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Estimation of changes in volume of individual lower-limb muscles using magnetic resonance imaging (during bed-rest)

Muscle size in the lower limb is commonly assessed in neuromuscular research as it correlates with muscle function and some approaches have been assessed for their ability to provide valid estimates of muscle volume. Work to date has not examined the ability of different measurement approaches (such as cross-sectional area (CSA) measures on magnetic resonance (MR) imaging) to accurately track changes in muscle volume as a result of an intervention, such as exercise, injury or disuse. Here we assess whether (a) the percentage change in muscle CSA in 17 lower-limb muscles during 56 days bed-rest, as assessed by five different algorithms, lies within 0.5% of the muscle volume change and (b) the variability of the outcome measure is comparable to that of muscle volume. We find that an approach selecting the MR image with the highest muscle CSA and then a series of CSA measures, the number of which depended upon the muscle considered, immediately distal and proximal, provided an acceptable estimate of the muscle volume change. In the vastii, peroneal, sartorius and anterior tibial muscle groups, accurate results can be attained by increasing the spacing between CSA measures, thus reducing the total number of MR images and hence the measurement time. In the two heads of biceps femoris, semimembranosus and gracilis, it is not possible to reduce the number of CSA measures and the entire muscle volume must be evaluated. Using these approaches one can reduce the number of CSA measures required to estimate changes in muscle volume by â¼60%. These findings help to attain more efficient means to track muscle volume changes in interventional studies

Simulated microgravity and the lumbo-pelvic musculature Development and application of novel analysis techniques and implications for lumbo-pelvic pain ætiology

The presence of gravity throughout evolution has shaped the human body. The European Space Agencys Berlin Bed-Rest Study (BBR) offered a unique opportunity to researchers from The University of Queensland to study the effects of a lack of weightbearing (inactivity, unloading and/or sedentarism) on the lumbo-pelvic (LP) region. LP pain has been linked to a lack of muscular stabilisation and some authors have suggested a link between LP pain and inactivity. Furthermore, studies in bed-rest and microgravity have largely ignored the LP region, hampering the development of effective countermeasures. The muscular systems of the LP region are differentially involved in postural control and joint stabilisation. By its effect on the body and environment, gravity generates continual challenge to the central nervous system (CNS) for controlling the muscles of the LP region. As part of coping with this challenge, the CNS selectively recruits the deep (local) muscles to stabilise the joints with more task-oriented activation in the superficial (global) muscle systems. Concomitantly, the CNS exploits a number of motor control strategies: modulation ongoing (tonic) muscle activity and overall activation levels as well as anticipatory muscle function and co-contraction. Studies where the gravitational challenge is removed (bed-rest, spaceflight and related unloaded environments) show significant effects on the neuromuscular system. Greater atrophy of deep anti-gravity extensor muscles occurs. A down-regulation of anticipatory muscle activity occurs. Underactivity of the deep muscles with little change or overactivity in the superficial and flexor systems is observed. Tonic muscle contraction is inhibited and there is an increase in superficial muscle co-contraction. These findings bear parallels to changes observed in LP pain. Selective atrophy of the deep extensor muscles occurs. A delay of anticipatory muscle activity, especially in the deep muscles, is also observed. Superficial LP muscle overactivity and increased co-contraction has also been shown. Recent studies have also found a reduction in tonic muscle contraction in the deep systems. Importantly, however, there are distinct limitations in the quantification methods used to measure tonic and phasic muscle activity. The goals of this work were firstly to develop novel electromyographic quantification algorithms and secondly to examine the effect of bed-rest on the LP musculature; specifically in terms of muscle size (cross-sectional area, CSA), tonic and phasic muscle contraction, timing of muscle activity, activation levels and co-contraction. As part of the BBR, twenty subjects underwent 8-weeks bed-rest with 1-year follow-up. Ten subjects received a vibration exercise countermeasure, whilst the remaining ten were completely inactive. Non-invasive magnetic resonance imaging was used to study CSA changes in the deep and superficial muscles and superficial electromyography during a repetitive-movement task provided data on the motor control parameters. In addition to the development of novel analysis techniques, the key outcomes of this thesis were findings on the effect of bed-rest: (a) selective atrophy of the deep multifidus muscle (b) increased CSA of the LP flexor muscles, which appears to persist up to 6-months after bed-rest in the oblique muscles, (c) a shift from tonic to phasic muscle contraction in the superficial LP muscles, (d) a delay of LP muscle activation, (e) superficial LP muscle overactivity, (f) decreased co-contraction and, critically, (g) that a number of the changes persist up to the end of the 1-year follow-up period. Another important finding is that the vibration exercise countermeasure employed in the BBR prevented an overwhelming number of the changes observed in the inactive subjects. However, whilst reducing multifidus atrophy, it did not prevent it, and did not reduce lumbar erector spinae muscle atrophy. The significance of these results are that, firstly, it suggests the pattern of LP muscle and motor control change occurring in bed-rest is indeed similar to that observed in LP pain. This could suggest that long-term inactivity results in neuromuscular changes that reduce LP stabilization and increase risk of LP pain. Importantly, also, this thesis is the first detailed study of the LP musculature in bed-rest and provides information to space agencies necessary for the development of countermeasures. Furthermore, the vibration exercise countermeasure was in part effective in ameliorating the effects of bed-rest, and further steps can be taken for its optimization

The effects of bed rest and countermeasure exercise on the endocrine system in male adults: Evidence for immobilization-induced reduction in sex hormone-binding globulin levels

Background and Aim. There is limited data on the effects of inactivity (prolonged bed-rest) on parameters of endocrine and metabolic function; we therefore aimed to examine changes in these systems during and after prolonged (56-day) bed-rest in male adults. Subjects and Methods. 20 healthy male subjects underwent 8 weeks of strict bed-rest and 12 months follow-up as part of the Berlin Bed-Rest Study. Subjects were randomised to an inactive group or a group that performed resistive vibration exercise (RVE) during bed-rest. All outcome parameters were measured before, during and after bed-rest. These included body composition (by whole body dual X-ray absorptiometry), sex hormone-binding globulin (SHBG), testosterone (T), estradiol (E2), prolactin (PRL), cortisol (C), thyroid stimulating hormone (TSH) and free triiodothyronine (FT3). Results. Serum SHBG levels decreased in inactive subjects but remained unchanged in the RVE group (p<.001). Serum T concentrations increased during the first 3-weeks of bed-rest in both groups (p<.0001), while E2 levels sharply rose with re-mobilisation (p<.0001). Serum PRL decreased in the CTRL group but increased in the RVE group (p=.021). C levels did not change over time (p≥.10). TSH increased whilst FT3 decreased during bed-rest (p all≤.0013). Conclusions. Prolonged bed-rest has significant effects on parameters of endocrine and metabolic function, some of which are related to, or counteracted by physical activity

Changes in intervertebral disc morphology persist 5 mo after 21-day bed rest

As part of the nutrition- countermeasures (NUC) study in Cologne, Germany in 2010, seven healthy male subjects underwent 21 days of head-down tilt bed rest and returned 153 days later to undergo a second bout of 21-day bed rest. As part of this model, we aimed to examine the recovery of the lumbar intervertebral discs and muscle cross-sectional area (CSA) after bed rest using magnetic resonance imaging and conduct a pilot study on the effects of bed rest in lumbar muscle activation, as measured by signal intensity changes in T2-weighted images after a standardized isometric spinal extension loading task. The changes in intervertebral disc volume, anterior and posterior disc height, and intervertebral length seen after bed rest did not return to prebed-rest values 153 days later. While recovery of muscle CSA occurred after bed rest, increases (P 0.016) in multifidus, psoas, and quadratus lumborum muscle CSA were seen 153 days after bed rest. A trend was seen for greater activation of the erector spinae and multifidus muscles in the standardized loading task after bed rest. Greater reductions of multifidus and psoas CSA muscle and greater increases in multifidus signal intensity with loading were associated with incidence of low back pain in the first 28 days after bed rest (P 0.044). The current study contributes to our understanding of the recovery of the lumbar spine after 21-day bed rest, and the main finding was that a decrease in spinal extensor muscle CSA recovers within 5 mo after bed rest but that changes in the intervertebral discs persist

Resistive vibration exercise reduced lower limb atrophy during 56-day bed-rest

Objectives: The current study aimed to examine the effectiveness of a resistive vibration exercise countermeasure during prolonged bed-rest in preventing lower-limb muscle atrophy. Methods: 20 male subjects underwent 56-days of bed-rest and were assigned to either an inactive control, or a countermeasure group which performed high-load resistive exercises (including squats, heel raises and toe raises) with whole-body vibration. Magnetic resonance imaging of the lower-limbs was performed at twoweekly intervals. Volume of individual muscles was calculated. Results: Countermeasure exercise reduced atrophy in the triceps surae and the vastii muscles (F>3.0, p<.025). Atrophy of the peroneals, tibialis posterior and toe flexors was less in the countermeasure- subjects, though statistical evidence for this was weak (F≤2.3, p≥.071). Atrophy in the hamstring muscles was similar in both groups (F.38). The adductor longus, sartiorius and rectus femoris muscles showed little loss of muscle volume during bed-rest (F.15). Conclusions: The countermeasure exercise programme was effective in reducing atrophy in the extensors of the knee and ankle but not the hamstrings

T2-relaxation time increases in lumbar intervertebral disks after 21d head-down tilt bed-rest

Objectives: Spaceflight back pain and intervertebral disc (IVD) herniations cause problems in astronauts. Purpose of this study was to assess changes in T2-relaxation-time through MRI measurements before and after head-down tilt bed-rest, a spaceflight analog. Methods: 8 men participated in the bed-rest study. Subjects remained in 6° head down tilt bed-rest in two campaigns of 21 days, and received a nutritional intervention (potassium bicarbonate 90 mmol/d) in a cross-over design. MRI measurements were performed 2 days before bed-rest, as well as one and five days after getting up. Image Segmentation and data analysis were conducted for the IVDs Th12/L1 to L5/S1. Results: 7 subjects, average age of 27.6 (SD 3.3) years, completed the study. Results showed a significant increase in T2-time in all IVDs (p < 0.001), more pronounced in the nucleus pulposus than in the annulus fibrosus (p<0.001). Oral potassium bicarbonate did not show an effect p=0.443). Pfirrmanngrade correlated with the T2-time (p<0.001). Conclusions: 6° head-down tilt bed-rest leads to a T2-time increase in lumbar IVDs. Oral potassium bicarbonate supplementation does not have an effect on IVD T2-time

Measuring the growing impact of <i>BOSEM</i>:halfway there or living on a prayer?

Measuring the growing impact of BOSEM: halfway there or living on a prayer

Influence of prolonged bed-rest on spectral and temporal electromyographic motor control characteristics in the superficial lumbo-pelvic musculature

Little is known about the motor control of the lumbo-pelvic musculature in microgravity and its simulation (bed-rest). Analysis of spectral and temporal electromyographic variables can provide information on motor control relevant for normal function. This study examined the effect of 56-days of bed-rest with 1-year follow-up in 10 male subjects on the median frequency and the activation timing in surface electromyographic recordings from five superficial lumbo-pelvic muscles during a repetitive knee movement task. Trunk fat mass (from whole body-composition measurements) and movement accuracy as possible explanatory factors were included. Increased median frequency was observed in the lumbar erector spinae starting late in bed-rest, but this was not seen in its synergist, the thoracic erector spinae (p < .0001). These changes persisted up to 1-year after bed-rest and were independent of changes in body-composition or movement accuracy. Analysis suggested decreases of median frequency (p < .0001) in the abdominal and gluteal muscles to result from increased (p < .01) trunk fat levels during and after bed-rest. No changes in lumbo-pelvic muscle activation timing were seen. The results suggest that bed-rest particularly affects the shorter lumbar erector spinae and that the temporal sequencing of superficial lumbo-pelvic muscle activation is relatively robus

Resistive vibration exercise attenuates bone and muscle atrophy in 56-days of bed-rest: whole body DXA and biochemical markers of bone metabolism

Summary During and after prolonged bed rest, changes in bone metabolic markers occur within 3 days. Resistive vibration exercise during bed rest impedes bone loss and restricts increases in bone resorption markers whilst increasing bone formation. Introduction To investigate the effectiveness of a resistive vibration exercise (RVE) countermeasure during prolonged bed rest using serum markers of bone metabolism and whole-body dual X-ray absorptiometry (DXA) as endpoints. Methods Twenty healthy male subjects underwent 8 weeks of bed rest with 12 months follow-up. Ten subjects performed RVE. Blood drawings and DXA measures were conducted regularly during and after bed rest. Results Bone resorption increased in the CTRL group with a less severe increase in the RVE group (p = 0.0004). Bone formation markers increased in the RVE group but decreased marginally in the CTRL group (p < 0.0001). At the end of bed rest, the CTRL group showed significant loss in leg bone mass (−1.8(0.9)%, p = 0.042) whereas the RVE group did not (−0.7(0.8)%, p = 0.405) although the difference between the groups was not significant (p = 0.12). Conclusions The results suggest the countermeasure restricts increases in bone resorption, increased bone formation, and reduced bone loss during bed rest