Exercise intensity, training, diet, and lactate concentration in muscle and blood

With some, but not all, types and intensities of exercise, lactate accumulates in the blood and in the muscles engaged in the exercise. A great deal of attention has been directed towards attempting to understand the dynamics of lactate production and removal at the onset of exercise, during exercise, and during the recovery process following exercise. It has been hoped that an unravelling of these events would provide a key to understanding cellular metabolism and its regulation during exercise. The purpose of this introductory paper to a symposium on lactate is to present a brief overview of some of the conditions that influence the rate and magnitude of lactate accumulation during exercise. It is pointed out that many conditions influence the rate and magnitude of the accumulation of lactate in blood and muscles. Included are diet, state of physical fitness, and the type and duration of the exercise. We have cautioned against trying to evaluate the state of oxygen delivery to muscle and the state of tissue oxygenation from the appearance of lactate in blood. We have pointed out the positive aspects of lactate production based on how it augments the cellular supply of ATP, thereby allowing for high intensity exercise, and also the negative aspects that develop as a result the reduction in pH which adversely influences many cellular processes essential for muscular activity.     

Physiological differences between genders. Implications for sports conditioning

It is commonly accepted that there are physiological and morphological gender differences. These differences become evident in the specific responses or magnitude of response to various training regimens. Very little difference is seen in the response to different modes of progressive resistance strength training. Men and women experience similar relative strength gains when training under the same programme. The evidence on body composition changes that occur with strength training is equivocal at this point. Researchers, however, suggest that there appears to be less muscle hypertrophy with strength improvement in women when compared to men. The data suggest that there are no differences between genders in central or peripheral cardiovascular adaptations to aerobic training. However, women in general have a reduced O2 carrying capacity. Another factor that may be responsible for the sex differences seen in the metabolic responses to exercise may be the greater, essential sex specific fat of women. Sparling and Cureton (1983) have shown that differences in similarly trained male and female distance runners are due largely to percentage body fat, less to cardiorespiratory fitness and least to running economy. Pate et al. (1985) determined that men and women who are capable of similar performances, in this case a 15 mile race, do not differ in body composition, cardiorespiratory response or metabolic response. There appear to be no differences in relative increases in VO2max for men and women when they are trained under the same intensity, frequency and duration. Mode of training also appears to elicit no sex difference. Hormonal factors lead to greater initial levels of high density lipoproteins in women. This appears to cause a smaller change in the total cholesterol-high density lipoprotein ratio than occurs with aerobic training in men. Generally, the menstrual cycle phase makes no difference to performance in women. The special cases of exercise in hot and cold environments present conflicting evidence. When men and women are matched for surface area:mass, VO2max and percentage body fat, the major disadvantages women have in the heat disappear. The question of gender differences in the cold has yet to be fully explored. When the general population is compared, men appear to have an advantage over women.     

The many uses of the U tube

U tube placement was employed as an adjunct to complicated biliary procedures in 14 patients. We found the transhepatic tubes to be useful for stenting biliary anastomoses, maintaining biliary drainage, delivering localized irradiation, and acting as permanent external conduits. The tubes remained in placed an average of 15 months and as long as 40 months. The frequency of cholangitis was minimized by frequent tube exchange. The U-shaped configuration makes tube exchange easy and inexpensive to perform.     

An analysis of injury rates after the seasonal change in rugby league.

OBJECTIVES: To determine whether the increase in the incidence of injury found for the first summer season in which rugby league (RL) was played in the UK was repeated in subsequent summer seasons. DESIGN: A retrospective and prospective cohort study design. SETTING AND PARTICIPANTS: Injuries were recorded from all players who took part in 141 games over 3 summer seasons (1997 to 1999) for 1 professional team. These were compared against rates from previously collected data for 3 earlier winter and 1 summer season. ASSESSMENT OF RISK FACTORS: For each injury it was recorded in which season it occurred; how many games or training sessions, if any, were subsequently missed; the type, site and severity of injury. MAIN OUTCOME MEASURES: Injuries were reported as rate per 1000 hours, also broken down into severity according to the number of games missed and whether subsequent training sessions were missed. RESULTS: A sustained increase in injury incidence has been found comparing summer RL over RL played in the winter. There was an increase in injury rates for all sites and types, but not all reached significance. CONCLUSIONS: Data collected over 6 seasons indicate a higher risk of sustaining an injury playing summer RL, but the cause may be related to a combination of factors. These may include the ground or weather conditions associated with summer rugby, player characteristics or changes in the game itself and future research needs to investigate these further.     

Central nervous system decompression sickness: latency of 1070 human cases

Many aspects of central nervous system (CNS) decompression sickness (DCS) are poorly understood, including the temporal pattern of its presentation and the pathogenic mechanisms involved in the development of the disease. Using case histories and clinical series published in the literature and retrieved from treatment center records, this study is an attempt to define the interval between surfacing from a hyperbaric exposure and the onset of symptoms of CNS DCS. The results of 1070 cases of human CNS DCS were included in the study. The results show that the disease generally occurs rapidly: over 50% became symptomatic within 10 min of returning to 1 ATA, and in only 15% of cases was the onset of symptoms delayed for more than 1 h. Cerebral DCS had a more rapid onset than spinal cord disease: 50% of cerebral cases became apparent within about 3 min and a similar proportion of spinal cord cases within about 9 min from surfacing. The influence of these results on the diagnosis and treatment of dysbaric illness, on the safety of certain diving practices, and on possible pathogenic mechanisms is discussed.     

Hepatic resections for primary and metastatic tumors using the ultrasonic surgical dissector.

We have previously described the development of new hepatic surgical techniques using the ultrasonic surgical dissector. With 10 years' experience, we have found that major liver resections have been simplified and that the technique is repeatable in hands other than our own. Thirty-three patients had 37 tumors, averaging 5.65 cm in size, resected with an average blood loss of only 1,020 mL per case, which included 5 right trisegmentectomies, 12 lobectomies, 15 segmental resections, and 4 subsegmental resections. Twenty-two patients had metastatic colorectal cancer. Blood transfusion requirements averaged only 2.24 units in long-term survivors, which was significantly less than the 3.5 units received by patients who have since died (p = 0.092). There were no operative deaths. The median survival of these 22 patients was 56 months, and the 5-year actuarial survival rate was 35%. All of the early deaths occurred in patients with more than four tumors, and no patient with less than four tumors died before 42 months with recurrent disease. Six patients had bilateral tumors, and the fact that patients survived into the fourth and fifth post-resectional year indicates that resection was worthwhile. All these patients had Dukes' C primary tumors, but we found no statistical difference in survival between patients with Dukes' B and Dukes' C lesions. The results indicate that hepatic resection with the ultrasonic surgical dissector decreases blood loss, requires few transfusions, is safe to perform, and is associated with excellent long-term survival.     

Ventilatory response of moderately obese women to submaximal exercise

To investigate the effect of moderate obesity on ventilatory responses to graded exercise, we compared the ventilatory responses of ten moderately obese (35 +/- 5 percent body fat) and nine leaner women (22 +/- 2 percent body fat) during walking on a treadmill with incremental increases in percent grade. Speed remained constant at 3.0 mph. In the obese women, VO2 in l/min and ml/FFW/min, fb (b/min), VE (l/min), and HR were significantly greater (P less than 0.05) at all four absolute workloads. At 10.0 and 12.5 percent grade, VO2 (ml/kg/min) was smaller and VE/VO2 was greater in the obese women. The difference in VE/VO2 suggests a lower ventilatory threshold for the obese women. Percent VO2 max and R (VCO2/VO2) were significantly different at 12.5 percent grade only. When VO2 was divided by HR (oxygen pulse), the two groups were not significantly different at any of the four workloads tested. The groups were compared further at workloads representing approximately 55, 65, 75, and 85 percent of VO2 max. HR was not significantly different at any of the four relative exercise intensities. VE was significantly greater in the obese at 85 percent of maximum only (P less than 0.05) and fb was significantly greater at 55, 75, and 85 percent of maximum. Whereas cardiorespiratory responses of moderately obese women are increased at absolute workloads when compared to that of leaner women, HR is similar at comparable intensities of exercise. VE is also similar at comparable intensities of exercise below ventilatory threshold but fb is greater. The effect of the higher fb on exercise tolerance is unknown.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of Health and Safety Executive and Cumbrian birth cohort studies of risk of leukaemia/non-Hodgkin's lymphoma in relation to paternal preconceptional irradiation.

In 1993, a case-control study by the Health and Safety Executive (HSE) assessed the risk of leukaemia and non-Hodgkin's lymphoma (LNHL) among children of fathers employed at the Sellafield nuclear installation in relation to paternal preconceptional irradiation (PPI). It concluded that the statistical association between risk of LNHL and PPI was confined to children born in the village of Seascale, where the dose-response was extremely high and very significant. In contrast, in 2002, a Cumbrian birth cohort study, investigating largely the same cases, concluded that this statistical association was not significantly different among children born inside and outside Seascale and estimated the dose-response inside Seascale to be much lower. This review makes a detailed comparison of the two studies, considering their design, data and analyses. The differences between their findings are due to: (i) differences in the distribution of offspring-years which are differential with respect to dose category and Seascale birth status, (ii) a non-Seascale high-dose case included in the Cumbrian but not the HSE study, (iii) differences between analyses using categorical and continuous PPI dose and (iv) the presence of Seascale controls with PPI over 200 mSv in the Cumbrian but not the HSE study.