Table 3.
Skeletal muscle responses to microgravity in humans - Study Characteristics
| Author, Year | Mission, Duration | Subjects | Test & Method | Exercise Regimen | Anatomic Site | Main Outcomes |
|---|---|---|---|---|---|---|
| Edgerton et al. 1995) | STS 32: 5 days STS 33: 5 days STS 34: 11 days |
N=8 5 M, 3 F |
Muscle biopsy | Aerobic running: n=3 No exercise: n=5 |
Midportion of VL muscle | Short duration flights affect muscle fiber thickness, metabolism, & blood supply |
| (Antonutto et al. 1995) | Euromir: 94, 31 days | N=1 M |
MEP was measured by a MED | Unstated | Lower limbs | Lower limbs’ functional capacity is negatively affected by SF |
| (Antonutto 1998) | MIR 97, 21 days | N=1 M |
EMG activities, & MEP were measured | Unstated | Lower limbs (RF, VL, VM) | Short duration flights affect lower limbs’ functional capacity |
| (Antonutto et al. 1999) | Euromir 94 & 95, 31 to 180 days | N=5 | Wpeak and Wmean of both MEP and MCP were measured using MED. | Unstated | Lower limbs | SF leads to reductions in muscle mass & decreases in lower limbs’ functional capacity |
| (Akima et al. 2000) | Unstated, 9, 15, 16 days | N=3 | The muscle volume was measured using MRI | Unstated | Knee extensors, knee flexors, and PL | Muscle atrophy varies among individuals and muscle groups |
| (Riley et al. 2000) | STS-78, 17 days | N=4 M |
Myofilament density & length were determined using biopsies. | Undocumented ad libitum aerobic exercise | SOL | Atrophied muscle fibers risk damage to sarcomeres |
| (Lambert et al. 2001) | EuroMir 94, 95, 98-E, & EO 19–24, 90–180 days | N=14 | Contractile and elastic characteristics were measured using an ankle ergometer and a strain-gauge torque transducer. | Everyone had access to a bike, a treadmill, and a muscular reinforcement device. No exercise data was collected. | PL | Muscle strength decreases while muscle stiffness increases as a result of SF |
| (Trappe et al. 2001) | STS-78, 17 days | N=12 SF: 4 BR: 8 M |
Fiber composition & size, & contractile characteristics were determined using biopsies & torque velocity dynamometer. | Undocumented mandatory exercise | GAS & SOL | Calf muscle function, fiber size, & enzyme activity were not significantly changed |
| (Tesch et al. 2005) | STS-78, 17 days | N=12 SF: 4 GC: 8 M |
Muscle function was measured by MVC, concentric, and eccentric actions. Muscles CSA were measured using MRI | In-flight exercise on a cycle ergometer. | Knee extensor/flexor and gluteal muscle groups | Knee extensor muscle strength & size decreased due to SF |
| (Chang et al. 2016) | ISS mission, 117–213 days | N=6 1 F, 5 M |
Supine lumbar spine MRI | There were routine pre, in and post-flight exercise programs | Paraspinal muscle, Intervertebral disc | Lumbar paraspinal muscle atrophied following long duration SF |
| (Bailey et al. 2018) | ISS mission, 180 days | N=6 1 F, 5 M |
Lumbar lordosis, CSA, and FCSA were determined using MRI and dynamic fluoroscopy | Unstated | Lumbar extensor muscles | MF atrophy lead to lumbar flattening & increased stiffness |
| (Puglia et al. 2018) | increment 7: 180 days increment 8: 191 days |
N=2 M |
Isometric handgrip and pinch force were measured by HGD and PFD tools | Unstated | Upper limbs (fingers, hand, wrist, etc.) | Strength & functionality of the arm & hand decreased due to long duration SF |
| (Burkhart et al. 2019) | Various ISS missions, Average length: 180 days | N=17 | The CSA and attenuation changes of paraspinal muscles were measured using CT scans | Nine subjects kept in-flight workout logs. Using a treadmill, a cycle ergometer, & iRED | L1, L2, ES, MF, PS, QL | In-flight exercise helped prevent paraspinal muscle mass loss |
| (Koryak 2019) | Various ISS missions, 115–380 days | N=8 M |
Architectural and contractile properties were measured using the tendometry method. | A four-day cycle exercise regimen. | TS muscle | Exercise was not able to prevent muscle atrophy or weakness in TS muscles |
| (McNamara et al. 2019) | Various ISS missions, 120 – 180 days | N=16 15 M, 1 F |
Muscle volume and attenuation were determined using Helical CT images | 6 subjects kept in-flight workout logs. The subjects had access to a CEVIS, TVIS, & iRED. | PS, QL, paraspinal muscle groups | Degradation in the QL & paraspinal muscles occurred despite in-flight exercise |
| (McNamara et al. 2019) | Various ISS missions, 120 – 180 days | N=6 | MRI was used to measure CSA and fatty infiltration. | 4 subjects kept in-flight exercise logs. The subjects had access to a CEVIS, TVIS, & ARED. | Neck muscles at the C1–C2, C4–C5, C7–T1, & T1–T2 intervertebral disc levels | In-flight exercise helped prevent neck musculature atrophy |
Note: All the studies in this section have pre-posttest design.