OpenUCT :: Browsing by Subject "Exercise Science "

Browsing by Subject "Exercise Science "

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Open Access
A description of the profiles of U18 rugby players who attended the Craven Week tournament between 2002-2012
(2018) Durandt, Justin; Lambert, Mike
Rugby union has rich tradition in South Africa with the national team having won the Rugby World Cup in 1995 and 2007. The major rugby nations South Africa competes against have clearly defined rugby talent identification (TID) and development (TDE) pathways. These pathways are not as well described in South Africa where the South African Rugby Union (SARU) has adopted a model of identifying talent at an early age through competition. For example, national competitions occur at U13 (Craven Week), U16 (Grant Khomo Week) and U18 (Craven Week and Academy Week) levels. Previous research on talent identification has highlighted the pitfalls of early talent identification. In particular different rates of maturation can influence the manifestation of talent. In a collision sport such as rugby the early maturers have a distinct advantage. An added complexity in the South African context is the need to provide an appropriate development environment within which transformation can take place. At all levels in South African professional rugby, white players dominate team selection. One of the reasons suggested for this dominance is the physical size of white players compared to their black and mixed race (coloured) counterparts. Rugby is a contact sport and physical size is associated with success, so the need to quantify physical difference between racial groups at a junior level over time is important. The first objective of the thesis was to examine the profiles of U18 Craven Week rugby players to gain insight into the development pathway from U13 to U18. A second aim was to understand factors influencing transformation by measuring the physical profiles of the various racial groups over time. The thesis consists of two studies. The specific objective of the first study was quantify how many players in the 2005 U13 Craven Week (n=349) participated in the subsequent U16 Grant Khomo and U18 Craven Week. The study showed that 31.5% of the players who played in the U13 Craven Week, were selected to play at U16 Grant Khomo Week and 24.1% were selected for the U18 Craven Week tournaments. Another interpretation is that 76% of the players selected for the U13 tournament did not play at the U18 Craven Week tournament. The objective of the second study was to determine whether there are differences in body mass, stature and body mass index (BMI) between racial groups in U18 Craven Week players. Another objective was to determine whether these measurements changed between 2002-2012. Self-reported body mass and stature were obtained from U18 players (n=4007) who attended the national tournament during this period. BMI was calculated for each player. The body mass, stature and BMI of these players in South Africa were significantly different between racial groups. For example, white players were 9.8 kg heavier than black players, who were 2.3 kg heavier than coloured players (p<0.0001). The body mass of all groups increased from 2002-2012 (p < 0.0001). White players were 7.0 cm taller than black players, who were 0.5 cm taller than coloured players (p < 0.0001). The stature of players did not change significantly during the study period. The average BMI of white players was 0.9 kg.m⁻² greater than black players who were on average 0.7 kg.m⁻² greater than coloured players (p<0.0001). The BMI of all groups changed similarly over the study period. To conclude, these results question the effectiveness of the u13 tournament in identifying talent and providing an effective development pathway to U18 Craven Week. The SARU also needs to be aware of the ongoing disparities in size between the racial groups playing rugby at an U18 level in South Africa. These size differences may have implications for transforming the game and making it representative of the South African population.
Open Access
The association between cardiorespiratory fitness and performance in a submaximal stepping test standardised for external workload
(2016) Huchu, Linet; Lambert, Michael I
Submaximal step tests are used to predict maximal oxygen consumption and work capacity. However, if the external workload is not controlled the interpretation of the test results may be inaccurate. The purpose of the research was to develop a submaximal test of cardiorespiratory fitness using a novel step test designed specifically to overcome the weaknesses of the previously published step tests. A series of studies contributed to the theoretical development of the submaximal step protocol, piloting the protocol, reliability studies, validation of the protocol and finally a cross-validation of the protocol. The first study tested the hypothesis that stepping tests configured for the same external workload, but varying in stepping frequency, elicit the same physiological stress. Participants (n = 31) performed three step tests at 16, 20 and 24 steps per minutes in random order. External workload was standardised at 45 kJ. Energy expenditure, heart rate recovery, rating of perceived exertion, maximum heart rate and total heart beats were significantly different between tests (p < 0.05) with the biggest differences occurring between 16 and 24 steps per minute. Maximum heart rate as a percentage of age predicted heart rate increased from 70% at 16 steps per minute to 81% at 24 steps per minute. The study concluded that standardisation of external workload with different exercise intensities does not result in the same physiological responses. The second study tested the reliability of the step test. Participants (n = 34) performed a step test three times in a week at a cadence of their choice (16, 20 or 24 steps per minute). The study showed that the step test is repeatable for most variables measured and therefore is a reliable test of fitness. The third study used the outcome variables measured during the step test to develop equations which predicted VO₂max measured directly in a maximal test on a treadmill. A diverse sample of participants (n = 273), differing in sex, level of habitual physical activity and age were recruited for the study. Several models for predicting VO₂max were determined. The most parsimonious equation was: VO₂max (ml.kg⁻¹.min⁻¹) = -0.10911 (age) - 0.06178 (body mass) - 0.75481 (body fat %) +0.00208 (METS) + 0.11636 (HRR) - 0.019551 (MHR) + 0.07955 (Av HR) + 83.34846 (R² = 0.75, standard error of estimate = 5.51 ml.kg.min⁻¹) where METS is metabolic equivalent, HRR is heart rate recovery, MHR is maximum heart rate and Av HR is average heart rate. Cross validation was done (n = 50) to test the accuracy of the prediction equation. The relationship between the predicted VO₂max and the measured VO₂max was r = 0.87. In conclusion the standardised step test can predict VO₂max in a heterogeneous population of males and females, varied ages (20 to 60 years), physical activity levels and fitness levels.
Open Access
The batting backlift technique in cricket
(2017) Noorbhai, Mohammed Habib; Noakes, Timothy
The batting technique in cricket consists of various elements such as the grip, stance, backlift, downswing, impact with the ball and follow through. Whilst there has been an extensive amount of research into these batting elements, there is little research specifically on the backlift technique. Therefore, we aimed to investigate and provide a scientific understanding of the batting backlift technique (BBT) in cricket. We aimed to investigate the BBT of the most successful batsmen (n = 65) in the last 120 years as well as players in the Indian Premier League (IPL) (n = 30). It was found that these batsmen did not conform to the current cricket coaching method that advocates a straight batting backlift technique (SBBT). Instead, 77% of successful batsmen and 90% of IPL batsmen employed a lateral batting backlift technique (LBBT) in which they lifted their bats in the direction of second slip or beyond with the bat face towards the off-side. Using this technique, both the toe of the bat and face of the bat points directly towards the off-side (usually between slips and point). The number of players using the LBBT was significantly greater than those using the SBBT (χ2 = 19.2, df = 1, p < 0.001). Given these findings, we were curious to determine whether this finding was similar at other levels of cricket. The second study therefore employed biomechanical and video analyses to evaluate the BBT of current semi-professional, professional and international cricketers (n = 155) from South Africa and the United Kingdom. The backlift of these batsmen was then compared to their career statistics. It was found that a LBBT is more prevalent at the highest levels of the professional game and a likely contributor factor for successful batting at the highest level (p≤0.05). The LBBT was also found to positively affect other components of the batting technique such as the stance and scoring areas. We then proceeded to investigate the BBT amongst the lower levels of cricket (junior and adolescent cricketers). The third study consists of an intervention study that employed a biomechanical analysis of coached and uncoached cricketers (n = 80). It was found that more than 70% of uncoached cricketers adopted a LBBT, whereas more than 70% of coached cricketers adopted the SBBT. Having found that the LBBT is a likely contributing factor for past and current successful batsmen, it was then important to understand what BBT the current cricket coaches are teaching at various proficiency levels. The fourth study explored the teachings of the BBT among international cricket coaches (n = 161) using a mixed methods approach through an online evaluation survey. This study was able to show that a majority of cricket coaches teach what is advocated in coaching manuals and mostly coach the SBBT as opposed to the LBBT at various levels of the game. In the fifth and sixth studies, this thesis further describes two innovative coaching tools that can improve and assist with the coaching of the LBBT. Firstly, a novel coaching cricket bat was investigated through a pilot and intervention study. In the pilot group, cricketers using the coaching bat scored approximately 1 more run per ball or an average of approximately three more runs in total when using the coaching bat than the normal bat (F = 6.70, df = 1, p = 0.012). In the intervention study, the experimental group scored double the total number of runs (an additional 16 runs) and an average of approximately 3 more runs per player in the post-match than in the pre-match, which showed a large effect (ES = 5.41) (t = 3.32, df = 5, p = 0.021). The coaching cricket bat might be used to coach young cricket players to hit the ball more effectively as well as how to adopt a more LBBT. Secondly, a mobile application was developed, which can be used by players, coaches and scientists to analyse and improve the BBT among cricketers at all levels. In summary, this thesis has shown that the LBBT is a likely contributing factor to successful batsmanship at all levels of cricket ability (junior cricketers, adolescent cricketers, semi-professional cricketers, professional cricketers, international cricketers and former elite/successful cricketers). Coaching a LBBT to young batsman may be challenging and therefore a coaching cricket bat has been developed and has shown to be a promising training aid for coaching the LBBT to young cricketers. A mobile application has also been designed and tested to assist in the coaching of the BBT in cricket. A way forward for further research in this area of cricket batting is documented at the end of the thesis.
Open Access
Cardiorespiratory, kinematic, neuromuscular and metabolic characteristics during the recovery period after an ultramarathon race
(2009) Burgess, Theresa Lee; Lambert, Mike
The aim of this study was to investigate the effects of exercise-induced muscle damage caused by a 90 km ultramarathon on submaximal oxygen consumption and stride length. The experimental group consisted of 11 male runners (39.7 ± 9.3 years) competing in a 90 km ultramarathon. Ten male runners (41.0 ± 10.8 years) who did not run the 90 km ultramarathon formed the control group. Maximum oxygen consumption and peak treadmill running speed were measured two weeks before the ultramarathon. Daily measurements of muscle pain and plasma creatine kinase (CK) activity were recorded for seven days after the ultramarathon. Muscle pain, plasma CK activity, and blood lactate concentrations were recorded before, and oxygen consumption, respiratory exchange ratio (RER), heart rate, rate of perceived exertion (RPE), and stride length were all measured during a 15-minute submaximal treadmill test seven days before the ultramarathon, and on days 4, 7, 14, 21, and 28 after the ultramarathon. Peak blood lactate concentrations were determined 3 minutes after the completion of each treadmill test. Plasma CK activity and muscle pain remained significantly elevated in the experimental group for two days (p < 0.00002) and four days (p < 0.02) respectively after the ultramarathon. There was a significant increase in the post-submaximal treadmill test blood lactate concentrations, compared to pre-test values for each day (p < 0.00001). Submaximal oxygen consumption was significantly reduced in the experimental group for up to 28 days (p < 0.0004), and stride length was significantly reduced for 14 days (p < 0.05) after the ultramarathon. Furthermore, in the experimental group RER was significantly increased for up to seven days (p < 0.05), and RPE was significantly increased for up to four days (p < 0.04) after the ultramarathon. In conclusion, the decreased submaximal oxygen consumption following the ultramarathon may be interpreted as a positive training adaptation. However, other responses to the ultramarathon were not compatible with improved running performance. Furthermore, symptoms other than pain should be used to define the recovery period after an ultramarathon race.
Open Access
Collected studies
(2002) Noakes, Timothy
A collection of published studies establishing the central governor model of exercise physiology, and the aetiology of the hyponatraemia of exercise.
Open Access
Comparative effects of calcium channel antagonism and beta-1 selective blockade on exercise performance in physically active hypertensive patients
(1997) Selvey, Christine Enid; Derman, Wayne
The current recommendations by the American Heart Association for health promotion are that all persons should partake in regular physical activity in order to reduce the risk of cardiovascular disease. Regular physical exercise reduces blood pressure and is an important component of the management of hypertension. It is therefore important that patients with hypertension participate in habitual physical exercise. Many hypertensive patients who exercise will require anti-hypertensive medication. However, some antihypertensive agents cause fatigue during exercise. In order for patients to gain the full benefits of an active lifestyle, it is important that the prescribed antihypertensive agent does not prevent them performing and enjoying sustained exercise. It has been well documented that β-blockers cause premature fatigue during physical exercise. The effects on exercise performance of other first line antihypertensive medications, such as calcium channel antagonists have not been extensively investigated. In particular, the effects of these agents on prolonged submaximal exercise endurance have not been well studied. The object of this thesis was to compare the effects of isradipine, a dihydropyridine calcium channel antagonist, to those of atenolol, a β₁-selective antagonist, on maximal and submaximal exercise performance and on short duration high-intensity exercise in physically active hypertensive patients. The study design was a crossover trial where drug treatments were double blinded and randomised. Physically active volunteers with mild to moderate hypertension were recruited. 11 subjects performed i) progressive exercise to exhaustion for determination of maximal oxygen consumption (VO₂max), maximal work load and cardiorespiratory responses to maximal exercise, ii) prolonged submaximal exercise for determination of exercise endurance, cardiorespiratory responses and ratings of perceived exertion (APE), and iii) short duration, high intensity exercise consisting of a 30 second maximal exercise test (Wingate test) to determine skeletal muscle power output, following 4 weeks ingestion of isradipine (2.5mg bd), atenolol (50mg bd) or placebo. Diastolic blood pressure at rest was reduced by both atenolol and isradipine, but was lowered to a greater extent by atenolol (83.3 vs 89.0 vs 96.1 mmHg, atenolol vs isradipine vs placebo, p<.0005). Systolic blood pressure at rest tended to be similarly reduced by both agents, but was significantly reduced during maximal and submaximal exercise by atenolol only (p<.001, atenolol vs isradipine, placebo). Heart rate at rest and during maximal and submaximal exercise was decreased by atenolol only (p<.0005, atenolol vs isradipine, placebo). Maximal exercise performance was reduced after atenolol ingestion compared to placebo but not after isradipine ingestion. Peak workload achieved during the maximal exercise test was decreased after atenolol but unchanged after isradipine ingestion (214 vs 243 W, atenolol vs placebo, p<.01). Similarly, VO₂max was reduced after atenolol compared to placebo but was unchanged after isradipine ingestion (33.6 vs 36.4, 33.6 vs 36.1 mlO₂/kg/min, atenolol vs placebo, atenolol vs isradipine, p<.05). Both atenolol and isradipine ingestion reduced submaximal endurance time compared to placebo (27.8 vs 46.4, 34.4 vs 46.4 min, atenolol vs placebo, isradipine vs placebo, p<.005), and increased rating of perceived exertion (APE) after 30 min of submaximal exercise (p<.05). Submaximal oxygen consumption (VO₂), ventilation, respiratory exchange ratio (REA) and blood lactate, glucose and free fatty acid concentrations were not altered after the ingestion of either agent. Neither agent influenced peak skeletal muscle power, total work done, or rate of fatigue during the Wingate test compared to placebo. The results of these studies indicate that impaired performance and increased RPE during submaximal exercise after ingestion of either atenolol or isradipine is not due to alterations of ventilation, VO₂, RER, or blood lactate, glucose and free fatty acid concentrations during prolonged submaximal exercise. Similarly, reduced submaximal exercise performance after atenolol or isradipine ingestion is not due to factors which would also limit the ability of skeletal muscle to perform short duration, high intensity exercise before a bout of prolonged exercise. This study demonstrates that prolonged submaximal exercise testing can reveal an impairment in exercise performance after ingestion of antihypertensive medication which is not evident during maximal exercise testing. This finding is important as prolonged submaximal exercise is the form of exercise which most hypertensive patients actually perform. Further research is required on the effects of anti-hypertensive medications on submaximal exercise performance before firm recommendations can be made regarding medications most suitable for the physically active hypertensive patient. The results of these and other studies indicate that it is not yet possible to make claims that the calcium channel antagonist agents are without effect on physical exercise performance in physically active hypertensive patients.
Open Access
The effect of branched-chain amino acid ingestion on physical performance during prolonged exercise
(1996) Velloza, Peter Edward; Lambert, Michael I
It has been hypothesized that an increase in the ratio of plasma tryptophan (TRP) to branched-chain amino acid (BCAA) concentrations may mediate an increase in cerebral serotonin synthesis, through an increased cerebral tryptophan uptake. It is postulated that the increased brain serotonin content may induce central fatigue during prolonged exercise. Until present, this postulate had not been subject to rigorous scientific testing during prolonged exercise. Therefore the aim of this study was to investigate whether ingesting a BCAA supplement during prolonged exercise improves physical performance and central fatigue. The use of such a supplement during prolonged exercise could then be expected to have a large effect on performance. Eight trained cyclists (VO₂ max= 61.9 ± 4.3 ml 02/kg/min) ingested, in random order, a drink containing either 10% carbohydrate (CHO), 10% CHO and 0.16% branched-chain amino acid (BCAA) or 0.16% BCAA. Every hour, for the duration of the exercise (4 hours, 55% VO₂ max) blood samples were analysed for amino acids, ammonia, free fatty acids, glycerol, glucose and insulin concentrations. Urine was analysed for urea and creatinine concentrations. Heart rate, oxygen consumption (VO₂), respiratory exchange ratio (RER) and rating of perceived exertion were also analysed. Thereafter, subject's 40km time trial performance and RPE was assessed on a Velodyne windtrainer. Central fatigue following the time trial was quantified using the Sternberg reaction-time paradigm. The serum concentration of the BCAA's declined as a result of the exercise, in the BCAA only trial. Tryptophan concentration, however, did not change during the exercise. The serum TRP:BCAA ratio increased (0.16 ± 0.06 to 0.20 ± 0.10; p≤0.05) in the CHO trial only. The BCAA trial differed from the two trials in which CHO was ingested because plasma ammonia and glucose concentrations did not increase, while free fatty acids (FF A's) and glycerol concentrations increased significantly (p≤0.05). The lower RER in the BCAA trials suggests a higher proportion of fat was oxidised in these trials, compared to the other two trials. Cycling performance, over a 40km time trial, (CHO= 68.59 ± 6.02; CHO+ BCAA = 68.00 ± 3.01; BCAA = 69.43 ± 5.35 min/sec), ratings of perceived exertion, submaximal or maximal heart rates, and mental performance were not different between trials. Data from this study appears to refute the thesis hypothesis that an increase in serum TRP:BCAA decreases physical performance and central fatigue, during prolonged exercise.
Open Access
The effect of muscle glycogen status on control of substrate metabolism during exercise
(1998) Weltan, Sandra Mary; Noakes, Timothy D; Dennis, Steve
Glycogen depletion has frequently been shown to result in a decrease in respiratory exchange ratio (RER). However, the metabolic response to glycogen depletion has generally been studied in overnight fasted subjects or in subjects who were already fatigued, or hypoglycaemic, or both, raising the question of whether the differences seen were due to general "carbohydrate deficiency" or due specifically to muscle or liver glycogen depletion. If euglycaemia and especially hyperglycaemia is maintained, the " carbohydrate deficiency" is overcome. In addition, because insulin stimulates muscle glucose uptake and not liver glucose uptake during euglycaemia (except at very high concentrations), insulin infusion would differentiate between liver and muscle glycogen depletion, since if the decrease in RER previously observed is abolished with insulin infusion while euglycaemia is maintained, this would indicate that the decrease is specifically due to muscle glycogen depletion. Thus, the aim of this study was to investigate the metabolic effect of glycogen content while an adequate amount or an excess of carbohydrate was provided in the form of an intravenous glucose infusion and when plasma insulin concentrations are raised.
Open Access
The effect of oral creatine supplementation on one hour cycling performance and metabolism
(1995) Bellinger, Brett; Myburgh, Kathryn Helen
The effect of oral creatine (Cr) supplementation with 20 g/day for 7 days on one-hour cycling performance and metabolism was investigated in a double-blind placebo controlled study. Twenty endurance-trained male cyclists volunteered for the study that was approved by the University of Cape Town ethics committee. The subjects' peak sustained power output was measured and they underwent a familiarization one-hour cycle on a cycle ergometer. Five days later subjects had a muscle biopsy and an indwelling cannula was inserted into a forearm vein before performing a maximal one-hour cycle (T1) during which blood samples were taken at regular intervals. Following the cycle, the subjects each received either Cr or placebo tablets to be ingested four times per day for the following week. After the loading week the subjects again reported to the laboratory, had a muscle biopsy and underwent and the same test routine (T2) with blood sampling as the previous week. Resting muscle total Cr measured by HPLC increased significantly (p<0.001) in the Cr group from 123.0 ± 3.8 mmol/kg dry wt to 159.8 ± 7.9 mmol/ kg dry wt, but was unchanged in the placebo group. The extent of Cr loading was not related to baseline Cr levels (r=0.46, NS). No differences were noted in the resting levels of adenine nucleotides in either group. Analyses of the plasma samples indicated no change in plasma lactate concentration, but a significant lowering of indicators of adenine nucleotide degradation including concentrations of plasma ammonia (p<0.05) and hypoxanthine (p<0.01) in the Cr group from T1 to T2. Plasma urate concentration was significantly lowered (p<0.01) from T1 to T2 but there were no differences between groups. Cr supplementation did not significantly improve performance in the one-hour trial (Cr group: 39.1 ± 0.9 km vs 39.8 ± 0.8 km and placebo group: 39.3 ± 0.8 km vs 39.2 ± 1.1 km). We hypothesised that Cr supplementation affects the purine nucleotide cycle through improved maintenance of low intracellular ADP during exercise as a result of enhanced efficiency of the Cr-PCr shuttle. Cr supplementation had no effect on lactate and carbohydrate metabolism and did not improve performance significantly during a one-hour cycle trial.
Open Access
The effect of repeated bouts of downhill training on running performance and recovery after a 30-km time trial
(2001) Schutte, Lynne; Lambert, Michael I; Rogers, G; Lombard, R
Purpose: The present study was designed to examine the effect of repeated bouts of either downhill or level running on running performance in, and recovery from, a 30-km time trial. Methods: Sixteen male subjects with a mean (± SD) age of 33.8 ± 5.8 years, body mass of 72.0 ± 7.3 kg and a stature of 176.6 ± 4.5 cm were randomly allocated to either a downhill (n=9) or a level group (n=7). The protocol consisted of a training phase, followed by a 30-km time trial and a recovery phase. During the training phase subjects ran either at a -10% grade (downhill group) or a 0% grade (level group) on a treadmill for nine 40-minute training runs [70% of peak treadmill running speed (PTRS)]. Thereafter all the subjects participated in a 30-km time trial (70% of PTRS), where heart rate (HR), rate of perceived exertion (RPE) and stride length (SL) were recorded, followed by five 15-minute submaximal recovery runs. The first recovery run was performed before the start of the training phase and again on four occasions after the 30-km time trial. HR, RPE, SL, minute ventilation (Vi), oxygen consumption (VO₂), carbon dioxide production (VCO₂) and respiratory exchange ratio (RER) were recorded during these 15-minute runs. Plasma creatine kinase (CK) activity and muscular soreness were assessed for the duration of the study. Results: HR decreased in the downhill group during the training phase, suggesting a HR training effect. Muscle pain and plasma CK activity in the downhill group increased after the first 40-minute downhill training run. These indicators of muscle damage did not show any further increases during the training phase, suggesting a "repeated bout effect". Towards the end of the 30-km time trial the level group, showed a greater heart rate drift (HRD) and an increased RPE, suggesting that they were not able to resist fatigue to the same extent as the downhill group. HR and RPE recorded during the recovery phase suggested that the downhill group showed a better recovery after the 30-km time trial. During the recovery phase the downhill group experienced no increase in muscle pain after performing the 30-km time trial, in contrast to the level group who experienced muscle pain for five days after the 30-km time trial. Plasma CK activity, was blunted after the 30-km time trial in the downhill group in contrast to the level group. Conclusion: The results of the investigation support the hypothesis that the inclusion of downhill training into a training program cause changes, which can be interpreted as enhancing performance during an endurance event and recovery after the event.
Open Access
The effects of prior oral creatine supplementation on performance and metabolism after 7 days of sprint cycle training
(1996) Bold, Antoinette; Myburgh, Kathryn Helen
Oral creatine supplementation has been shown to increase skeletal muscle total creatine (TCr) content, and in some cases improve performance in high-intensity short duration exercise. A variety of factors related to an enhanced efficacy of adenine nucleotide metabolism have been demonstrated as partly responsible for this ergogenic effect. Also, there is evidence that high-intensity sprint training results in a decrease in muscle total adenine nucleotide (TAN) and/or ATP stores. This placebo controlled double-blind study examined whether an oral creatine supplementation regimen would 1) increase muscle TCr content, 2) attenuate any loss in TAN or ATP during intermittent sprint training, and 3) have an ergogenic effect on performance after sprint training. Thirteen male endurance trained cyclists ingested 20 g of creatine monohydrate supplement or placebo per day for 7 days, after which they ingested a maintenance dose of 2 g creatine or placebo per day for the remainder of the trial (15d). While on the maintenance dose, subjects performed intermittent sprint training (ST) on a cycle ergometer (10 x 10 s sprints with 140 s active recovery) for 6 consecutive days and a 7th day after one day of rest. Performance tests were performed before and after ST, and metabolic tests were performed on the 1st and 7th day of ST. TCr increased significantly with creatine supplementation (creatine group pre: 121 ± 4, post: 147 ± 9; vs. placebo group pre: 122 ± 4, post: 125 ± 4 mmol/kg dm; mean± SEM; p<0.05). The increase in TCr correlated with the percentage Type IIB fibres (r=0.95, p<0.005). By day 7 of ST, TCr content was no longer significantly higher than pre-supplementation levels despite the maintenance dose of creatine. ST resulted in a significant decrease in resting muscle TAN and ATP content in both groups (ATP content in creatine group pre: 24.1 ± 0.8, post: 17.2 ± 0.5; and placebo group pre: 26.5 ± 1.1, post: 18.0 ± 0.6 mmol/kg dm; p<0.001). During and in recovery from ST on day 7, both groups had lower plasma ammonia (p<0.05), hypoxanthine (p<0.001) and urate (p<0.001) accumulation than on day 1 of ST. There was no improvement in 1-hr cycle distance performance after ST, but peak sustained power output increased in the creatine group and not in the placebo group after ST (p<0.05). Peak and mean power during a 30 s Wingate test increased significantly (p<0.05) after ST but there was no additional ergogenic effect of creatine supplementation. In conclusion, this study shows that 1) the efficacy of muscle creatine uptake was dependent on the percentage of Type IIB fibres, 2) creatine supplementation and maintenance (2 g/d) did not attenuate ATP or TAN loss during 7 days of ST, 3) ST decreased the accumulation of plasma products of adenine nucleotide degradation and improved 30 s sprint performance, and 4) creatine supplementation and ST did not improve I-hr cycle distance performance.
Open Access
Endogenous glucose production and gluconeogenesis during exercise in athletes on either a low-carbohydrate or mixed diet
(2015) Webster, Christopher Charles; Noakes, Timothy; Smith, James
INTRODUCTION. The LCHF diet produces major changes in whole-body substrate metabolism and energy stores such as reduced muscle and liver glycogen content, increased rates of fat oxidation and decreased rates of carbohydrate (CHO) oxidation. Despite reduced CHO availability, the rate of CHO oxidation that can be sustained during exercise in LCHF athletes is surprisingly high. The most probable source of this glucose is via the process of gluconeogenesis (GNG). However, endogenous glucose production (EGP) and GNG has not been studied during exercise in athletes on a LCHF diet. Therefore, the aim of this study was to determine if there are differences in EGP, GNG and glycogenolysis (GLY) during exercise in endurance-trained athletes who habitually eat either a mixed or LCHF diet. METHODS. Fourteen (7 LCHF, 7 Mix) endurance-trained male cyclists (VO₂max 61 ± 5 ml/kg/min LCHF; 6 3 ± 8 ml/kg/min Mix), matched for age (36 ± 6 y LCHF; 32 ± 5 y Mix), body composition (BMI 23.6 ± 1.8 LCHF; 23.4 ± 2.0 Mix) and relative peak power output (4.8 ± 0.4 W/kg LCHF; 5.0 ± 0.4 W/kg Mix), were recruited. Diets were analysed using the Automated Self-Administered 24-hour Recall (ASA24) analysis software. Participants cycled for 2 h at 55% of peak power output during which EGP was measured by infusion of [6,6- ²H₂ ]glucose, and fractional gluconeogenesis was measured by ingestion of ²H₂O. Blood samples were collected at regular intervals for isotope enrichment analysis. R ESULTS. Rates of GNG were similar during exercise in both the LCHF and mixed diet groups (2.8 ± 0.4 mg/kg/min LCHF; 2.5 ± 0.3 mg/kg/min Mix). The rates of GLY during exercise were significantly higher in the mixed diet group than the LCHF group (3.2 ± 0.7 mg/kg/min LCHF; 5.3 ± 0.9 mg/kg/min Mix) which resulted in significantly higher rates of EGP in the mixed diet group (6.0 ± 0.9 mg/kg/min LCHF; 7.8 ± 1.1 mg/kg/min Mix). There were significant differences in the mean fat oxidation rates (1.2 ± 0.2 g/min LCHF; 0.5 ± 0.2 g/min Mix) and CHO oxidation rates (1.3 ± 0.5 g/min LCHF; 3.1 ± 0.5 g/min Mix). Blood beta-hydroxbutyrate (βHB) concentrations were significantly higher in the LCHF group than in the mixed diet group throughout exercise but there were no differences in plasma glucose, plasma lactate, serum insulin or serum FFA concentrations. The diets of the two groups differed only in fat and CHO intake (%Protein / %Fat / %CHO: 21/72/7 LCHF; 16/33/51 Mix). DISCUSSION. Rates of fat oxidation and CHO oxidation were not associated with the rates of GNG. Apart from βHB, the precursor, substrate and insulin concentrations were remarkably similar in both groups and may have influenced GNG similarly in both groups. We conclude that rates of GNG are relatively stable across a broad range of habitual diets that can significantly alter substrate utilisation, and that dietary CHO modulates the rates of EGP via alterations in rates of GLY, both at rest and during exercise.
Open Access
Epidemiology and prevention of rugby injuries amongst schoolboy, senior club and provincial rugby players in the Western Cape
(2000) Upton, Patrick Anthony Howard; Noakes, Timothy D
This thesis comprises a series of independent investigations examining rugby injuries occurring to players from under 14 to senior provincial level in the Cape Province (now the Western Cape). The first two studies report data aimed at gaining a more detailed understanding of rugby injuries in specific populations or under specific conditions, whilst the remainder of the thesis reports injury data from both a retrospective and a prospective epidemiological survey involving the same 3990 boys from 25 high schools. Following publication of data showing a progressive rise in the number of spinal cord injuries in the Western Cape, coupled with a sustained media attack on the attitudes of the (then) South African Rugby Board, certain experimental law changes were introduced to South African schoolboy rugby in 1990 and 1991. The purpose of the law changes was either to make the game safer or to make it more open and flowing, or both. Accordingly, the studies described in chapters 4 -8 set out to analyse the effects of these law changes on the incidence and nature of rugby injuries. This was accomplished by comparing data with a similar study conducted in 1983 and 1984 in the same 25 schools (Roux, 1992). The study reported in chapter 2 determined whether the use of neoprene (thermal) pants might reduce the risk of hamstring injury amongst 60 senior club rugby players, all of whom had previously sustained a hamstring muscle tear. The rationale was that the few seasons prior to this 1992 study had been characterised by an increasing use by rugby players of thermal or neoprene pants; a practice which seemed to have evolved spontaneously and without any scientific assessment of its value. We concluded that the wearing of thermal pants can reduce the risk of hamstring injury during rugby. However, other risk factors for injury are probably more important. These include levels of preseason physical fitness, correct warm up and stretching procedures before activity and adequate rehabilitation before returning to activity following injury. The objective of the study reported in chapter 3 was to determine the influence of preseason strength and endurance training on risk of injury in rugby players from two South African provincial teams during the 1992 rugby season. Players from one province followed a supervised scientifically-designed physical training programme, while those from the other did not follow a structured programme. The findings of the study, the first study to prove the relationship between pre-season preparation and early season injury, showed that inadequate pre-season endurance training is a major contributor to the high injury rate at the beginning of the season amongst provincial rugby players. Further, strength and endurance training are interrelated as risk factors. Thus, compared to players with adequate strength and endurance training, those with adequate strength training and insufficient endurance training are at greatest risk of injury, followed by players with insufficient strength and endurance training. It was also shown that contact practices 2 days after inter-provincial match contributed more to an increased number of injuries than to success; that "niggling" injuries may develop into more serious injury if players attempt to "play through" them; and that the lack of structured treatment and rehabilitation of an injury places players at risk of being re-injured.
Open Access
Exercise and bone mass in mature premenopausal women
(1996) Micklesfield, Lisa Kim; Myburgh, Kathryn Helen
Open Access
Exercise associated muscle cramping : investigating a novel hypothesis
(2003) Sulzer, Nicole Uschi; Schwellnus, Martin P; St Clair Gibson, Alan
This thesis on Exercise Associated Muscle Cramping (EAMC) comprised three individual studies. The aims of this series of investigations were firstly to investigate the nature and prevalence of EAMC in a group of lronman triathletes with a past history of EAMC, secondly to compare the serum electrolyte concentrations in cramping and control Ironman triathletes as well as to record the baseline electromyography (EMG) of cramping lronman triathletes during recovery and thirdly to compare the EMG activity of cramping and control runners before, during and after a fatiguing bout of exercise.
Open Access
Exercise tolerance and skeletal muscle structure and function in patients with chronic obstructive pulminary disease
(1998) Coleman, Kirsty Lee; Derman, Wayne
Exercise intolerance is well documented in patients with chronic obstructive pulmonary disease (COPD). Historically, this exercise intolerance has been attributed to the central factors of lung damage and subsequent heart failure. However, recent evidence suggests that (i) patients with cardiac and renal failure suffer from skeletal muscle (SM) abnormalities that impair exercise tolerance and (ii) patients with chronic obstructive pulmonary disease (COPD) may have metabolic and functional abnormalities of SM. However, no studies have conducted a detailed investigation of SM structure and function and their relation to exercise tolerance in patients with COPD.
Open Access
Exercise tolerance and skeletal muscle structure and function in patients with severe chronic heart failure
(1995) Derman, Kirsten Louise; Noakes, Timothy D
Fatigue and exercise intolerance are common symptoms experienced by patients with chronic heart failure (CHF). Historically it has been argued that central cardiopulmonary factors including pulmonary congestion and reduced lung compliance cause dyspnoea that limits the exercise tolerance of such patients. But recent studies have indicated that exercise capacity in patients with CHF may not be limited solely by central cardiorespiratory factors. Rather the focus has shifted to aspects of the peripheral circulation and skeletal muscle function as possible factors limiting the exercise tolerance of patients with CHF. However there are few studies describing both the structural and functional abnormalities in the skeletal muscle of patients with CHF. In the first study of this dissertation, 11 patients with end-stage heart failure (NYHA class Ill-IV) and 10 healthy control subjects (C) underwent i) graded exercise to exhaustion for determination of peak oxygen consumption (VO₂ peak) and peak work load (Wlpeak); ii) isometric and isokinetic tests of skeletal muscle function and iii) radionuclide angiography for determination of ejection fraction (EF%). VO₂ peak (12.5 ± 1.0 vs 34.3 ± 3.5 mlO₂fkg/min; p<0.001), Wlpeak (73 ± 10 vs 224 ± 14 W; p<0.001), total work performed by the quadriceps muscles (TWQ) in a 30 sec isokinetic test (TWQ; 1565 ± 166 vs 2892 ± 345 J; p<0.05), and hamstring muscles (TWH) (TWH; 604 ± 163 vs 2003 ± 326 J; p<0.05), maximum voluntary isometric contraction (MVC) of the quadriceps muscles (MVC; 134 ± 12 vs 194 ± 11 Nm; p<0.001) and isokinetic peak torque of the ~uadriceps (PKTQ) (PKTQ; 133 ± 15 vs 203 ± 23 Nm; p<0.05) and hamstring muscles (PKTH) (PKTH; 60 ± 8 vs 108 ± 16 Nm; p<0.05) and time to fatigue during a test of isometric endurance (68 ± 12 vs 100 ± 10 sec; p<0.05) were all significantly lower in patients with CHF. However when corrected for the reduced lean thigh volume (muscle mass) in patients with CHF, PKTQ, PKTH and MVC were no longer different from control values. But the total work performed by the quadriceps and hamstring muscles in a 30 second isokinetic test was reduced even when corrected for the reduced lean thigh volume in patients with CHF. Furthermore, patients with CHF terminated progressive cycle exercise to exhaustion at heart rates, rates of ventilation, respiratory exchange ratios and blood lactate concentrations that were significantly lower than values achieved by control subjects during maximal dynamic exercise. These data suggest that skeletal muscle functional abnormalities including a decreased resistance to the development of fatigue exist in patients with severe CHF. In the second study of this dissertation, 10 patients with CHF who participated in the first study and eight control subjects underwent a skeletal muscle biopsy of the vastus lateralis muscle for light and electron microscopic analysis. Significant histological and ultrastructural changes were found in all SM biopsies from patients with CHF. These included atrophy and hypertrophy of fibres, fibre splitting, internalized nuclei, nuclear knots, moth-eaten fibres, increased lipid droplets. Electron microscopy showed a large variety of nonspecific abnormalities, including mitochondrial changes, Z-band degeneration and accumulation of intracellular glycogen. Ultrastructural morphometry revealed capillary basement membrane width significantly increased in the SM of patients with CHF, (409 ± 13 vs 121 ± 3 nm; p<0.01). A novel, blinded, impartially scored method for grading SM pathology showed that SM biopsies of patients with CHF had higher scores for myopathic changes compared to C (12.0 ± 1.5 vs 1.6 ± 1.0 arbitrary units; p<0.05). SM pathology score correlated significantly with VO₂ peak, Wlpeak, and TWQ (p<0.05 to p<0.02) but not with EF%. EF% did not correlate with either VO₂ peak, Wlpeak or TWQ. These data support the hypothesis that: i) severe SM structural and functional abnormalities may limit exercise capacity in patients with CHF; ii) the severity of SM pathology but not resting systolic cardiac function, predicts exercise performance in patients with CHF.
Open Access
Exercise-induced protection against insulin resistance and type 11 diabetes : the role of calcium
(2008) Smith, James Antony Harris; Ojuka, Edward; Collins, Malcolm
Regular exercise protects individuals against developing insulin resistance and type II diabetes. This effect of exercise does not appear to be due to an improvement in the insulin signalling pathway but instead due to an increase in the content of the insulin-regulatable glucose transporter (GLUT4) in skeletal muscle (84). Understanding the mechanisms by which exercise increases GLUT4 levels in skeletal muscle may reveal targets for pharmaceuticals to treat insulin resistance and type II diabetes. Although in vitro binding assays have shown that GLUT4 expression during exercise is mediated by the binding of myocyte enhancer factor-2A (MEF2A) to its cis-element on the Glut4 promoter (122), this has not been demonstrated in vivo. Moreover, the mechanisms by which exercise increases MEF2A binding to the Glut4 promoter have not been fully characterised.
Open Access
Inactivity and overfeeding related changes in skeletal muscle composition and metabolism in captive felids - are they at risk of developing metabolic syndrome?
(2016) Feldmann, Daneil; Kohn, Tertius; Tordiffe, Adrian S W
Obesity and physical inactivity are established key risk factors in the development of skeletal muscle insulin-resistance and type II diabetes in human and domestic animal populations. Wild animals are similarly exposed to these risk factors as a result of captivity. This study aimed at describing the skeletal muscle properties of captive lions (Panthera leo) who present with obesity and are physically inactive, with a group of free roaming wild lions. Skeletal muscle biopsies were collected from the Triceps brachii and analysed for fibre type composition, fibre size, and maximum oxidative (citrate synthase (CS), 3-hydroxyacyl CoA dehydrogenase (3HAD) and glycolytic (phosphofructokinase (PFK) and lactate dehydrogenase (LDH) enzyme capacities. The type IIA fibres were the predominant fibre type in both the wild (48%) and captive (44%) lions. No significant differences were evident in the overall fibre type composition between groups, although a trend towards less type I (28% vs 36%) and more type IIX (28% vs 16%) fibres in the captive group were observed. The captive lions displayed significantly larger cross-sectional areas (CSA) of the type I (5847μm² vs 3318 μm²) and IIA fibres (8344μm² vs 4360μm²) with no difference evident in the CSA of the IIX fibres. Relationships were observed between body mass and the CSAs of type I (r = 0.68, P = 0.0002) and IIA (r = 0.44; P = 0.03) fibres. Metabolically, the captive lions displayed higher flux through the glycolytic pathway as represented by their higher PFK activities (551 ± 287 vs. 338 ± 123 μmol/min/g protein, P < 0.05). In contrast, their CS activities (11 ± 3 vs. 14 ± 2 μmol/min/g protein) were lower than free roaming lions, suggesting lower oxidative capacity. No differences in LDH and 3HAD activities were observed between the two groups. Relationships were observed between 3HAD activity and MHC IIx fibre content (r = -0.43, P = 0.001), 3HAD activity and MHC I content (r = 0.55, P = 0.001). A positive correlation was observed between CS activity and MHC I content (r = 0.35, P = 0.009). In light of previous research, the data collected from this project follows that observed in exercise training models, where a sedentary lifestyle decreases oxidative capacity of muscle and increases type II fibre content. However, due to the low sample size in the free roaming wild lion group, interpretation of the data is difficult. Therefore, future research must strive to increase the sample number of the free roaming group.
Open Access
The influence of methylphenidate on heart rate and brain connectivity
(2018) Van Breda, Keelyn; Rauch, Laurie; Stein, Dan J; King, Michael; Jankiewicz, Marcin
The central governor model (CGM) proposes that muscle recruitment is regulated by the brain through subconscious homeostatic control of afferent feedback. It has been suggested that the dopaminergic system plays a key role in the CGM, with dopaminergic activation leading to lower fatigue thresholds. Key neural circuits, including the central autonomic network (CAN), may also play a role in altering thresholds by reducing conscious bodily awareness, known as interoception. However, few studies have directly examined the dopaminergic neurotransmitter system and CAN connectivity, during exercise-induced fatigue. Although there is reason to suspect that subjects with high activity (HA) and low activity (LA) levels have different fatigue thresholds, potential differences in dopaminergic function and related circuity have not been compared across these groups. In this thesis, I was therefore interested in examining the impact of a dopaminergic agent, methylphenidate (MPH) on: a) brain connectivity at rest before exercise and during exercise, b) on heart rate (HR) at rest before exercise and during exercise. Furthermore, c) I was interested in whether the effect of MPH administration (MA) on HR and functional connectivity (FC), between CAN regions, pre-exercise impacted HR and FC during exercise and whether this differed between HA and LA subjects. In order to measure the effect of MA on brain connectivity at rest and during exercise I used a functional magnetic resonance imaging (fMRI) scanner. To measure the effect of MA on fatigue thresholds, I used a MRI compatible handgrip device which recorded grip force output during a fatiguing handgrip task. To measure HR before and during handgrip exercise I used a MRI compatible electrocardiogram (ECG) machine. My first study aimed to determine the effect of MA on resting state (R-fMRI) FC between CAN regions and its correlation with HR before exercise. My second study aimed to see the effect of MA on task HR, force output and, FC and EC between CAN regions, during a fatiguing handgrip task. My third study aimed to see the effect of MA on the relationship between HR and FC pre-exercise and HR and FC during exercise and whether this differed between LA and HA subjects. I found that: 1.) MA decreased R-fMRI FC between CAN regions, and that this was associated with an increase in HR during resting state 2.) MA decreased FC between CAN regions with an associated increase in task HR and force output during a fatiguing handgrip task 3.) After MA, R-fMRI FC determines task FC independent of HR 4.) MA significantly increased task HR in LA but not HA subjects 5.) After MA, R-fMRI FC determines task FC independent of HR in LA but not HA subjects. Taken together, the functional uncoupling of CAN regions and increased HR after MA suggests that MA increases the fatigue threshold by diverting attention away from interoceptive cues, such as HR. However, this finding may be more relevant in LA subjects, where MA is also associated with increased HR during exercise.