Increased intrinsic stiffness and mineralization in femurs of adult rats after high intensity treadmill running training

Physical activity plays a tremendous role in determining bone mechanical behavior, which is superimposed to gravidity. OBJECTIVE: Compare the geometric and material responses of the rat femur to a high intensity treadmill running training of a relatively short duration, as assessed by 3-point mechanical test. METHODS: Mature male rats (180.0±30 g) were assigned (7 rats/group) to no exercise (NE) or treadmill exercise (EX). After preconditioning period, the running speed was set at 45 cm.seg−1 during 2 wks, frequency 5 d/wk, 2-hour sessions/day. Body weight and weight of the crural quadriceps were registered at euthanasia. The right femur was mechanically tested through 3-point bending. The left femur was ashed to estimate bone mineral content. Geometric and material bone properties were estimated directly or calculated by appropriate equations. RESULTS: Final body weight was 14% reduced in EX rats, while the crural quadriceps was 47% increased. Yield and fracture loads, and structural stiffness were significantly higher in the EX rats, as were the apparent elastic modulus, the bone mineral content and the degree of mineralization. Geometric properties were not affected. CONCLUSIONS: High intensity treadmill running training increases bone strength and stiffness by increasing material stiffness and mineralization, without affecting geometric bone parameters

A semiquantitative scoring tool to evaluate eccentric exercise-induced muscle damage in trained rats

Unaccustomed eccentric exercise is a welldocumented cause of exercise-induced muscle damage. However, in trained subjects muscle injury involves only light or moderate tissue damage. Since trained rats are widely used as a model for skeletal muscle injury, here we propose a semiquantitative scoring tool to evaluate muscle damage in trained rats. Twenty male Sprague-Dawley rats were trained for two weeks following a two-week preconditioning period, and randomly divided into two groups: control rats (CTL; n=5) and rats with eccentric exercise-induced muscle damage (INJ; n=15). Injured rats were sacrificed at three time points: 1, 3 and 7 days post injury (n=5 each). Transverse sections from the right soleus were cut (10 μm) and stained with haematoxylineosin. Samples were evaluated by two groups of observers (four researchers experienced in skeletal muscle histopathology and four inexperienced) using the proposed tool, which consisted of six items organised in three domains: abnormal fibre morphology, necrotic/(re) degenerating fibres (muscle fibre domain), endomysial and perimysial infiltration (inflammatory state domain) and endomysium and perimysium distension (interstitial compartment domain). We observed the expected time course in the six evaluated items. Furthermore, agreement among observers was evaluated by measuring the Intraclass Correlation Coefficient (ICC). Within the experienced group, items from the muscle fibre and interstitial compartment domains showed good agreement and the two items from the infiltration compartment domain showed excellent agreement. In conclusion, the proposed tool allowed quick and correct evaluation of light to moderate muscle damage in trained rats with good agreement between observers

Contractile activity is necessary to trigger intermittent hypobaric hypoxia-induced fiber size and vascular adaptations in skeletal muscle

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

The Effect of intermittent hypobaric hypoxia and exercise on the recovery of induced skeletal muscle damage in trained laboratory rats: performance evaluation, plasma markers and M. Soleus differential gene expression = El efecto de hipoxia hipobárica intermitente y ejercicio de la recuperación del daño muscular esquelético inducido en ratas de laboratorio entrenadas: evaluación de rendimiento, marcadores plasmáticos y expresión génica diferencial del M. Soleus

[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

Application of Near-Infrared Spectroscopy methods to functional and patophysiological alterations of skeletal muscle

<p>A project focused in new applications of NIRS technique for monitoring skeletal muscle conditions in sports and occupational medicine</p

Increased intrinsic stiffness and mineralization in femurs of adult rats after high intensity treadmill running training

Physical activity plays a tremendous role in determining bone mechanical behavior, which is superimposed to gravidity. OBJECTIVE: Compare the geometric and material responses of the rat femur to a high intensity treadmill running training of a relatively short duration, as assessed by 3-point mechanical test. METHODS: Mature male rats (180.0±30 g) were assigned (7 rats/group) to no exercise (NE) or treadmill exercise (EX). After preconditioning period, the running speed was set at 45 cm.seg−1 during 2 wks, frequency 5 d/wk, 2-hour sessions/day. Body weight and weight of the crural quadriceps were registered at euthanasia. The right femur was mechanically tested through 3-point bending. The left femur was ashed to estimate bone mineral content. Geometric and material bone properties were estimated directly or calculated by appropriate equations. RESULTS: Final body weight was 14% reduced in EX rats, while the crural quadriceps was 47% increased. Yield and fracture loads, and structural stiffness were significantly higher in the EX rats, as were the apparent elastic modulus, the bone mineral content and the degree of mineralization. Geometric properties were not affected. CONCLUSIONS: High intensity treadmill running training increases bone strength and stiffness by increasing material stiffness and mineralization, without affecting geometric bone parameters

A three-criteria performance score for rats exercising on a running treadmill.

In this study, we propose a novel three-criteria performance score to semiquantitatively classify the running style, the degree of involvement and compliance and the validity of electric shock count for rats exercising on a treadmill. Each score criterion has several style-marks that are based on the observational registry of male Sprague-Dawley rats running for 4-7 weeks. Each mark was given a score value that was averaged throughout a session-registry and resulting in a session score for each criterion, ranging from "0" score for a hypothetical "worst runner", to score "1" for a hypothetical "perfect runner" rat. We found significant differences throughout a training program, thus providing evidence of sufficient sensitivity of this score to reflect the individual evolution of performance improvement in exercise capacity due to training. We hypothesize that this score could be correlated with other physiological or metabolic parameters, thus refining research results and further helping researchers to reduce the number of experimental subjects

Contractile activity is necessary to trigger intermittent hypobaric hypoxia-induced fiber size and vascular adaptations in skeletal muscle

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

Determination of the utility of near-infrared spectroscopy in the study of exertional myalgia and chronic exertional compartment syndrome in musicians’ forearms

<p>The non-invasive and real-time near-infrared spectrometry (NIRS) has been proven to distinguish<br>between 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.</p

Contractile Activity Is Necessary to Trigger Intermittent Hypobaric Hypoxia-Induced Fiber Size and Vascular Adaptations in Skeletal Muscle

Altitude training has become increasingly popular in recent decades. Its central and peripheral effects are well-described; however, few studies have analyzed the effects of intermittent hypobaric hypoxia (IHH) alone on skeletal muscle morphofunctionality. Here, we studied the effects of IHH on different myofiber morphofunctional parameters, investigating whether contractile activity is required to elicit hypoxia-induced adaptations in trained rats. Eighteen male Sprague-Dawley rats were trained 1 month and then divided into three groups: (1) rats in normobaria (trained normobaric inactive, TNI); (2) rats subjected daily to a 4-h exposure to hypobaric hypoxia equivalent to 4,000 m (trained hypobaric inactive, THI); and (3) rats subjected daily to a 4-h exposure to hypobaric hypoxia just before performing light exercise (trained hypobaric active, THA). After 2 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 fibers; and (3) endothelial-ATPase to stain capillaries. Fibers were classified as slow oxidative (SO), fast oxidative glycolytic (FOG), fast intermediate glycolytic (FIG) or fast glycolytic (FG) and the following parameters were measured: fiber cross-sectional area (FCSA), number of capillaries per fiber (NCF), NCF per 1,000 μm2 of FCSA (CCA), fiber 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 fiber size. Compared to TNI rats, FOG fibers from the lateral/medial fields, as well as FIG and FG fibers from the lateral region, had smaller FCSA in THA rats. Moreover, THA rats had increased NCF in FG fibers from all fields, in medial and posterior FIG fibers and in posterior FOG fibers. All fiber types from the three analyzed regions (except the posterior FG fibers) 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 tested hypoxic conditions is enough to trigger a morphofunctional response that improves muscle capillarisation