Tobias Weber

Changes in corticospinal transmission following 8 weeks of ankle joint immobilization

OBJECTIVES Joint immobilization has previously been shown to modulate corticospinal excitability. The present study investigated changes in the excitability of distinct fractions of the corticospinal pathway by means of conditioning the H-reflex with transcranial magnetic stimulation (TMS) of the primary motor cortex (Hcond). This method allows assessment of transmission in fast (monosynaptic) and slow(er) (polysynaptic) corticospinal pathways. METHODS 9 subjects underwent 8weeks of unilateral ankle joint immobilization during daytime, 7 subjects served as controls. The measures obtained before and after immobilization included stretch- and H-reflexes assessing excitability of the spinal reflex circuitries, TMS recruitment curves estimating overall changes in corticospinal excitability, and Hcond. RESULTS TMS recruitment curves showed an overall increase in corticospinal excitability following immobilization. Importantly, Hcond revealed significant facilitation of conditioned reflexes, but only for longer conditioning intervals, suggesting that immobilization increased excitability only of slower, indirect corticospinal pathways. No changes were observed in the control group. Immobilization had no significant effects on spinal reflex measures. CONCLUSIONS 8weeks of ankle joint immobilization was accompanied by pathway-specific modulation of corticospinal transmission. SIGNIFICANCE It is particularly interesting that fast corticospinal projections were unaffected as these are involved in controlling many, if not most, movements in humans.

The relationship between exercise‐induced muscle fatigue, arterial blood flow and muscle perfusion after 56 days local muscle unloading

In the light of the dynamic nature of habitual plantar flexor activity, we utilized an incremental isokinetic exercise test (IIET) to assess the work‐related power deficit (WoRPD) as a measure for exercise‐induced muscle fatigue before and after prolonged calf muscle unloading and in relation to arterial blood flow and muscle perfusion. Eleven male subjects (31 ± 6 years) wore the HEPHAISTOS unloading orthosis unilaterally for 56 days. It allows habitual ambulation while greatly reducing plantar flexor activity and torque production. Endpoint measurements encompassed arterial blood flow, measured in the femoral artery using Doppler ultrasound, oxygenation of the soleus muscle assessed by near‐infrared spectroscopy, lactate concentrations determined in capillary blood and muscle activity using soleus muscle surface electromyography. Furthermore, soleus muscle biopsies were taken to investigate morphological muscle changes. After the intervention, maximal isokinetic torque was reduced by 23·4 ± 8·2% (P<0·001) and soleus fibre size was reduced by 8·5 ± 13% (P = 0·016). However, WoRPD remained unaffected as indicated by an unchanged loss of relative plantar flexor power between pre‐ and postexperiments (P = 0·88). Blood flow, tissue oxygenation, lactate concentrations and EMG median frequency kinematics during the exercise test were comparable before and after the intervention, whereas the increase of RMS in response to IIET was less following the intervention (P = 0·03). In conclusion, following submaximal isokinetic muscle work exercise‐induced muscle fatigue is unaffected after prolonged local muscle unloading. The observation that arterial blood flow was maintained may underlie the unchanged fatigability.

Vascular adaptations induced by 6 weeks WBV resistance exercise training.

The impact of whole‐body vibration (WBV) upon the cardiovascular system is receiving increasing attention. Despite numerous studies addressing the acute cardiovascular effects of WBV training, very little is known regarding long‐term adaptations in healthy humans.

The specific role of gravitational accelerations for arterial adaptations

It is mostly agreed that arterial adaptations occur, among others, in response to changes in mechanical stimuli. Models like bed rest, spinal cord injury, or limb suspension have been applied to study vascular adaptations to unloading in humans. However, these models cannot distinguish the role of muscle contractions and the role of gravitational accelerations for arterial adaptation. The HEPHAISTOS orthosis allows normal ambulation, while it significantly reduces force generation in the lower leg muscles. Eleven subjects wore HEPHAISTOS unilaterally for 56 days and were followed up for another 4 wk. Arterial diameters, intima media thickness (IMT), flow-mediated dilation (FMD), and resting blood flow (BF(rest)) were measured using high-frequency ultrasonography. Arterial adaptations were investigated in the superficial femoral artery (SFA), the brachial artery (BA), and the carotid artery (CA). Mean SFA resting diameter was decreased from 6.57 mm (SD = 0.74 mm) at baseline to 5.77 mm (SD = 0.87 mm) at the end of the intervention (P < 0.001), whereas SFA wall-to-lumen ratio, SFA BF(rest), and SFA FMD remained unaffected throughout the study. The application of HEPHAISTOS had no effect on structure and function of the systemic control sites, the BA, and the CA. Our findings highlight the importance of muscular contractions for arterial diameter adaptations. Moreover, we propose that FMD and wall-to-lumen ratio are unaffected by ambulating with the HEPHAISTOS orthosis, which is suggestive of habitual acceleration profiles in the lower leg constituting an important stimulus for the maintenance of FMD and wall-to-lumen ratio.

Trunk muscle activation during movement with a new exercise device for lumbo‐pelvic reconditioning

Gravitational unloading leads to adaptations of the human body, including the spine and its adjacent structures, making it more vulnerable to injury and pain. The Functional Re‐adaptive Exercise Device (FRED) has been developed to activate the deep spinal muscles, lumbar multifidus (LM) and transversus abdominis (TrA), that provide inter‐segmental control and spinal protection. The FRED provides an unstable base of support and combines weight bearing in up‐right posture with side alternating, elliptical leg movements, without any resistance to movement. The present study investigated the activation of LM, TrA, obliquus externus (OE), obliquus internus (OI), abdominis, and erector spinae (ES) during FRED exercise using intramuscular fine‐wire and surface EMG. Nine healthy male volunteers (27 ± 5 years) have been recruited for the study. FRED exercise was compared with treadmill walking. It was confirmed that LM and TrA were continually active during FRED exercise. Compared with walking, FRED exercise resulted in similar mean activation of LM and TrA, less activation of OE, OI, ES, and greater variability of lumbo‐pelvic muscle activation patterns between individual FRED/gait cycles. These data suggest that FRED continuously engages LM and TrA, and therefore, has the potential as a stationary exercise device to train these muscles.

Microcirculation of skeletal muscle adapts differently to a resistive exercise intervention with and without superimposed whole-body vibrations

Whole‐body vibration (WBV) training is commonly practiced and may enhance peripheral blood flow. Here, we investigated muscle morphology and acute microcirculatory responses before and after a 6‐week resistive exercise training intervention without (RE) or with (RVE) simultaneous whole‐body vibrations (20 Hz, 6 mm peak‐to‐peak amplitude) in 26 healthy men in a randomized, controlled parallel‐design study. Total haemoglobin (tHb) and tissue oxygenation index (TOI) were measured in gastrocnemius muscle (GM) with near‐infrared spectroscopy (NIRS). Whole‐body oxygen consumption (VO2) was measured via spirometry, and skeletal muscle morphology was determined in soleus (SOL) muscle biopsies. Our data reveal that exercise‐induced muscle deoxygenation both before and after 6 weeks training was similar in RE and RVE (P = 0·76), although VO2 was 20% higher in the RVE group (P<0·001). The RVE group showed a 14%‐point increase in reactive hyperaemia (P = 0·007) and a 27% increase in blood volume (P<0·01) in GM after 6 weeks of training. The number of capillaries around fibres was increased by 15% after 6 weeks training in both groups (P<0·001) with no specific effect of superimposed WBV (P = 0·61). Neither of the training regimens induced fibre hypertrophy in SOL. The present findings suggest an increased blood volume and vasodilator response in GM as an adaptation to long‐term RVE, which was not observed after RE alone. We conclude that RVE training enhances vasodilation of small arterioles and possibly capillaries. This effect might be advantageous for muscle thermoregulation and the delivery of oxygen and nutrients to exercising muscle and removal of carbon dioxide and metabolites.

Diameter Measurement of Vascular Structures in Ultrasound Video Sequences

Abstract Today, computer aided assessment of ultrasound video sequences is considered the gold standard. Ultrasound analysis forms an integral part of the medical research studies performed at the DLR. Currently, two studies are being performed that obtain ultrasound measurements of vascular structures. In this project, a software is developed that supports these and future studies in providing a framework for ultrasound analysis. Furthermore a method for obtaining assessment of diameter measurements from vascular structures in ultrasound video material is provided. Following the problem analysis based on scenarios and tasks the use cases were constructed and used for an system design. A virtual window was derived from the requirements specification—use cases. After consulting the customer with the virtual window, it was later realized by implementing the GUI. The developed software is clearly structured and focuses on extensibility. To be able to achieve this goal, the softwares main components clearly separated by integrating the model view controller pattern into the software’s architecture. The facade pattern is utilized to provide easy access to the frameworks interface models and hides the complexity. In the approach of developing the image processing, the image material was examined in depth and characteristics defined. The approach for determining the edges on the vessel walls for diameter measurement is to differentiate the image with a first order derivate of a Gaussian filter. The edges are then detected by analyzing the differentiated image. Diameter measurement between the edges follows certain assumptions that have been made. The diameter measurement algorithm was later evaluated. The evaluation of the diameter measurement algorithm showed that there is considerable variability between the gold standard of manual measurement and the software results. Furthermore, it was shown that the video quality and the definition of the region of interest have an impact on measurement accuracy. Concluding the software developed here delivers a framework for ultrasound image analysis and enables the further refinement of the measurement algorithm and flexible implementation into future ultrasound applications.

Muscular forces affect the glycosaminoglycan content of joint cartilage: unloading in human volunteers with the HEPHAISTOS lower leg orthosis.

Background and purpose — Unloading alters the thickness of joint cartilage. It is unknown, however, to what extent unloading leads to a loss of glycosaminoglycans (GAGs) in the cartilage tissue. We hypothesized that muscle forces, in addition to axial loading, are necessary to maintain the joint cartilage GAG content of the knee and the upper and lower ankle. Patients and methods — The HEPHAISTOS orthosis was worn unilaterally by 11 men (mean age 31 (23–50) years old) for 56 days. The orthosis reduces activation and force production of the calf muscles while it permits full gravitational loading of the lower leg. MRI measurements of the knee and ankle were taken before the intervention, during the intervention (on day 49), and 14 days after the end of the intervention. Cartilage segmentation was conducted semiautomatically for the knee joint (4 segments) and for the upper (tibio-talar) and lower (subtalar) ankle joints (2 segments each). Linear mixed-effects (LME) models were used for statistical analysis. Results — 8 volunteers completed the MRI experiment. In the lower ankle joint, differences in ΔT1 were found between the end of the intervention and 14 days after (p = 0.004), indicating a decrease in GAG content after reloading. There were no statistically significant differences in ΔT1 values in the knee and upper ankle joints. Interpretation — Our findings suggest that in addition to gravitational load, muscular forces affect cartilage composition depending on the local distribution of forces in the joints affected by muscle contraction.

Functional behaviour of spinal muscles after training with an exercise device developed to recruit and train postural muscles

This study investigated the effects of a single exercise session using a device developed for postural muscle training on the function of postural muscles in healthy, pain free individuals. During standardised rapid arm movements, timing of onset of electromyography (EMG) was measured using intramuscular and surface recordings of the transversus abdominis (TrA), obliquus internus abdominis (OI), obliquus externus abdominis (OE), lumbar multifidus (LM) and lumbar erector spinae (LES) muscles. A single exercise session with the device led to significantly (main effect of time: P = 0.03) earlier LES EMG onset in advance of the postural perturbation induced by rapid forward arm movements from -1 ms (SD: 32 ms) at baseline to -11 ms (SD: 27 ms) post-exercise and -16 ms (SD: 22 ms) at 10-min Wash-Out after the FRED exercise bout. The timing of EMG onset of the other trunk muscles was not affected by the single bout of exercise. A significant correlation was found between background activity and the EMG onset times of of TrA (r = 0.6; P < 0.001), OI (r = 0.59; P < 0.001), LES (r = 0.32; P = 0.046) and LMs (r = 0.77; P < 0.001). Higher levels of trunk muscle background activity were associated with later onset times. The present findings suggest that a single exposure to the postural training device can induce small changes in spinal muscle function in healthy pain free individuals.