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The purpose of this study was to display increase in eccentric hamstring strength after 10-weeks training program. Secondly, if such an increase occurred, would this strength change result in altered landing kinetics and improved jumping performance? 27 recreational female athletes assigned into experimental (n = 14) and control (n = 13) groups. Baseline measures of landing kinetics were collected using a force plate, strength data and proprioceptive measurements were evaluated using an isokinetic dynamometer and vertical jump performance were determined by a jumping mat. Results indicated that NHST group increased their eccentric hamstring strength after eccentric strength training program (week-1 = 233.6&plusmn / 27.5, week-10 = 253.8&plusmn / 28.4 Nm/kgbw / p&lt / .05). The results demonstrated that there were significant differences in landing mechanics for NHST group. PVGRF (week-1 = 6.2&plusmn / 0.9, week-5 = 5.3&plusmn / 0.9 / p&lt / .05), PAPGRF (week-1 = 1.1&plusmn / 0.2 &amp / week-10 = 0.8&plusmn / 0.3 / p&lt / .05) and APImp results demonstrated significant differences in trained group (week-1 = 78.1&plusmn / 13.6 &amp / week-10 = 67.8&plusmn / 9.2 / p&lt / .05). NHST group exhibited significant increase in vertical jumping ability (week-1 = 0.25&plusmn / 0.0 &amp / week-10 = 0.27&plusmn / 0.0 cm / p&lt / .01). This study supported the following points: 1) increases in the eccentric hamstring strength were evident after NHST program, 2) the increases in isokinetic strength were sufficient to cause alterations in landing kinetics to decrease the applied joint forces, so the NHST program would be an influential factor in decreasing the lower extremity injuries, and 3) the increase in the efficiency of force transfer at the final take off phase of jumping contributed to a higher performance in vertical jump.

This study determined if insulin resistance (IR), induced by an acute bout of eccentrically-biased contractions that resulted in muscle injury, was attenuated following a repeated bout of contractions. Female subjects (n = 10, age 24.7 ± 3.0 yr, weight 64.9 ± 7.4 kg, height 1.67 ± 0.02 m, body fat 29.1 ± 1.9 %) performed two 30 minute bouts of downhill treadmill running (DTR 1 and DTR 2, -12 % grade, 8.0 mph) separated by 14 days. Oral glucose tolerance tests (OGTT) were administered at baseline and 48 hours following DTR 1 and DTR 2, with IR assessed by calculation of insulin and glucose areas under the curve (AUC). Maximum isometric quadriceps strength (MVC), muscle soreness (SOR), and serum creatine kinase (CK) were assessed pre-, immediately post-, and 48 hours post-DTR 1 and DTR 2 to determine the presence of muscle injury. Compared to baseline OGTT, insulin and glucose AUC (37.6 ± 8.4 and 21.4 ± 4.7 % increase, respectively), and peak insulin (44.1 ± 5.1 vs. 31.6 ± 4.0 uU·mL-1) and glucose (6.5 ± 0.4 vs. 5.5 ± 0.4 mmol·L-1) were elevated following DTR 1. These same insulin and glucose measures showed no increase above baseline 48 hours following DTR 2 (p > 0.05). MVC was reduced to a greater degree immediately following DTR 1 (16.7 ± 2.6 vs. 8.6 ± 1.2 % decline) and, although demonstrating a significant degree of recovery, remained reduced by 9.4 ± 2.7 % 48 hours following exercise. In contrast, MVC made a full recovery back to baseline values 48 hours after DTR 2. SOR was elevated to a greater degree 48 hours following DTR 1 than after DTR 2 (48.08 ± 6.16 vs. 12.70 ± 3.24 mm). There was a tendency for an attenuated serum CK response 48 hours following DTR 2 (812.8 ± 365.1 vs. 162.5 ± 42.5 U·L-1, p = 0.08). In conclusion, a novel bout of eccentrically-biased contractions resulting in a moderate degree of muscle injury confers a protective effect, whereby a subsequent bout of contractions 14 days later results in complete elimination of the IR observed following the initial bout.

Neįprasti didelio intensyvumo (ypač ekscentriniai) raumenų susitraukimai gali sukelti raumenų pažaidą (Yanagisawa et al., 2011; Neme et al., 2013), kuri pasireiškia sumažėjusia raumenų susitraukimo jėga Byrne et al., 2004; Skurvydas et al., 2010) miofibrilių Z linijos morfologiniais pokyčiais (Feasson et al., 2002), baltymų ištekėjimu iš pažeistų raumens skaidulų, raumenų skausmu, patinimu ir padidėjusiu standumu (Malisoux et al., 2006; Chen et al., 2013). Pažaida dažna pradėjus intensyviai treniruotis po santykinai mažo fizinio aktyvumo laikotarpio arba kaitant krūvio parametrus (intensyvumą, apimtį) siekiant išvengti monotonijos ir sukelti didžiausią adaptacinį atsaką (Bompa, 1999; Issurin, 2010). Ankstesniuose tyrimuose taikyti vienodo dydžio krūviai neatitinka sportinių pratybų specifiškumo (Nosaka, Clarkson, 1995; Chen, Hsieh, 2001): pratybose krūvio apimtis ir intensyvumas nuolatos keičiami, taikomos įvairios krūvio didinimo strategijos. Išlieka neaišku, kaip kinta raumenų pažaida ir motorinė funkcija didinant fizinį krūvį taikant skirtingas strategijas. Kėlėme hipotezę, kad: 1) nuosekliai didinamas krūvis sukelia mažesnę raumenų pažaidą, palyginti su staigiai didinamu krūviu, nes motorinė sistema labai jautriai reaguoja į krūvio didinimo greitį; 2) treniruotės ciklo metu periodiškai pasireiškianti didesnė raumenų pažaida dėl superkompensacijos gali sukelti didesnę ilgalaikę griaučių raumenų adaptaciją (masės ir jėgos prieaugį). R. Lynn ir D. L. Morgan (1994) nustatė... [toliau žr. visą tekstą] / Unaccustomed muscle exercise, especially when it involves high-strain eccentric contractions, causes muscle damage (Yanagisawa et al., 2011; Neme et al., 2013). Muscle damage manifests in altered Z-disk morphology (Feasson et al., 2002), prolonged impairment of muscle force (Byrne et al., 2004; Skurvydas et al., 2010), protein leakage from injured muscle fibres, delayed-onset muscle soreness, and increased passive muscle stiffness and swelling (Malisoux et al., 2006; Chen et al., 2013). Muscle damage is frequently induced by sports training, where physical load parameters are being varied on the temporal scale to avoid monotony and maximize the adaptations (Bompa 1999; Issurin, 2010). However, there are limited data on the development of muscle damage and its impact on muscle function when variant exercise training schemes are applied. More needs to be learned about the impact of different strategies of load increase on exercise-induced muscle damage in order to identify progression regimes that can optimize neuromuscular adaptation processes. Therefore, we have followed the dynamics of muscle function during the stretch–shortening exercise with differently increasing load. We increased training stimulus by varying the volume, intensity, and range of motion. According to Nosaka (2008), these components of the eccentric contraction training are the most important for adaptation of the skeletal muscle. We hypothesized that the progressive increase in training load would induce... [to full text]

Supporters of a nutritional supplement, β-Hydroxy-β-Methylbutyrate (HMB) supplementation, claim that it will increase the muscular strength gains and lean muscle mass gains seen during a resistance training program. It has been suggested that HMB supplementation does this by preventing muscle damage or by regenerating damaged muscle cell membranes. However, no research has evaluated the effect of HMB supplementation on low frequency fatigue. Therefore, the purpose of this study was to determine if three weeks of HMB supplementation could attenuate the effects of low frequency fatigue caused by eccentric muscle contractions of the tibialis anterior muscle. A total of 33 healthy recreationally active subjects (18 males, 15 females; 23.2 ± 4.3 yr) were recruited for this study. All subjects preformed 4 sets of 25 eccentric contractions of the tibialis anterior muscle through a range of motion of 30 degrees. Recovery measures were taken for 20 minutes after the fatigue protocol and at 48 and 96 hours of recovery. The recovery measures included: Maximum voluntary contraction peak torque, 10 Hz peak torque, 50 Hz peak torque, 10/50 Hz peak torque ratio, and EMG measurements. Each subject served as their own control and limbs were randomly assigned to pre-supplement or post-supplement limbs. Following the pre-supplement fatigue protocol and recovery measures each subject completed three weeks of 3g/day HMB supplementation. After the supplementation period the post-supplement fatigue protocol was completed and recovery measures were taken. The 10 Hz peak torque and the 10/50 Hz torque ratio in the pre-supplement limb was still significantly reduced at the 96-hour recovery measurement time, indicating that it was still showing low frequency muscle fatigue at this time. Furthermore, the post-supplement limb, recovered from the fatigue protocol faster, and did not show any signs of low frequency muscle fatigue at the 48-hour recovery measurement time. In addition the pre-supplement limb had significant maximum voluntary contraction torque deficit at the 48-hour recovery measurement time and the post-supplement limb showed no significant deficits. The main findings of this study were that three weeks of HMB supplementation attenuated low frequency fatigue and maximum voluntary contraction torque reduction after an eccentric fatigue protocol.

国立情報学研究所で電子化したコンテンツを使用している。

Doctor of Philosophy / In this thesis, three experiments were conducted to monitor: (i) muscle oxygenation and electromyographic activity of the biceps brachii after exercise-induced muscle damage (ii) muscle oxygenation after downhill walking-induced muscle damage, and, (iii) muscle oxygenation following a bout of vigorous concentric exercise. Maximal eccentric exercise (EE) of biceps brachii resulted in significantly increased mean resting oxygen saturation and decreased deoxyhaemoglobin. During isometric contractions at 50% and 80% of subjects’ maximum voluntary torque (MVT), oxygen desaturation and resaturation kinetics and volume were significantly decreased after EE, and these declines were significantly prevalent over the following 6 days. Additionally, a significant shift in median frequency intercept (measured by electromyography; EMG) towards lower frequencies was observed during isometric contractions at both 50% and 80% MVT after EE in the exercised arm. After an exhaustive session of downhill walking, another form of EE, resting total haemoglobin and oxyhaemoglobin decreased. Furthermore, during isometric contractions at 30%, 50% and 80% of MVT, prolonged and significant increases were observed in oxygen desaturation and resaturation kinetics and volumes after ambulatory EE. In contrast to the two EE experiments, concentric contractions did not evoke any prolonged changes in muscle oxygenation. Collectively, the findings of this thesis revealed significant and prolonged changes in muscle oxygenation at rest and during exercise, following sessions of strenuous eccentric exercise. Although not clear, the possible mechanism responsible for the changes in muscle oxygenation after EE could be increased resting muscle oxygen utilization due to probable muscle damage and a subsequent requirement of energy demanding repair processes. Concentric exercise resulted in fatigue, but it did not affect muscle oxygenation. Although a prolonged reduction in EMG median frequency intercept was observed after EE, this was not closely time-associated with the biochemical, anthropometric or functional markers of muscle damage.

Thesis (Ph. D.) -- University of Western Sydney, Hawkesbury, 2000. / Includes bibliographical references (leaves 225-241).

Esta dissertação apresenta um estudo da caracterização numérica do comportamento mecânico de um músculo esquelético estriado sujeito à combinação de diferentes contrações. A partir dos mecânismos fisiológicos da contração do tecido muscular esquelético, são apresentadas as principais características da produção de força do músculo em diferentes tipos de contrações (isométrica, concêntrica, excêntrica) e suas combinações. A representação numérica da resposta mecânica do músculo esquelético foi investigada por diferentes autores. Dos diversos modelos encontrados na literatura, alguns foram escolhidos para a continuidade deste estudo, segundo sua capacidade representativa e facilidade de implementação em métodos numéricos de solução para grandes deformações. Os modelos disponíveis na literatura foram implementados e avaliados para diferentes sequências de contrações, sendo também realizado um ajuste de parâmetros para dados experimentais de contrações isométricas e isométricas-excêntricas-isométricas. Nenhuma das propostas avaliadas apresentou resultados satisfatórios. A principal deficiência dos modelos foi a incapacidade de reproduzir a dependência do histórico de carregamentos, ou seja, da combinação de contrações. Desta maneira, uma nova proposta de modelo constitutivo foi desenvolvida e implementada para testes uniaxiais e em um código de elementos finitos para testes tridimensionais. A partir destas implementações, foram executados testes numéricos para diferentes sequências de contrações, avaliando a capacidade representativa do modelo proposto neste trabalho. O modelo proposto apresentou bons resultados para contrações isométricas e a combinação de contrações com diferentes níveis de alongamento, ou encurtamento, a uma mesma velocidade. A principal contribuição deste modelo é a capacidade de representar a resposta associada à fadiga muscular e o ganho, ou perda de força, observados experimentalmente. / This work present a striated skeletal muscle numerical characterization subjected to different contractions. From the physiological contraction mechanism of the skeletal muscle tissue the force produced in different kinds of contraction (isometric, concentric and eccentric), and their combination, are presented. The numerical representation of these response was investigated by different authors. From the diverse models found in literature, some were selected to be studied according to their representation capability and the implementation ease in numerical methods for large strains. The models available in literature were implemented and evaluated for different contractions combinations and a parameter identification for experimental results of two isometric contraction and a isometric-eccentric-isometric contraction. None of the proposed models presented satisfactory results. The main deficiency of these models were the incapability of reproducing the loading history dependence, in other words, the contraction combination. In this way, a new material model was proposed and implemented to uniaxial and tridimensional finite element method tests. From these, different contractions sequences evaluated the proposed model representation capabilities. The proposed model present good results to isometric contraction, as well as contraction combination with different stretch, or shortening, level in the same speed. The main contribution of this model is the capability of represent the the response associated to the muscle fatigue and the force gain or loss, experimentally observed.

O dano muscular induzido pelo exercício (DMIE) é um fenômeno que ocorre ao realizarmos um exercício com o qual não estamos habituados, seja pela modalidade, volume ou intensidade. Além disso, esta condição está fortemente relacionada com contrações excêntricas ou gestos que predominantemente envolvam este tipo de contração, causando prejuízos funcionais importantes e diminuindo o desempenho. Diante disto, estratégias para acelerar o processo de recuperação muscular vem sendo investigadas. Dentre elas, a recuperação ativa, técnica muito utilizada no meio prático e que consiste na execução de exercícios com intensidade baixa ou moderada buscando melhorar a recuperação após uma sessão de treino mais intensa. No entanto, nenhum estudo comparou duas formas de recuperação ativa com exercícios aeróbios até o momento, além dos estudos experimentais da área apresentarem qualidade metodológica frágil. Com isso, o objetivo desta dissertação é comparar o efeito da recuperação ativa em esteira e em cicloergômetro sobre marcadores de dano muscular. Para isso, trinta voluntários do sexo masculino foram alocados de forma randomizada em três grupos: grupo esteira (GE, n = 10), grupo cicloergômetro (GCI, n = 10) e grupo controle (GC, n = 10). Avaliações da contração isométrica voluntária máxima (CIVM), dor, concentração plasmática de creatina kinase (CK) e lactato desidrogenase (LDH) e espessura e ecogenicidade dos músculos reto femoral (RF) e vasto lateral (VL) foram realizadas pré, 24h, 48h e 72h após um protocolo indutor de dano muscular, constituído por cinco séries de 10 contrações excêntricas máximas em dinamômetro isocinético. Após o protocolo indutor de dano muscular, os sujeitos realizaram a intervenção de acordo com o grupo em que foram alocados, com duração de 30 minutos e intensidade de 60% do VO2máx, independente da modalidade. Não foram observadas diferenças significativas entre os grupos nos parâmetros de caracterização da amostra. Não houve diferença significativa entre os grupos em todas as variáveis analisadas. Houve redução significativa no torque nos períodos imediatamente após (IP), 24h, 48h e 72h comparado ao período Pré em todos os grupos. Houve aumento significativo da dor nos períodos 24h, 48h e 72h comparado ao período Pré em todos os grupos. Houve aumento significativo na espessura do músculo RF 24h após o protocolo de dano muscular. A ecogenicidade foi maior tanto no RF quanto no VL nos períodos de 48h e 72h quando comparada ao período Pré. Não houve diferença significativa nas concentrações plasmáticas de CK e LDH entre os períodos de avaliação. Os resultados do presente estudo permitem concluir que a execução de recuperação ativa nos parâmetros adotados, seja em cicloergômetro ou esteira, não modifica o processo de recuperação após dano muscular. / The exercise-induced muscle damage (EIMD) is a phenomenon that occurs when we execute an unusual exercise, either by type, volume or intensity. Furthermore, this condition is strongly associated with eccentric contractions or gestures which predominantly involve this type of contraction, causing significant loss of function and decreasing performance. In view of this, the search for strategies to accelerate muscle recovery process has been investigated. Among them, active recovery, technique widely used in practical means and which consists in carrying out exercises with low or moderate intensity seeking to improve recovery after a more intense training session. However, no studies have compared two types of active recovery yet, besides the experimental studies presented fragile methodological quality. Thus, the aim of this study is to compare the effect of active recovery on a treadmill and cycle ergometer on muscle damage markers. For this, thirty male volunteers were randomly divided into three groups: treadmill group (EG, n = 10), cycle ergometer group (GCI, n = 10) and control group (CG, n = 10). Evaluations of maximal voluntary isometric contraction (MVIC), pain, plasma concentration of creatine kinase (CK) and lactate dehydrogenase (LDH) and muscle thickness and echo intensity of the rectus femoris (RF) and vastus lateralis (VL) were performed before, 24h, 48h and 72h after the muscle damage protocol, comprising five sets of 10 maximum eccentric contractions using an isokinetic dynamometer. After muscle damage protocol, the subjects performed the intervention according to the group they were allocated, lasting 30 minutes with an intensity of 60% VO2max, regardless of the type. Significant differences between the groups in the sample characterization parameters were observed. There was no significant difference between groups in all variables. There was a significant reduction in torque in the periods immediately after (IP), 24h, 48h and 72h compared to the Pre period in all groups. There was a significant increase in pain at times 24h, 48h and 72h compared to the Pre period in all groups. A significant increase in muscle thickness of RF was observed in 24h period. The echo intensity was higher in both RF and VL in periods of 48h and 72h compared to the Pre period. There was no significant difference in plasma concentrations of CK and LDH between the evaluation periods. Our results illustrate that the performance of active recovery, in the adopted parameters, either in cycle ergometer or treadmill, does not change the process of recovery after muscle damage.