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Mitochondria undergo frequent morphological changes, altering the mitochondrial network organization. Reorganization of mitochondria networks is the result of coordinated processes of mitochondrion fusion and fission, which ensures the proper distribution of mitochondria to fulfill cellular energetic requirements. Dysregulation of mitochondria fusion and fission results in bioenergetic deficiencies and/or production of damaging reactive oxygen species (Park & Choi, 2012). Changes in mitochondria network organization have been described in a variety of diseases, such as diabetes and obesity (Bach et al., 2003;Makino et al., 2010;Sebastian et al., 2012). The complexity and shape of skeletal muscle mitochondria networks is fiber type dependent. We have developed an immunohistochemical technique to perform 3D reconstructions of skeletal muscle mitochondria networks in human single muscle fibers. The results show that in type I muscle fibers mitochondria are complex interconnected tubular shaped, while in type II muscle fibers the structural organization of mitochondria network was more diverse; from individual ellipsoid mitochondrion with few connections to tubular interconnected mitochondria networks. Two percent of type I muscle fibers contained ellipsoid-shaped mitochondrion. Interestingly; in both type I and type II fibers the different morphological variants could be found within the same muscle fiber.
(2003) J Biol Chem 278, 17190-17197. Makino A, Scott BT, & Dillmann WH (2010) Diabetologia 53, 1783-1794. Park J & Choi C (2012) Commun Integr Biol 5, 81-83. Sebastian D et al. (2012) Proc Natl Acad Sci U S A 109, 5523-5528.
MITOCHONDRIAL FUNCTIONAL ADAPTATION TO EXERCISE TRAININGDela, F.
University of Copenhagen The effect of physical activity and inactivity per se on muscle mitochondrial respiratory capacity per mitochondrion in humans is largely unknown. What is well-known is the several fold increase in skeletal muscle mitochondrial content that occurs in response to (primarily) aerobic training. In this sense the respiratory capacity is enlarged, but whether there is a qualitative adaptation of mitochondrial respiration in response to training is less well studied. The effect of physical inactivity is even less studied, and given the fact that physical inactivity is associated with the prevalence of type 2 diabetes and some types of cancer and is an independent predictor of mortality, there is clearly a need. It is possible that the detrimental effects of physical inactivity are mediated through a lack of adequate muscle oxidative capacity.
ROLE OF MITOCHONDRIAL FUSION PROTEINS ON MUSCLE METABOLISMZorzano, A.
IRB Barcelona - University of Barcelona - CIBERDEM Mitochondrial fusion and fission are key processes regulating mitochondrial morphology. Mitochondrial fusion is catalyzed by Mfn1, Mfn2 and OPA1 in mammalian cells whereas mitochondrial fission is operated by Drp1, Fis1 and Mff proteins. Mfn2 protein seems to play a specifically complex role in mitochondria. It regulates mitochondrial morphology, and in addition, it also controls endoplasmic reticulum morphology and function. Mfn2 expression is exquisitely regulated in skeletal muscle. It is up-regulated in skeletal muscle response to chronic exercise and upon cold exposure. In contrast, Mfn2 is repressed in muscle from high-fat fed mice or in obese or in type 2 diabetic individuals. Changes in Mfn2 expression have a marked impact on mitochondrial metabolism. Skeletal muscles obtained from Mfn2 KO mice show a reduced respiratory control ratio, which occurs in the absence of significant changes in state 3 and state 4 oxygen consumption. Mfn2-ablated soleus muscles also show reduced glucose oxidation, and reduced expression of some OXPHOS subunits.
Additional evidence indicating that Mfn2 deficiency causes mitochondrial dysfunction comes from studies in muscle cells in culture. The content of hydrogen peroxide was also enhanced in skeletal muscle upon Mfn2 depletion or in Mfn2-silenced muscle cells. These results occurred in the presence of a normal anti-oxidant defense. Skeletal muscle Mfn2 KO mice also show susceptibility to develop insulin resistance in response to a high fat diet or to aging. In keeping with this, a defective insulin signaling is detected in Mfn2-deficient mice treated with a HFD in response to in vivo insulin administration. Mfn2 knockdown muscle cells also show an impaired capacity to respond to insulin. In all, available data indicate that Mfn2 regulates metabolism and insulin signaling in skeletal muscle, and it may contribute to the pathophysiology in obesity and type 2 diabetes.
10:20 - 11:50 Invited symposia IS-BN07 New trends in motor learning
ROBOTICS AS A TOOL TO UNDERSTAND HUMAN MOTOR LEARNING
Karlsruhe Institute of Technology In 2010 Wolpert and Flanagan gave an overview of how robotics advanced research in neuroscience. Based on this work I will focus in my talk on the question of how robotics advanced research in human motor learning and how research in the field of human motor learning could benefit from robotics in the future. In the seminal experiment of Shadmehr and Mussa-Ivaldi (1994) subjects grasped the end of a robotic device while performing 2D point-to-point reaching movements in the horizontal plane. Meanwhile the device could apply forces to the subject’s hand. Numerous experiments have shown that subjects can learn to compensate for the novel dynamics, thereby restoring their movements to normal after a short training period. This compensatory adjustment in motor output is thought to reflect a change in the neural representations related to the dynamics of the musculoskeletal system and external objects. The robotic devices used in these experiments can simulate objects with novel dynamical properties in real time (Wolpert & Flanagan, 2010). In the first part of my talk I will present the classic experimental design of motor adaptation experiments and the underlying theoretical considerations. Based on this, I will give a brief overview of current research topics and findings in the field of motor adaptation. In addition to their use in motor adaptation tasks, robotic devices could also valuable for research in other fields, such as skill acquisition in sports (Reinkensmeyer & Patton, 2009). However, the upper limb movements occurring in sports take place in 3D space. Moreover, the forces occurring during sports movements are much greater than the forces occurring in the previously described motor adaptation experiments. At the moment the relationship between motor adaptation and skill learning in sports is far from clear (Yarrow et al., 2009). In the second part of my talk I will concentrate on the topic robotics and skill learning. I will present new robotic devices that can be used to investigate skill learning in more natural movement tasks (Bartenbach et al., 2013). Based on these developments, I will present ideas on how the existing experimental designs need to be enhanced to be able to investigate skill learning with robotic devices. References Bartenbach, V., Sander, C., Pöschl, M., Wilging, K., Nelius, T., Doll, F., Burger, W., Stockinger, C., Focke, A. & Stein, T. (2013). J Neurosci Methods, 213, 282– 297. Reinkensmeyer, D. & Patton, J. (2009). Exerc Sports Sci Rev, 37(1), 43–51. Shadmehr, R. & Mussa-Ivaldi, F. (1994). J Neurosci, 14 (5), 3208–3224. Wolpert, D. & Flanagan, J. (2010). BMC Biol, 8:92. Yarrow, K., Brown, P. & Krakauer, J. (2009). Nat Rev Neurosci, 10, 585–596.
IMPLICIT MOTOR LEARNING: A NEW TREND OR AN OLD ATTRIBUTE?Masters, R.
University of Hong Kong An important distinction that arises from cognitive approaches to learning is between conscious and unconscious aspects of human behavior. Much human interaction with the environment takes place at a non-conscious level of awareness, yet humans display a pervasive tendency to acquire not only procedural knowledge but also declarative knowledge when learning motor skills. Usually, this knowledge is accrued by explicit hypothesis testing during an extended trial-and-error process of resolving a motor problem. Instructions from an agent (such as a coach) may add to the quantity of declarative knowledge that is accrued. The ability to test hypotheses and to store and manipulate information that can be used to make motor responses is made possible by the information processing capabilities of the brain. Implicit motor learning tries to discourage hypothesis testing about motor responses or to disrupt storage of information that can be used for hypothesis testing, thereby limiting the amount of declarative knowledge that is accumulated during learning. While it is unlikely that any form of human motor learning is purely implicit or explicit, implicit motor learning techniques appear to augment the role of non-conscious processes in motor performance and thus reduce potential destabilization of automatic movement by conscious thought processes.
INFLUENCE OF SLEEP ON CONSOLIDATION IN MOTOR LEARNINGVan der Werf, Y.
Netherlands Institute for Neuroscience Sleep enhances memory for learned skills. Typically, humans acquire motor skills by forming a motor memory through performance.
Motor skills can also be learnt through observation. We investigated whether sleep aids learning by action observation, and whether the enhancement of the motor memory depends on the time of observation relative to sleep. Our results show that sleep is necessary for the enhancement of a motor skill by prior observations. This effect happened only if sleep occurs within a limited time window upon observation. The results indicate that observed activity might undergo sleep-dependent re-activation leading to consolidation and subsequent enhancement of motor programs, possibly through a mechanism involving the human mirror neuron system.
10:20 - 11:50 Oral presentations OP-PM17 Neuromuscular Physiology [NP] 4
MECHANICAL PROPERTIES OF THE RECTUS FEMORIS MUSCLE IN PROFESSIONAL FOOTBALLERS FROM START TO MIDSEASONWarner, M.1, Mullix, J.1, Gimpel, M.2, Stokes, M.1 (1): Faculty of Health Sciences, University of Southampton, UK. (2): Southampton Football Club, Southampton, UK.
Introduction Quadriceps’ strain is the second most common injury in football players, accounting for 5% of all injuries (Ekstrand et al., 2011). Musculoskeletal screening tests are important to help avoid overtraining and injury (Gabbe et al., 2004). However, measurements of muscle are often made using subjective palpation and observational techniques. Novel technology enables objective measurement of tone and mechanical properties of muscle using a hand-held device (MyotonPRO), and has recently been used to examine thigh muscles in young males (Mullix et al., 2012). The present study aimed to quantify the stability of mechanical properties of the rectus femoris (RF) muscle in professional football players from start to mid-season. Method Nine English Premier League male football players (aged 22-30 years) were studied at the start and mid-way through the season. The MyotonPRO device (Myoton Ltd, London) applied brief mechanical impulses to the resting RF muscle belly on the dominant side, eliciting damped oscillations, which were recorded via the device’s accelerometer. Parameters of non-neural tone (frequency), elasticity (logarithmic decrement) and stiffness (N/m) were calculated automatically.
None of the participants suffered an injury during the study period. A paired-samples T-test assessed for statistical differences between the two testing sessions. Results There were no significant differences in the mechanical parameters tested between the start and midseason (p0.05; tone 15.9±0.6 to 15.6±0.7 Hz; stiffness 277.7±11.4 to 283.3±15.7 N/m; elasticity 1.3±0.1 to 1.3±0.2 decrement). On average there was only a -0.5% change in muscle tone, 3.4% in stiffness, with an 8.3% change in elasticity. Discussion These preliminary data suggest that the mechanical properties of the RF muscle remained constant during the first-half of a football season in players that had not suffered an injury. Monitoring changes in these parameters over the course of a season may provide an indication of injury risk.
Further studies are warranted to develop large databases of normal reference values in professional footballers and to document abnormal parameters in injured muscles. References GABBE, B., BENNELL, K. L., WAJSWELNER, H. & FINCH, C. F. 2004. Phys Ther Sport, 5, 90EKSTRAND, J., HÄGGLUND, M. & WALDÉN, M. 2011. Br J Sports Med, 45, 553-558. MULLIX, J., WARNER, M., STOKES, M. 2012. Working Papers in the Health Sciences, 1, 1-8.
METABOLIC AND NEUROMUSCULAR FATIGUE IN HEALTHY WOMEN DURING A WINGATE TESTKokova, M., Pencheva, N., Kitanoska, D.
South-West University Introduction The reasons for the anaerobic fatigue, the power limitation factors and the factors that could improve performance have been studied mostly on trained subjects. Such data on untrained subjects especially females are scarce and insufficient. The aim of this study is to evaluate the heart rate responses, blood lactate and glucose concentration changes, sEMG RMS and MPF profiles of six muscles involved in cycling as factors for the anaerobic performance and fatigue in healthy untrained women. Methods Nine women (24.0±3.4 years) performed a 30-s Wingate cycling test (load 0.075W/kg). Lactate and glucose levels were determined before and after the test. The sEMG activity of the following muscles of the right lower limb : vastus lateralis (VL), rectus femoris (RF), semitendinosus (ST),