Neural contributions to maximal muscle performance

Neural activation is thought to be essential for the expression of maximal muscle performance, but the exact contribution of neural mechanisms such as the level of agonist, antagonist and stabiliser muscle activation to muscle strength is not fully understood. Explosive neuromuscular performance, including the ability to initiate (the electromechanical delay, EMD) and develop force rapidly (termed, rate of force development, RFD) are considered essential for the performance of explosive sporting tasks and joint stabilisation and thus injury avoidance. The thesis aimed to improve our understanding of the contribution of neural factors to muscle performance, with a specific focus on explosive neuromuscular performance. The work in this thesis utilised a range of approaches to achieve this aim. Initially, the association between muscle activation and rate of force development and EMD was established. Comparison of unilateral and bilateral actions was then undertaken. Finally interventions with the aim to both negatively affect and improve muscle strength, which included fatigue and resistance training (RT), respectively was undertaken and the neural contributions to changes in performance established. Agonist activation during the early phase of voluntary force production was shown to be an important determinant of voluntary EMD, explaining 41% of its inter-individual variability. Agonist activation was an important determinant of early, but not late phase RFD. Use of bilateral actions resulted in a reduction in explosive strength, which was thought to be due to differences in postural stability between unilateral and bilateral strength tasks. The level of stabiliser activation was strongly related to the level of agonist activation during the early phase of explosive force development and had a high association with explosive force production. Task-specific adaptations following isoinertial RT, specifically, the greater increase in isoinertial lifting strength than maximal isometric strength were due to training-specific changes in the level of agonist activation. High-intensity fatigue achieved a more substantial decline in explosive than maximal isometric strength, and this was postulated to be due to neural mechanisms, specifically decreased agonist activation. This work provides an in depth analysis of the neural contributions to maximal muscle performance

Bilateral deficit in explosive force production is not caused by changes in agonist neural drive

Bilateral deficit (BLD) describes the phenomenon of a reduction in performance during synchronous bilateral (BL) movements when compared to the sum of identical unilateral (UL) movements. Despite a large body of research investigating BLD of maximal voluntary force (MVF) there exist a paucity of research examining the BLD for explosive strength. Therefore, this study investigated the BLD in voluntary and electrically-evoked explosive isometric contractions of the knee extensors and assessed agonist and antagonist neuromuscular activation and measurement artefacts as potential mechanisms. Thirteen healthy untrained males performed a series of maximum and explosive voluntary contractions bilaterally (BL) and unilaterally (UL). UL and BL evoked twitch and octet contractions were also elicited. Two separate load cells were used to measure MVF and explosive force at 50, 100 and 150 ms after force onset. Surface EMG amplitude was measured from three superficial agonists and an antagonist. Rate of force development (RFD) and EMG were reported over consecutive 50 ms periods (0–50, 50–100 and 100–150 ms). Performance during UL contractions was compared to combined BL performance to measure BLD. Single limb performance during the BL contractions was assessed and potential measurement artefacts, including synchronisation of force onset from the two limbs, controlled for. MVF showed no BLD (P = 0.551), but there was a BLD for explosive force at 100 ms (11.2%, P = 0.007). There was a BLD in RFD 50–100 ms (14.9%, P = 0.004), but not for the other periods. Interestingly, there was a BLD in evoked force measures (6.3–9.0%, P,0.001). There was no difference in agonist or antagonist EMG for any condition (P$0.233). Measurement artefacts contributed minimally to the observed BLD. The BLD in volitional explosive force found here could not be explained by measurement issues, or agonist and antagonist neuromuscular activation. The BLD in voluntary and evoked explosive force might indicate insufficient stabiliser muscle activation during BL explosive contractions

Recommendations for Plyometric Training after ACL Reconstruction – A Clinical Commentary

This paper presents a four-stage plyometric program to be undertaken as part of criterion-based rehabilitation for athletes with anterior cruciate ligament reconstruction (ACLR). After ACLR, the patient experiences alterations of joint mobility, gait and movement patterns, neuromuscular function and general physical fitness. Plyometric training is an important component for neuromuscular and movement re-conditioning after ACLR. Effective use of plyometrics can support enhancements in explosive sporting performance, movement quality and lower risk of injury. Plyometric training, as a component of the ACL functional recovery process, can aid in restoring function and supporting timely return to sport. However, few patients undertake or complete a plyometric program prior to return-to-sport. To truly impact individual patients, a stronger focus on research implementation is needed from researchers to translate efficacious interventions into practice. In designing a plyometric program, it is important to match the specific plyometric tasks to the functional recovery status of the ACLR patient. To do this, it is important to understand the relative intensity of plyometrics tasks, align these tasks to the ACL functional recovery process and monitor the athlete as part of criterion based rehabilitation. Plyometric intensity is based on the intensity of efforts, the vertical and/or horizontal momentum prior to ground contact, the ground contact time and the surface or environment on which they are performed on/in. Furthermore, how the person technically performs the task will influence joint loading. There should be a gradual increase in task intensity and specificity throughout the program, with all tasks used for both neuromuscular and motor control re-conditioning. The aim of this paper is to provide recommendations to clinicians on how to design and implement plyometric training programs for the ACLR patient, as part of the functional recovery process

The High Temperature Gas-cooled Reactor: Safety considerations of the (V)HTR-Modul

Nuclear energy production is a recent technology. The first nuclear reactor demonstrating the feasibility of a sustained and controlled chain reaction was built in Chicago in 1942. In 1957, a nuclear reactor produced electricity for the first time. For the past 60 years, since then a significant technological progress has been achieved. Three generations of nuclear reactors have been successively developed and a fourth is currently being developed, demonstrating the constant progress and technical and industrial vitality of nuclear energy. The technology is mature, with approximately 450 nuclear reactors currently providing 17% of the world’s electricity, without greenhouse gas emissions. It must also be stressed that the technological progress and innovations achieved or currently being developed are all based on the same fundamental physical principles of nuclear fission, whose feasibility was demonstrated some 70 years ago. Heavy nuclides, like uranium, plutonium or thorium are fissioned by neutrons and release heat within the fuel material confining the radioactivity. This heat is extracted while simultaneously cooling the fuel by circulating a coolant (water in current European light water reactors). The heat recovered is used to run a turbine and a generator, which produces electricity. A lot of effort has been invested in international cooperation to define goals for the nuclear energy systems of the future, and also select the key technologies for achieving them. The effort has been made primarily through the Generation IV International Forum (GIF) that the American Department of Energy has initiated in 2000. The technology roadmap, developed by GIF is the starting point to identify and organize research and development of the new generation of reactors to be built around 2030 to 2040. To do so, 4 goals have been defined. Each of the systems comprises a nuclear reactor, an energy conversion system and the necessary fuel cycle, fuel manufacturing, spent fuel and final waste management equipment. The 4 major goals: • Sustainability • Economics • Safety and reliability • Proliferation Resistance and physical protection have been separated out into fifteen criteria and twenty-four performance indicators or metrics. A final selection criterion was the degree of technological innovation in the candidate systems – which provides an excellent grounds for wide-reaching international cooperation – and the possible spin-offs for the other nuclear systems, or for the current or next generation of nuclear reactors. The following six systems deemed the most promising at the end of this evaluation exercise were called on to rally Forum cooperation on development work starting from 2004: • VHTR - Very High-Temperature Reactor system, over 1,000 °C, helium-cooled, dedicated to hydrogen production or hydrogen/electricity cogeneration; • GFR - Gas-cooled Fast Reactor system – Helium-cooled fast reactor; • SFR - Sodium-cooled Fast Reactor system; • SCWR - SuperCritical Water-cooled Reactor system; • LFR - Lead-cooled Fast Reactor system – Lead or Pb-Bi alloy-cooled Fast reactor; • MSR - Molten Salt Reactor. VHTR scored very well with the exception concerning sustainability because of its open fuel cycle, which requires reprocessing to increase sustainability. From a technological point of view the VHTR is a further development of the High Temperature Reactor (HTR) which has been developed in the years from 1960 to 2001. Two basic fuel element designs of the HTR have been developed and implemented, one in Germany, the other in USA. The main characteristic of the German design is the conditioning of compacted microparticles in a graphite matrix in the form of 60-mm diameter spheres. They are continuously inserted in and extracted from the reactor at a rate of one pebble approximately every 20 seconds. When a pebble reaches its maximum depletion rate, it is replaced with a new one. The first German HTR was the AVR built at the Jülich research centre. This centre has maintained very high competence in this technology. The AVR set new records (for HTRs) in terms of performance and operating duration. Its construction began in 1961. It was connected to the electric power network in 1966 (15 MWel) and shut down in 1988. It served as an experimental platform for fuel technology development within the scope of cooperation between the Jülich research centre and NUKEM, the fuel industrial manufacturer still considered as a reference today. The core temperature of 850 °C at the start of operation was increased to 950 °C. The steel pressure vessel design served to achieve design transients (e.g., core cooling loss) that contributed to validating the safety concepts applied in this type of reactor. The AVR showed the viability of the pebble bed concept and demonstrated its reliability through physical tests for which the plant was not initially designed. A loss of coolant flow without scram was simulated in 1970, and a loss of coolant transient was also achieved prior to final shutdown. The fuel has undergone significant developments and improvements at the Jülich research centre, in partnership with NUKEM (manufacturer). The second HTR built in Germany was the THTR-300 (Thorium High-Temperature Reactor), which went critical in 1983. This was a 300 MWel commercial reactor with a concrete vessel, built by Brown Boveri. The operation of the THTR was marked by a number of technical problems that did not seem impossible to overcome. In particular, a planned inspection in 1988 revealed the rupture of a number of bolts securing hot duct insulation plates which, combined with an unfavourable political context, led to the decision to permanently decommission the facility in 1989 after only 423 equivalent full power days The American family differs from the German family mainly in terms of core and fuel organization. The core is composed of prismatic graphite blocks containing the fuel compacts. The first commercial implementation was Peach Bottom (40 MWel), which went critical in early 1966 and was shut down in 1974. After the discovery of an increasing number of fuel cladding ruptures, a second core was fabricated using a more advanced technology improving the quality of the first porous graphite layer and the characteristics of successive layers. 93% availability was achieved during irradiation of this second core, and reactor coolant system activity remained extremely low, indicating the excellent quality of the new fuel. The reactor subsequently operated without major problems and was shut down for economic reasons. The second implementation was Fort Saint-Vrain (330 MWel), whose construction began in 1968 and which went critical in 1974. Its operation was marked by technical problems (namely accidental water ingress in the reactor coolant system causing accelerated corrosion of steel components and poor availability) and it was finally decommissioned in 1989. Despite the negative functional aspects of its operation, the excellent leak-tightness of the fuel elements led to very positive radiological results for operation and maintenance activities, with the exception of tritium releases due to water leaks. On the whole, the operating experience from German and American prototypes has largely confirmed the technical expectations regarding HTRs, i.e.: • Very good behaviour of the particle fuel under irradiation, even at high temperatures, and low release of fission products in the coolant gas providing very clean reactors; • Possibility of using high-temperature helium as coolant gas; • Easy control, high thermal inertia and significant operating safety margins (demonstrated at real scale with the AVR). The impact of the Three Mile Island accident and the excellent safety characteristics of HTRs (thermal inertia, good apparent core conductivity, low power density) have led to research on configurations allowing completely passive residual power evacuation. Low-power HTRs are particularly well suited to satisfy this new passive safety requirement, like the concept of the German HTR Modular reactor which has been developed by Siemens-Interatom. This 80 MWel reactor uses the radiating capacity of a metal vessel to ensure passive cooling of the fuel, whose temperature remains below 1600 °C regardless of accident conditions. This reactor was never build, but a detailed design has been completed and some licensing issues have been solved. HTR reactors like the HTR Modul with an electric power of 100 to 300 MWel set the trend of current design, whilst in current European research projects cogeneration is in favour of electricity generation.JRC.G.I.4-Nuclear Reactor Safety and Emergency Preparednes

Systematic Video Analysis of Anterior Cruciate Ligament Injuries in Professional Male Rugby Players: Pattern, Injury Mechanism, and Biomechanics in 57 Consecutive Cases

Background: Anterior cruciate ligament (ACL) injuries represent a significant burden to rugby players. Improving our understanding of the patterns and biomechanics that result in ACL injury may aid in the design of effective prevention programs. Purpose: To describe, using video analysis, the mechanisms, situational patterns, and biomechanics of ACL injuries in professional rugby matches. Further aims were to document injuries according to pitch location and timing within the match. Study Design: Case series; Level of evidence, 4. Methods: A total of 62 ACL injuries were identified in players of the 4 most important rugby leagues across 4 consecutive seasons. We analyzed 57 (92%) injury videos for injury mechanism and situational patterns; biomechanical analysis was performed on indirect and noncontact ACL injuries only (38 cases available). Three reviewers independently evaluated each video. Results: More injuries occurred while attacking than defending (41 [72%] vs 16 [28%]; P <.01). Regarding mechanism, 18 (32%) injuries were direct contact; 15 (26%), indirect contact; and 24 (42%), noncontact. Most direct contact injuries involved being tackled directly to the knee (n = 10). Three situational patterns were identified for players who had a noncontact or indirect contact injury: offensive change of direction (COD) (n = 18), being tackled (n = 10), and pressing/tackling (n = 8). Injuries generally involved a knee-loading strategy in the sagittal plane, which was accompanied by knee valgus loading in most cases (94%). Overall, 73% of injuries occurred during the first 40 minutes of effective playing time. Conclusion: Most ACL injuries in professional male rugby players happened through a noncontact or indirect contact mechanism (68%). Three situational patterns were described, including offensive change of direction, being tackled, and pressing/tackling. Biomechanical analysis confirmed a multiplanar mechanism, with a knee-loading pattern in the sagittal plane accompanied by dynamic valgus. As most injuries occurred in the first 40 minutes, accumulated fatigue appears not to be a major risk factor for ACL injury

Scientific Assessment in support of the Materials Roadmap enabling Low Carbon Energy Technologies: Technology Nuclear Energy

This scientific assessment serves as the basis for a materials research roadmap for the nuclear fission technology, itself an integral element of an overall "Materials Roadmap Enabling Low Carbon Technologies", a Commission Staff Working Document published in December 2011. The Materials Roadmap aims at contributing to strategic decisions on materials research funding at European and Member State levels and is aligned with the priorities of the Strategic Energy Technology Plan (SET-Plan). It is intended to serve as a guide for developing specific research and development activities in the field of materials for energy applications over the next 10 years. This report provides an in-depth analysis of the state-of-the-art and future challenges for energy technology-related materials and the needs for research activities to support the development of nuclear fission technology both for the 2020 and the 2050 market horizons. It has been produced by independent and renowned European materials scientists and energy technology experts, drawn from academia, research institutes and industry, under the coordination the SET-Plan Information System (SETIS), which is managed by the Joint Research Centre (JRC) of the European Commission. The contents were presented and discussed at a dedicated hearing in which a wide pool of stakeholders participated, including representatives of the relevant technology platforms, industry associations and the Joint Programmes of the European Energy Research Associations.JRC.F.4-Safety of future nuclear reactor

Reliability and validity of a low-cost portable force platform

BACKGROUND: A small, portable, inexpensive FP is a helpful test instrument in many strength and conditioning settings. OBJECTIVE: To assess the reliability and validity of a portable FP. METHODS: The FP was assessed statically for linearity and regionality using known weights and known weight placements across nine regions. Dynamic assessment was conducted by placing the FP on a laboratory-grade one-dimensional FP and performing static jumps, countermovement, and drop jumps with synchronized data acquisition. Frequency response of the FP was assessed by striking the top surface with a hammer. RESULTS: Excellent static linearity (r> 0.99), trivial differences in regional forces, excellent correlation between FPs in the static, countermovement, and anchored FP for the drop jump (all r> 0.98) were observed. Frequency response from an impact was poor when the FP was not anchored. However, once anchored the FP showed a dominant frequency of more than 10 times the typical jump frequencies and excellent synchrony with the laboratory FP (r> 0.98). CONCLUSION: The FP showed good to excellent characteristics in the static and countermovement jumps and the drop jumps when anchored. The primary limitation of the FP is its small size and light weight

Can off-field ‘brains’ provide a competitive advantage in professional football?

‘Working-fast and working-slow’ in sport describes the concept that practice and research can be integrated to improve high-performance outcomes and enhance professional practice.1 ‘Working-fast’ is the task of the fast-thinking, intuitive practitioner operating on ‘the ground’ at a frenetic pace, interacting with coaches and athletes, and delivering the daily preparation programme. ‘Working-slow’ is key for the team's deliberate, focused researcher acting as the resident sceptic, operating behind the scenes on tasks that the ‘fast-practitioner’ may not have time and/or skills to undertake. Such hidden, but important, tasks include determining measurement noise/error in performance tests, establishing proof of concept for new ideas and ensuring validity of methods. Embedding research into the fast environment of high-performance football may provide a competitive advantage using ethical and evidence-based methods.