Neuromuscular adaptations in football athletes with prior history of hamstring strain injury

Background: Hamstring strain injuries (HSI) are one of the most common injuries in a wide variety of running-sports, resulting in a considerable loss of competition and training time. One of the most problematic consequences regarding HSI is the recurrence rate and its non-decrease over the past decades, despite increasing evidence. Recent studies also found several maladaptations post-HSI probably due to neuromuscular inhibition and it has been proposed that these adaptations post-injury may contribute as risk factors for the injury-reinjury cycle and high recurrence rates. Furthermore it has been recently proposed not to disregard the inter-relationship between these adaptations and risk-factors post-injury in order to better understand the mechanisms of this complex injury. Objective: To determine, analyze and correlate neuromuscular adaptations in amateur football players with prior history of HSI per comparison to uninjured athletes in similar conditions. Methodology: Every participant was subjected to isokinetic concentric (60 and 240deg.sec) and eccentric (30 and 120deg.sec¯¹) testing, and peak torque, angle of peak torque and hamstrings to quadriceps (H:Q) conventional ratios were measured, myoelectrical activity of Bicep Femoris (BF) and Medial Hamstrings (MH) were also measured during isokinetic eccentric testing at both velocities and muscle activation percentages were calculated at 30, 50 and 100ms after onset of contraction. Furthermore active and passive knee extension, knee joint position sense (JPS) test, triple-hop distance (THD) test and core stability (flexors and extensors endurance, right and left side bridge test) were used and correlated. Results: Seventeen players have participated in this study: 10 athletes with prior history of HSI, composing the Hamstring injury group (HG) and 7 athletes without prior severe injuries as control group (CG). We found statistical significant differences between HG injured and uninjured sides in the BF myoelectrical activity at almost all times in both velocities and between HG injured and CG non-dominant sides at 100ms in eccentric 120deg.sec¯¹ velocity (p<.05). We found no differences in MH activity. Regarding proprioception we found differences between the HG injured and uninjured sides (p=.027). We found no differences in the rest of used tests. However, significant correlation between myoelectrical activation at 100ms in 120deg.sec¯¹ testing and JPS with initial position at 90º (r-.372; p=0.031) was found, as well as between isokinetic H:Q ratio at 240deg.sec and THD score (r=-.345; p=.045). Conclusion: We found significant differences that support previous research regarding neuromuscular adaptations and BF inhibition post-HSI. Moreover, to our knowledge, this was the first study that found correlation between these adaptations, and may open a door to new perspectives and future studies.

Control of uncertain compartmental systems

Os sistemas compartimentais são frequentemente usados na modelação de diversos processos em várias áreas, tais como a biomedicina, ecologia, farmacocinética, entre outras. Na maioria das aplicações práticas, nomeadamente, aquelas que dizem respeito à administração de drogas a pacientes sujeitos a cirurgia, por exemplo, a presença de incertezas nos parâmetros do sistema ou no estado do sistema é muito comum. Ao longo dos últimos anos, a análise de sistemas compartimentais tem sido bastante desenvolvida na literatura. No entanto, a análise da sensibilidade da estabilidade destes sistemas na presença de incertezas tem recebido muito menos atenção. Nesta tese, consideramos uma lei de controlo por realimentação do estado com restrições de positividade e analisamos a sua robustez quando aplicada a sistemas compartimentais lineares e invariantes no tempo com incertezas nos parâmetros. Além disso, para sistemas lineares e invariantes no tempo com estado inicial desconhecido, combinamos esta lei de controlo com um observador do estado e a robustez da lei de controlo resultante também é analisada. O controlo do bloqueio neuromuscular por meio da infusão contínua de um relaxante muscular pode ser modelado como um sistema compartimental de três compartimentos e tem sido objecto de estudo por diversos grupos de investigação. Nesta tese, os nossos resultados são aplicados a este problema de controlo e são fornecidas estratégias para melhorar os resultados obtidos.

Mitochondrial plasticity in pathophysiological conditions

Both skeletal and cardiac muscles daily burn tremendous amounts of ATP to meet the energy requirements for contraction. So, it is not surprising that the maintenance of mitochondrial morphology, number, distribution and functionality in striated muscle are important for muscle homeostasis. In these tissues mitochondria present the added dimension of two populations, the intermyofibrillar (IMF) and the subsarcolemmal (SS) mitochondria, being IMF the most abundant one. In the present thesis, the molecular mechanisms harboured in mitochondria of striated muscles were studied using animal models, to better comprehend the role of mitochondrial plasticity in several pathophysiological conditions such as aging, diabetes mellitus and bladder cancer. The comparative analysis of IMF and SS populations isolated from heart evidenced a higher respiratory chain activity of mitochondria interspersed in the contractile apparatus. The higher susceptible of SS respiratory chain complexes subunits to carbonylation, but not to nitration, seems to justify the lower respiratory chain activity observed in this mitochondrial population. Our results showed that in heart from aged mice there is an accumulation of dysfunctional mitochondria. The age-related decrease of oxidative phosphorylation activity seems to be justified, at least partially, by the increased proneness of mitochondrial proteins as OXPHOS subunits and MnSOD to oxidative modifications. Moreover, a sedentary lifestyle seems to worsen the functional consequences of aging in heart by increasing mitochondrial proteins susceptibility to nitration. In skeletal muscle from rats with type 1 diabetes mellitus induced by streptozotocin administration, we verified the accumulation of dysfunctional mitochondria due, at least in part, to the impairment of PQC system. Indeed, the decreased activity of AAA proteases was accompanied by the accumulation of oxidatively modified mitochondrial proteins with impact in respiratory chain activity. The diminishing of mitochondria activity also underlies cancer-induced muscle wasting. Indeed, using a rat model of chemically induced urothelial carcinoma we verified that the loss of gastrocnemius mass was related to mitochondrial dysfunction due to, at least partially, the down-regulation of PQC system involving the mitochondrial proteases paraplegin and Lon. PQC impairment resulted in the accumulation of oxidatively modified mitochondrial proteins. In overall, regardless the pathophysiological stimuli that promote mitochondrial alterations, there are similarities in the pattern of disease-related mitochondrial plasticity. The diminished capacity for ATP production in striated muscle seems to be due to increased oxidative damage of mitochondrial proteins, namely subunits of respiratory chain complexes, metabolic proteins and MnSOD. Our data highlighted, for the first time, the impact of mitochondrial PQC system impairment in the accumulation of oxidized proteins, exacerbating the dysfunction of this organelle in striated muscle in several pathophysiological conditions.

A ingerência do conhecimento explícito no conhecimento tácito: a técnica Alexander e a prática e ensino da flauta

O presente trabalho é o resultado duma investigação heurística sobre os efeitos do estudo da Técnica Alexander (TA) na prática e no ensino da flauta. Submeti-me a uma centena de aulas de Técnica Alexander e procedi a uma análise reflexiva da minha aprendizagem e prática individual e pedagógica, registando a sua evolução através da progressiva incorporação dos princípios e metodologias daquela técnica. A primeira parte descreve os princípios e procedimentos da TA enquadrando-a na problemática das relações entre conhecimento tácito e explícito, nos processos de controlo motor voluntário e involuntário, e na eficácia e eficiência dos automatismos neuromusculares. A segunda parte constitui a descrição e análise do processo transformador catalisado pelo estudo da TA: modificações na coordenação muscular; na técnica respiratória; no empunhar da flauta e na preparação para a emissão da primeira nota, e na relação entre o equilíbrio do instrumento e o movimento dos dedos. Vários procedimentos e exercícios desenvolvidos para a resolução de problemas pessoais são apresentados justificando a sua eficácia. A TA não proporciona apenas alterações na coordenação muscular mas pode modificar os processos mentais. Por isso alguns princípios para uma organização eficiente da prática são discutidos e concretizados nalguns exercícios que promovem maior variabilidade, alternância entre análise e integração e clareza na concepção do gesto técnico-musical. Por último, a evolução da minha abordagem pedagógica, incorporando procedimentos inspirados na TA e desenvolvidos ao longo da investigação são ilustrados com alguns alunos. A tese argumenta que a TA pode desempenhar um papel fundamental na melhoria do desempenho dum músico e revela-se uma ferramenta pedagógica que merece ser explorada mais sistematicamente num ensino mais baseado numa experimentação guiada que promova uma maior autoconsciência dos processos neuromusculares do que na instrução prescritiva e explícita.