6° Head-down tilt bed rest, 20 days, 20 days | MRI (m. quadriceps femoris; CSA in cm2) | –10.2 % | NA |
| Kawakami et al. (19) | Healthy adults, n = 4 (0 women), age 18-28 yr, height 172 ± 5 cm, mass 68 ± 11 kgc | 6° Head-down tilt bed rest, 20 days, 20 days | 1.0T MRI (m. quadriceps femoris CSA in cm2); MVIC with hip angle at 80° and knee angle at 90° | –7.8 % | –10.2 % |
| Kubo et al. (6) | Healthy adults, n = 6 (0 women), age 24 ± 5 yr, height 172 ± 5 cm, mass 68 ± 11 kg | 6° Head-down tilt bed rest, 20 days, 21 days | 0.5T MRI (m. quadriceps femoris CSA); MVIC with hip and knee angles both 80° | –7.5 % | –19.2 % |
| Kubo et al. (7) | Healthy adults, n = 8 (0 women), age 24 ± 4 yr, height 172 ± 9 cm, mass 69 ± 13 kg | 6° Head-down tilt bed rest, 20 days, 20 days | MRI (m. quadriceps femoris volumed); MVIC with hip and knee angles both 80° | –10.4 % | –20.4 % |
| Shinohara et al. (40) | Healthy adults, n = 6 (0 women), age 23 ± 3 yr, height 170 ± 8 cm, mass 67 ± 14 kg | 6° Head-down tilt bed rest, 20 days, 20 days | MVIC at a 90° knee angle and 80° hip angle | NA | –17.6 % |
| Suzuki et al. (41) | Healthy adults, n = 11 (5 women), mean age 21 yr, height NA, mass NA | Horizontal bed rest, 20 days, 20 days | Max isokinetic torque at 90° knee and hip angles | NAe | –15.8 % |
| Liphardt et al. (42) | Healthy adults, n = 11 (0 women), age 35 ± 8 yr, height 176 ± 6 cm, mass 70 ± 8 kg | 6° Head-down tilt bed rest, 21 days, 21 days | 1.5T MRI (knee extensors: m. quadriceps femoris CSA in cm2) | –9.9 % | NA |
| Germain et al. (43) | Healthy adults, n = 6 (0 women), age 34 ± 2 yr, height 178 ± 1 cm, mass 79 ± 3 kg | 6° Head-down tilt bed rest, 28 days, 28 days | MVIC at 0° × s−1, the lower leg was fixed at an angle of 105° compared with full extension (0°) | NA | –12.0 % |
| Alkner and Tesch (44)f | Healthy adults, n = 9 (0 women), age 32 ± 4 yr, height 173 ± 3 cm, mass 72 ± 5 kg | 6° Head-down tilt bed rest, 29 days, 29 days | 1.0T MRI (knee extensors: m. quadriceps femoris; volume in cm3) | –9.8 % | NA |
| Berry et al. (45) | Healthy adults (professional divers), n = 6 (0 women), age 31.5 yr (range: 27–36 yr) | 6° Head-down tilt bed rest, 30 days, 31–32 days | 0.5T MRI (m. quadriceps femoris CSA in cm2) | –11.0 % | NA |
| Dudley et al. (46) | Healthy adults, n = 7g | 6° Head-down tilt bed rest, 30 days, R + 1 = 31days | MVIC with hip angle at 100° | NA | –24.0 % |
| Greenleaf et al. (47) | Healthy adults, n = 5 (0 women), age 36 ± 1 yr, height 178 ± 2 cm, mass 75 ± 5 kg | 6° Head-down tilt bed rest, 30 days, 30 days | MVIC during knee extension at 100°/s | NA | –16 % |
| Schneider et al. (48)h | Healthy twins, n = 15 (7 women), age 34 ± 7 yr, height 179 ± 7 cm, mass 76 ± 6 kg | 6° Head-down tilt bed rest 30 days, 28 days | MVIC at a 60° knee angle | NA | –13.0 % |
| Berg et al. (18) | Healthy adults, n = 10 (0 women), age 25 ± 5 yr, height 180 ± 9 cm, mass 71 ± 8 kg | Horizontal bed rest, 35 days, 35 days CSA; 36 days MVIC | Computed tomography (knee extensors: m. quadriceps femoris CSA in cm2); MVIC with hip and knee angles at 90°; 15° reclined back support from vertical | –9.5 | –16.9 % |
| Gogia et al. (49) | Healthy adults, n = 9 (0 women), age 29 ± 10 yri | Horizontal bed rest, 35 days, 35 days | MVIC at 60 °s/s from 0° to 180° extension | NA | –19 % |
| Krainski et al. (20) | Healthy adults n = 9 (1 women), age 33 ± 13 yr, height 174 ± 11 cm, mass 71 ± 10 kg | 6° Head-down tilt bed rest, 35 days, 35 days | 1.5 T MRI (m. quadriceps femoris volume in ml); max isokinetic torque at 60°/s | –8.9 % | –13.7 % |
| Berg et al. (23) | Healthy adults, n = 7 (0 women), age 28 ± 2 yr, height 176 ± 3 cm, mass 74 ± 9 kg | 6° Head-down tilt bed rest, 42 days, 37 days CSA; 44 days MVIC | 1.5T MRI (m. quadriceps femoris CSA in cm2); MVIC at 95° knee and 180° hip angle | –14.2 % | –25.8 % |
| Ferretti et al. (50) | Healthy adults, n = 7 (0 women), age 28 ± 1 yr, height 176 ± 1 cm, mass 74 ± 3 kg | 6° Head-down tilt bed rest, 42 days, 37 days | 1.5T MRI (thigh CSA in cm2) | –13.4 | NA |
| Ferretti et al. (51) | Healthy adults, n = 7 (0 women), age 28 ± 1 yr, height 176 ± 1 cm, mass 75 ± 9 kg | 6° Head-down tilt bed rest, 42 days, 47 days | 1.5T MRI (thigh CSA in cm2) | –17.0 % | NA |
| Belavy et al. (52) | Healthy adults, n = 10 (0 women),j age 33 ± 7 yr, height 185 ± 7 cm, mass 79 ± 10 kg | Horizontal bed rest, 56 days, 56 days | 1.5T MRI (knee extensors: m. quadriceps femoris volume in cm3) | –14.4 %k | NA |
| Mulder et al. (5)l | Healthy adults, n = 10 (0 women), age 33 ± 7 yr, height 185 ± 8 cm, mass 80 ± 11 kg | Horizontal bed rest, 56 days, 56 days | 1.5T MRI (m. quadriceps femoris CSA in cm2); MVIC with hip angle at 115° and knee angle at 90° | –14.2 % | –14.8 % |
| Arbeille et al. (53)m | Healthy adults, n= 8 (8 women), age 34 ± 1 yr, height 163 ± 2 cm, mass 56 ± 1 kg | 6° Head-down tilt bed rest, 60 days, 57 days | 1.5T MRI (knee extensors: m. quadriceps femoris volume in cm3) | –21.2 % | NA |
| Lee et al. (54) | Healthy adults, n = 8 (8 women), age 34 ± 1 yr, height 163 ± 2 cm, mass 56 ± 1 kg | 6° Head-down tilt bed rest, 60 days, 66 days | Max isokinetic torque between 20 and 95°; 60°/s | NA | –31.8 % |
| Miokovic et al. (55) | Healthy adults, n = 9 (0 women), age 31 ± 8 yr, height 181 ± 6 cm, mass 81 ± 5 kg | 6° Head-down tilt bed rest, 60 days, 55/56 daysn | 1.5T MRI (m. rectus femoris volume in cm3) | –14.6 % | NA |
| Mulder et al. (8) | Healthy adults, n = 9 (0 women), age 31 ± 8 yr, height 181 ± 6 cm, mass 81 ± 5 kg | 6° Head-down tilt bed rest, 60 days, 55/56 days MRI, 56 days MVIC | 1.5T MRI (m. quadriceps femoris CSA in cm2); MVIC with hip angle at 130° and knee angle at 60° | –13.7 % | –21.5 % |
| Trappe et al. (30) | Healthy adults, n = 8 (8 women), age 34 ± 1 yr, height 163 ± 2 cm, mass 56 ± 1 kg | 6° Head-down tilt bed rest, 60 days, 57 dayso | 1.5T MRI (knee extensors: m. quadriceps femoris volume in cm3) | –21.2% | NAp |
| Ploutz-Snyder et al. (56) | Healthy adults, n = 8 (1 woman), age 37 ± 8 yr, height NA, mass 79 ± 10 kg | 6° Head-down tilt bed rest, 70 days, 70 days | 1.5T MRI (m. quadriceps femoris CSA in cm2); max isokinetic torque at 60°/s | –9.6 % | –22.8 % |
| Alkner et al. (57)q | Healthy adults, n = 9 (0 women), age 32 ± 4 yr, height 173 ± 3 cm, mass 72 ± 5 kg | 6° Head-down tilt bed rest, 90 days, 89 days MRI; R + 1 = 91 days MVIC | 1.0T MRI (knee extensors: m. quadriceps femoris volume in cm3); MVIC at a 90° rad of knee flexionr | –18.0 % | –45 % |
| LeBlanc et al. (58) | Healthy adults, n = 8 (0 women), age 32 ± 12 yr, height 173 ± 7 cm, mass 74 ± 7 kg | Horizontal bed rest, 119 days, 126 days | 0.36-1.0T MRI (m. quadriceps femoris); max isokinetic torque at 60°/s and 180°/s | –15.0 % | –30.7 % |
| Shackelford et al. (59)s | Healthy adults, n = 8 (3 women), age 32 ± 9 yr, height 171 ± 9 cm, mass 74 ± 9 kg | Horizontal bed rest, 119 days, 119 days | 1.5T MRI (m. quadriceps femoris; volume); max isokinetic torque at 60°/s; range 10-95° | –15.8 % | –35.0 % |
aThis study shows a trend toward greater muscle atrophy and strength decline in old (–8.4%; –12.8%) vs. young adults (–6.1%; –9.8%). n, no. of subjects; MRI, magnetic resonance imaging; CSA, cross-sectional area; MVIC, maximal voluntary isometric contraction, T, tesla. bRF, rectus femoris; VL, vastus lateralis; VI, vastus intermedius; VM, vastus medialis. cAge and body characteristics are reported for total sample (n = 9). dRelative change reported only. eCross-sectional area decline of –10.4% reported by dual energy X-ray absorption (DEXA); reported in footnotes due to the fact that knee extensors cannot be extracted by DEXA alone and therefore changes were not included in the calculations in RESULTS. fThis paper reports on data from the initial 29 days of the 90-day bed rest campaign published in Alkner and Tesch (44) and Alkner et al. (57). gOther data not reported. hThis study shows a trend toward greater muscle strength decline in women (–16%) vs. men (–10%) after 28 days of bed rest. iAge reported for a total sample (n = 15). jMissing data on BR1 and BR28 due to magnetic resonance imaging (MRI) scanner failure and movement artifacts during data acquisition. kAuthors measured with MRI also on days 14, 28, and 42 with volumetric decline of –6.4, –9.1, and –12.0%, respectively. lStudy addressed muscle size and strength during a 56-day bed rest on 8 time points (6 during the bed rest) that might affect the outcome measures and was therefore removed from the calculations. mThis paper reports data that were published also in Trappe et al. (30). nAuthors measured with MRI also on day 27/28 with volumetric decline of –8.4%. oAuthors measured with MRI also on day 29 with volumetric decline of –16.8%. pMuscle strength was measured on a specifically designed flywheel inertial ergometer adapted for the 6° head-down tilt experiments (21). Pre-Post (R + 2) isometric force declined for –33.7%. For the regression analysis, muscle strength values were taken from Lee et al. (54), which belong to the same bed rest campaign. qReported also in Alkner and Tesch (21). rAuthors reported maximal voluntary isometric contraction (MVIC) also at a 120° rad of knee flexion where knee extension strength decline was –60.1%. sThis study shows a trend toward greater muscle strength decline in women (–21%) vs. men (–13%) after 119 days of bed rest.