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Rapid air travel across several time zones exposes the traveller to a shift in his/her internal biological clock. The result is a transient desynchronisation of the circadian rhythm, called jet lag, lasting until the rhythm is rephased to the new environmental conditions. The most commonly experienced symptoms are sleep disorders, difficulties with concentrating, irritability, depression, fatigue, disorientation, loss of appetite, and gastrointestinal disturbance. Apart from the decrements in mental and physical performance directly consequent on such symptoms, competitive athletes are also exposed to the additional negative consequences of a shift from the optimal circadian window of performance. A brief summary of the possible negative effects of jet lag on athletic performance and potentially alleviating strategies is given. [ABSTRACT FROM AUTHOR]

OBJECTIVE: To find the individual intensity for aerobic endurance training, the lactate minimum test (LMT) seems to be a promising method. LMTs described in the literature consist of speed or work rate-based protocols, but for training prescription in daily practice mostly heart rate is used. The aim of the present study was to investigate the reproducibility of a new heart rate-based LMT protocol. DESIGN: 20 subjects each underwent four LMTs on a cycle ergometer. The LMT consisted of a first part (Conconi test) to induce lactate accumulation and a second part (incremental protocol) with stages of 5 min starting beyond the aerobic threshold. During these stages work rate was adjusted to reach predetermined heart rates, which were calculated for every single test from heart rate (HR) at rest and maximum HR. Lactate was measured after each stage to define the lactate minimum (LM) and the corresponding HR. SETTING: Institute of Sports Medicine. PARTICIPANTS: 20 healthy and endurance-trained individuals (13 men, seven women). MAIN OUTCOME MEASURES: Reproducibility of heart rate at LM. RESULTS: The reproducibility of heart rate at LM was high (coefficient of variation (CV) = 2.1%). The reproducibility of work rate at LM was good (CV = 6.7%). CV for lactate concentrations at LM was 17.4%. High interindividual differences at LM were found in heart rate (range 149–178 beats/min) and lactate levels (range 1.2–6.8 mmol/l). CONCLUSION: The LMT using a heart rate-based protocol is a reproducible method of assessing HR at an exercise intensity where an equilibrium exists between blood lactate accumulation and elimination. [ABSTRACT FROM AUTHOR]

Objective: To test the hypothesis that sodium citrate administered two hours before exercise improves performance in a 5 km running time trial. Methods: A total of 17 male well trained college runners (mean (SD) &Vdot;o2MAX 61.3 (4.9) mI/kg/min) performed a 5 km treadmill run with and without sodium citrate ingestion in a random, double blind, crossover design. In the citrate trial, subjects consumed 1 litre of solution containing 0.5 g of sodium citrate/kg body mass two hours before the run. In the placebo trial, the same amount of flavoured mineral water was consumed. Results: The time required to complete the run was faster in the citrate trial than the placebo trial (1153.2 (74.1) and 1183.8 (91 .4) seconds respectively; p =0.01). Lower packed cell volume and haemoglobin levels were found in venous blood samples taken before and after the run in the citrate compared with the placebo trial. Lactate concentration in the blood sample taken after the run was higher in the citrate than the placebo trial (11.9 (3.0) v 9.8 (2.8) mmol/l; p<0.001), and glucose concentration was lower (8.3 (1.9) v8.8 (1.7) mmol/I; p=0.02). Conclusion: The ingestion of 0.5 g of sodium citrate/kg body mass shortly before a 5 km running time trial improves performance in well trained college runners. [ABSTRACT FROM AUTHOR]

Develops a badminton-specific test to determine on-court aerobic and anaerobic performance. Validation of a field test for the non-invasive determination of aerobic performance specific to badminton; Assessment of heart rate turn point levels; Evaluation of individual physical working capacity.

Objective: To determine the influence of lactic acidosis, the Bohr effect, and exercise induced hyperkalaemia on the occurrence of the heart rote deflection point (HRDP) in elite (professional) cyclists. Methods: Sixteen professional male road cyclists (mean (SD) age 26 (1) years) performed a romp test on a cycle ergometer (workload increases of 5 W/12 s, averaging 25 W/min). Heart rate (HR), gas exchange parameters, and blood variables (lactate, pH, P50 of the oxyhaemoglobin dissociation curve, and K+) were measured during the tests. Results: A HRDP was shown in 56% of subjects at about 88% of their maximal HR (HRDP group; n = 9) but was linear in the rest (No-HRDP group; n = 7). In the HRDP group, the slope of the HR-workload regression line above the HRDP correlated inversely with levels of K+ at the maximal power output (r = -0.67; p < 0.05). Conclusions: The HRDP phenomenon is associated, at least partly, with exercise induced hyperkalaemia. [ABSTRACT FROM AUTHOR]

It is apparent that bone density in male athletes can be reduced without a concomitant decrease in testosterone, suggesting that bone density and testosterone concentrations in the normal range are not closely related in male athletes. Further research is necessary to monitor concurrent changes in bone density and testosterone over a period of time in exercising males. In any case, the effect of exercise on the male reproductive system does not appear as extreme as that which can occur in female athletes, and any impact on bone density is not nearly as evident. These results imply that factors apart from testosterone concentrations must be responsible for the observed osteopenia in some male athletes. Many factors have the potential to adversely affect bone density, independently of alterations in reproductive function. These include low calcium intake, energy deficit, weight loss, psychological stress, and low body fat, all of which may be associated with intense endurance training. Future research investigating skeletal health in male athletes should include a thorough assessment of reproductive function in addition to these other factors. [ABSTRACT FROM AUTHOR]

Venous blood samples were taken from eight competitors in mid-evening after a racing day, and in the early morning before the next day's race, three times during the course of the Milk Race, 1992. These were used to gather information about the changes in circulating leucocyte levels in response to the exceptionally high sustained daily workload required during a major multi-stage race. The primary objective was to provide knowledge of 'normal' values against which future clinical judgements of abnormality might be made in these unusual circumstances. During the race, estimated energy output was about 25 MJ (6000 kCal)/day. The mean total circulating leucocyte numbers (per litre of blood), and those of individual leucocyte classes (neutrophil, lymphocyte, monocyte, eosinophil and basophil) were all inside the normal range both in the morning and in the evening. Evening counts were, however, 30-50% higher than morning counts, for all classes except eosinophils. We conclude that individual clinical decisions about leucocyte levels can best be made using normal (sedentary man) values if a morning sample is taken. [ABSTRACT FROM AUTHOR]

Intravascular haemolysis has been found to result from prolonged endurance competition, rigorous military training and participation in impact sports. Haematological research involving the recreational runner is sparse. Recreational runners frequently vary their training to avoid monotony and improve endurance capacity. This study investigated the haematological effects of a typical day of increased distance training in 15 male recreational runners (62.4(3.1) ml kg-1 min-1 treadmill VO2max; 44.6(8.4) km per week training (means(s.d.)). Venous blood samples were collected before, immediately after, 1 day, 4 days, and 10 days after a 13-km training run (about twice the subjects' typical running distance) and analysed for changes in bilirubin, serum potassium, haematocrit, haemoglobin, red blood cell count, haptoglobin, poikilocytosis and reticulocytosis. Urine samples were collected at the same times as the blood samples and analysed for urobilinogen. Significant (P less than 0.05) 1-day and 4-day decreases in mean haemoglobin, red blood cell count, and haptoglobin values, compared to before training venous blood values and significant (P less than 0.05) post-training increases in bilirubin, serum potassium, urobilinogen and poikilocytosis provided evidence for increased intravascular haemolysis. After 10 days the values for haematocrit, bilirubin, serum potassium, red blood cell count, urobilinogen and poikilocytosis were not significantly (P less than 0.05) different from pre-training values while haemoglobin remained significantly (P less than 0.05) lower, exhibiting a constant but not significant increase over the period from 1 to 10 days. The results indicate that mild intravascular 'footstrike' haemolysis can occur in the recreational runner when typical training distance is increased. This condition appears to be transient and benign. [ABSTRACT FROM PUBLISHER]