Timothy D Noakes

• MBChB, MD, DSc, PhD (hc)
• Professor (Associate) at Cape Peninsula University of Technology

The hypothesis that fatigue during prolonged exercise arises from insufficient intramuscular glycogen, which limits tricarboxylic acid cycle (TCA) activity due to reduced TCA cycle intermediates (TCAI), was tested in this experiment. Seven endurance-trained men cycled at similar to70% of peak O-2 uptake ((V)over dot (O2 peak)) until exhaustion with...

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

Purpose: This study was designed to determine whetherthe acceptance of self-responsibility is an important determinant of the successful outcome of coronary artery bypass graft (CABG) surgery. The success of this costly intervention may be limited unless patients understand and adhere to the prescribed medical regimen, including diet and exercise a...

During endurance exercise, about 75% of the energy produced from metabolism is in the form of heat, which cannot accumulate. The remaining 25% of energy available can be used for movement. As running pace increases, the rate of heat production increases. Also, the larger one's body mass, the greater the heat production at a particular pace. Sweat e...

A plateau in oxygen consumption (VO(2)) has long been considered the criterion for maximal effort during an incremental exercise test. But, surprisingly, the termination of a maximum exercise test often occurs in the absence of a VO(2) plateau. To explain this inconsistency, some have proposed that an oxygen limitation in skeletal muscle occurs onl...

To determine the neuromuscular recruitment characteristics during supramaximal exercise. Ten healthy subjects completed the Wingate anaerobic test (WAT) cycling protocol. Electromyographic (EMG) data and rate of fatigue were recorded throughout the cycling. The mean (SD) rate of fatigue (decrease in power output) was 44.5 (8.6)%. No significant cha...

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 s...

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 ca...

This study investigated the effects of the neu-romuscular and force–velocity characteristics in distance running performance and running economy. Eighteen well-trained male distance runners performed five different tests: 20 m maximal sprint, running economy at the velocity of 4.28 m s À1 , 5 km time trial, maximal anaerobic running test (MART), an...

Purpose: The aim of this study was to compare the biomechanical changes during natural heel-toe running with learned midfoot and Pose running. Methods: Twenty heel-toe runners were instructed in midfoot running and a novel running style in which the acromium, greater trochanter, and lateral malleolus are aligned in stance (Pose running). Clinical g...

Exercise-associated collapse (EAC) is the most common reason that athletes are treated in the medical tent following an endurance event. The pathophysiology of EAC is postural hypotension that results when the loss of muscle pumping action caused by the cessation of exercise is combined with cutaneous vasodilation. EAC usually occurs after an athle...

In this review, fatigue is described as a conscious sensation rather than a physiological occurrence. We suggest that the sensation of fatigue is the conscious awareness of changes in subconscious homeostatic control systems, and is derived from a temporal difference between subconscious representations of these homeostatic control systems in neura...

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A study was conducted to determine the outcome of Coronary artery bypass graft (CABG) surgery in terms of patients’ improved quality of life one year after the intervention. Quality of life was assessed in terms of return to work, absence of angina and increased activity. The analysis of the variables identified on admission between two groups (tho...

This study analysed the effect of different electromyographic (EMG) capture rates during maximal voluntary contraction, submaximal and maximal dynamic cycling activity on EMG amplitude and signal characteristics. Ten healthy subjects participated in this study. Peak power output (PPO) and maximal isometric force output (MVC) were measured, followed...

This study analysed the effect of different electromyographic (EMG) capture rates during maximal voluntary contraction, submaximal and maximal dynamic cycling activity on EMG amplitude and signal characteristics. Ten healthy subjects participated in this study. Peak power output (PPO) and maximal isometric force output (MVC) were measured, followed...

AIM: To determine the neuromuscular recruitment characteristics during supramaximal exercise. METHODS: Ten healthy subjects completed the Wingate anaerobic test (WAT) cycling protocol. Electromyographic (EMG) data and rate of fatigue were recorded throughout the cycling. RESULTS: The mean (SD) rate of fatigue (decrease in power output) was...

The aim of the study was to determine the effects of a 12-over fast bowling spell on bowling pace, accuracy and selected physiological variables. Subjects were randomly divided into an experimental (bowled 12 overs and performed physiological tests after each over) and a control group (only bowled the 1st and 12th over and performed physiological t...

To establish relationships between body weight changes and serum sodium during and after an Ironman Triathlon, and postrace fluid status and rectal temperature, including the incidence of hyponatremia. Descriptive research. The 2000 South African Ironman Triathlon, in which each athlete swam 3.8 km, cycled 180 km, and ran 42.2 km. All entrants in t...

This study analysed the effect of hot (35 degrees C) and cold (15 degrees C) environments on electromyographic (EMG) signal characteristics, skin and rectal temperatures and heart rate during progressive endurance exercise. Eight healthy subjects performed three successive 15-min rides at 30%, 50% and 70% of their peak sustained power output and th...

Since its first description in 1985, two opposing theories have evolved to explain the etiology of symptomatic hyponatremia of exercise. The first holds that the condition occurs only in athletes who lose both water and sodium during exercise, and fail to fully replace their sodium losses. The second theory holds that the symptomatic form of this c...

Since its first description in 1985, two opposing theories have evolved to explain the etiology of symptomatic hyponatremia of exercise. The first holds that the condition occurs only in athletes who lose both water and sodium during exercise, and fail to fully replace their sodium losses. The second theory holds that the symptomatic form of this c...

While the bicycle frame and other parts of the bicycle have undergone many improvements, the bicycle saddle has remained relatively unchanged since it was first designed more than 100 years ago. Given the number and range of cycling injuries believed to result from the saddle, this is surprising. This study investigated the effects of a novel bicyc...

Although androgenic hormones decrease HDLC concentration, no direct evidence has linked them to atherosclerosis. The present study was undertaken to extend our ability to assess risk associated with androgen induced lipoprotein(Lp) changes by simultaneously gathering information about postprandial triglyceridaemia (PPT), LDL particle size, HDL and...

The aim of this study was to determine the physical demands on female club-level hockey players during a match. These demands were determined by using video analysis to quantify the horizontal displacement of the players (n=11) every 15s during a match (n=3). A scale diagram of the hockey field was used to plot the position of each player every 15s...

The aim of this study was to examine the role of fasting insulin concentrations and tissue insulin sensitivity on whole-body substrate oxidation in 61 well-trained subjects. Subjects underwent a frequently sampled intravenous glucose tolerance test (FSIVGT) after a 10- to 12-hour overnight fast. Minimal model analysis was used to determine insulin...

To determine whether rates of intestinal fluid absorption and renal diuresis can match high rates of fluid ingestion in healthy humans exposed to oral fluid overload, thereby preventing the development of hyponatraemia either by reverse sodium movement across the intestine (the Priestley-Haldane effect) or by expansion of the extracellular fluid vo...

An enduring hypothesis in exercise physiology holds that a limiting cardiorespiratory function determines maximal exercise performance as a result of specific metabolic changes in the exercising skeletal muscle, so-called peripheral fatigue. The origins of this classical hypothesis can be traced to work undertaken by Nobel Laureate A. V. Hill and h...

To determine whether athletes who had previously developed hyponatremia during an ultradistance triathlon show an impaired ability to excrete a large fluid load compared with athletes who had completed the same race without developing hyponatremia. Six athletes who had developed hyponatremia ([Na] < 135 mmol x L(-1)) in the 1997 Ironman Triathlon (...

We examined neuromuscular activity during stochastic (variable intensity) 100-km cycling time trials (TT) and the effect of dietary carbohydrate manipulation. Seven endurance-trained cyclists performed two 100-km TT that included five 1-km and four 4-km high-intensity epochs (HIE) during which power output, electromyogram (EMG), and muscle glycogen...

We examined the effects of a high-fat diet (HFD-CHO) versus a habitual diet, prior to carbohydrate (CHO)-loading on fuel metabolism and cycling time-trial (TT) performance. Five endurance-trained cyclists participated in two 14-day randomized cross-over trials during which subjects consumed either a HFD (> 65% MJ from fat) or their habitual diet (C...

The aim of the study was to determine the effects of 8 weeks of moderate exercise training, on 24-hour free living energy expenditure in previously sedentary post-menopausal women. The experimental group (EX) included 9 women. Ten non-exercising control subjects (CON) were recruited to undergo pre- and post-testing. Estimated total daily energy exp...

Aim: To assess electromyographic (EMG) gait pattern changes during stair descent in subjects with chronic anterior cruciate ligament (ACL) deficiency, and in subjects after ACL reconstruction.Methods: Thirteen ACL deficient subjects (ACLdef), 8 ACL reconstructed subjects (ACLrec), and 10 controls (CON) participated in the study. All subjects were a...

In the study presented here, we examined the affects of a close to complete replacement of sweat water and Na+ losses on fluid shifts during exercise. Six cyclists performed three 4-h rides at 55% of their peak oxygen uptake in a 20 degrees C environment while consuming 3.85 l of an 8% carbohydrate solution containing 5, 50 or 100 mEq.l-1 of Na+. I...

Physical activity (PA) assessment has become increasingly important in establishing the relationship between inactivity and disease. However, there are few examples of validated PA questionnaires used in a cross-cultural context. The International Physical Activity Questionnaire (IPAQ) was developed by a World Health Organisation/ Centres for Disea...

This paper reviews the extensive literature on hyponatremia, a common and potentially serious complication of ultra-distance exercise. Fluid overload is the likely aetiology. Fluid intakes are typically high in athletes who develop hyponatremia, although hyponatremia can occur with relatively modest fluid intakes. The development of fluid overload...

The aim of the present study was to determine the reliability of a modified 5-m multiple shuttle test. The 'match-related fitness' of 23 female hockey players was assessed on four occasions within 4 weeks. The results of each test session and each shuttle were analysed using analysis of variance with repeated measures to determine the reliability o...

The perception of effort during exercise and its relationship to fatigue is still not well understood. Although several scales have been developed to quantify exertion Borg's 15-point ratings of perceived exertion (RPE) scale has been adopted as a valid and reliable instrument for evaluating whole body exertion during exercise. However, Borg's cate...

A common belief in exercise physiology is that fatigue during exercise is caused by changes in skeletal muscle metabolism. This 'peripheral' fatigue results either from substrate depletion during submaximal exercise or metabolite accumulation during maximal exercise in the exercising muscles. However, if substrate depletion alone caused fatigue, in...

Despite its long history and global appeal, relatively little is known about the physiological and other requirements of cricket. It has been suggested that the physiological demands of cricket are relatively mild, except in fast bowlers during prolonged bowling spells in warm conditions. However, the physiological demands of cricket may be underes...

Aim. The purpose of this study was to determine the neuromuscular fatigue profiles during 100 s isometric (ISO), concentric (CON), and eccentric (ECC) activity.Methods. Twelve subjects (age 25.1+/-3.7 years, mass 70.1+/-8.2 kg, mean+/-SD) performed ISO, CON and ECC maximal voluntary contractions and 100 s endurance trials on an isokinetic dynamomet...

We examined the variability and determinants of the respiratory exchange ratio (RER) at rest and during exercise in 61 trained cyclists. Fasting (10-12 h) RER was measured at rest and during exercise at 25, 50, and 70% of peak power output (W(peak)), during which blood samples were drawn for [lactate] and [free fatty acid] ([FFA]). Before these mea...

Patellofemoral pain (PFP) is a common overuse injury in cycling, but its etiology in cycling is not well understood. It is associated with poor patellar alignment during knee movement from flexion to extension. Biomechanical factors associated with patellar malalignment include poor quadriceps function, vastus medialis obliquus insufficiency, exten...

The 20th century witnessed the globalization of international sporting competitions, most notably in Olympic Competition. Thus whereas fewer than 20 countries competed in the 1900 Olympic Games, close to 200 countries were represented at the 2000 Olympic Games in Sydney. There has also been a progressive improvement in athletic performance during t...

The purpose of the current investigation was to determine whether sodium citrate enhances endurance cycling performance and, if so, what dosage(s) produces this effect. Eight trained [peak power output: 362 (48) W; power:weight: 5.1 (0.4) W x kg(-1), mean (SD)] male cyclists were requested to complete four, 40-km time-trials, each separated by 3-7...

The major objective of medical care is to preserve life. If patients cannot be cured and are left with residual chronic diseases then the aim is to provide them with the means to lead a life of quality within the confines of their disease. Rehabilitation in chronic disease means restoring or creating a life of acceptable quality. This is achieved b...

We investigated the effect of oral creatine supplementation (20 g d−1 for 7 days) on metabolism during a 1-h cycling performance trial. Twenty endurance-trained cyclists participated in this double-blind placebo controlled study. Five days after familiarization with the exercise test, the subjects underwent a baseline muscle biopsy. Thereafter, a c...

We investigated the effect of oral creatine supplementation (20 g d(-1) for 7 days) on metabolism during a 1-h cycling performance trial. Twenty endurance-trained cyclists participated in this double-blind placebo controlled study. Five days after familiarization with the exercise test, the subjects underwent a baseline muscle biopsy. Thereafter, a...

To study fluid and sodium balance during overnight recovery following an ultradistance triathlon in hyponatremic athletes compared with normonatremic controls. CASE CONTROL STUDY: Prospective descriptive study. 1997 New Zealand Ironman Triathlon (3.8 Km swim, 180 Km cycle, 42.2 Km run). Seven athletes ("subjects") hospitalized with hyponatremia (me...

The 20th century witnessed the globalisation of international sporting competitions, most notably in Olympic Competition. Thus whereas fewer than 20 countries competed in the 1900 Olympic Games, close to 200 countries were represented at the 2000 Olympic Games in Sydney. There has also been a progressive improvement in athletic performance during t...

Purpose: In this study, we examined the effects of greater than ad libitum rates of fluid intake on 2-h running performances. Methods: Eight male distance runners performed three runs on a treadmill at 65% of peak oxygen uptake (VO2peak) for 90 min and then ran "as far as possible" in 30 min in an air temperature of 25 degrees C, a relative humi...

Editor,—Professor Schwenk makes the important point that elite athletes are not immune to serious mental illness and that many of the symptoms of overtraining may, in another context, be considered diagnostic of …

The strength of modern medicine is its relentless quest for an elusive perfection. That quest requires that we examine our errors even more closely than our successes. It is for this reason that the case report of Flinn and Sherer ("Seizure After Exercise in the Heat: Recognizing Life-Threatening Hyponatremia," page 61) is so important. For it reco...

Aim: The aim of this study was to assess the relationship between the quadriceps muscle atrophy and strength deficits caused by chronic ACL deficiency, and to ascertain whether these deficits were rectified in subjects who had undergone ACL reconstruction. Methods: Thirteen ACL deficient subjects (ACLD) and eight subjects who had undergone ACL reco...

Cross-sectional analytical study in which subjects served as their own controls. To assess the concentric and eccentric peak torque in the hamstrings and quadriceps muscles, hamstrings/quadriceps amplitude ratios, and lean thigh volume differences in the involved and uninvolved limb of subjects with anterior cruciate ligament (ACL) deficiency. [cor...

The unique physiologic characteristics of an ironman triathlete present challenges to physicians covering ultraendurance events. Cardiovascular emergencies at the finish line are rare. Occult blood in postrace urine is common but rarely of clinical significance. Medical volunteers must distinguish between signs of dehydration, heatstroke, hyponatre...

A popular concept in the exercise sciences holds that fatigue develops during exercise of moderate to high intensity, when the capacity of the cardiorespiratory system to provide oxygen to the exercising muscles falls behind their demand inducing "anaerobic" metabolism. But this cardiovascular/anaerobic model is unsatisfactory because (i) a more ri...

To study fluid and sodium balance in two ultradistance triathletes. Prospective case study. An ultradistance triathlon (3.8 km swim, 180 km cycle, 42.2 km run), and during overnight recovery. Ambient air temperature at 12:00 p.m. race day was 21 degrees C, with a relative humidity of 91%. Water temperature was 20.7 degrees C. Two female ultradistan...

To establish whether there was a relationship between the total accumulated distances of racing in veteran runners and the neuromuscular efficiency of the quadriceps muscles before and after a downhill run. University of Cape Town, Sports Science Institute of South Africa. Twenty male veteran long distance runners (45-50 years of age) with a range...

Four days after competing in an Olympic-distance National Triathlon Championship (1500-m swim, 40-km cycle, 10-km run), five male and five female triathletes underwent comprehensive physiological testing in an attempt to determine which physiological variables accurately predict triathlon race time. All triathletes underwent maximal swimming tests...

We evaluated the effect of carbohydrate (CHO) loading on cycling performance that was designed to be similar to the demands of competitive road racing. Seven well-trained cyclists performed two 100-km time trials (TTs) on separate occasions, 3 days after either a CHO-loading (9 g CHO. kg body mass(-1). day(-1)) or placebo-controlled moderate-CHO di...

The stress electrocardiogram (sECG) is routinely used to screen individuals for underlying cardiac pathology before an exercise programme is prescribed. The underlying assumption is that the cardiac responses elicited during the sECG test are similar to those achieved during participation in sporting activities. However, this premise may be incorre...

To evaluate a method of medical care at an ultradistance triathlon, with the aim of reducing the incidence of hyponatremia. Descriptive research. New Zealand Ironman triathlon (3.8 km swim, 180 km cycle, 42.2 km run). 117 of 134 athletes seeking medical care after the triathlon (involving 650 race starters). A prerace education program on appropria...

Zusammenfassung Das 20. Jahrhundert zeugt von einer Globalisierung der internationalen Sportwettkmpfe. Dies ist wohl am eindrucksvollsten an den olympischen Spielen zu sehen. Whrend 1900 noch weniger als 20 Lnder an den olympischen Spielen teilgenommen hatten, waren im Jahr 2000 in Sydney bereits um die 200 Lnder vertreten. berdies kam es im letzt...