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Altitude training has become increasingly popular in recent decades. Its central and peripheral effects are well-described; however, few studies have analysed the effects of intermittent hypobaric hypoxia (IHH) alone on skeletal muscle morphofunctionality. Here, we studied the effects of IHH on different myofibre morphofunctional parameters, investigating whether contractile activity is required to elicit hypoxia-induced adaptations in trained rats. Eighteen male Sprague-Dawley rats were trained one month and then divided into three groups: (1) rats in normobaria (trained normobaric inactive, TNI); (2) rats subjected daily to a 4-hour exposure to hypobaric hypoxia equivalent to 4,000 m (trained hypobaric inactive, THI); and (3) rats subjected daily to a 4-hour exposure to hypobaric hypoxia just before performing light exercise (trained hypobaric active, THA). After two weeks, the tibialis anterior muscle (TA) was excised. Muscle cross-sections were stained for: (1) succinate dehydrogenase to identify oxidative metabolism; (2) myosin-ATPase to identify slow- and fast-twitch fibres; and (3) endothelial-ATPase to stain capillaries. Fibres were classified as slow oxidative (SO), fast oxidative glycolytic (FOG), fast intermediate glycolytic (FIG) or fast glycolytic (FG) and the following parameters were measured: fibre cross-sectional area (FCSA), number of capillaries per fibre (NCF), NCF per 1,000 µm2 of FCSA (CCA), fibre and capillary density (FD and CD), and the ratio between CD and FD (C/F). THI rats did not exhibit significant changes in most of the parameters, while THA animals showed reduced fibre size. Compared to TNI rats, FOG fibres from the lateral/medial fields, as well as FIG and FG fibres from the lateral region, had smaller FCSA in THA rats. Moreover, THA rats had increased NCF in FG fibres from all fields, in medial and posterior FIG fibres and in posterior FOG fibres. All fibre types from the three analysed regions (except the posterior FG fibres) displayed a significantly increased CCA ratio compared to TNI rats. Global capillarisation was also increased in lateral and medial fields. Our results show that IHH alone does not induce alterations in the TA muscle. The inclusion of exercise immediately after the hypoxic exposure is enough to trigger a morphofunctional response that overall improves muscle capillarisation.

[eng] One of the key players in the regenerating injured skeletal muscle fibers are their surrounding satellite cells (specific stem cells), arranged between the basal lamina and the sarcolemma, in relatively few numbers per fiber. The satellite cells, which are myogenic precursor cells are activated during injury to fuse and mature into the injured fiber. Some studies have demonstrated that exercise and hypoxia facilitate the activation and migration into the blood circulation, moving more stem cells to an injured or activated area which in turn aids the repairing of the injury. The aim of this thesis was to study the regeneration profile over fourteen days after an eccentric-exercise induction of skeletal muscle damage in treadmill-trained laboratory rat, submitting them to series of daily (4 h) intermittent hypobaric hypoxia (with the simulated altitude of 4000 m) with or without the combination of light exercise as part of their rehabilitation. The rats could potentially react differently to the exercise training prior and post the induction of muscle damage, and furthermore, be differently susceptible to the injury-induction protocol, influenced by their training. This premise led to the formation of the rat AEY performance score, throughout the study, as a complementary tool for the data acquired during the injury regeneration. The regeneration was profiled four times over the recovery fourteen days from the injury induction via the concentration of myoglobin and creatine kinase (CK-MM) plasma markers and differential gene expression analysis in m. soleus, which is generally considered to be one of the most susceptible muscle to eccentric-exercise injury when running downhill. The plasma marker results indicate that the effect of the injury-induction protocol was very short lived, as after the significantly different peak concentrations for the control (passive recovery) and they hypoxia groups (sessions of intermittent hypoxia during recovery) 1 day post injury, had dropped down to basal level again 3 days post injury. However, the hypoxia+exercise group (sessions of intermittent hypoxia followed by light exercise during recovery) had a distinct profile with its slowly rising peak 3 days post injury and then dropping down again. Still, this profile was only significant for the CK-MM measurements, whilst myoglobin did not show any significant change following injury. It is clear that the hypoxia-exercise conditions cause different physiological reactions to the injury. However, the level of the injury would need to be greater in order to obtain a more significant pattern and to be able to interpret if the pattern is reflecting potentially beneficial effects or not. The differential gene expression analysis also indicates that the injury induction needed to have been greater to achieve differential expression. The hypoxia and hypoxia+exercise profiles are not parallel to each other, still the data also suggest that the hypoxia sessions could have been more effective. Therefore, it is difficult to give a general conclusion to which hypoxia or hypoxia+exercise facilitate the injury regeneration to a higher degree. The certain fact is that there are ethical and humane factors that need to be respected, but limit the margin of how the injury-induction can be carried out in the way it was done in this study., [spa] Uno de los actores clave en la regeneración de fibras musculares esqueléticas dañadas son las células satélite circundantes (células madre específicas), dispuestos entre la lámina basal y el sarcolema, en relativamente pocos números por fibra. Las células satélite, que son células precursoras miogénicas se activan durante lesión para fusionar y madurar en la fibra heridos. Algunos estudios han demostrado que el ejercicio y la hipoxia facilitan la activación y la migración en la circulación sanguínea, moviéndose más células a un área lesionada o activados que a su vez ayuda a la reparación de la lesión del tallo. El objetivo de esta tesis fue estudiar el perfil de regeneración más de catorce días después de una inducción excéntrico ejercicio de daño muscular esquelético en ratas de laboratorio caminadora entrenados, sometiéndolos a la serie de diario (4 h) la hipoxia hipobárica intermitente (con la altitud simulada de 4000 m), con o sin la combinación de ejercicio ligero, como parte de su rehabilitación. Las ratas podrían potencialmente reaccionan de manera diferente a la práctica de ejercicio, previa y la inducción de daño muscular, y además, ser diferente susceptible al protocolo de inducción de lesiones, influenciado por su formación. Esta premisa conducía a la creación de la puntuación de rendimiento AEY de las ratas a lo largo del estudio, como una herramienta complementaria para los datos adquiridos durante la regeneración de la lesión. La regeneración se perfila cuatro veces en los catorce días de recuperación de la inducción de lesiones a través de la concentración de mioglobina y la creatina quinasa (CK-MM) marcadores de plasma y análisis de la expresión diferencial de genes en m. sóleo, que generalmente se considera ser uno de el músculo más susceptibles a las lesiones excéntrica-ejercicio cuando se ejecuta cuesta abajo. Los resultados de los marcadores de plasma indican que el efecto del protocolo de la lesión de la inducción fue muy corta duración, ya que después de las muy diferentes concentraciones máximas para el control (recuperación pasiva) y la hipoxia grupos (sesiones de hipoxia intermitente durante la recuperación) después de la lesión de 1 día, había caído hasta el nivel basal de nuevo 3 días después de la lesión. Sin embargo, el grupo de hipoxia + ejercicio (sesiones de hipoxia intermitente seguido de ejercicio ligero durante la recuperación) tenía un perfil distinto con su pico lento aumento de 3 días después de la lesión y luego de descender de nuevo. Sin embargo, este perfil sólo fue significativa para las mediciones de CK-MM, mientras que la mioglobina no mostró ningún cambio significativo después de una lesión. Es evidente que las condiciones de hipoxia de ejercicio causan diferentes reacciones fisiológicas a la lesión. Sin embargo, el nivel de la lesión tendría que ser mayor con el fin de obtener un patrón más significativa y para ser capaz de interpretar si el patrón está reflejando efectos potencialmente beneficiosos o no. El análisis de la expresión diferencial de genes también indica que la inducción de lesiones necesario haber sido mayor para lograr la expresión diferencial. Los perfiles de la hipoxia y la hipoxia + ejercicio no son paralelas entre sí, siendo los datos también sugieren que las sesiones de hipoxia podría haber sido más eficaz. Por lo tanto, es difícil dar una conclusión general a la que la hipoxia o hipoxia + ejercicio facilitan la regeneración lesión a un grado superior. El hecho cierto es que hay factores éticos y humanos que necesitan ser respetado, pero limitan el margen de cómo la lesión de la inducción puede llevarse a cabo en la forma en que se llevó a cabo en este estudio.

The non-invasive and real-time near-infrared spectrometry (NIRS) has been proven to distinguishbetween individuals with chronic exertional compartment syndrome (CECS) and healthy individuals based on a significantly lower tissue oxygenation index (TOI) or tissue saturation index (TSI), during exercise provocation. The use of abnormal Intracompartmental pressure values remain as the most solid method to diagnose individuals as CECS. However, supposedly healthy individuals with CECS-like criteria in terms of abnormal ICP values are harder to distinguish and require further looking into each patient's medical history. In addition, as the nature of the method is quite prone to cause discomfort in subjects and is not risk-free, an alternative methodology that causes less discomfort and is less time consuming may be preferable. Our results reinforce the real-time NIRS measurement as being a fair non-invasive replacement for direct ICP measure to detect CECS indirectly, focusing on the TOI trace.

NIRS measurements are a suitable way to studythe muscle's oxygenation profile during exerciseand acute exposure to high altitude in a hypoxicchamber. At 5000 m, the range of variation of muscleoxygen extraction (during the entire exerciseprotocol) was about 50% less compared to sea levelmeasurements. The fact that the total peripheral resistance reaches a plateau whilst the local oxygen extraction increases more readily, indicates that the main limiting factor for oxygen delivery in active muscle at high altitude is the low oxygen saturation in arterial blood rather than local capacity for vasodilation.

The main technical limitation of the real time NIRS in vivo measurement is the difficulty in obtaining a calibrated scale for quantification purposes, because a zero setting is impossible to reach under physiological conditions. A lower arm exercise during the occlusion allows the lowest O2-Hb level to be reached as quickly as possible without causingexcessive discomfort due to the pressure exertion. Once the plateau is evident the exerted pressure is relieved. Although this is a rough estimate of the absolute concentration levels of O Hb and HHb, it still gives us a more accurate description of the dynamic changes of the oxygen supply at tissular level. The ischemic arrest is not a new method to evaluate the lowest O2-Hb concentration, but in order to map the oxygenation profile in a detailed way; we propose some alterations to this technique.

We describe the usefulness of NIRS technology in order to the non-invasive diagnosis of chronic exertional compartment syndrome (CECS).

ELISA tests on plasma were used as a rapid method to determine the existence of muscle damage in trained rats. Myoglobin in plasma showed a different dynamics in the active recovery group, perhaps indicating a different degree of injury in theoxidative fibres. However, the CK level might not be the best representative parameter to accurately evaluate the actual level of the muscle damage produced.

Intermittent hypobaric hypoxia and light aerobic exercise could be beneficial for a skeletal muscle damage recovery. Rats combining hypoxic exposure and light runing for 15 minutes showed a higher increase of haematopoietic stem cells inthe peripheral blood after muscle damage.

An intermittent protocol of cyclic breaking bouts at distinct submaximal intensity of the maximal voluntary contraction does not reflect any significant changes in order to differentiate between the control group and the group of the professional motorcyclist, in terms of the TSI% value, or the other traces, separately. We feel that several trial and error measurements for developmental purposes, will eventually give us a good map for oxygenation profiling as it is not yet explored to its potential advantages.

In rat soleus muscle, a recuperation programme of IHH combined with light exercise seems to induce a fasterrecovery of the mean muscle fibres size and a significant decrease in the percentage of abnormal fibres, without affecting neither the percentage of fibre types nor the fibre shape.