A novel approach to activate deep spinal muscles in space - results of a biomechanical model

Introduction Exposure to microgravity has various effects on the human musculoskeletal system. During spaceflight many astronauts experience low back pain and the risk of spine injuries is significantly greater post-flight. Nonetheless, the increased lumbo-pelvic injury risk is not specifically addressed by current countermeasures. Considering this, a novel exercise device has been developed to specifically counteract atrophy of deep spinal and postural muscles. The aim of the present study was to test the possibility of transferring this exercise concept from earth to space using a biomechanical simulation. Methods A biomechanical model of the exercise device was developed and validated using intramuscular electromyographic (EMG) data as previously acquired on a terrestrial prototype of the exercise device. The model was then modified to the needs of a 0-g environment, creating gravity-like conditions using shoulder straps. Results Modelled activation patterns of the investigated muscles were in line with the experimental data, showing a constant activation during exercise. The microgravity modifications of the model lead to increased muscle activation of deep spinal muscles and to decreased activation of superficial moment creating trunk muscles. Discussion The results of the biomechanical model suggest that the exercise concept can be transferred from 1-g to space conditions. The present study is a first step in the investigation process of a novel exercise concept and human studies should be conducted to confirm the present theoretical investigation

Hypogravity reduces trunk admittance and lumbar muscle activation in response to external perturbations

Reduced paraspinal muscle size and flattening of spinal curvatures have been documented after spaceflight. Assessment of trunk adaptations to hypogravity can contribute to develop specific countermeasures. In this study, parabolic flights were used to investigate spinal curvature and muscle responses to hypogravity. Data from five trials at 0.25g, 0.50g and 0.75g were recorded from six participants, positioned in a kneeling-seated position. During the first two trials, participants maintained a normal, upright posture. In the last three trials, small-amplitude perturbations were delivered in the anterior direction at the T10 level. Spinal curvature was estimated using motion capture cameras. Trunk displacement and contact force between the actuator and participant were recorded. Muscle activity responses were collected using intramuscular electromyography (iEMG) of the deep and superficial lumbar multifidus, iliocostalis lumborum, longissimus thoracis, quadratus lumborum, transversus abdominis, obliquus internus and obliquus externus muscles. The root mean square iEMG and the average spinal angles were calculated. Trunk admittance and muscle responses to perturbations were calculated as closed-loop frequency response functions. Compared with 0.75g, 0.25g resulted in: lower activation of the longissimus thoracis (P=0.002); lower responses of the superficial multifidus at low frequencies (P=0.043); lower responses of the superficial multifidus (P=0.029) and iliocostalis lumborum (P=0.043); lower trunk admittance (P=0.037) at intermediate frequencies; and stronger responses of the transversus abdominis at higher frequencies (p=0.032). These findings indicate that exposure to hypogravity reduces trunk admittance, partially compensated by weaker stabilizing contributions of the paraspinal muscles and coinciding with an apparent increase of the deep abdominal muscle activity

Intermittent short-arm centrifugation is a partially effective countermeasure against upright balance deterioration following 60-day head-down tilt bed rest

This study investigated whether artificial gravity (AG), induced by short-radius centrifugation, mitigated deterioration in standing balance and anticipatory postural adjustments (APAs) of trunk muscles following 60-day head-down tilt bed rest. Twenty-four participants were allocated to one of three groups: control group (N=8); 30 minutes continuous AG daily (N=8); intermittent 6x5 minutes AG daily (N=8). Before and immediately after bed rest, standing balance was assessed in four conditions: eyes open and closed on both stable and foam surfaces. Measures including sway path, root-mean-square, and peak sway velocity, sway area, sway frequency power, and sway density curve were extracted from the centre of pressure displacement. APAs were assessed during rapid arm movements using intramuscular or surface electromyography electrodes of the rectus abdominis, obliquus externus and internus abdominis, transversus abdominis, erector spinae at L1, L2, L3, and L4 vertebral levels, and deep lumbar multifidus muscles. The relative latency between the EMG onset of the deltoid and each of the trunk muscles was calculated. All three groups had poorer balance performance in most of the parameters (all P<0.05) and delayed APAs of the trunk muscles following bed rest (all P<0.05). Sway path and sway velocity were deteriorated, and sway frequency power was less in those who received intermittent AG than in the control group (all P<0.05), particularly in conditions with reduced proprioceptive feedback. These data highlight the potential of intermittent AG to mitigate deterioration of some aspects of postural control induced by gravitational unloading, but no protective effects on trunk muscle responses were observed

Lumbar muscle atrophy and increased relative intramuscular lipid concentration are not mitigated by daily artificial gravity after 60-day head-down tilt bed rest

Exposure to axial unloading induces adaptations in paraspinal muscles, as shown after spaceflights. This study investigated whether daily exposure to artificial gravity (AG) mitigated lumbar spine flattening and muscle atrophy associated with 60-day head-down tilt (HDT) bed rest (Earth-based space analogue). Twenty-four healthy individuals participated in the study: Eight received 30 minutes continuous AG; eight received 6x5 minutes AG, interspersed with rest periods; eight received no AG exposure (control group). Magnetic Resonance Imaging (MRI) of the lumbopelvic region was conducted at baseline (BDC) and at day 59 of HDT (HDT59). T1-weighted images were used to assess morphology of the lumbar spine (spinal length, intervertebral disc angles, disc area) and volumes of the lumbar multifidus (LM), lumbar erector spinae (LES), quadratus lumborum (QL), and psoas major (PM) muscles from L1/L2 to L5/S1 vertebral levels. A chemical shift-based 2‐point lipid/water Dixon sequence was used to evaluate muscle composition. Results showed that: spinal length and disc area increased (P<0.05); intervertebral disc angles (P<0.05) and muscle volumes of LM, LES, and QL reduced (P<0.01); and fat/water ratio for the LM and LES muscles increased (P<0.01) after HDT59 in all groups. Neither of the AG protocols mitigated the lumbar spinal deconditioning induced by HDT bed rest. The increase in lipid/water ratio in LM and LES muscles indicates an increased relative intramuscular lipid concentration. Altered muscle composition in atrophied muscles may impair lumbar spine function after body unloading, which could increase injury risk to vulnerable soft tissues. This relationship needs further investigation

Gluteal muscle atrophy and increased intramuscular lipid concentration are not mitigated by daily artificial gravity following 60-day head-down tilt bed rest

Exposure to spaceflight and head-down tilt (HDT) bed rest leads to decreases in the mass of the gluteal muscle. Preliminary results have suggested that interventions, such as artificial gravity (AG), can partially mitigate some of the physiological adaptations induced by HDT bed rest. However, its effect on the gluteal muscles is currently unknown. This study investigated the effects of daily AG on the gluteal muscles during 60-day HDT bed rest. Twenty-four healthy individuals participated in the study: eight received 30 minutes of continuous AG; eight received 6x5 minutes of AG, interspersed with rest periods; eight belonged to a control group. T1-Weighted Dixon magnetic resonance imaging of the hip region was conducted at baseline and day 59 of HDT bed rest to establish changes in volumes and intramuscular lipid concentration (ILC). Results showed that, across groups, muscle volumes decreased by 9.2 for gluteus maximus (GMAX), 8.0 for gluteus medius (GMED), and 10.5 for gluteus minimus after 59-day HDT bed rest (all P<0.005). The ILC increased by 1.3 for GMAX and 0.5 for GMED (both P<0.05). Neither of the AG protocols mitigated deconditioning of the gluteal muscles. Whereas all gluteal muscles atrophied, the ratio of lipids to intramuscular water increased only in GMAX and GMED muscles. These changes could impair the function of the hip joint and increased the risk of falls. The deconditioning of the gluteal muscles in space may negatively impact the hip joint stability of astronauts when reexpose to terrestrial gravity