Maximal lactate steady state,critical power and EMG during cycling

We hypothesised that: (1) the maximal lactate steady state (MLSS), critical power (CP) and electromyographic fatigue threshold (EMG_FT) occur at the same power output in cycling exercise, and (2) exercise above the power output at MLSS (P-MLSS) results in continued increases in oxygen uptake (V˙O₂), blood lactate concentration ([La]) and integrated electromyogram (iEMG) with time. Eight healthy subjects [mean (SD) age 25 (3) years, body mass 72.1 (8.2) kg] performed a series of laboratory tests for the determination of MLSS, CP and EMG_FT. The CP was determined from four exhaustive trials of between 2 and 15 min duration. The MLSS was determined as the highest power output at which the increase in blood [La] was less than 1.0 mM across the last 20 min of a series of 30-min trials. The EMG_FT was determined from four trials of 2 min duration at different power outputs. The surface electromyogram was recorded continuously from the vastus lateralis muscle. The CP was significantly higher than the P-MLSS [242 (25) vs. 222 (23) W; P<0.05], although the two variables were strongly correlated (r=0.95; P<0.01). The EMG_FT could not be determined in 50% of the subjects. Blood [La], V˙O₂ and minute ventilation all increased significantly with time for exercise at power outputs above the P-MLSS. In conclusion, the P-MLSS, and not the CP, represents the upper limit of the heavy exercise domain in cycling. During exercise above the P-MLSS, there is no association between changes in iEMG and increases in V˙O₂ and blood [La] with time. Electronic Publication     

Energy consumption in static muscle contraction

Energy consumption during static contraction of the human triceps surae muscles was studied in 11 healthy subjects. The subjects had to stand intermittently on the left and then right foot at different frequencies (for periods of 15 s, 10 s or 5 s), first on the whole foot and then on the forefoot. The mean static energy consumption of all subjects was 13.4 (15) W [mean (s.d.)] at a calf muscle moment of 105 Nm. Assuming that static energy consumption (in W)is proportional to static moment (in Nm), a proportionality factor of 0.17 (0.19) s⁻¹ is found. Because of the limited attainable accuracy, no significant differences between endurance athletes and sprinters could be found. Electronic Publication     

A comparison of two time-domain analysis procedures in the determination of .VO(2) kinetics by pseudorandom binary sequence exercise testing

The purpose of this study was to apply and compare two time-domain analysis procedures in the determination of oxygen uptake (V˙O₂) kinetics in response to a pseudorandom binary sequence (PRBS) exercise test. PRBS exercise tests have typically been analysed in the frequency domain. However, the complex interpretation of frequency responses may have limited the application of this procedure in both sporting and clinical contexts, where a single time measurement would facilitate subject comparison. The relative potential of both a mean response time (MRT) and a peak cross-correlation time (PCCT) was investigated. This study was divided into two parts: a test-retest reliability study (part A), in which 10 healthy male subjects completed two identical PRBS exercise tests, and a comparison of the V˙O₂ kinetics of 12 elite endurance runners (ER) and 12 elite sprinters (SR; part B). In part A, 95% limits of agreement were calculated for comparison between MRT and PCCT. The results of part A showed no significant difference between test and retest as assessed by MRT [mean (SD) 42.2 (4.2) s and 43.8 (6.9) s] or by PCCT [21.8 (3.7) s and 22.7 (4.5) s]. Measurement error (%) was lower for MRT in comparison with PCCT (16% and 25%, respectively). In part B of the study, the V˙O₂ kinetics of ER were significantly faster than those of SR, as assessed by MRT [33.4 (3.4) s and 39.9 (7.1) s, respectively; P<0.01] and PCCT [20.9 (3.8) s and 24.8 (4.5) s; P<0.05]. It is possible that either analysis procedure could provide a single test measurement of V˙O₂ kinetics; however, the greater reliability of the MRT data suggests that this method has more potential for development in the assessment of V˙O₂ kinetics by PRBS exercise testing. Electronic Publication     

Oxygen uptake and heart rate kinetics during heavy exercise: a comparison between arm cranking and leg cycling

This study examined the oxygen uptake (V˙O₂) and heart rate (HR) kinetics during arm cranking and leg cycling at work rates above the anaerobic threshold (AT). Ten untrained male subjects [21.6 (1.3) years] completed two 7 min 15 s constant-load arm cranking and two leg cycling tests at a power output halfway between the mode-specific AT and peak V˙O₂. The time constants for phase II V˙O₂ (τ) and HR (τ) kinetics were determined by fitting a monoexponential curve from the end of phase I until 3 min of exercise. V˙O₂ τ and HR τ values were significantly (P<0.001) slower in arm cranking [V˙O₂ τ = 66.4 (3.0) s; HR τ = 74.7 (4.4) s] than in leg cycling [V˙O₂ τ = 42.0 (1.9) s; HR τ = 55.6 (3.5) s]. The V˙O₂ slow component (V˙O_2SC) accounted for a significantly (P<0.001) greater percentage of the total exercise response during arm cranking [23.8 (1.6)%] than during leg cycling [14.2 (1.5)%]. The greater relative V˙O_2SC and the slower V˙O₂ τ with arm exercise are consistent with a greater recruitment of metabolically inefficient type II muscle fibres during arm cranking than during leg cycling. Electronic Publication     

Specificity effects of run versus cycle training on ventilatory threshold

Summary This study compared the effects of 9 weeks of run (RT) versus cycle (CT) training on ventilatory threshold (Th_v) determined during treadmill (TM) and cycle ergometer (CE) graded exercise testing. Sixteen college age men were assigned to a RT or CT group and performed a TM and a CE test before and after training. Both training groups performed similar training protocols which initially consisted of continuous exercise 4 days·week^–1 at 75–80% maximum heart rate (fc,_max) for 45 min. Training intensity was later increased to 80–85% fc _max and interval training (90–95% fc,_max) was incorporated 2 days·week^–1 into the continuous training. Both groups showed significantly improved maximal oxygen consumption ( O_2max) on both TM and CE tests (P<0.01) with no significant differences between the groups. Significant Th_v increases (P<0.05) were found on TM tests for RT (n=8) and CT (n=8) groups [mean (SD); 443 (438) and 373 (568) ml O₂·min^–1, respectively] with no difference between the groups. Results from the CE tests revealed a significant Th_v increase (P<0.01) for the CT group [566 (663) ml O₂·min^–1] with no change for the RT group. The Th_v improvement noted for the RT group was significantly different (P< 0.05) comparing CE with TM tests but not for the CT group. The results indicate that CT and RT improvement in Th_v for runners is dependent upon mode of training and testing, and there is an apparent dissociation of O_2maxand Th_v specific to training.     

Physiological predictors of flat-water kayak performance in women

This study was conducted to investigate the relationship between selected physiological variables and 500-m flat-water kayak (K₅₀₀) performance. Nine female, high-performance kayak paddlers, mean (SD) age 23 (5) years, participated in this investigation. Testing was conducted over 6 days and included anthropometric measurements (height, body mass and skinfolds), an incremental test to determine both peak V˙O₂ and the “anaerobic threshold” (Th_an), and a 2-min, all-out test to calculate accumulated oxygen deficit (AOD). Blood lactate concentrations were measured during the incremental test and at the completion of both tests. Subjects also completed a K₅₀₀ race under competition conditions. K₅₀₀ time was significantly correlated with both peak V˙O₂ (r=−0.82, P < 0.05) and the power output achieved at the end of the incremental test (r=−0.75, P < 0.05). However, the variable most strongly correlated with K₅₀₀ time was Th_an (r=−0.89, P < 0.05). A stepwise multiple regression, for which r=0.95 and the standard error of estimate=1.6 s, yielded the following equation: K₅₀₀time(s)=160.60.154×AOD·kg⁻¹−0.250 × Th_an. In conclusion, the results of this study have demonstrated that although K₅₀₀ performance is a predominantly aerobic activity, it does require a large anaerobic contribution. The importance of both the aerobic and anaerobic energy systems is reflected by the K₅₀₀ time being best predicted by a linear combination of Th_an and AOD · kg⁻¹. This suggests the need to develop and implement training programmes that develop optimally both of these physiological attributes. Further research is required to elucidate the most effective means by which to develop both the aerobic and anaerobic energy systems. Accepted: 29 December 1999     

The influence of lecithin on plasma choline concentrations in triathletes and adolescent runners during exercise

Summary An investigation was carried out on the effect of lecithin (phosphatidylcholine, 90%) on the plasma choline concentrations during continuous strain in 10 top level triathletes (4 women and 6 men), trial I, and 13 excellent adolescent runners (3 girls and 10 boys), trial II. Venous blood, collected before and immediately after the race, was separated and plasma was assayed by an improved high performance liquid chromatography method for choline. Each study comprised three experiments. In trial I the triathletes performed two periods of bicycle exercise each lasting 2 h at an average speed of 35 km · h^–1, and in the second study (trial II) the subjects were subjected to severe physical stress on two occasions during cross-country races of durations between 30–60 min according to their ages. The participants received either a placebo or 0.2 g lecithin · kg body mass^–1, 1 h before each exercise. As a control the same dose of lecithin was administered without any exercise (both trials I and II). Bicycle exercise without lecithin supply decreased plasma choline concentrations in all the triathletes, on average by 16.9% (P0.01). When lecithin was given before exercise, average plasma choline concentrations remained at the same level as the initial values. The supply of lecithin without exercise led to a significant increase of the plasma choline concentrations, on average by 26.9% (P0.01). In trial II, when running without a supply of lecithin, the mean plasma choline concentrations in the adolescent runners remained stable which may have been due to the duration of the physical stress. When lecithin was given before exercise, plasma choline concentrations increased, on average by 18.9% (P0.01). The administration of lecithin without exercise led in these participants to an increase in plasma choline concentrations, on average by 54% (P0.001).It was found from the present study that a combination of both lecithin intake and hard physical stress prevented in most subjects a decrease in plasma choline and this could affect performance.Presented in part at the Symposium: 29. Wissenschaftlicher Kongreß der Deutschen Gesellschaft für Ernährung (DGE), Stuttgart-Hohenheim (March 1992)     

Specificity of routine parasite serological tests in autoimmune disorders,neoplastic disease,EBV-induced mononucleosis,and HIV infection

Summary Sera from 120 patients with rheumatological disorders, neoplastic disease, infectious mononucleosis, and HIV infection, and from 30 healthy blood donors were tested for nonspecific reactivity in 13 routinely used parasite serological tests. Responses were detected in 3/30 healthy blood donors (10%) vs 25/120 patients (21%). Of 40 responses in these 28 responders most were weakly reactive, and 25 out of 40 responses were only at borderline level. Response rates were highest in patients with mononucleosis presumably due to heterophile antibodies. Only four patients had responses in at least two different serodiagnostic tests for the same parasitic infection. Response patterns indicative of a possible underlying, concurring, or superimposed parasitic infection, thus, were rare. Especially susceptible to nonspecific reactivity seemed to be immunofluorescent antibody tests for filariasis, schistosomiasis, and amebiasis. In conclusion, compared to healthy controls, false-positive serological responses seem to be more frequent in certain disease groups dependent on the test methods used. Second, the use of more than one serodiagnostic test for the same parasitic disease will substantially facilitate the identification of nonspecific reactivity. Third, for better defining the specificity of parasitological serodiagnosis, more studies should include control sera from patients with nonparasitic diseases that frequently show immunological abnormalities.Abbreviations EBV Epstein-Barr virus - HIV Human immunodeficiency virus - IHA Indirect hemagglutination - IIFT Indirect immunofluorescent antibody test - CIE Countercurrent immunoelectrophoresis - EIA Enzyme-linked immunosorbent assay Herrn Prof. Dr. Helmut Jusatz zum 80. Geburtstag gewidmet     

Specificity of physiological adaptation to endurance training in distance runners and competitive walkers

Summary The present study was designed to evaluate the specificity of physiological adaptation to extra endurance training in five female competitive walkers and six female distance runners. The mean velocity ( ) during training, corresponding to 4 mM blood lactate [onset of blood lactate accumulation (OBLA)] during treadmill incremental exercise (training was 2.86 m·s^–1 SD 0.21 in walkers and 4.02 m·s^–1, SD 0.11 in runners) was added to their normal training programme and was performed for 20 min, 6 days a week for 8 weeks, and was called extra training. An additional six female distance runners performed only their normal training programme every day for about 120 min at an exercise intensity equivalent to their lactate threshold (LT) (i.e. a running of about 3.33 m·s^–1). After the extra training, there were statistically significant increases in blood lactate variables (i.e. oxygen uptake ( O₂) at LT, at LT, O₂ at OBLA, at OBLA; P<0.05), and running F for 3,000m (P<0.01) in the running training group. In the walking training group, there were significant increases in blood lactate variables (i.e., at LT, at OBLA; P<0.05), and walking economy. In contrast, there were no significant changes in lactate variables, running and economy in the group of runners which carried out only the normal training programme. It is suggested that the changes in blood lactate variables such as LT and OBLA played a role in improving F of both the distance runners and the competitive walkers. Furthermore, the significant improvement in walking economy brought about by extra endurance training might be a specific phenomenon for competitive walkers compared to runners.     

Maximal torque- and power-pedaling rate relationships for elite sprint cyclists in laboratory and field tests

Most studies that have set out to quantify the test–retest reliability of the multi-stage shuttle run test (MSSRT) have typically used inappropriate statistics (correlation coefficients) and/or one of two possible calculation methods for deriving predictions of maximal oxygen uptake and have not considered the impact of habituation on performance in the MSSRT and whether its reliability improves beyond a single repeat trial. In this context, the aim of this study was to assess the reliability of the MSSRT over three trials. Thirty-five healthy and active university games players (22 males and 13 females) performed the MSSRT on three occasions, 1 week apart. Individual total numbers of completed shuttles were recorded and estimated values were derived via established equation and table methods. Analysis revealed that the overall mean score from the equation method (52.5 ± 7.8 ml kg⁻¹ min⁻¹) was significantly higher than that for the table (46.9 ± 8.9 ml kg⁻¹ min⁻¹), whilst the mean trial 2 and trial 3 scores were significantly higher than that for trial 1, but not different to each other. The Limits of Agreement for the table method were −1.4 ± 5.0 (trial 1–trial 2) and 0.0 ± 5.5 ml kg⁻¹ min⁻¹ (trial 2–trial 3), and for the equation method −1.1 ± 4.7 (trial 1–trial 2) and 0.0 ± 5.0 ml kg⁻¹ min⁻¹ (trial 2–trial 3). These results suggest that systematic bias is eliminated after the first trial (due to habituation), but a considerable amount of random error remains, regardless of the type of score calculated. Hence, among our sample, the MSSRT does not appear to be reliable enough for the purpose of monitoring changes in due to non-random reasons.     

Effects of treadmill running on plasma beta-endorphin,corticotropin, and cortisol levels in male and female 10K runners

Summary Reports of plasma beta-endorphin (BEN) levels in response to submaximal exercise have been highly disparate. Variations in experimental design have complicated interpretation of previous research. The present study was designed to determine whether a sequential change in plasma beta-endorphin (B-EN), corticotropin (ACTH), and cortisol levels occurs in response to a 30-min submaximal run. Twenty-three subjects were divided into four groups: male runners, female runners, sedentary males and sedentary females. Subjects ran on a treadmill at 80% of previously determined maximum heart rate. Five plasma samples were obtained through an indwelling catheter before exercise (−30 and 0 min), at 15 and 30 min of exercise, and after 30 minutes of recovery. The run resulted in no rise in B-EN, ACTH, and cortisol despite an elevated rectal temperature. B-EN values were significantly higher in males than in females (p<0.01). No sex or training differences were seen with respect to change of hormone concentrations over the course of the run. Three male runners developed symptoms of vasovagal syncope after the catheter placement and had high initial B-EN, ACTH, and cortisol concentrations which decreased throughout the run. These data indicate that gender and training do not affect ACTH and cortisol concentrations before, during, and after 30 min of treadmill running at 80% of maximum heart rate, whereas B-EN concentrations are higher in males under these conditions.     

Influence of treadmill training on motor performance and organization of exploratory behavior in Meriones unguiculatus with unilateral ischemic stroke: histological correlates in hippocampal CA1 region and the neostriatum

This study examined the effects of motor stimulation via treadmill on the behavior of male gerbils after external carotid ischemic brain lesion. The animals were assigned to five groups; ischemic with no stimulation (SIG), ischemic with stimulation (SIG 12/24/48/72h after surgery), non-ischemic with no stimulation (CC), non-ischemic with stimulation (CE) and sham, surgery without occlusion with no stimulation (SH). All the animals were tested in the open-field (OF) and rotarod (RR), 4 days after surgery in order to evaluate exploratory behaviors and motor performance. Data were submitted to one-way variance (ANOVA) and Dunnett's post hoc comparisons. SIG and SIG 12 groups showed a significant decrease in motor response (crossing) when compared to the control group (CC) (F=20.65, P<0.05) in the OF. SIG 12 group showed an increase in grooming behavior (F=23.136, P<0.05) and all ischemia groups (SIG, SIG12/24/48/72) spent less time on the RR (F=10.40, P<0.05), when compared to the control group (CC). Histological analyses show extensive lesions in the hippocampus and neostriatum for all groups with ischemia (SIG, SIG12/24/48/72), which are structures involved in the organization of motor behavior. Interestingly, the most pronounced damage was found in animals submitted to motor stimulation 12h after ischemia which can be correlated to the increased number of grooming behavior showed by them in the OF. These findings suggest that motor stimulation through treadmill training improve motor behavior after ischemia, except when it starts 12h after surgery.     

Correlation between inflection of heart rate/work performance curve and myocardial function in exhausting cycle ergometer exercise

Summary The heart rate/work performance (f _c/W) curve is usually S-shaped but a flattening at the top is not always seen. By means of radionuclide ventricular scintigraphy, the left ventricular ejection fraction (LVEF) of 15 sports students was investigated. The behaviour of the f _c/W curve during cycle ergometry with increasing exercise intensities was examined. During exercise, the LVEF showed a distinct initial increase reaching roughly constant values at stress levels below-maximum, and sometimes even falling again. The inflections of the f _c/W curve and left ventricular ejection fraction/performance curve (LVEFPC) were calculated from a second degree polynomial fit. From this function, the slopes of the tangents at the points of aerobic threshold and maximum performance were calculated together with the differences of the angles as a measure of the f _c/W curve and LVEFPC inflections. It follows that the f _c/W curve inflection became less pronounced or was even absent altogether when the decrease in LVEF towards the end of the ergometer exercise became more distinct. A significant negative correlation was found between the existence and extent of the f _c/W curve inflection and the stress-dependent myocardial function, expressed as the inflection of the LVEFPC (P<0.01, r=0.673). Thus, it would seem that the absence of a f _c/W curve inflection was related to a diminished stress-dependent myocardial function.     

Comparison of the predictive value of myelography, computed tomography and MRI on the treadmill test in lumbar spinal stenosis

To date, there have been no prospective, objective studies comparing the accuracy of the MRI, myelo-CT and myelography. The purpose of this study is to compare the diagnostic and predictive values of MRIs, myelo-CTs, and myelographies. Myelographies with dynamic motion views, myelo-CTs, MRIs and exercise treadmill tests were performed in 35 cases. The narrowest AP diameter of the dural sac was measured by myelography. At the pathologic level, dural cross-sectional area (D-CSA) was calculated in the MRI and Myelo-CT. The time to the first symptoms (TAF) and the total ambulation time (TAT) were measured during the exercise treadmill test and used as the standard in the comparison of correlation between radiographic parameters and walking capacity. The mean D-CSA by CT was 58.3 mm(2) and 47.6 mm(2) by MRI. All radiographic parameters such as AP diameters and D-CSA have no correlation to TAF or TAT (p > 0.05). Our data showed no statistically significant differences in the correlation of the patients' walking capacity to the severity of stenosis as assessed by myelography, myelo-CT and MRI.     

Regulation by cytokines (IL‐12, IL‐15, IL‐4 and IL‐10) of the Vγ9Vδ2 T cell response to mycobacterial phosphoantigens in responder and anergic HIV‐infected persons

Human Vγ9Vδ2 T cells contribute to immunity against intracellular pathogens and recognize nonpeptidic antigens, such as the mycobacterial phosphoantigen TUBAg. HIV infection is associated with a polyclonal decrease of peripheral Vγ9Vδ2 T cells and we previously reported that the remaining cells show a proliferative anergy to stimulation with Mycobacterium tuberculosis in 60 % of patients. Because of alterations in the Th1/Th2 cytokine balance reported in HIV infection, we analyzed, at the single‐cell level, the influence of exogenous IL‐4, IL‐10, IL‐12 and IL‐15 on the response to mycobacterial phosphoantigens of γ δ T cells from HIV‐infected patients and healthy donors. We report that the strong γ δ T cell response to TUBAg is characterized by the rapid and selective production of the Th1/proinflammatory cytokines IFN‐γ and TNF‐α in responder HIV‐infected donors. In addition, a positive regulation by IL‐12 and IL‐15 of the production of these cytokines by Vγ9Vδ2 T cells in response to nonpeptidic ligands was observed, whereas IL‐4 and IL‐10 had no effect. In contrast, Vγ9Vδ2 T cells from the anergic HIV‐infected donors had lost the ability to produce Th1 cytokines and were not shifted towards a Th2 profile. Furthermore, neither IL‐12 nor IL‐15 could reverse this functional anergy. The consequences of these observations are discussed in the context of HIV pathogenesis.     

Sars-Cov-2 antigen tests predict infectivity based on viral culture: comparison of antigen,PCR viral load,and viral culture testing on a large sample cohort

ObjectiveTo define the relationship of SARS-CoV-2 antigen, viral load determined by RT-qPCR, and viral culture detection. Presumptively, viral culture can provide a surrogate measure for infectivity of sampled individuals and thereby inform how and where to most appropriately deploy antigen and nucleic acid amplification-based diagnostic testing modalities.MethodsWe compared the antigen testing results from three lateral flow and one microfluidics assay to viral culture detection and viral load determination performed in parallel in up to 189 nasopharyngeal swab samples positive for SARS-CoV-2. Sample viral loads, determined by RT-qPCR, were distributed across the range of viral load values observed in our testing population.ResultsAntigen tests were predictive of viral culture positivity, with the LumiraDx microfluidics method showing enhanced sensitivity (90%; 95% CI 83–94%) compared with the BD Veritor (74%, 95% CI 65–81%), CareStart (74%, 95% CI 65–81%) and Oscar Corona (74%, 95% CI 65–82%) lateral flow antigen tests. Antigen and viral culture positivity were also highly correlated with sample viral load, with areas under the receiver operator characteristic curves of 0.94 to 0.97 and 0.92, respectively. A viral load threshold of 100 000 copies/mL was 95% sensitive (95% CI, 90–98%) and 72% specific (95% CI, 60–81%) for predicting viral culture positivity. Adjusting for sample dilution inherent in our study design, sensitivities of antigen tests were ≥95% for detection of viral culture positive samples with viral loads >10⁶ genome copies/mL, although specificity of antigen testing was imperfect.DiscussionAntigen testing results and viral culture were correlated. For culture positive samples, the sensitivity of antigen tests was high at high viral loads that are likely associated with significant infectivity. Therefore, our data provides support for use of antigen testing in ruling out infectivity at the time of sampling.     

Prevalence of positive skin prick tests, allergic asthma, and rhinoconjunctivitis in teenagers in northern Sweden

The prevalence of positive skin prick tests (SPT) for common allergens and symptoms of allergic rhinoconjunctivitis or asthma was investigated in Umeå in northern Sweden in 1987. Skin prick tests with 10 allergens common in Sweden and a questionnaire were used to examine 1112 teenagers. All subjects with a positive skin prick test or symptoms were interviewed, and they were further investigated by a serum specific IgE test, a ventilatory lung function test, and a physical examination. At least one skin prick test was positive in 43% of the subjects. Ninety-three percent had at least one positive skin prick test to one of the three most common allergens: cat, timothy grass, and birch. The prevalence of current allergic rhinoconjunctivitis was 17%, current allergic asthma 2.8%, and current asthma (both allergic and nonallergic) 6.8%. Multiple logistic regression analysis showed that the most important risk factors for current asthma were sex (being a girl) and atopy. Heredity of asthma or rhinoconjunctivitis and being born in the winter (October-March) also increased the risk. In atopic subjects, having a mother who smoked and heredity of asthma increased the risk. For allergic rhinoconjunctivitis, heredity increased the risk of getting rhinoconjunctivitis.     

高压氧舱内防燃的技术保障

介绍了高压氧舱内防燃的材料选用及有关舱内燃烧的原因、防燃的技术保障。