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Biomedical subjects

T D Noakes

Publications and source records attributed to T D Noakes.

At least 91 records · Page 5Linked to original sources
PubMed2000

Veteran athletes exercise at higher maximum heart rates than are achieved during standard exercise (stress) testing.

OBJECTIVE: 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 incorrect since the physical demands of different modes of exercise vary substantially. DESIGN: Ten veteran league squash players (LSP), 10 social squash players (SSP), 10 league runners (LR), 10 social runners (SR) and 10 sedentary individuals (SED) were recruited for the study. All subjects completed a lifestyle questionnaire, a full medical examination and a routine sECG. Thereafter each subject's heart rate (HR) was monitored on two separate occasions while participating in sporting activity. RESULTS: No sECG exercise-induced abnormalities were observed, although five subjects showed resting abnormalities. Maximal HR during the sECG, and maximal and mean HR during the field tests, were not significantly different between groups. However, maximal HR was significantly higher in all groups during their sporting activities than during stress testing in the laboratory (P < 0.01). CONCLUSIONS: Maximal HR in veteran athletes during specific sporting activities was significantly higher than that attained during a routine sECG. This finding was not sport-specific, nor was it related to the level of competitiveness of the trial participants. These data show that a routine sECG is a submaximal test of exercise performance, and should be interpreted as such.

Blood Pressure Determination↗
PubMed1999

Advantages of a smaller bodymass in humans when distance-running in warm, humid conditions.

Using a 65-kg athlete running a 2 h 10 min marathon as an example, we estimated that imbalances between approximately 1400 W of heat production and dissipation would occur in ambient temperatures of 17 degrees C at 90% relative humidity (rh) to 37 degrees C at 50% rh. Because heat production during running depends on body mass and heat loss depends on surface area, intercepts between predicted heat production and maximal heat loss with increasing speeds depend on an athlete's body mass. At 35 degrees C and 60% rh, a 45-kg athlete could maintain thermal balance by running a 2 h 13 min marathon at 19.1 km x h(-1) but a 75-kg athlete would only be able run a 3 h 28 min marathon at 12.2 km x h(-1). In both cases, the production of 970-1020 W of heat would necessitate the evaporation of at least 1.5-1.6 l of sweat per hour. A lower metabolic heat production in lighter runners at any given speed may be one reason why smallness of stature is an asset in distance running.

Adult↗
PubMed1999

Water and electrolyte shifts with partial fluid replacement during exercise.

In this study, we examined whether athletes, who typically replace only approximately 50% of their fluid losses during moderate-duration endurance exercise, should attempt to replace their Na+ losses to maintain extracellular fluid volume. Six male cyclists performed three 90-min rides at 65% of peak O2 uptake in a 32 degrees C environment and ingested either no fluid (NF), 1.21 of water (W), or saline (S) containing 100 mmol of NaCl x l(-1) to replace their electrolyte losses. Both W and S conditions decreased final heart rates by approximately 10 betas min(-1) (P<0.005) and reduced falls in plasma volume (PV) by approximately 4% (P<0.05). Maintenance of PV after 10 min in the W trial prevented further rises in plasma concentrations of Na+ [Na+], Cl- and protein but in the S and NF trials, plasma [Na+] continued to increase by approximately 4 mEq x l(-1). Differences in plasma [Na+] had little effect on the approximately 2.4 l fluid, approximately 120 mEq Na+ and approximately 50 mEq K+ losses in sweat and urine in the three trials. The main effects of W and S were on body fluid shifts. During the NF trial, PV and interstitial fluid (ISF) and intracellular fluid (ICF) volumes decreased by approximately 0.1, 1.2 and 1.0 l, respectively. In the W trial, the approximately 1.2 l fluid and approximately 120 mEq Na+ losses contracted the ISF volume, and in the S trial, ISF volume was maintained by the movement of water from the ICF. Since the W and S trials were equally effective in maintaining PV, Na+ ingestion may not be of much advantage to athletes who typically replace only approximately 50% of their fluid losses during competitive endurance exercise.

Adult↗
PubMed1999

Metabolic adaptations to a high-fat diet in endurance cyclists.

We examined the time course of metabolic adaptations to 15 days of a high-fat diet (HFD). Sixteen endurance-trained cyclists were assigned randomly to a control (CON) group, who consumed their habitual diet (30% +/- 8% mJ fat), or a HFD group, who consumed a high-fat isocaloric diet (69% +/- 1% mJ fat). At 5-day intervals, the subjects underwent an oral glucose tolerance test (OGTT); on the next day, they performed a 2.5-hour constant-load ride at 70% peak oxygen consumption (VO2peak), followed by a simulated 40-km cycling time-trial while ingesting a 10% 14C-glucose + 3.44% medium-chain triglyceride (MCT) emulsion at a rate of 600 mL/h. In the OGTT, plasma glucose concentrations at 30 minutes increased significantly after 5 days of the HFD and remained elevated at days 10 and 15 versus the levels measured prior to the HFD (P < .05). The activity of carnitine acyltransferase (CAT) in biopsies of the vastus lateralis muscle also increased from 0.45 to 0.54 micromol/g/min over days 0 to 10 of the HFD (P < .01) without any change in citrate synthase (CS) or 3-hydroxyacyl-coenzyme A dehydrogenase (3-HAD) activities. Changes in glucose tolerance and CAT activity were associated with a shift from carbohydrate (CHO) to fat oxidation during exercise (P < .001), which occurred within 5 to 10 days of the HFD. During the constant-load ride, the calculated oxidation of muscle glycogen was reduced from 1.5 to 1.0 g/min (P < .001) after 15 days of the HFD. Ingestion of a HFD for as little as 5 to 10 days significantly altered substrate utilization during submaximal exercise but did not attenuate the 40-km time-trial performance.

Adaptation, Physiological↗
PubMed1999

Effects of ingesting a sports bar versus glucose polymer on substrate utilisation and ultra-endurance performance.

The purpose of this study was to determine whether the ingestion of a sports bar (BAR) containing a mixture of fat (7 g), protein (14 ) and carbohydrate (CHO; 19 ) improved ulta-endurance cycling performance compared to when an equicaloric amount of CHO was consumed. On two occasions separated by a minimum of 7 days, six highly trained (peak power output [PPO] 414 +/- 8 W) endurance cyclists rode for 330 min at approximately 50% of PPO (203 +/- 8 W) while ingesting either the BAR or just CHO, before performing a 400 k] time trial as fast as possible. Rates of fat oxidation were significantly greater at the end of the submaximal ride when subjects ingested the BAR compared to CHO (1.09 +/- 0.08 vs 0.73 +/- 0.08g x min(-1); P<0.05), and accordingly total fat oxidation was significantly higher (280 +/- 24 vs 203 +/- 25 g, P < 0.05). However, two subjects failed to complete the time trial after they consumed the BAR during the prolonged, submaximal ride, whereas all subjects managed to finish the time trial when ingesting CHO. In conclusion, ingestion of the sports bar enhanced fat metabolism during prolonged, submaximal exercise, but impaired subsequent high-intensity time-trial performance.

Adult↗
PubMed1999

The effect of a prophylactic dose of flurbiprofen on muscle soreness and sprinting performance in trained subjects.

The aim of this study was to examine the effects of a prophylactic dose of a local, transcutaneously administered, non-steroidal anti-inflammatory drug on muscle soreness, muscle damage and sprinting performance in young trained males. Twenty-five subjects aged 19+/-3 years, actively participating in rugby union and field hockey, were familiarized with the test procedure and then divided at random into an experimental group (n = 13) and a control group (n = 12). The experimental group received two patches, each containing 40 mg flurbiprofen (TransAct LAT), 12 h before an exercise bout designed to produce delayed-onset soreness (DOMS). The control group received identical non-medicated placebo patches at the same time. Delayed-onset muscle soreness was induced by an exercise protocol consisting of drop jumps (seven sets of 10 repetitions). Serum creatine kinase activity, muscle soreness, muscle girth and acceleration in a maximal sprint over 30 m were measured before the induction of DOMS and at 12, 24, 48 and 72 h thereafter. Plasma lactate concentration was measured 3 min after the 30-m sprint tests. Subjects in both groups had significantly more pain at 24 and 48 h compared with at 12 and 72 h (P < 0.05; Friedman two-way analysis of variance). Thigh girth and serum creatine kinase did not change throughout the experiment. Although plasma lactate concentrations were elevated after the 30-m sprint, there were no differences between groups or as a result of DOMS. The greatest acceleration occurred between 5 and 10 m. This was not affected by the anti-inflammatory drug or DOMS. In conclusion, the aetiology of the DOMS induced in the trained subjects in this study seems to be independent of inflammatory processes or, more specifically, of increases in prostaglandin synthesis in the muscles.

Adult↗
PubMed1999

The effect of a preexercise meal on time to fatigue during prolonged cycling exercise.

PURPOSE AND METHODS: Seven subjects exercised to exhaustion on a bicycle ergometer at a workload corresponding to an intensity of 70% maximal oxygen uptake (VO2max). On one occasion (FED), subjects consumed a preexercise carbohydrate (CHO) containing breakfast (100 g CHO) 3 h before exercise. On the other occasion (FASTED), subjects exercised after an overnight fast. Exercise time to fatigue was significantly longer (P < 0.05) when subjects consumed the breakfast (136+/-14 min) compared with when they exercised in the fasted state (109+/-12 min). RESULTS: Pre- and post-exercise muscle glycogen concentrations, respiratory exchange ratio, carbohydrate and fat oxidation, and lactate and insulin concentrations were not significantly different between the two trials. Insulin concentrations decreased significantly (P < 0.05) from 4.7+/-0.05 microIU.mL(-1) to 2.8+/-0.4 microIU.mL(-1) in FED and from 6.6+/-0.6 microIU.mL(-1) to 3.7+/-0.6 microIU.mL(-1) in FASTED subjects and free fatty acid concentrations (FFA) increased significantly (P < 0.05) from 0.09+/-0.02 mmol.L(-1) to 1.4+/-0.6 mmol.L(-1) in FED and from 0.17+/-0.02 mmol.L(-) to 0.74+/-0.27 mmol.L(-1) in FASTED subjects over the duration of the trials. CONCLUSIONS: In conclusion, the important finding of this study is the increased time to fatigue when subjects ingested the CHO meal with no negative effects ascribed to increased insulin concentrations and decreased FFA concentrations after CHO ingestion.

Adult↗
PubMed1999

Hyponatremia in ultradistance triathletes.

PURPOSE: Hyponatremia ([plasma sodium] <135 mmol x L(-1)) is a potentially serious complication of ultraendurance sports. However, the etiology of this condition is still uncertain. This observational cohort study aimed to determine prospectively the incidence and etiology of hyponatremia in an ultradistance triathlon. METHODS: The subjects consisted of 605 of the 660 athletes entered in the New Zealand Ironman triathlon (3.8-km swim, 180-km cycle, and 42.2-km run). Subjects were weighed before and after the race. A blood sample was drawn for measurement of plasma sodium concentration after the race. RESULTS: Complete data on pre- and postrace weights and plasma sodium concentrations were available in 330 race finishers. Postrace plasma sodium concentrations were inversely related to changes in body weight (P = 0.0001). Women (N = 38) had significantly lower plasma sodium concentrations (133.7 vs 137.4 mmol x L(-1); P = 0.0001) than men (N = 292) and lost significantly less relative weight (-2.7 vs -4.3%; P = 0.0002). Fifty-eight of 330 race finishers (18%) were hyponatremic; of these only 18 (31%) sought medical care for the symptoms of hyponatremia (symptomatic). Eleven of the 58 hyponatremic athletes had severe hyponatremia ([plasma sodium] < 130 mmol x L(-1)); seven of these 11 severely hyponatremic athletes were symptomatic. The relative body weight change of the 11 severely hyponatremic athletes ranged from 2.4% to +5%; eight (73%) of these athletes either maintained or gained weight during the race. In contrast, relative body weight changes in the 47 athletes with mild hyponatremia ([plasma sodium] 130-134 mmol x L(1)) were more variable, ranging from -9.25% to +2.2%. CONCLUSIONS: Hyponatremia is a common biochemical finding in ultradistance triathletes but is usually asymptomatic. Although mild hyponatremia was associated with variable body weight changes, fluid overload was the cause of most (73%) cases of severe, symptomatic hyponatremia.

Adult↗
PubMed1999

Ventilatory responses to exercise in patients with asymptomatic left ventricular dysfunction.

PURPOSE: Based on reports that patients with severe left ventricular (LV) dysfunction have a greater ventilatory response to effort than healthy people, we evaluated the ventilatory responses to effort of patients with coronary artery disease and various degrees of LV impairment before and after 6 months of exercise training in a community-based cardiac rehabilitation program. METHODS: Out of 171 patients consecutively referred for cardiac rehabilitation, 102 were enrolled in the study. Fifteen patients were excluded because of lung disease and 54 because of poor adherence to the exercise program. Patients were divided into three groups according to their ejection fraction (EF): Group 1 (G1) included 63 patients with EF > or = 50%, Group 2 (G2) included 21 patients with EF > or = 35 and < 50% and group 3 (G3) included 18 patients with EF < 35%. Peak oxygen uptake, minute ventilation (V(E)), and minute carbon dioxide production (VCO2) were measured before and after training in all participants. RESULTS: All groups showed a significant increase in peak oxygen uptake and treadmill time after training (G1: P = 0.0001 and P = 0.0001; G2: P = 0.0001 and P = 0.001; G3: P = 0.01 and P = 0.01; respectively). Patients in G3 had a significantly higher V(E)/VCO2 ratio than patients in G2 and G1 at 9 min and peak exercise, before (9 min: P = 0.046 and P = 0.025, peak: P = 0.024 and P = 0.002, respectively) and after training (9 min: P = 0.011 and P = 0.005, peak: P = 0.001 and P = 0.0001, respectively). The slope of the relation V(E) to VCO2 was significantly higher in G3 patients than in those in G2 and G1 (P = 0.0001, respectively) and was not reduced by exercise training in any group. CONCLUSIONS: Patients with severe LV dysfunction had a greater ventilatory response to exercise than those with moderately impaired or normal LV function. Exercise training increased the effort tolerance of all patients irrespective of their degree of LV dysfunction but failed to reduce the higher ventilatory responses to effort of patients with EF below 35%.

Adult↗
PubMed1999

Effect of myocardial ischaemia on left ventricular function and adaptability to exercise training.

PURPOSE: We evaluated the possible interaction between exercise-induced myocardial ischemia and abnormalities in left ventricular function in 72 patients with coronary artery disease at entry and upon discharge from a 6-month exercise training program. METHODS: Twenty-two patients with myocardial ischemia (MIS) defined by electrocardiographic and radionuclide imaging criteria constituted our experimental group (EG). Fifty patients without MIS were assigned to the control group for exercise training (CG-ET) and 31 healthy subjects to the control group for measures of left ventricular function (CG-LV). RESULTS: Both groups EG and CG-ET showed significant and comparable increases in peak oxygen uptake (EG: 25.2 +/- 5.1 to 26.9 +/- 5.4 mL x kg(-1) x min(-1), P < 0.02; CG-ET: 25.1 +/- 0.6 to 27.4 +/- 0.7 mL x kg(-1) x min(-1), P < 0.001) after exercise training, but only CG-ET showed significant reductions in heart rate, systolic blood pressure, and rate-pressure product during submaximal exercise. A significant increase in end-diastolic volume contributed to the increase in cardiac output during exercise in patients with MIS. Heart rate or treadmill time at onset of ST segment depression failed to increase as a result of training, and stroke counts and the product of stroke counts and heart rate showed a trend toward a decrease in response to exercise, suggesting progression of disease. CONCLUSIONS: Patients with myocardial ischemia showed improvements in maximal exercise capacity but failed to elicit physiologic adaptations during submaximal exercise or to increase the threshold for ischemia after exercise training. It is possible that the main emphasis in the management of this type of patient in a cardiac rehabilitation setting should be placed more on coronary risk factor modification to slow progression of disease than on improving cardiovascular efficiency.

Adaptation, Physiological↗
PubMed1999

Measurement of maximal oxygen uptake from two different laboratory protocols in runners and squash players.

PURPOSE: The aims of the study were to assess whether different test protocols used to elicit maximal oxygen uptake values (VO2max) attain similar results, whether different VO2max protocols were preferable for different athletic groups, and to assess whether the noninvasive criteria used to indicate the attainment of VO2max are achieved similarly in different VO2max testing protocols. METHODS: This study evaluated the attainment of either VO2max or peak VO2 (VO2peak) during two treadmill VO2max protocols: a progressive speed protocol (PSP) and a progressive incline protocol (PIP). Ten runners and 10 squash players were studied to assess whether achievement of VO2max criteria was either sport-specific or protocol-specific, or both. RESULTS: There were no significant differences in the VO2peak values reached in either PSP or PIP protocol (64.4 +/- 5.9 vs 66.5 +/- 6.0 mLO2 x kg(-1) x min(-1)). But HRmax (196 +/- 5 vs 189 +/- 5 beats x min(-1); PSP vs PIP; P < 0.01) and RER (1.14 +/- 0.05 vs 1.07 +/- 0.04; PSP vs PIP; P < 0.01) were significantly higher during the PSP test. Fifty percent of the subjects reached a plateau in either test, and of these subjects, 90% satisfied the three noninvasive criteria for VO2max in the PSP group, compared with 10% in the PIP group. CONCLUSIONS: The indirect criteria used to assess the attainment of VO2max may be limited, as the VO2peak values were higher in the PIP protocol compared with the PSP protocol, although not significantly different, whereas the HR and RER values were significantly lower in the PIP than PSP protocol. Furthermore, only 50% of subjects demonstrated the plateau phenomenon in oxygen uptake with either protocol. It may be concluded that the measured physiological variables coinciding with VO2peak may differ when different protocols are used to elicit VO2max.

Adult↗
PubMed1999

Effects of medium-chain triaclyglycerol ingested with carbohydrate on metabolism and exercise performance.

The effects of ingesting different amounts of medium-chain triacylglycerol (MCT) and carbohydrate (CHO) on gastric symptoms, fuel metabolism, and exercise performance were measured in 9 endurance-trained cyclists. Participants, 2 hr after a standardized lunch, cycled for 2 hr at 63% of peak oxygen consumption and then performed a simulated 40-km time trial (Ttrial). During the rides, participants ingested either 10% 14C-glucose (GLU), 10% 14C-GLU + 1.72% MCT (LO-MCT), or 10% 14C-GLU +3.44% MCT (HI-MCT) solutions: 400 ml at the start of exercise and then 100 ml every 10 min. MCT ingestion did not affect gastrointestinal symptoms. It only raised serum free fatty acid (FFA) and beta-hydroxybutyrate concentrations. Higher FFA and beta-hydroxybutyrate concentrations with MCT ingestion did not affect fuel oxidation or T-trial performance. The high CHO content of the pretrial lunch increased starting plasma insulin levels, which may have promoted CHO oxidation despite elevated circulating FFA concentrations with MCT ingestion.

3-Hydroxybutyric Acid↗
PubMed1999

Incidence and causes of tenosynovitis of the wrist extensors in long distance paddle canoeists.

OBJECTIVES: To investigate the incidence and causes of acute tenosynovitis of the forearm of long distance canoeists. METHOD: A systematic sample of canoeists competing in four canoe marathons were interviewed. The interview included questions about the presence and severity of pain in the forearm and average training distances. Features of the paddles and canoes were determined. RESULTS: An average of 23% of the competitors in each race developed this condition. The incidence was significantly higher in the dominant than the nondominant hand but was unrelated to the type of canoe and the angle of the paddle blades. Canoeists who covered more than 100 km a week for eight weeks preceding the race had a significantly lower incidence of tenosynovitis than those who trained less. Environmental conditions during racing, including fast flowing water, high winds, and choppy waters, and the paddling techniques, especially hyperextension of the wrist during the pushing phase of the stroke, were both related to the incidence of tenosynovitis. CONCLUSION: Tenosynovitis is a common injury in long distance canoeists. The study suggests that development of tenosynovitis is not related to the equipment used, but is probably caused by difficult paddling conditions, in particular uneven surface conditions, which may cause an altered paddling style. However, a number of factors can affect canoeing style. Level of fitness and the ability to balance even a less stable canoe, thereby maintaining optimum paddling style without repeated eccentric loading of the forearm tendons to limit hyperextension of the wrist, would seem to be important.

Athletic Injuries↗
PubMed1999

African runners exhibit greater fatigue resistance, lower lactate accumulation, and higher oxidative enzyme activity.

Nine African and eight Caucasian 10-km runners resident at sea level volunteered. Maximal O2 consumption and peak treadmill velocity (PTV) were measured by using a progressive test, and fatigue resistance [time to fatigue (TTF)] was measured by using a newly developed high-intensity running test: 5 min at 72, 80, and 88% of individual PTV followed by 92% PTV to exhaustion. Skeletal muscle enzyme activities were determined in 12 runners and 12 sedentary control subjects. In a comparison of African and Caucasian runners, mean 10-km race time, maximal O2 consumption, and PTV were similar. In African runners, TTF was 21% longer (P < 0.01), plasma lactate accumulation after 5 min at 88% PTV was 38% lower (P < 0.05), and citrate synthase activity was 50% higher (27.9 +/- 7.5 vs. 18.6 +/- 2.1 micromol. g wet wt-1. min-1, P = 0.02). Africans accumulated lactate at a slower rate with increasing exercise intensity (P < 0.05). Among the entire group of runners, a higher citrate synthase activity was associated with a longer TTF (r = 0.70, P < 0.05), a lower plasma lactate accumulation (r = -0.73, P = 0.01), and a lower respiratory exchange ratio (r = -0.63, P < 0.05). We conclude that the African and Caucasian runners in the present study differed with respect to oxidative enzyme activity, rate of lactate accumulation, and their ability to sustain high-intensity endurance exercise.

Adolescent↗
PubMed1999

Metabolic and performance responses to constant-load vs. variable-intensity exercise in trained cyclists.

We studied glucose oxidation (Glu(ox)) and glycogen degradation during 140 min of constant-load [steady-state (SS)] and variable-intensity (VI) cycling of the same average power output, immediately followed by a 20-km performance ride [time trial (TT)]. Six trained cyclists each performed four trials: two experimental bouts (SS and VI) in which muscle biopsies were taken before and after 140 min of exercise for determination of glycogen and periodic acid-Schiff's staining; and two similar trials without biopsies but incorporating the TT. During two of the experimental rides, subjects ingested a 5 g/100 ml [U-(14)C]glucose solution to determine rates of Glu(ox). Values were similar between SS and VI trials: O(2) consumption (3.08 +/- 0.02 vs. 3.15 +/- 0.03 l/min), energy expenditure (901 +/- 40 vs. 904 +/- 58 J x kg(-1) x min(-1)), heart rate (156 +/- 1 vs. 160 +/- 1 beats/min), and rating of perceived exertion (12.6 +/- 0.6 vs. 12.7 +/- 0.7). However, the area under the curve for plasma lactate concentration vs. time was significantly greater during VI than SS (29.1 +/- 3.9 vs. 24.6 +/- 3. 7 mM/140 min; P = 0.03). VI resulted in a 49% reduction in total muscle glycogen utilization vs. 65% for SS, while total Glu(ox) was higher (99.2 +/- 5.3 vs. 83.9 +/- 5.2 g/140 min; P < 0.05). The number of glycogen-depleted type I muscle fibers at the end of 140 min was 98% after SS but only 59% after VI. Conversely, the number of type II fibers that showed reduced periodic acid-Schiff's staining was 1% after SS vs. 10% after VI. Despite these metabolic differences, subsequent TT performance was similar (29.14 +/- 0.9 vs. 30.5 +/- 0.9 min for SS vs. VI). These results indicate that whole body metabolic and cardiovascular responses to 140 min of either SS or VI exercise at the same average intensity are similar, despite differences in skeletal muscle carbohydrate metabolism and recruitment.

Adolescent↗
PubMed1999

An apparent reduction in the incidence and severity of spinal cord injuries in schoolboy rugby players in the western Cape since 1990.

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.

Adolescent↗
PubMed1998

Fuel metabolism during ultra-endurance exercise.

Cyclists either ingested 300 ml 100 g/l U-[14C] glucose solution every 30 min during 6 h rides at 55% of VO2max (n=6) or they consumed unlabelled glucose and were infused with U-[14C] lactate (n=5). Maintenance of euglycaemia limited rises in circulating free fatty acids, noradrenaline and adrenaline concentrations to 0.9+/-0. 1 mM, 27+/-4 nM and 2.0+/-0.5 nM, respectively, and sustained the oxidation of glucose and lactate. As muscle glycogen oxidation declined from 100+/-13 to 71+/-9 micromol/min/kg in the last 3 h of exercise, glucose and lactate oxidation and interconversion rates remained at approximately 60 and 50 and at about 4 and 5 micromol/min/kg, respectively. Continued high rates of carbohydrate oxidation led to a total oxidation of around 270 g glucose, 130 g plasma lactate and 530 g muscle glycogen. Oxidation of some 530 g of muscle glycogen far exceeded the predicted (about 250 g) initial glycogen content of the active muscles and suggested that there must have been a considerable diffusion of unlabelled lactate from glycogen breakdown in inactive muscle fibres to adjacent active muscle fibres via the interstitial fluid that did not equilibrate with 14C lactate in the circulation.

Beverages↗