Variability of aerobic performance in the laboratory and its physiologic correlates

To study the physiologic basis of variability of physical performance in the laboratory, ten male subjects were studied once a week, during a 9-12 month period. Previously, the reference maximal work load attained (Wref) was determined in each subject. The test protocol of the actual study was based on the individual Wref and started at 70% Wref for 5 min whereupon the work load was increased by 5% Wref every 2.5 min to exhaustion. The maximal work load attained (Wmax) was considered as the test performance. Heart rate, respiratory variables, oxygen uptake (VO2), and blood lactate concentration were determined at each work load. The rate of perceived exertion during submaximal and maximal work was also scored. In all subjects, Wmax and VO2max varied randomly, while the coefficient of variation in VO2max (4.20% - 11.35%) exceeded that in Wmax (2.95%-6.83%). No seasonal influences on VO2 max and Wmax were observed. In all subjects the physiologic variables, when plotted as a function of external work load, were shifted to the right with higher Wmax values and to the left with lower Wmax values. With lower Wmax values, the rate of perceived exertion during submaximal work tended to increase. The results suggest that the magnitude of physiologic responses to exercise is related to relative work load and that variability of physical performance is related to changes in gross mechanical efficiency.

Acid-base balance during repeated bouts of exercise: influence of HCO3

Ten men and one woman were studied before, during, and following five 1-min cycling bouts (100% VO2 max) 1 h after consuming either 0.2 g/kg B.W. of NaHCO3 or a placebo drink (NaCl). The fifth exercise bout was performed until exhaustion and the time recorded to judge the effects of the NaHCO3 drink on performance. Blood samples taken from a forearm vein revealed that the intake of NaHCO3 increased resting pH (7.34 to 7.41), HCO3 (27.5 to 31.0 mM), and base excess (1.1 to 4.6 mM). During and following the exercise, blood pH and HCO3 were always higher (P less than 0.05) in the NaHCO3 than placebo trial. Performance times during the fifth cycling bout averaged 113.5 (SE +/- 12.4) and 160.8 (SE +/- 19.1) s in the NaCl and NaHCO3 trials, respectively. This 42% difference between the means was significant at the 0.01 level. The blood hydrogen ion to lactic acid ratios (nM/mM) measured between each exercise bout and during recovery from the exhaustive fifth bout suggests that the enhanced performance during the NaHCO3 trial was the result of greater buffer capacity. Thigh muscle (vastus lateralis) pH measured immediately before the fifth cycling bout in four of the subjects revealed that the working muscles were less acid in the NaHCO3 trial (pH = 6.81) than during the NaCl treatment (pH = 6.73). Thus, the alkalizing influence of oral HCO3 supports the concept that the hydrogen ion concentration in blood and muscle has a direct influence on performance during repeated, supramaximal exercise.

Some mechanical properties of aggregates of top soils from the IJsselmeer polders. 1. Undisturbed soil aggregates

Aggregates were collected from the arable layer at eight sites in the IJsselmeer polders. The compositions of the soils were determined, and measurements were made of porosities, tensile strengths and water stabilities of undisturbed aggregates. Porosity was negatively correlated with the age of the soils since reclamation. Tensile strength of dry aggregates and water stability were both positively correlated with the clay content. The soils had extremely high values of friability. Tensile strength was negatively correlated with porosity. Porosity had no clear influence on water stability. (Abstract retrieved from CAB Abstracts by CABI’s permission)

Infection with cytomegalovirus in homosexual men

The prevalence and incidence of cytomegalovirus (CMV) infections were studied in a group of homosexual men. Of the 710 participants, 501 (70.6%) had complement fixing antibodies to CMV on entry to the study. During the follow up (maximum 23 months) 69 CMV infections were found: 50 primary infections among the 209 seronegative men (attack rate 27.3%), and 19 recurrent infections among the 501 seropositive men (attack rate 6.2%). The prevalence of antibody to CMV was correlated with four characteristics of the participants' lifestyles: duration of homosexual activity, number of different sexual partners, history of syphilis, and anal sexual contact. Among the seronegative men, the incidence of primary infection with CMV correlated with a history of syphilis and anal sexual contact. We conclude that infections with CMV are highly prevalent among homosexual men, and that anal sexual contact plays an important part in the transmission of this virus.

Some mechanical properties of aggregates of top soils from the IJsselmeer polders. 2. Remoulded soil aggregates and the effects of wetting and drying cycles

The mechanical properties of remoulded samples of eight soils from the IJsselmeer polders were investigated. The Atterberg (Plastic and Liquid) Limits were positively correlated with the soil clay content, but were not significantly correlated with the organic matter content. Artificial aggregates of the remoulded soil age-hardened when moist. The tensile strength of artificial aggregates was positively correlated with the soil clay content and negatively correlated with the porosity. Friability of the dried, remoulded soil was much lower than that of natural, undisturbed soil. Factors affecting the rates of wetting and drying of aggregates in the laboratory were examined in detail. Wetting resulted in mellowing (or softening) of artificial aggregates. Mellowing was investigated as a function of the potential of the source of water causing the wetting. Multiple wetting and drying cycles may result in increased mellowing or in no mellowing depending on the water potential. New terminology is introduced to facilitate discussion of these phenomena. (Abstract retrieved from CAB Abstracts by CABI’s permission)

Prevalence and incidence of hepatitis A among male homosexuals

In a study of 689 male homosexuals 290 (42%) were found to have antibodies to hepatitis A virus. The 399 men who did not have antibodies were followed up for up to 690 days, and 35 cases of hepatitis A were detected. The attack rate at the end of the study was 14%. The incidence climbed steadily, indicating that the cases of hepatitis A did not occur in clusters. Statistical analysis showed that the prevalence of antibodies to hepatitis A virus was significantly correlated with the duration of homosexual activity (p less than 0.006), and this was independent of age. The incidence of hepatitis A was found to be correlated with the number of different sexual partners in the preceding six months. It is concluded that hepatitis A is a sexually transmitted disease among homosexual men in countries with a low rate of exposure to hepatitis A during childhood.

Muscle degeneration after exercise in rats

To search for morphological changes in muscle, related to overuse syndromes of muscle due to exercise, groups of untrained rats ran on a treadmill for 1 h at submaximal intensity. Each group was sacrificed at a different interval after the end of the exercise. To evaluate the physiologic load, the colonic temperature and blood lactate level were determined. The right hindlimb was fixated with buffered glutaraldehyde, injected into the femoral artery, and different muscles were dissected and prepared for electron and light microscopy. The muscles of the left limb were frozen in liquid Freon and used for histochemistry. Signs of degeneration were noted in the soleus, rectus femoris, and vastus lateralis muscles, but were absent in the gastrocnemius, tibialis anterior, extensor digitorum, and biceps femoris muscles. Immediately after exercise, only minor signs of degeneration were observed at the ultrastructural level, while after 2-3 h degeneration became clearly visible at the light microscopic level. The most pronounced changes were observed 24-48 h after exercise, whereafter regeneration occurred. Only 2%-5% of all fibers in the soleus muscle showed signs of degeneration, while in the vastus lateralis and rectus femoralis muscle less than 0.5% of the fibers were affected. The affected fibers showed degeneration only in segments with a length between 150-1250 micrometers. The affected fibers in the soleus and vastus lateralis muscles belong to the type I population, while in the rectus femoris type I as well as type II fibers were affected.

Limitations of concentration measurements for evaluation of endocrine status of exercising women

The impact of changes in metabolic clearance rates (MCR), biologic activity of sex-steroids, steroid-protein interaction and steroid-binding properties of plasma proteins in relation to physical exercise are reviewed. The MCR of estradiol is decreased during physical exercise but this phenomenon is only partly explained by a decreased hepatic blood flow. Changes in concentration of high-affinity steroid binding proteins (testosterone-estradiol-binding globulin, TeBG) affect predominantly the amount of free testosterone (T) and its MCR. During exercise both the lower sex-steroids binding affinities of plasma proteins due to increased body temperature and the increased concentration of these hormones cause a shift towards an increased free concentration. Due to competitive interactions between androgens and estrogens for the binding site of TeBG the free concentration of estrogens will probably increase more than expected. The physiological meaning of these changes are discussed.

Influence of therapeutic doses of amoxicillin on aerobic work capacity and some strength characteristics

The purpose of this study was to investigate whether or not amoxicillin in therapeutic doses could have an influence on maximal aerobic work capacity and some strength characteristics in trained subjects. Fifteen volunteers (men; age range, 21 to 38 years; mean, 28.8 years) were examined once weekly for 4 consecutive weeks, and on these occasions the following variables and parameters were measured: maximum workload attained on the bicycle ergometer, maximum heart rate, maximum serum lactate concentration, heart rate and serum lactate concentration after 10 min at 80% of the maximum workload attained, maximum isometric extension force of the legs, vertical jump height, and body weight. During the baseline period, the determined variables and parameters did not show any significant difference between Test 1 and Test 2. During the 3rd and 4th week of the test period, the subjects received at random either placebo (6-aminopenicillanic acid) or amoxicillin in therapeutic doses (375 mg, 3 times a day) every day for 5 days. After the third test in the 3rd week, there was a cross-over, ensuring that each volunteer was examined during placebo as well as during amoxicillin medication. The serum amoxicillin levels were determined. After statistical analysis, no influence of amoxicillin or placebo on the parameters and physiologic variables was demonstrable.