Abstract not available

This thesis comprises one review paper and five experimental studies, all of which are presented in the form of journal article submissions. These six research papers attempt to further our understanding of the physiological and metabolic requirements of repeated-sprint activity, specific to field-based team sports. Although coaches and sport scientists have suggested that repeated-sprint ability is an important fitness component of team sports, this area of investigation has only become more common in the past 10 years.

Recovery from exhaustive exercise in the white muscle of rainbow trout (Oncorhynchus mykiss) was used to examine the role of the adenylates in the control of energy metabolism and to assess the validity of equilibrium models of the behaviour of the high energy phosphates. The difficulty of obtaining muscle samples from fish makes detailed analysis of the behaviour of the labile high energy phosphates complex. The use of a new sampling procedure, the infusion of a lethal dose of anaesthetic via an indwelling cannula, minimized this problem. At exhaustion [ATP] and [PCr] were depressed by 75 and 80% respectively relative to the resting values. [ATP] depletion was mirrored by a stoichiometric increase in [IMP]. During recovery [PCr] returned to the resting level within 2 hours, but [ATP] recovery was slow and not complete until 24 hours post exercise. In contrast, energy charge and RATP(the proportion of the free adenylate pool phosphorylated to ATP) were, if anything, higher than the resting values by 2 hours post exercise. Therefore, [ATP] and energy status can be dissociated in tissues like fish white muscle because of the action of the purine nucleotide cycle. At 2 hours post exercise the calculated free ADP concentration dropped to less than one tenth the value at rest. As a result the [ATP] / [ADP] free ratio increased by nearly 6 fold. This condition may be required for glycogen resynthesis from lactate in muscle. Several similar equilibrium models of the behaviour of the adenylates and PCr were applied to the fish white muscle system. In general, the models well describe the relationship between the high energy phosphates. However, the definition of the high energy phosphate pool introduces some complications since this includes the total [ATP]. Because of the action of AMP deaminase the [ATP] concentration can change without measurable changes in the energy status, which is not considered in any of the models. As long as the extent of IMP formation is known the models can be applied, but since the formation of IMP may vary from fish to fish or with exercise regime the models lose much of their predictive power. / Science, Faculty of / Zoology, Department of / Graduate

Thesis (PhD)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: Skeletal muscle adapts to stimuli by modifying structural and metabolic protein expression. Furthermore, a muscle group may vary within itself to accommodate specialisation in regions. Structural and metabolic characteristics of an individual are regulated partly by genotype, but contraction duration and intensity may play a greater role in muscle phenotype. The aims of this dissertation were to investigate: structural and metabolic regionalisation in a muscle group, possible relationships between training volume and intensity and hybrid fibres, muscle characteristics of athletes from two different ethnic groups, and muscle adaptation in already well-trained athletes subjected to high intensity interval training. Myosin heavy chain (MHC) isoform content and citrate synthase (CS) activities were measured in the Quadriceps femoris (QF) muscle of 18 female rats. Muscle was divided into superficial, middle and deep, distal, central and proximal parts. MHC IIb and IIx were more abundant in superficial regions (P < 0.05) with low CS activities compared to deeper parts. Isoform content varied along the length of deep regions. This study showed that the QF has regional specialisation. Therefore, standardisation of sampling site is important. Hybrid fibre proportions in muscle biopsies of 12 middle distance runners and 12 non-runners were investigated. MHC IIa/IIx correlated with training volume/week in runners (r = -0.66, P < 0.05) and MHC IIa/IIx correlated with exercise hours/week in non-runners (r = -0.72, P < 0.01). Average preferred racing distance (PRDA) correlated better with MHC IIa/IIx in runners (r = -0.85, P < 0.001). MHC IIa/IIx may therefore be more closely related to exercise intensity than previously thought. Fibre type characteristics and performance markers were investigated in 13 Xhosa and 13 Caucasian distance runners, matched for performance, training volume and PRDA. Xhosa runners had less MHC I and more MHC IIa fibres in muscle biopsies than Caucasian runners (P < 0.05). Xhosa runners had lower plasma lactate at 80% peak treadmill speed (PTS) (P < 0.05), but higher lactate dehydrogenase (LDH) (P < 0.01) and phosphofructokinase (P = 0.07) activities in homogenate muscle samples. LDH activities in MHC I (P = 0.05) and IIa (P < 0.05) fibre pools were higher in Xhosa runners. Xhosa athletes may thus have a genetic advantage or they may have adapted to running at a higher intensity. Six weeks of individually standardised high intensity interval treadmill training (HIIT) were investigated in 15 well-trained runners. PTS increased after HIIT (P < 0.01), while maximum oxygen consumption (VO2max) only showed a tendency to have increased as a result of HIIT (P = 0.06). Sub-maximal tests showed lower plasma lactate at 64% PTS (P = 0.06), with lower heart rates at workloads from 64% to 80% PTS (P < 0.01) after HIIT. No changes were observed for cross-sectional area, capillary supply and enzyme activities in homogenates muscle samples. LDH activity showed a trend (P = 0.06) to have increased in MHC IIa pools after HIIT. Higher HIIT speed was related to decreases in MHC I fibres, but increases in MHC IIa/IIx fibres (r = -0.70 and r = 0.68, respectively, P < 0.05). Therefore, HIIT may alter muscle fibre composition in well-trained runners, with a concomitant improvement in performance markers. / AFRIKAANSE OPSOMMING: Skeletspier kan adapteer deur strukturele en metaboliese protein ekspressie te verander as gevolg van stimulante. ‘n Spiergroep kan ook intern verskil om spesialisering in spierdele toe te laat. Strukturele en metaboliese karaktereienskappe van ‘n individu word deels gereguleer deur gene, maar kontraksie tydperk en intensiteit mag ‘n groter rol speel in spierfenotipe. Die doelwitte van hierdie tesis was om ondersoek in te stel in: strukturele en metaboliese eienskappe in spiergroepstreke, moontlike verhoudings tussen oefeningsvolume of intensiteit en baster vesels, spier eienskappe in atlete van twee etniese groepe, en spier adaptasie in goed geoefende atlete blootgestel aan hoë intensiteit interval oefening. Miosien swaar ketting (MSK) isovorm inhoud en sitraat sintase (SS) aktiwiteite is gemeet in die Quadriceps femoris (QF) spier van 18 wyfie rotte. Spiere was opgedeel in oppervlakkig, middel en diep, asook distaal, sentraal en proksimale dele. MSK IIb en IIx was meer oorvloedig in oppervlakkige dele (P < 0.05) met lae SS aktiwiteite in vergelyking met dieper dele. Isovorm inhoud het ook verskil oor die lengte van diep dele. Dus bevat die QF gespesialiseerde streke en is die area van monsterneming belangrik. Baster vesel proporsies is ondersoek in spiermonsters van 12 middel afstand hardlopers en 12 niehardlopers. MSK IIa/IIx van hardlopers het met oefeningsvolume/week gekorreleer (r = -0.66, P < 0.05), asook MSK IIa/IIx van nie-hardlopers met oefeningsure/week (r = -0.72, P < 0.01). Gemiddelde voorkeur wedloop afstand (VWAG) het beter met MSK IIa/IIx gekorreleer in hardlopers (r = -0.85, P < 0.001). MSK IIa/IIx mag dus meer verwant wees aan oefeningsintensiteit. Veseltipe eienskappe en prestasie merkers was ondersoek in 13 Xhosa en 13 Caucasian langafstand atlete, geëweknie vir prestasie, oefeningsvolume en VMAG. Xhosa hardlopers het minder tipe I en meer tipe IIA vesels in hul spiermonsters gehad as die Caucasian hardlopers (P < 0.05). Xhosa hardlopers het laer plasma laktaat by 80% van hul maksimale trapmeul spoed (MTS) (P < 0.05), maar hoër laktaat dihidrogenase (LDH) (P < 0.01) en fosfofruktokinase (P = 0.07) aktiwiteite in homogene spiermonsters gehad. LDH aktiwiteite in MSK I (P = 0.05) en IIa (P < 0.05) veselbondels was hoër in Xhosa hardlopers. Xhosa atlete mag dus ‘n genetiese voorsprong geniet, of hulle het geadapteer om by hoër intensiteite te hardloop. Ses weke van geïndividualiseerde gestandardiseerde hoë intensiteit interval trapmeul oefening (HIIT) was ondersoek in 15 goed geoefende hardlopers. MTS het verhoog na HIIT (P < 0.01), en maksimale surrstof verbruik (VO2max) het ‘n neiging getoon om te verhoog het na HIIT (P = 0.07). Submaksimale toetse het laer plasma laktaat by 64% MTS getoon (P = 0.06), met laer harttempos by werkladings 64% tot 80% MTS (P < 0.01). Geen veranderings was gemerk vir deursnit area, kapillêre toevoer en ensiem aktiwiteite in homogene spiermonsters nie. LDH aktiwiteit het ‘n neiging getoon om te verhoog het (P = 0.06) in MSK IIa veselbondels na HIIT. Hoër HIIT snelhede was verwant aan ‘n daling in MSK I vesels, maar ‘n verhoging in MSK IIa/IIx vesels (r = -0.70 en r = 0.68, respektiwelik, P < 0.05). HIIT mag dus spier veseltipe verander in goed geoefende hardlopers, met gevolglike verbetering in prestasie merkers.

Introdução: A dermatomiosite juvenil (DMJ) é uma doença autoimune idiopática caracterizada pela presença de lesão cutânea, perda de massa muscular, fraqueza muscular proximal, fadiga e redução da aptidão física. Nesse contexto, a suplementação de creatina emerge como estratégia terapêutica não farmacológica para atenuar os sintomas ocasionados pela disfunção muscular e perda de massa muscular em diversas condições, como nas doenças reumatológicas pediátricas; Objetivo: O objetivo deste estudo foi avaliar a eficácia e a segurança da suplementação de creatina em pacientes com DM de início juvenil; Métodos: Trata-se de um estudo duplo-cego, crossover, balanceado e controlado por placebo. Todos os voluntários (n = 15) receberam dois tratamentos, a saber: creatina (0,1 g/kg/dia) ou dextrose (placebo - 0,1 g/kg/dia). Para cada tratamento, o período de suplementação foi de 12 semanas, interpassadas por um período de washout de oito semanas. A ordem dos tratamentos foi determinada de forma aleatória e contrabalanceada. Tanto nos períodos pré-suplementação, como nos períodos pós-suplementação foram avaliadas a força e função musculares (desfechos primários), além da composição corporal, densidade mineral óssea, marcadores bioquímicos do remodelamento ósseo, citocinas inflamatórias, aptidão aeróbia, qualidade de vida, parâmetros relacionados à atividade da doença, consumo alimentar e conteúdo intramuscular de fosforilcreatina. Nos mesmos períodos de tempo, a segurança da intervenção foi avaliada por parâmetros laboratoriais e por clearance de 51Cr-EDTA. Os eventos adversos foram registrados durante todo o estudo; Resultados: Não houve diferença significativa no conteúdo intramuscular de fosforilcreatina entre as condições, antes e após as intervenções (Creatina - Pré: 21,4 ± 5,3/Pós: 20,6 ± 2,7, delta escore = -0,3 ± 2,5 mmol/kg peso úmido; Placebo - Pré: 20,4 ± 3,7/Pós: 20,7 ± 3,6, delta escore = -0,1 ± 4,2 mmol/kg peso úmido, p = 0,45 da interação entre as condições). Também, não houve diferença significativa entre as condições placebo e creatina para função muscular, capacidade aeróbia, composição corporal, densidade mineral óssea e qualidade de vida. Além disso, não houve alteração na função renal após a suplementação de creatina e nenhum efeito adverso foi observado; Conclusão: O protocolo de suplementação de creatina (0,1 g/kg/d) por 12 semanas foi bem tolerado e livre de efeitos adversos. Entretanto, a suplementação de creatina não foi capaz de aumentar o conteúdo intramuscular de fosforilcreatina, o que se traduziu em ausência de melhora da função muscular, aptidão aeróbia, composição corporal e parâmetros de qualidade de vida em pacientes com DM de início juvenil / Introduction: Juvenile dermatomyositis (JDM) is an autoimmune idiopathic disease characterized by skin rashes, insidious loss of muscle mass, symmetrical proximal muscle weakness, decreased physical capacity, and fatigue. In this context, creatine supplementation has emerged as a promising non-pharmacological therapeutic strategy to counteract muscle dysfunction and low lean mass in a variety of conditions, including in pediatric and rheumatic diseases. Objective: To examine the safety and efficacy of creatine supplementation in Juvenile Dermatomyositis (JDM) patients; Methods: JDM patients (n = 15) received placebo or creatine supplementation (0.1 g/kg/d) in a randomized, crossover, double-blind design. Subjects were assessed at baseline and after 12 weeks, with an 8-week washout period. Primary outcome was muscle function. Secondary outcomes included body composition, bone mineral density, biochemical markers of bone remodeling, inflammatory cytokines, aerobic conditioning, health-related quality of life, disease-related parameters, dietary intake and muscle phosphorylcreatine (PCR) content. Safety was assessed by laboratory parameters and kidney function measurements such as 51Cr-EDTA clearance; Results: Intramuscular PCR content was not significantly different between creatine and placebo before or after the intervention (Creatine - Pre: 21.4 ± 5.3, Post: 20.6 ± 2.7, delta score = -0.3 ± 2.5 mmol/kg wet muscle, ES = -0.15; Placebo - Pre: 20.4 ± 3.7, Post: 20.7 ± 3.6, delta score = -0.1 ± 4.2 mmol/kg wet muscle, ES = -0.15; 95% CI for delta score = -2.8 ± 2.4, p = 0.45 for interaction between intervention). No significant changes between placebo and creatine for muscle function and aerobic conditioning, body composition, bone mineral density, and quality of life were detected, probably due to the lack of change in intramuscular PCR content. Kidney function was not changed after creatine supplementation and no side effects were noticed; Conclusion: a 12-week creatine supplementation protocol is well tolerable and free of adverse effects but did not affect intramuscular PCR, muscle function, body composition, bone mineral density or quality of life in JDM patients

Introdução: A dermatomiosite juvenil (DMJ) é uma doença autoimune idiopática caracterizada pela presença de lesão cutânea, perda de massa muscular, fraqueza muscular proximal, fadiga e redução da aptidão física. Nesse contexto, a suplementação de creatina emerge como estratégia terapêutica não farmacológica para atenuar os sintomas ocasionados pela disfunção muscular e perda de massa muscular em diversas condições, como nas doenças reumatológicas pediátricas; Objetivo: O objetivo deste estudo foi avaliar a eficácia e a segurança da suplementação de creatina em pacientes com DM de início juvenil; Métodos: Trata-se de um estudo duplo-cego, crossover, balanceado e controlado por placebo. Todos os voluntários (n = 15) receberam dois tratamentos, a saber: creatina (0,1 g/kg/dia) ou dextrose (placebo - 0,1 g/kg/dia). Para cada tratamento, o período de suplementação foi de 12 semanas, interpassadas por um período de washout de oito semanas. A ordem dos tratamentos foi determinada de forma aleatória e contrabalanceada. Tanto nos períodos pré-suplementação, como nos períodos pós-suplementação foram avaliadas a força e função musculares (desfechos primários), além da composição corporal, densidade mineral óssea, marcadores bioquímicos do remodelamento ósseo, citocinas inflamatórias, aptidão aeróbia, qualidade de vida, parâmetros relacionados à atividade da doença, consumo alimentar e conteúdo intramuscular de fosforilcreatina. Nos mesmos períodos de tempo, a segurança da intervenção foi avaliada por parâmetros laboratoriais e por clearance de 51Cr-EDTA. Os eventos adversos foram registrados durante todo o estudo; Resultados: Não houve diferença significativa no conteúdo intramuscular de fosforilcreatina entre as condições, antes e após as intervenções (Creatina - Pré: 21,4 ± 5,3/Pós: 20,6 ± 2,7, delta escore = -0,3 ± 2,5 mmol/kg peso úmido; Placebo - Pré: 20,4 ± 3,7/Pós: 20,7 ± 3,6, delta escore = -0,1 ± 4,2 mmol/kg peso úmido, p = 0,45 da interação entre as condições). Também, não houve diferença significativa entre as condições placebo e creatina para função muscular, capacidade aeróbia, composição corporal, densidade mineral óssea e qualidade de vida. Além disso, não houve alteração na função renal após a suplementação de creatina e nenhum efeito adverso foi observado; Conclusão: O protocolo de suplementação de creatina (0,1 g/kg/d) por 12 semanas foi bem tolerado e livre de efeitos adversos. Entretanto, a suplementação de creatina não foi capaz de aumentar o conteúdo intramuscular de fosforilcreatina, o que se traduziu em ausência de melhora da função muscular, aptidão aeróbia, composição corporal e parâmetros de qualidade de vida em pacientes com DM de início juvenil / Introduction: Juvenile dermatomyositis (JDM) is an autoimmune idiopathic disease characterized by skin rashes, insidious loss of muscle mass, symmetrical proximal muscle weakness, decreased physical capacity, and fatigue. In this context, creatine supplementation has emerged as a promising non-pharmacological therapeutic strategy to counteract muscle dysfunction and low lean mass in a variety of conditions, including in pediatric and rheumatic diseases. Objective: To examine the safety and efficacy of creatine supplementation in Juvenile Dermatomyositis (JDM) patients; Methods: JDM patients (n = 15) received placebo or creatine supplementation (0.1 g/kg/d) in a randomized, crossover, double-blind design. Subjects were assessed at baseline and after 12 weeks, with an 8-week washout period. Primary outcome was muscle function. Secondary outcomes included body composition, bone mineral density, biochemical markers of bone remodeling, inflammatory cytokines, aerobic conditioning, health-related quality of life, disease-related parameters, dietary intake and muscle phosphorylcreatine (PCR) content. Safety was assessed by laboratory parameters and kidney function measurements such as 51Cr-EDTA clearance; Results: Intramuscular PCR content was not significantly different between creatine and placebo before or after the intervention (Creatine - Pre: 21.4 ± 5.3, Post: 20.6 ± 2.7, delta score = -0.3 ± 2.5 mmol/kg wet muscle, ES = -0.15; Placebo - Pre: 20.4 ± 3.7, Post: 20.7 ± 3.6, delta score = -0.1 ± 4.2 mmol/kg wet muscle, ES = -0.15; 95% CI for delta score = -2.8 ± 2.4, p = 0.45 for interaction between intervention). No significant changes between placebo and creatine for muscle function and aerobic conditioning, body composition, bone mineral density, and quality of life were detected, probably due to the lack of change in intramuscular PCR content. Kidney function was not changed after creatine supplementation and no side effects were noticed; Conclusion: a 12-week creatine supplementation protocol is well tolerable and free of adverse effects but did not affect intramuscular PCR, muscle function, body composition, bone mineral density or quality of life in JDM patients