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The introduction of the needle muscle biopsy technique in the 1960s allowed muscle tissue to be sampled from exercising humans for the first time. The finding that muscle glycogen content reached low levels at exhaustion suggested that the metabolic cause of fatigue during prolonged exercise had been discovered. A special pre-exercise diet that maximized pre-exercise muscle glycogen storage also increased time to fatigue during prolonged exercise. The logical conclusion was that the athlete’s pre-exercise muscle glycogen content is the single most important acutely modifiable determinant of endurance capacity. Muscle biochemists proposed that skeletal muscle has an obligatory dependence on high rates of muscle glycogen/carbohydrate oxidation, especially during high intensity or prolonged exercise. Without this obligatory carbohydrate oxidation from muscle glycogen, optimum muscle metabolism cannot be sustained; fatigue develops and exercise performance is impaired. As plausible as this explanation may appear, it has never been proven. Here, I propose an alternate explanation. All the original studies overlooked one crucial finding, specifically that not only were muscle glycogen concentrations low at exhaustion in all trials, but hypoglycemia was also always present. Here, I provide the historical and modern evidence showing that the blood glucose concentration—reflecting the liver glycogen rather than the muscle glycogen content—is the homeostatically-regulated (protected) variable that drives the metabolic response to prolonged exercise. If this is so, nutritional interventions that enhance exercise performance, especially during prolonged exercise, will be those that assist the body in its efforts to maintain the blood glucose concentration within the normal range.

Objective. To establish the previous rugby experience, the knowledge and the use of injury prevention techniques by South African schoolboy rugby players.Design. Before the first full-contact match of the 1991 rugby season, 2 330 players completed a detailed questionnaire.Setting. I-!igh schools in the Cape Province. Three thousand three hundred and thirty players from 25 schools selected because of a record of excellence in and commitment to schoolboy rugby.Main outcome measures. Personal data including age, height, mass and rugby experience; history and nature of previous rugby injuries; knowledge of techniques known to prevent rugby injuries; parental and personal reasons for playing rugby.Results. The incidence and distribution of the different types of injuries previously sustained by the players were the same as those identified prospectively in the same population. A-team players were significantly heavier and taller than players in lower teams in most playing positions in most age groups. Although A-team players were more likely to participate in pre-season endurance or strength training, fewer than 40% of players overall trained adequately in the pre-season. Less than 30 minutes was allocated to the practice of tackJing and falling techniques prior to the first full-contact match. Knowledge of different high-risk situations during play was generally sketchy, and only 24% of players wore gumguards all the time. Morefathers (84%) than mothers (63%) encouraged their sons to play rugby.Conclusions. The resutts indicate that the incidence and nature of the injuries reported retrospectively were similar to those reported in prospective studies at the same schools. The players' knowledge of techniques known to prevent rugby injuries was inadequate and too little attention was paid at the start of the rugby season totraining and coaching techniques to reduce injury risk. Coaching errors may therefore have predisposed players to injury.

One of the first principles of cricket batsmanship for batting coaches is to teach junior cricketers to play using a straight bat. This requires the bat to be lifted directly towards the stumps with the bat face facing downwards. No study has yet examined whether there are differences in the batting back lift techniques (BTT) of coached cricketers (CC) and uncoached cricketers (UC). With the study sample, CC comprised of both adolescent (n=30) and amateur (n=10) cricketers, whereas the UC comprised of only young cricketers (n=40). Various types of deliveries were bowled to the participants utilising a bowling machine. Biomechanical and video analyses were performed on both participant groups. Classifiers were utilised to identify the type of BTT employed by all batsmen. More than 70% of uncoached cricketers adopted a lateral BTT, whereas more than 70% of CC adopted the straight BTT. Coaching implications from this study suggest that if players are not coached, they automatically hit the ball using a lateral BTT, which indirectly suggests that coaching emphasising traditional techniques could be disadvantageous to the young cricketer.Key words: Video analysis; Batting back lift techniques; Cricket; Coached and uncoached batsmen.

No Abstract.

to the editor: The importance of considering the complex interaction of various biological responses to exercise in the process of explaining the limitation to human performance has previously been re-emphasized ([5][1]). In his timely Viewpoint, Hargreaves ([4][2]) now specifically highlights the

The following letters are in response to the Point:Counterpoint series “Positive effects of intermittent hypoxia (live high:train low) on exercise performance are/are not mediated primarily by augmented red cell volume” that appeared in the November issue (vol. 99: 2056–2061, 2005

The world's first successful human heart transplantation on 2 December 1967 inspired me to study medicine at the University of Cape Town's Faculty of Health Sciences. There I learned 5 key elements for a successful career in either medicine or science or both - perfectionism, passion, compassion, the dispassionate investigation of all the available evidence, and the need to challenge established beliefs for which the scientific evidence appears imperfect. Challenging such beliefs enabled us to prove that hyponatraemic encephalopathy was caused by persistent and heroic over-drinking during prolonged exercise, usually lasting more than 4 hours, and was unrelated to salt losses in sweat and urine; to understand that the brain not the muscles must regulate the exercise performance, and thus develop the Central Governor Model of Exercise; and to reconsider the dietary causes of the obesity and diabetic epidemic.

Objectives. To evaluate common factors associated with the development of acute renal failure (ARF) in Comrades Marathon runners.Methods. This was a retrospective case series of 4 runners hospitalised post-race with ARF in the 89 km 2010 Comrades Marathon. The outcome measures were incidence of analgesic use, levels of creatine phosphokinase (CPK) and degree of electrolyte supplementation (sodium, potassium, calcium and magnesium).Results. The prevalence of ARF was 1/4 125 runners. They presented with rhabdomyolysis (mean admission CPK of 36 294 IU) and hyponatraemia (mean admission blood sodium level of 133 mEq/l). All had ingested an analgesic during the run (3 ingested a non-steroidal anti-inflammatory drug) and the same readily available anti-cramp electrolyte supplement. The average amount of supplemental sodium (452 mg), potassium (393 mg), calcium (330 mg) and magnesium (154 mg) ingested via this particular electrolyte supplement before and during the run did not exceedthe recommended upper limits of daily intake. Three of the runners were Comrades Marathon novices.Conclusions. There is a continuing need to clarify the specific cluster variants that cause ARF in Comrades Marathon runners, as the risk factors appear to have evolved since the first case was described over 40 years ago.S Afr Med J 2011;101:876-878.

OBJECTIVE: To compare the effect of two training programmes and advice to exercise at home on physiological adaptations in patients with peripheral arterial disease (PAD). DESIGN: 30 patients with a typical history of PAD and intermittent claudication were randomised to either an upper body strength training programme (UBST), a dynamic (walking, cycling, circuit) conventional exercise rehabilitation programme (CER), or advice to 'walk as much as possible at home' (CONT). Before and after intervention groups performed a standard graded treadmill exercise test (GTET) and a 6-minute walk test (SMWT) to determine peak physiological parameters and walking distances. Maximal walking distance (MWD), pain-free walking distance (PFWD), peak oxygen uptake (VO2) , heart rate and perceived pain were measured. RESULTS: MWD on the GTET increased significantly in the CER group compared with the CONT and UBST groups (93.9±79% v. 7.0±19.8% v. 7.3±46%; CER v. UBST v. CONT p=0.003). Similarly, peak VO2 increased with CER compared with the CONT and UBST groups (28.4±20 v. -6.2±15 v. -1.0±21%; CER v. UBST v. CONT p=0.004). During the SMWT the CER and UBST groups improved in PFWD compared with the CONT group (37±47% v. 27±71% v. -30±29%; CER v. UBST v. CONT p=0.03), and perceived pain decreased in the CER group compared with the UBST group (-24±39% v. 27±48%; CER v. UBST p=0.01). CONCLUSION: CER improves physiological parameters and walking distances more than UBST does. CER is effective within 6 weeks. Verbal encouragement to exercise is an ineffective form of management.

Humans evolved as an athletic species able to run in the midday heat, to throw with exquisite accuracy and to strike powerfully despite relatively weak upper arms compared to those of the great apes. The true extent to which humans could run long distances was first tested in a unique series of 6-day foot races contested between 1874 and 1888 by professional athletes from England and the United States. These athletes typically would have expended approximately 60,000 kcal (24.12 MJ) of energy during these races. The discovery of the bicycle soon caused the replacement of these races by 6-day cycling races which, in turn, led to the modern day Tour de France, the cycling race across America (RaAM) and two running races across the width of the United States in 1928 and 1929. The total energy expenditures during these different events can be estimated at approximately 168,000, 180,000 and 340,000 kcal respectively. But, in terms of the total energy expenditure, all these performances pale somewhat when compared to that of Robert Falcon Scott's Polar party during the 1911/12 British Antarctic Expedition. For most of 159 consecutive days, Scott's team man-hauled for 10 hours a day to the South Pole and back covering a distance of 2500 km. Their predicted total energy expenditure per individual would have been about 1 million kcal, making theirs, by some margin, the greatest sustained endurance athletic performance of all time. Interestingly, the dogs that provided the pulling power for Norwegian Roald Amundsen's team that was the first to reach the South Pole, 35 days before Scott's party, would have expended about 500,000 kcal in their 97 day trip, making theirs the greatest animal "sporting" performance on record. By contrast, mountain climbers expend only approximately 4000 kcal/day when climbing at extreme altitudes (above 4000 m). This relatively low rate of energy expenditure results from the low exercise intensities that can be sustained at extreme altitude. Here I argue that this slow rate of energy expenditure is caused, not by either myocardial or skeletal muscle hypoxia as is usually argued, but is more likely the result of a process integrated centrally in the brain, the function of which is to protect the body from harm. At extreme altitude the organ at greatest risk is the brain which must be protected from the catastrophic consequences of profound hypoxia. A key feature of this control is that it acts "in anticipation" specifically to insure that a catastrophic biological failure does not occur. The evidence for this interpretation is presented.

Philosophy and the Sciences of Exercise, Health and Sport is a unique interdisciplinary study that calls on researchers in these disciplines to reflect more critically on the nature and aims of scientific enquiry. In doing so, the book questions the underlying assumptions and development of science itself. Written by a range of internationally respected philosophers, scientists and social scientists, each chapter addresses a key issue in research methodology. Questions asked by the authors include: Do natural and social scientists need to understand the philosophy of science? Are statistics misused in sport and exercise science research? Is sport science research gender-biased? How do external and commercial interests skew professional guidelines in health and sport reserach? Should scientists focus their attention on confirmation of theories, or on attempts to falsify them? Philosophy and the Sciences of Exercise, Health and Sport serves notice to exercise, health and sport researchers to think more philosophically about their subject and its scientific bases. It is essential reading for postgraduate researchers seeking to establish a sound theoretical foundation for their work.

Three exercise-related heat illnesses are described in the literature -- heat cramps, heat exhaustion or heat syncope, and heat stroke. Of these, only exercise-induced heat stroke, which occurs infrequently, is definitely a heat illness caused by an increased rate of heat production unmatched by adequate heat loss causing progressive heat retention with the body temperature rising to dangerously high levels (> 41 degrees C). The terms heat cramps and heat exhaustion are misleading as neither is caused by an elevated body temperature; nor is there evidence that either is caused by specific fluid or electrolyte abnormalities. Cramps occur during or after exercise regardless of whether the exercise is performed in the heat or the cold, or in water. Current evidence suggests that a spinal neural mechanism may induce cramping that is unrelated to biochemical changes in either blood or in the affected skeletal muscles. Historically, heat exhaustion has been described as a condition of postural hypotension that develops immediately on termination of exercise especially when performed in the heat by unacclimatised persons. No modern evidence conflicts with this historical interpretation. Nor have more modern studies shown that exercise-related heat exhaustion is necessarily caused by specific fluid or electrolyte abnormalities. Similarly, there is no published evidence that fluid and electrolyte abnormalities are critical determinants of exercise-related heat stroke. This does not negate firm evidence that dehydration has important physiological effects that impair heat loss and exercise performance especially in the heat. Rather, it shows that exercise-induced heat stroke requires powerful initiating factors, in addition to dehydration which occurs commonly during prolonged exercise, whereas heat stroke is an extremely rare event. The purpose of this review is to provide an alternate, more critical review of the conditions that are considered to be exercise-related heat disorders and to evaluate the aetiological role of fluid and electrolyte disturbances. There is a need to better understand these conditions so that their clinical management can be based on modern information rather than on dated ideas, many of which have survived unchallenged for more than 50 years.

The following is the abstract of the article discussed in the subsequent letter: We determined the effect of fat adaptation on metabolism and performance during 5 h of cycling in seven competitive athletes who consumed a standard carbohydrate (CHO) diet for 1 day and then either a high-CHO diet (11

Advice to overdrink may cause fatal hyponatraemic encephalopathy A recent report that a female participant in the 2002 Boston marathon died from hyponatraemic encephalopathy because she ingested excessive volumes of a sports drink before and during the race,1 exposes an emotive debate that has raged for more than a decade.2 At issue is how much should athletes drink during exercise.3 From antiquity to the late 1960s, athletes were advised not to drink during exercise since it was believed that fluid ingestion impaired athletic performance.2 The publication in 1969 of an incorrectly titled article, “The danger of an inadequate water intake during marathon running,”4 provided the impetus for change, even though the study neither examined a 42 km marathon race nor did it identify any dangers.2 Rather, the most dehydrated athletes won those 32 km races, as is usually the case.2 This article's incorrect title provided the intellectual incentive for numerous studies, many funded by a fledgling sports drinks industry, culminating …

Approximately 80% of the athletes who collapse in marathon and other long distance sporting events do so only after they have crossed the finish line.1 Although it is usually taught that “dehydration” explains this phenomenon, logic suggests this to be unlikely because any dehydration induced hypovolaemia should cause cardiovascular failure when cardiac stress is highest—that is, during rather than after exercise when cardiovascular function is returning to the resting state. Instead it is clearly the act of stopping exercise that is the consequent, albeit paradoxical, cause of post-exercise collapse. We have previously proposed that this form of exercise associated collapse is caused by the persistence into recovery of a state of low peripheral vascular resistance, compounded by removal of the skeletal muscle pump that maintains the right atrial filling pressure during exercise.1 According to this theory, the combination of a low peripheral vascular resistance and a sudden reduction in venous return would reduce stroke volume and cardiac output acutely, causing hypotension. Indeed this mechanism was used to explain the development of postural hypotension due to “dehydration exhaustion” in military personnel exposed to eight or more hours of exercise in desert heat without fluid replacement, in the classic studies of Adolph.2 Thus Adolph2 wrote that “the ultimate failure of the circulation (in dehydration exhaustion) is of a peripheral type . . . Dilated blood vessels of the skin require additional blood to fill them; correspondingly, …

The following letters are in response to the Point:Counterpoint series “In health and in a normoxic environment, Vo2 max is/is not limited primarily by cardiac output and locomotor muscle blood flow” that appeared in the February issue (vol 100: 744–748, 2006

Twelve boys with atopic asthma, ages 9-14 years, were divided equally into exercise and control groups. Identical measurements were made before and after a 3-month trial period during which the exercise group was trained. The trained group, but not the control group, showed significant improvements in parameters of physical fitness including maximum oxygen consumption (V̇O2max) and peak running velocity during the maximal treadmill test (p

OBJECTIVE: To determine which physiological variables conduce to walking intolerance in patients with peripheral arterial disease (PAD). DESIGN: The physiological response to a graded treadmill exercise test (GTT) in patients with PAD was characterised. SETTING: Patients were recruited from the Department of Vascular Surgery, Groote Schuur Hospital, Cape Town. SUBJECTS: Thirty-one patients diagnosed with PAD were included in the study. OUTCOME MEASURES: During a GTT, peak oxygen consumption (VO2peak), peak minute ventilation (VEpeak), peak heart rate and peak venous lactate concentrations were measured and compared with those from a comparison group. Ankle-brachial index (ABI) was measured at rest and after exercise. During the GTT, maximum walking distance (MWD) and pain-free walking distance (PFWD) were measured to determine walking tolerance. RESULTS: Peak venous lactate concentrations did not correlate significantly with either PFWD (r=-0.08; p=0.3) or MWD (r=-0.03; p=0.4). Resting ABI did not correlate with either MWD (r=0.09; p=0.64) or PFWD (r=-0.19; p=0.29). Subjects terminated exercise at significantly (p

This study was conducted on a South African cohort to establish the actors that may predict the successful outcome of coronary artery bypass surgery when assessed in terms of improved quality of life one year after the surgery. Information was sought on the socio-economic status of patients, their risk-factor profiles and clinical history. From the patient files, information was recorded on left ventricular ejection fraction, number of vessels bypassed, bypass time, and aortic cross-clamp time. The characteristics that were predictive of a successful outcome one year after surgery were identified. Patients in this study represented a high-risk population with multiple risk factors (obese, heavy smokers, hypertensive, hypercholesterolaemic, inactive, family history of heart disease, diabetes, and regular intake of alcohol). Measured medical parameters could not distinguish between the group with an improved quality of life and the group who did not have improved quality of life. One year after CABG all patients with an improved quality of life were men. The additional identified predictor variables for a successful outcome were: being married, patients' height, the knowledge that smoking affects the cardiovascular system, number of years that sporting activities were stopped prior to CABG surgery, a better quality sex life after the operation, acceptance of self-responsibility for rehabilitation, and the spouse knowing the diet the patient should follow. The predictors of a successful outcome at the time of the operation were: being married (OR = 22.6; p = 0.02); taller than 170 cm (OR = 15.5; p = 0.01); stopped all sporting activities for a period less than 20 years prior to their surgery (OR 11.4; p = 0.01). We concluded that the outcome of coronary artery bypass surgery could not be predicted on the basis of a medical model that considers exclusively the extent of the patient's disease and associated co-morbidities. Patients should be carefully selected and an intensive post-operative educational intervention should be provided to patients and their spouses/caregivers.

OBJECTIVE: To determine the impact of the 1990 rugby law changes in South African schoolboy rugby on the number of schoolboys suffering paralysing spinal cord injuries in the subsequent eight rugby seasons (1990-1997) in the former Cape Province (now the Western Cape, but including Port Elizabeth and East London). METHODS: The study was a retrospective analysis of all patients with rugby-related spinal cord injuries admitted to the Conradie and Libertas Spinal Units, Cape Town, between 1990 and 1997. Data were initially collected annually from patient files. From 1993 patients were interviewed in hospital and a standardised questionnaire was completed. Data were collated and analysed. RESULTS: There were 67 spinal cord injuries in adult and schoolboy rugby players in the eight seasons studied. Fifty-four (80%) injuries were in adults and 13 (20%) in schoolboys, representing a 23% increase and a 46% reduction in the number of injured adults and schoolboys, respectively. Fifty-two per cent of those injuries for which the mechanism was recorded occurred in the tackle phase of the game; of these approximately equal numbers were due to vertex impact of the tackler's head with another object, or to illegal (high) tackles. Twenty-five per cent of injuries occurred in the ruck and maul and the remainder (23%) in the collapsed scrum. The only striking difference in the proportion of injuries occurring in the different phases of play was the absence of high-tackle injuries among schoolboys. The majority of injuries occurred at vertebral levels C4/5 (32%) and C5/6 (42%). Five players (8%) died, tetraplegia occurred in 48% and 35% recovered either fully or with minor residual disability. Playing position was recorded for half the injured players. Front-row forwards (props 33%, hookers 9%), locks (12%) wings and centres (21%) and loose forwards (15%), accounted for 90% of all injuries. CONCLUSIONS: Introduction of rugby law changes in South African schoolboy rugby in 1990 may have led to a 46% reduction in the number of spinal cord injuries in this group. In contrast, the number of these injuries in adult rugby players increased during the same time period due either to an increase in the number of adult players or to a real increase in the incidence of these injuries. More injured schoolboy than adult rugby players made total or near-complete recoveries from initially paralysing injuries (61% v. 28%). The reduced number of schoolboy injuries could not have resulted directly from the specific law changes introduced in 1990, which targeted scrum laws. Rather, the absence of illegal (high) tackle injuries among schoolboys appears to be the principal factor explaining fewer injuries in schoolboys, who suffered a higher proportion of injuries in the ruck and maul than did adult players. Accordingly we conclude that a further reduction in spinal cord injuries in adult and schoolboy rugby players in the Western Cape requires: (i) the elimination of injuries occurring in the ruck and maul, and to the tackler; (ii) the strict application of the high-tackle rule in adult rugby; and (iii) a continuing, high level of vigilance. Concern must be expressed about the continuing number of paralysing spinal cord injuries in adult rugby players.

This study analyzed the effect of caffeine ingestion on performance during a repeated-measures, 100-km, laboratory cycling time trial that included bouts of 1- and 4-km high intensity epochs (HIE). Eight highly trained cyclists participated in 3 separate trials - placebo ingestion before exercise with a placebo carbohydrate solution and placebo tablets during exercise (Pl), or placebo ingestion before exercise with a 7% carbohydrate drink and placebo tablets during exercise (Cho), or caffeine tablet ingestion before and during exercise with 7% carbohydrate (Caf). Placebo (twice) or 6 mg · kg-1 caffeine was ingested 60 min prior to starting 1 of the 3 cycling trials, during which subjects ingested either additional placebos or a caffeine maintenance dose of 0.33 mg · kg-1 every 15 min to trial completion. The 100-km time trial consisted of five 1-km HIE after 10, 32, 52, 72, and 99 km, as well as four 4-km HIE after 20, 40, 60, and 80 km. Subjects were instructed to complete the time trial and all HIE as fast as possible. Plasma (caffeine) was significantly higher during Caf (0.43 ± 0.56 and 1.11 ± 1.78 mM pre vs. post Pl; and 47.32 ± 12.01 and 72.43 ± 29.08 mM pre vs. post Caf). Average power, HIE time to completion, and 100-km time to completion were not different between trials. Mean heart rates during both the 1-km HIE (184.0 ± 9.8 Caf; 177.0 ± 5.8 Pl; 177.4 ± 8.9 Cho) and 4-km HIE (181.7 ± 5.7 Caf; 174.3 ± 7.2 Pl; 175.6 ± 7.6 Cho;p less than .05) was higher in Caf than in the other groups. No significant differences were found between groups for either EMG amplitude (IEMG) or mean power frequency spectrum (MPFS). IEMG activity and performance were not different between groups but were both higher in the 1-km HIE, indicating the absence of peripheral fatigue and the presence of a centrally-regulated pacing strategy that is not altered by caffeine ingestion. Caffeine may be without ergogenic benefit during endurance exercise in which the athlete begins exercise with a defined, predetermined goal measured as speed or distance.

Objective. To determine the frequency and nature of injuries sustained by the 416 players from 16 countries participating in the 1995 Rugby World Cup played in South Africa in May/June 1995.Methods. The study was a prospective analysis of all injuries requiring medical attention during that competition. Data were collected by the match doctors on duty at each of the venues at which the matches were played. Data were collated and analysed.Results. There were 48 preliminary and 7 final-round matches. Of a total of 70 injuries during the tournament, 58 occurred during the preliminary matches (frequency 30 injuries per 1 000 player hours); the frequency was somewhat higher during the 7 final-round matches (43 injuries per 1 000 player hours). Overall injury frequency was 1 injury every 0.8 matches during the preliminary and 1 every 0.6 matches during the final-round matches. Thirty per cent of injuries were to ligaments, 27% were lacerations and 14% were muscle strains. The lower limb accounted for 42% of all injuries, the upper limb for 29% and the face for 17%. Fifty-six per cent of injuries occurred during the tackle phase of play, 23% during the ruck and maul, 11 % during open play and 9% during foul play. The scrum and line-out together contributed only 1% of all injuries. Loose forwards suffered 25% of all injuries; centres and wings 20%; prop forwards and half-backs 16% each; locks 14%; hookers 7% and fullbacks 3%. One player suffered a paralysing spinal cord injury during a preliminary match. The incidence of catastrophic neck injuries in the tournament was therefore 4.6 per 10 000 player hours.Conclusions. The frequency of injury in this competition is the highest yet recorded in any group of rugby players. The risk of rugby injury is therefore greatest in the best players in the game, challenging the view that superior fitness, skill and experience can reduce the risk of rugby injury. In contrast, the larger size, greater speed and superior competitiveness and commitment of the best rugby players in the world would explain why they are at the highest risk of injury. The high frequency of injury in international rugby has implications for: (I) the frequency with which such matches should be played; and (il) the number of players needed to complete a season of international rugby.