Muscle atrophy and bone loss pose substantial problems for long-term space flight and in clinical immobilization. We therefore tested the efficacy of flywheel resistive exercise and pamidronate to ...counteract such losses.
Twenty five young healthy males underwent strict bed rest with −6° head-down tilt for 90 days. Subjects were randomized into an exercise group that practiced resistive exercise with a ‘flywheel’ (FW) device every 2–3 days, a pamidronate group (Pam) that received 60 mg pamidronate i.v. 14 days prior to bed rest and a control group (Ctrl) that received none of these countermeasures.
During the study, Ca
++ and protein intake were controlled. Peripheral quantitative computed tomography (pQCT) was used to assess bone mineral content (BMC) and muscle cross sectional area (mCSA) of calf and forearm. Measurements were taken twice during baseline data collection, after 28 and after 89 days bed rest, and after 14 days recovery. On the same days, urinary Pyridinoline excretion and serum levels of alkaline phosphatase, Ca
++ and PTH were measured. Pre-study exercise habits were assessed through the Freiburg questionnaire.
Losses in calf mCSA were significantly reduced in FW (Ctrl: −25.6% ± 2.5% Pam: −25.6% ± 3.7%, FW: −17.3% ± 2.7%), but not in the forearm mCSA (Ctrl: −6.4% ± 4.33%, Pam: −7.7% ± 4.1%, FW: −7.6% ± 3.3%). Both diaphyseal and epiphyseal BMC losses of the tibia were mitigated in Pam and FW as compared to Ctrl, although this was significant only at the diaphysis.
Inter-individual variability was significantly greater for changes in BMC than in mCSA, and correlation of BMC losses was poor among different locations of the tibia. A significant
positive correlation was found between change in tibia epiphyseal BMC and serum cortisol levels.
These findings suggest that both countermeasures are only partly effective to preserve BMC (FW and Pam) and mCSA (FW) of the lower leg during bed rest. The partial efficacy of flywheel exercise as well as the bones' response to unloading per se underlines the importance of mechanical stimuli. The huge variability of BMC changes, however, suggests that other factors affect changes in whole-bone strength following acute mechanical disuse.
Abstract only
Ribosome biogenesis has been shown to increase following resistance exercise; yet, it is currently unknown how promoter methylation and dosage of rDNA genes influence translational ...capacity, as well as basal and post‐exercise rDNA transcription rates in skeletal muscle. Moreover, whether ribosome biogenesis is induced in response to acute aerobic exercise is not well characterized in skeletal muscle.
Healthy volunteers (n=30; 18 men and 12 women; 31 ±8 yrs, 25 ±4 kg/m
2
) were randomized to an acute bout of either aerobic (AE, 45 min biking, 70% VO
2
max) or resistance exercise (RE, 4 x 7 x 2 exercises), or control (no exercise). Skeletal muscle biopsies were obtained before and at 30 min, 3‐, 8‐and 24 hrs following the exercise session, and RNA/DNA was extracted. Ribosomal DNA transcription and rDNA copy number were assessed using qRT‐PCR. Average methylation of the rDNA promoter (−189 to +47) was investigated using the Agena massARRAY EpiTYPER.
rDNA transcription at baseline was negatively associated with rDNA copy number (r=−0,44, p<0.05) but not with average rDNA promoter methylation. Total RNA was not related to rDNA copy number or degree of methylation of the promoter. RE significantly induced rDNA transcription, whereas AE and control did not. Average methylation of the rDNA promoter (mean: 23%, range: 10–35%) varied among volunteers; however, it was not influenced by exercise at any timepoint. Gene dosage of rDNA strongly correlated to fold‐change in rDNA transcription at the 24h timepoint (r=0.85, p<0.01).
Transcription of the rRNA genes increased following resistance exercise but not following aerobic exercise, indicating specificity of exercise modality in stimulating ribosome biogenesis following exercise. Average rDNA promoter methylation varied between subjects but was not affected by exercise. Dosage of the rRNA genes strongly correlated to resistance exercise induced rDNA transcription suggesting the importance of rDNA copy number for ribosome biogenesis, and likely hypertrophic potential.
Support or Funding Information
Swedish Research Council for Sport Science (FvW); Futurum – the Academy for Health and Care, Region Jönköping County (BA)
This study compared the relationship between surface electromyographic (EMG) activity and isometric force of m. quadriceps femoris (QF) in the single-joint knee extension (KE) and the multi-joint leg ...press (LP) exercises.
Nine healthy men performed unilateral actions at a knee angle of 90 degrees at 20, 40, 60, 80, and 100% of maximal voluntary contraction (MVC). EMG was measured from m. vastus lateralis (VL), m. vastus medialis (VM), m. rectus femoris (RF), and m. biceps femoris (BF).
There were no differences in maximum EMG activity of individual muscles between KE and LP. The QF EMG/force relationship was nonlinear in each exercise modality. VL showed no deviation from linearity in neither exercise, whereas VM and RF did. BF activity increased linearly with increased loads.
The EMG/force relationship of all quadricep muscles studied appears to be similar in isometric multi-joint LP and single-joint KE actions at a knee angle of 90 degrees. This would indicate the strategy of reciprocal force increment among muscles involved is comparable in the two models. Furthermore, these data suggest a nonuniform recruitment pattern among the three superficial QF muscles and surface EMG recordings from VL to be most reliable in predicting force output.
A gravity‐independent flywheel exercise device (FWED) has been proven effective as a countermeasure to loss of strength and muscle atrophy induced by simulated microgravity. This study assessed ...muscle‐fiber conduction velocity (CV) and surface EMG instantaneous mean power spectral frequency (iMNF) during brief bouts of fatiguing concentric (CON) and eccentric (ECC) exercise on a FWED in order to identify electromyographic (EMG) variables that can be used to provide objective indications of muscle status when exercising with a FWED. Multichannel surface EMG signals were recorded from vastus lateralis and medialis muscles of nine men during: (1) isometric, 60‐s action at 50% of maximum voluntary action (MVC); (2) two isometric, linearly increasing force ramps (0–100% MVC); and (3) dynamic CON/ECC coupled actions on the FWED. Muscle‐fiber CV and iMNF were computed over time during the three tasks. During ramps, CV, but not iMNF, increased with force (P < 0.001). Conduction velocity and iMNF decreased with the same normalized rate of change in constant‐force actions. During CON/ECC actions, the normalized rate of change over time was larger for CV than iMNF (P < 0.05). These results suggest that, during fatiguing, dynamic, variable‐force tasks, changes in CV cannot be indirectly inferred by EMG spectral analysis. This underlines the importance of measuring both CV and spectral variables for muscle assessment in dynamic tasks. Muscle Nerve, 2006
Aim: This study determined changes in knee extensor and plantar flexor muscle volume during 29 days of bed rest with or without resistance exercise using a gravity‐independent flywheel ergometer.
...Methods: Seventeen men (26–41 years) were subjected to 29 days of bed rest with (n = 8) or without (n = 9) resistance exercise; Supine Squat (SS) and Calf Press (CP) performed every third day. Quadriceps and triceps surae muscle volume was determined before and after bed rest and force and power were measured during training. Prior to these interventions, reproducibility of this device for training and testing was assessed in 23 subjects who performed bilateral maximal concentric, eccentric and isometric (MVC) knee extensions and plantar flexions over repeated sessions with simultaneous measurements of force, power and electromyographic (EMG) activity.
Results: Quadriceps and triceps surae muscle volume decreased (P < 0.05) 10 and 16%, respectively, after 29 days bed rest. Exercise maintained quadriceps volume and mitigated triceps surae atrophy. Thus, either muscle showed different response across subject groups (P < 0.05). Force and power output during training were either maintained (P > 0.05) or increased (P < 0.05). EMG amplitude in the training mode was similar (SS; P > 0.05) or greater (CP; P < 0.05) compared with that elicited during MVC. Peak force and power test‐retest coefficient of variation (CV) ranged 5–6% and 7–8% for SS and CP, respectively.
Conclusion: The present data suggest that this resistance exercise paradigm counteracts quadriceps and abates the more substantial triceps surae muscle atrophy in bedridden subjects, and therefore should be an important asset to space travellers.
Exposure to microgravity, i.e., spaceflight, causes muscle unloading leading to muscle atrophy and dysfunction. Thus, there is a need for effective countermeasures to combat these effects. The ...present thesis aimed to study function, size and composition of anti-gravity muscles following long-duration bed rest, a valid spaceflight analogue. A further and even more important aim was to study the effects of concurrent resistance exercise using a gravityindependent device.Prior to this, the exercise paradigm was validated during space station-like conditions. Four healthy men trained 2-3 times weekly during 110 days of confinement in a ground-based chamber, severely restricting locomotor activity. Training performance progressed over time and maximal voluntary contraction (MVC) was either increased or maintained after confinement. Since the device showed feasibility and potential as a countermeasure against muscle function deterioration, it was subsequently employed during strict unloading.Nine healthy men performed 90 days of bed rest (BR), while another group of eight men in addition carried out resistance exercise for the knee extensors and plantar flexors every third day (BRE). Different indices of muscle function were obtained together with surface electromyographic (EMG) amplitude before and after the intervention. Muscle volume was assessed by means of magnetic resonance imaging (MRI) prior to and on day 29 and 89 during bed rest. Moreover, muscle biopsies were obtained from mm. vastus lateralis (VL; all subjects) and soleus (n=3 from each group) before and on day 84 during bed rest, for subsequent analyses of single fibre myosin heavy chain (MHC) content.In BR, muscle volume of the knee extensors decreased (p<0.05) by 10 and 18% on day 29 and 89, respectively. The corresponding decreases for the plantar flexors were 16 and 29%, respectively. In BRE, knee extensor atrophy was prevented (p>0.05), while the more pronounced plantar flexor atrophy was attenuated (-8 and -15%). Maximal torque, force and power, measured during different types of actions, decreased by 31-60% in BR. In BRE, MVC was maintained for the knee extensors but not for the plantar flexors. Training-specific force and power were unaltered for both muscles, while maximal torque measured in actions different from the training task, decreased. EMG amplitude decreased during maximal and increased during submaximal actions in BR, but not in BRE. BR, but not BRE, showed increased fatigability and decreased rate of force development (RFD). In BR, there was an increase in hybrid fibres and a shift towards faster phenotypes in both VL and soleus. In BRE, this effect was attenuated in VL and offset in soleus. The phenotype shift was not manifested in altered force-velocity characteristics.The greater atrophy of the plantar flexors compared to the knee extensors in response to unloading, may be explained by the greater content of slow fibres and the more frequent use of this particular muscle group in daily life. Further, muscle volume and single fibre data suggest that slow fibres are less responsive to the training protocol. The present findings also provide evidence that neural mechanisms, in addition to changes in muscle size, contribute to muscle function alterations induced by bed rest with or without resistance exercise, while phenotype shift may play a more modest role. Hence, it is clear that designing countermeasures for in-flight use extends beyond preserving muscle size only. Though the present work was spurred by questions addressed through the human spaceflight program, the results do have important clinical implications for e.g., aging populations or patients undergoing atrophy due to disease or injury.
Nitric oxide (NO) generated from NO synthases mediates normal skeletal muscle functions. Biosynthesis of NO apparently is linked to muscle activity, but the distribution and expression of the three ...major NO synthase 1-3 isoforms under conditions of extended muscle disuse and exercise are still unclear. Our aim
was to elucidate whether protein levels and the cellular or subcellular localization patterns of NO synthases underwent significant changes in a mixed fast/slow and slow type skeletal muscle after prolonged disuse in a long-term bed rest study, a useful experimental paradigm
of simulated microgravity in ground-based space
research. We examined whether resistance exercise performed regularly as a countermeasure to progressive atrophy within 12 wk of strict bed rest would support expression of one or more isoforms of NOS,
thereby maintaining normal skeletal muscle functions during immobilization in clinical settings or in human spaceflight.
Because few women have been studied, it is not known if gender specific responses to real or simulated spaceflight exist. We monitored muscle volume changes of the thigh (quadriceps femoris) and calf ...(triceps surae) of women and men exposed to 60 and 90 days of ‐6° head down tilt (HDT) bedrest (BR), respectively. Magnetic resonance imaging measurements were made pre‐BR, HDT29, HDT57 (women), and HDT89 (men). The women lost relatively more (P<0.05) thigh muscle volume than the men after one month (−17±1 vs. −10±1%). This amount of loss for the women at one month was similar (P>0.05) to the amount the men had lost in three months (−18±1%). The women also had lost relatively more (P<0.05) thigh muscle volume in two months (−21±1%) than the men had lost in three months. The women tended (P=0.08) to lose relatively more calf muscle volume in one month than the men (−18±1 vs. −16±1%), while the women had lost as much (P>0.05) calf muscle volume after two months (−29±1%) as the men had lost after three months (−29±2%). These results suggest that women are more susceptible to bedrest‐induced muscle loss than men and countermeasures specific to women will likely need to be developed.
Sponsors: NASA, ESA, CNES
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