Enhanced interleukin-6 in human adipose tissue vein after sprint exercise: Results from a pilot study.

BACKGROUND: Low-volume sprint exercise is likely to reduce body fat. Interleukin (IL-6) may mediate this by increasing adipose tissue (AT) lipolysis. Therefore, the exchange of AT IL-6 and glycerol, a marker of lipolysis, was examined in 10 healthy subjects performing three 30-s all-out sprints. METHODS: Blood samples were obtained from brachial artery (a) and a superficial subcutaneous vein (v) on the anterior abdominal wall up to 9 min after the last sprint and analysed for IL-6 and glycerol. RESULTS: Arterial IL-6 increased 2-fold from rest to last sprint. AT venous IL-6 increased 15-fold from 0.4 ± 0.4 at rest to 7.0 ± 4 pg × mL-1 (p < 0.0001) and AT v-a difference increased 45-fold from 0.12 ± 0.3 to 6.0 ± 5 pg x mL-1 (p < 0.0001) 9 min after last sprint. Arterial glycerol increased 2.5-fold from rest to 9 min postsprint 1 (p < 0.0001) and was maintained during the exercise period. AT venous and v-a difference of glycerol increased 2-fold from rest to 9 min postsprint 1 (p < 0.0001 and p = 0.01, respectively), decreased until 18 min postsprint 2 (p < 0.001 and p < 0.0001), and then increased again until 9 min after last sprint (both p < 0.01). CONCLUSIONS: The concurrent increase in venous IL-6 and glycerol in AT after last sprint is consistent with an IL-6 induced lipolysis in AT. Glycerol data also indicated an initial increase in lipolysis after sprint 1 that was unrelated to IL-6. Increased IL-6 in adipose tissue may, therefore, complement other sprint exercise-induced lipolytic agents.

Fast and accurate identification by MALDI-TOF of the zoonotic serovar E of Vibrio vulnificus linked to eel culture.

Vibrio vulnificus is a zoonotic pathogen that can cause death by septicaemia in farmed fish (mainly eels) and humans. The zoonotic strains that have been isolated from diseased eels and humans after eel handling belong to clade E (or serovar E (SerE)), a clonal complex within the pathovar (pv.) piscis. The aim of this study was to evaluate the accuracy of MALDI-TOF mass spectrometry (MS) in the identification of SerE, using the other two main pv. piscis-serovars (SerA and SerI) from eels as controls. MALDI-TOF data were compared with known serologic and genetic data of five pv. piscis isolates or strains, and with the non pv. piscis reference strain. Based on multiple spectra analysis, we found serovar-specific peaks that were of ~3098 Da and ~ 4045 Da for SerE, of ~3085 Da and ~ 4037 Da for SerA, and of ~3085 Da and ~ 4044 Da for SerI. Therefore, our results demonstrate that MALDI-TOF can be used to identify SerE and could also help in the identification of the other serovars of the species. This means that zoonosis due to V. vulnificus could be prevented by using MALDI-TOF, as action can be taken immediately after the isolation of a possible zoonotic V. vulnificus strain.

[Recommendations on physical activity and sedentary behaviour]. / Sitt mindre ­ all rörelse räknas.

Recommendations on physical activity and sedentary behaviour for improved health have been prepared by Professional Associations for Physical Activity (YFA) and approved by the Swedish Society of Medicine. All adults should do aerobic physical activity 150-300 minutes at moderate or 75-150 minutes at high intensity, or combined, at a weekly basis. For additional health benefits, muscle-strengthening activity should be performed on at least 2 days a week, and sedentary time should be limited and replaced by physical activity. Older adults should, as part of their weekly physical activity, do multicomponent physical activity that emphasizes balance and strength on at least 2-3 days a week to enhance functional capacity and prevent falls. The benefits of physical activity outweigh the risks. The Swedish National Board of Health and Welfare recommends that healthcare providers offer counselling with exercise on prescription to individuals with physical activity under the recommended dose.

[Accuracy of lifestyle data from Global Burden of Disease]. / ¼Äta ohälsosamt tio gånger så farligt som att vara inaktiv«.

Low physical activity is responsible for approximately 0,83 million deaths globally every year according to the Global Burden of Disease (GBD), whereas others have estimated that low physical activity is responsible for about 4-5 million deaths annually. The underlying evidence for the GBD estimate is debatable. It is based on a substantially lower maximal risk reduction with a relative risk of about 10 % compared with a maximal relative risk reduction of more than 30 % in the recent WHO global physical activity recommendations. According to GBD, dietary risks are responsible for 10 times more deaths compared to low physical activity. This estimate is based on 15 different dietary risk factors without systematically considering covariation between risk factors. It is of utmost importance that a reliable and transparent evidence base is presented in future GBD publications about the impact of disease risk factors on the global disease burden. Misleading messages about the importance of physical activity for reducing chronic diseases will undermine the work conducted to develop evidence-based knowledge about the health effects of physical activity.

Metabolic and morphological profile in skeletal muscle of healthy boys and girls.

It was hypothesized that the typical adult pattern of higher glycolytic capacity in skeletal muscle of males compared to females is not observed in children and that fiber cross-sectional area (CSA) is a determinant of glycolytic capacity in children. Biopsies were performed in vastus lateralis in 9-12 years-old healthy boys and girls (N = 27). Fiber types were classified by myofibrillar ATPase staining and CSA was measured using planimetry. Citrate synthase (CS) and lactate dehydrogenase (LD) were analyzed using fluorometric and spectrophotometric methods. There was no significant difference between boys and girls in CS activity (0.45 ± 0.1 µkat g-1 dry muscle in boys and 0.42 ± 0.1 in girls) or LD activity (24 ± 6 µkat g-1 dry muscle in boys and 25 ± 7 in girls). CSA did not differ between boys and girls. CS was inversely related to type I CSA (r = -0.62, p < 0.001) and LD was directly related to type IIA (r = 0.63, p < 0.001) and type IIB CSA (r = 0.72, p < 0.001). CSA was a significant determinant of CS and LD, even after adjusting for sex and relative fiber type area in multiple regression analysis. This suggests that the typical adult pattern of higher muscle glycolytic capacity in males than in females, as estimated by LD activity, was not observed in children. Sex-specific patterns in glycolytic capacity thus appear to develop during the transition from childhood to adulthood. In addition, fiber CSA was a strong determinant of both muscle glycolytic and oxidative capacity in children, regardless of sex.

Non-lethal sampling for the detection of Renibacterium salmoninarum by qPCR for diagnosis of bacterial kidney disease.

Bacterial kidney disease (BKD), caused by Renibacterium salmoninarum (Rs), can be transmitted both horizontally and vertically and there is no available cure or prophylaxis. The control of BKD requires continuous surveillance, which is challenging in aquaculture as well as in programs for conservation and restoration of salmonid fish strains. BKD is a notifiable disease in Sweden and is monitored through the mandatory health control program using a polyclonal ELISA for detection of the Rs p57 protein in kidney. Fish must be killed for sampling, an obvious disadvantage especially regarding valuable broodfish. The present study shows that gill-/cloacal swabs collected in vivo for real-time PCR (qPCRgc ), allow a sensitive and specific detection of Rs. The sensitivity of qPCRgc was estimated to 97.8% (credible interval (ci) 93.8%-100%) compared to 98.3% (ci 92.7%-100%) and 48.8% (ci 38.8%-58.8%) of kidney samples for qPCR (qPCRk ) and ELISA (ELISAk ) respectively, by use of the Bayesian Latent Class Analysis (BLCA). Since the goal of the program is eradication of BKD the most sensitive test is preferrable. Using qPCRgc instead of ELISAk will result in a lower false negative rate and can be useful for surveillance in aquaculture and in breeding programs with valuable fish. However, a higher false positive rate warrants confirmatory lethal testing before a previously Rs negative farm is subject to restrictions.

Assessing the presence and spread of Renibacterium salmoninarum between farmed and wild fish in Sweden.

Bacterial kidney disease (BKD) can be a devastating bacterial infection in salmonids, and it is present in aquaculture throughout the world. BKD is caused by the Gram-positive facultative intracellular bacterium Renibacterium salmoninarum (R. salmoninarum) that is spread both horizontally and vertically. Disease signs include external ulcerations and blisters and internal signs such as organ swelling, granulomas, petechiae and ascites. In Sweden, BKD accounts for a significant income loss in aquacultures due to expensive decontamination of the facility and increased disease susceptibility for the immunocompromised fish leading to higher mortality rates. In addition, uncontrolled spread in aquaculture may threaten the survival of wild fish populations. The aim of our study was to investigate the prevalence of R. salmoninarum in wild salmonids caught in Swedish waters where net pen farms with a recent history of BKD are present. Four rivers with at least one BKD-positive or recently BKD-positive farm were selected. In addition, we evaluated the use of environmental DNA (eDNA) for surveillance and monitoring of ongoing infections at these locations. In total, 1058 fish were sampled from four different river systems, and of them 52 (4.9%) were positive for R. salmoninarum by antigen ELISA. Surprisingly, these fish were not evenly distributed between the four river systems, but 50 were caught in the same river (Ljungan). This accounts for an alarmingly high rate of 17% R. salmoninarum-positive samples in wild salmonids in this area. This number is far above what was expected and clearly shows the risk with an open farming system as well as the importance of effective health monitoring programmes to avoid an uncontrolled spread of the disease. The use of eDNA for monitoring BKD is somewhat difficult to evaluate. Few of the water samples analysed were PCR positive for R. salmoninarum (2 of 38) and those were collected where no ELISA positive fish were identified. In addition to water, sediment samples were collected under a net pen farm that had recently slaughtered all fish due to ongoing R. salmoninarum infections. Sediment samples are more promising than water as 4 of 5 samples at one farming facility where positive for R. salmoninarum. Thus, sediment samples may be valuable for monitoring potential ongoing BKD in farms, without the need to sacrifice valuable fish.

Muscle fiber size in healthy children and adults in relation to sex and fiber types.

BACKGROUND: In adult males, cross-sectional area (CSA) for type II muscle fibers is generally larger than for type I fibers. In this cross-sectional study the aim was to compare sex-related CSAs of various muscle fiber types during childhood-to-adulthood transition. METHODS: Percutaneous biopsy samples were obtained from vastus lateralis in 10-y-old children (10 males and 5 females) and in young adults (9 males and 7 females). Fiber types were classified by myofibrillar ATPase and CSAs from NADH-dehydrogenase staining. RESULTS: Type IIA were larger than type I fibers in adult males, but not in adult females or children (age x sex x fiber type, P < .002). When including all participants, body weight and sex explained 78% of the variation in type IIA CSA but only body weight contributed for type I. CONCLUSIONS: Sex-specific patterns in CSA of the muscle fiber types appears to develop during the transition from childhood to adulthood.

Aerobic exercise capacity is maintained over a 5-year period in mild-to-moderate chronic kidney disease: a longitudinal study.

BACKGROUND: Aerobic exercise capacity is reduced in non-dialysis chronic kidney disease (CKD), but the magnitude of changes in exercise capacity over time is less known. Our main hypothesis was that aerobic ExCap would decline over 5 years in individuals with mild-to-moderate CKD along with a decline in renal function. A secondary hypothesis was that such a decline in ExCap would be associated with a decline in muscle strength, cardiovascular function and physical activity. METHODS: We performed a 5-year-prospective study on individuals with mild-to-moderate CKD, who were closely monitored at a nephrology clinic. Fiftytwo individuals with CKD stage 2-3 and 54 age- and sex-matched healthy controls were included. Peak workload was assessed through a maximal cycle exercise test. Muscle strength and lean body mass, cardiac function, vascular stiffness, self-reported physical activity level, renal function and haemoglobin level were evaluated. Tests were repeated after 5 years. Statistical analysis of longitudinal data was performed using linear mixed models. RESULTS: Exercise capacity did not change significantly over time in either the CKD group or controls, although the absolute workloads were significantly lower in the CKD group. Only in a CKD subgroup reporting low physical activity at baseline, exercise capacity declined. Renal function decreased in both groups, with a larger decline in CKD (p = 0.05 between groups). Peak heart rate, haemoglobin level, handgrip strength, lean body mass and cardiovascular function did not decrease significantly over time in CKD individuals. CONCLUSIONS: On a group level, aerobic exercise capacity and peak heart rate were maintained over 5 years in patients with well-controlled mild-to-moderate CKD, despite a slight reduction in glomerular filtration rate. In line with the maintained exercise capacity, cardiovascular and muscular function were also preserved. In individuals with mild-to-moderate CKD, physical activity level at baseline seems to have a predictive value for exercise capacity at follow-up.

Acute sprint exercise transcriptome in human skeletal muscle.

AIM: To examine global gene expression response to profound metabolic and hormonal stress induced by acute sprint exercise. METHODS: Healthy men and women (n = 14) performed three all-out cycle sprints interspersed by 20 min recovery. Muscle biopsies were obtained before the first, and 2h and 20 min after last sprint. Microarray analysis was performed to analyse acute gene expression response and repeated blood samples were obtained. RESULTS: In skeletal muscle, a set of immediate early genes, FOS, NR4A3, MAFF, EGR1, JUNB were markedly upregulated after sprint exercise. Gene ontology analysis from 879 differentially expressed genes revealed predicted activation of various upstream regulators and downstream biofunctions. Gene signatures predicted an enhanced turnover of skeletal muscle mass after sprint exercise and some novel induced genes such as WNT9A, FZD7 and KLHL40 were presented. A substantial increase in circulating free fatty acids (FFA) was noted after sprint exercise, in parallel with upregulation of PGC-1A and the downstream gene PERM1 and gene signatures predicting enhanced lipid turnover. Increase in growth hormone and insulin in blood were related to changes in gene expressions and both hormones were predicted as upstream regulators. CONCLUSION: This is the first study reporting global gene expression in skeletal muscle in response to acute sprint exercise and several novel findings are presented. First, in line with that muscle hypertrophy is not a typical finding after a period of sprint training, both hypertrophy and atrophy factors were regulated. Second, systemic FFA and hormonal and exposure might be involved in the sprint exercise-induced changes in gene expression.

Biogeography of the fish pathogen Aeromonas salmonicida inferred by vapA genotyping.

A recently described typing system based on sequence variation in the virulence array protein (vapA) gene, encoding the A-layer surface protein array, allows unambiguous subtyping of Aeromonas salmonicida. In the present study, we compile A-layer typing results from a total of 675 A. salmonicida isolates, recovered over a 59-year period from 50 different fish species in 26 countries. Nine novel A-layer types (15-23) are identified, several of which display a strong predilection towards certain fish hosts, including e.g. Cyprinidae and Pleuronectidae species. Moreover, we find indications that anthropogenic transport of live fish may have aided the near global dissemination of two cyprinid-associated A-layer types. Comparison of whole genome phylogeny and A-layer typing for a subset of strains further resulted in compatible tree topologies, indicating the utility of vapA as a phylogenetic as well as an epizootiological marker in A. salmonicida. A Microreact project (microreact.org/project/r1pcOAx9m) has been created, allowing public access to the vapA analyses and relevant metadata. In sum, the results generated provide valuable insights into the global population structure of A. salmonicida, particularly in relation to its piscine host spectrum and the geographic distribution of these hosts.

Genome analysis provides insights into the epidemiology of infection with Flavobacterium psychrophilum among farmed salmonid fish in Sweden.

The pathogen Flavobacterium psychrophilum is a major problem for the expanding salmonid fish farming industry in Sweden as well as worldwide. A better understanding of the phylogeography and infection routes of F. psychrophilum outbreaks could help to improve aquaculture profitability and the welfare of farmed fish while reducing the need for antibiotics. In the present study, high-throughput genome sequencing was applied to a collection of F. psychrophilum isolates (n=38) from outbreaks on fish farms in different regions of Sweden between 1988 and 2016. Antibiotic susceptibility tests were applied to a subset of the isolates and the results correlated to the presence of genetic resistance markers. We show that F. psychrophilum clones are not regionally biased and that new clones with a higher degree of antibiotic resistance have emerged nationwide during the study period. This supports previous theories of the importance of live fish and egg trade as a route of infection. Continuous monitoring of recovered isolates by high-throughput sequencing techniques in the future could facilitate tracing of clones within and between countries, as well as the detection of emergent virulent or antibiotic-resistant clones. This article contains data hosted by Microreact.

Gradual reduction in exercise capacity in chronic kidney disease is associated with systemic oxygen delivery factors.

BACKGROUND: The cause of reduced exercise capacity (ExCap) in chronic kidney disease (CKD) is multifactorial. The aim of this study was to investigate determinants of aerobic ExCap in patients with mild to severe CKD not undergoing dialysis. METHODS: We included 52 individuals with CKD stage 2-3, 47 with stage 4-5, and 54 healthy controls. Peak workload and peak heart rate (HR) were assessed by a maximal cycle exercise test. Cardiac function including stroke volume (SV) and vascular stiffness were evaluated by ultrasound at rest. Handgrip strength, body composition, haemoglobin level and self-reported physical activity were assessed. RESULTS: Peak workload (221±60, 185±59, 150±54 W for controls, CKD 2-3 and CKD 4-5 respectively), peak HR (177±11, 161±24, 144±31 beats/min) and haemoglobin level (14.2±1.2, 13.5±1.4, 12.2±1.3 g/dL) were all three significantly lower in CKD 2-3 than in controls, (p = 0.001, 0.001 and 0.03 respectively) and were even lower in stages 4-5 CKD than in CKD 2-3 (p = 0.01, 0.001 and <0.001 respectively). Resting SV and lean body mass did not differ between groups and handgrip strength was significantly lower only in CKD 4-5 compared to controls (p = 0.02). Peak workload was strongly associated with the systemic oxygen delivery factors: SV, peak HR and haemoglobin level. These three factors along with age, sex and height2 explained 82% of variation in peak workload. Peak HR contributed most to the variation; the peripheral variables handgrip strength and vascular stiffness did not improve the explanatory value in regression analysis. CONCLUSIONS: In this cross-sectional study of CKD patients not on dialysis, aerobic ExCap decreased gradually with disease severity. ExCap was associated mainly with systemic oxygen delivery factors, in particular peak HR. Neither muscle function and mass, nor vascular stiffness were independent determinants of aerobic ExCap in this group of CKD patients.

Influence of nutrient ingestion on amino acid transporters and protein synthesis in human skeletal muscle after sprint exercise.

Nutrient ingestion is known to increase the exercise-induced stimulation of muscle protein synthesis following resistance exercise. Less is known about the effect of nutrients on muscle protein synthesis following sprint exercise. At two occasions separated by 1 mo, 12 healthy subjects performed three 30-s sprints with 20-min rest between bouts. In randomized order, they consumed a drink with essential amino acids and maltodextrin (nutrient) or flavored water (placebo). Muscle biopsies were obtained 80 and 200 min after the last sprint, and blood samples were taken repeatedly during the experiment. Fractional synthetic rate (FSR) was measured by continuous infusion of l-[2H5]phenylalanine up to 200 min postexercise. The mRNA expression and protein expression of SNAT2 were both 1.4-fold higher ( P < 0.05) after nutrient intake compared with placebo at 200 min postexercise. Phosphorylated Akt, mammalian target of rapamycin (mTOR), and p70S6k were 1.7- to 3.6-fold higher ( P < 0.01) 80 min after the last sprint with nutrient ingestion as compared with placebo. In addition, FSR was higher ( P < 0.05) with nutrients when plasma phenylalanine (FSRplasma) was used as a precursor but not when intracellular phenylalanine (FSRmuscle) was used. Significant correlations were also found between FSRplasma on the one hand and plasma leucine and serum insulin on the other hand in the nutrient condition. The results show that nutrient ingestion induces the expression of the amino acid transporter SNAT2 stimulates Akt/mTOR signaling and most likely the rate of muscle protein synthesis following sprint exercise. NEW & NOTEWORTHY There is limited knowledge regarding the effect of nutrients on muscle protein synthesis following sprint as compared with resistance exercise. The results demonstrate that nutrient ingestion during repeated 30-s bouts of sprint exercise induces expression of the amino acid transporter SNAT2 and stimulates Akt/mTOR signaling and most likely the rate of muscle protein synthesis. Future studies to explore the chronic effects of nutritional ingestion during sprint exercise sessions on muscle mass accretion are warranted.

Exercise-induced upregulation of endothelial adhesion molecules in human skeletal muscle and number of circulating cells with remodeling properties.

Multipotent cells have received great interest because of their potential capacity to repair and remodel peripheral tissues. We examined the effect of an acute exercise bout on the number of circulating cells with known remodeling properties and the level of factors in plasma and skeletal muscle tissue with potential to recruit these cells. Twenty healthy male subjects performed a 60-min cycling exercise. Blood samples for flow cytometry were drawn from 10 subjects (group 1) before and up to 2 h after exercise, and absolute cell counts of the classical (CD14++CD16-), intermediate (CD14++CD16+), and nonclassical (CD14+CD16++) monocyte (MO) subpopulations and of CD45dimCD34+VEGFR2+ endothelial progenitor cells (EPCs) were measured by bead-based determination. Plasma samples and vastus lateralis muscle biopsies were obtained from the other 10 subjects (group 2). In group 1, all MO subsets were increased directly after exercise, with CD14+CD16++ MOs showing the greatest fold increase. After 2 h, only CD14++CD16- MOs were increased compared with resting levels. The number of EPCs showed a trend toward increasing with exercise (P = 0.08). In group 2, the mRNA levels of the endothelial adhesion molecules ICAM-1, VCAM-1, and E-selectin increased in the skeletal muscle tissue. VEGF-A increased in exercised skeletal muscle and stimulated the expression of VCAM-1 and E-selectin in human umbilical vein endothelial cells. In conclusion, exercise increases MO subsets with different temporal patterns and enhances the capacity of skeletal muscle tissue to recruit circulating cells as shown by increased expression of endothelial adhesion molecules.NEW & NOTEWORTHY In the present study we showed for the first time that the adhesion molecules ICAM-1, VCAM-1, and E-selectin, known to be able to recruit circulating cells to the peripheral tissue, increased in exercised human skeletal muscle concurrently with increased circulating levels of cells shown to have importance for skeletal muscle remodeling. These findings support the concept of cell recruitment from the circulation playing a role in skeletal muscle adaptation to exercise.

[Physical activity--new paths and choices in the recommendations for adults]. / Fysisk aktivitet - nya vägar och val i rekommendationerna för vuxna.

Recommendations for physical activity have been prepared by Professional Associations for Physical Activity and approved by the Swedish Society of Medicine in 2011. All adults are recommended regular aerobic and muscle strengthening physical activity. Lowest recommended dose (intensity x time) of aerobic physical activity is 150 minutes at moderate or 75 minutes at high intensity per week. More health benefits are achieved if the dose is higher than the lowest recommended dose. Longer periods of sedentary behavior should be avoided. Elderly are also recommended balance training. The benefits of physical activity outweigh the risks. The Swedish National Board of Health and Welfare recommends that the healthcare system offer counselling with the adjunct of exercise on prescription or a pedometer to persons with insufficient physical activity, i.e. less than the lowest recommended dose in the current recommendations for physical activity.

Criterion validation of two submaximal aerobic fitness tests, the self-monitoring Fox-walk test and the Åstrand cycle test in people with rheumatoid arthritis.

BACKGROUND: Aerobic capacity tests are important to evaluate exercise programs and to encourage individuals to have a physically active lifestyle. Submaximal tests, if proven valid and reliable could be used for estimation of maximal oxygen uptake (VO2max). The purpose of the study was to examine the criterion-validity of the submaximal self-monitoring Fox-walk test and the submaximal Åstrand cycle test against a maximal cycle test in people with rheumatoid arthritis (RA). A secondary aim was to study the influence of different formulas for age predicted maximal heart rate when estimating VO2max by the Åstrand test. METHODS: Twenty seven subjects (81% female), mean (SD) age 62 (8.1) years, diagnosed with RA since 17.9 (11.7) years, participated in the study. They performed the Fox-walk test (775 meters), the Åstrand test and the maximal cycle test (measured VO2max test). Pearson's correlation coefficients were calculated to determine the direction and strength of the association between the tests, and paired t-tests were used to test potential differences between the tests. Bland and Altman methods were used to assess whether there was any systematic disagreement between the submaximal tests and the maximal test. RESULTS: The correlation between the estimated and measured VO2max values were strong and ranged between r = 0.52 and r = 0.82 including the use of different formulas for age predicted maximal heart rate, when estimating VO2max by the Åstrand test. VO2max was overestimated by 30% by the Fox-walk test and underestimated by 10% by the Åstrand test corrected for age. When the different formulas for age predicted maximal heart rate were used, the results showed that two formulas better predicted maximal heart rate and consequently a more precise estimation of VO2max. CONCLUSIONS: Despite the fact that the Fox-walk test overestimated VO2max substantially, the test is a promising method for self-monitoring VO2max and further development of the test is encouraged. The Åstrand test should be considered as highly valid and feasible and the two newly developed formulas for predicting maximal heart rate according to age are preferable to use when estimating VO2max by the Åstrand test.

ACTN3 genotype and modulation of skeletal muscle response to exercise in human subjects.

α-Actinin-3 is a Z-disc protein expressed only in type II muscle fibers. A polymorphism in the ACTN3 gene (R577X) results in lack of α-actinin-3 in XX genotype. The prevalence of the mutated X-allele is lower among power/sprint oriented athletes compared with controls, indicating that the lack of α-actinin-3 is detrimental in these sports, but a mechanistic link has not been established. Results from Actn3-knockout (KO) mouse model suggest that α-actinin-3 may affect muscle mass and muscle glycogen levels. In the present investigation we examined muscle fiber type composition, cross-sectional fiber area (CSA), and muscle glycogen levels at baseline in 143 human subjects with different ACTN3 genotypes. In addition, hypertrophy signaling and glycogen utilization in response to sprint exercise were studied in a subset of subjects. Glycogen utilization was analyzed in separate pools of type I and type II fibers. No differences in fiber type composition, CSA, or muscle glycogen levels were observed at baseline across the ACTN3 genotypes. However, the sprint exercise-induced increase in phosphorylation of mTOR and p70S6k was smaller in XX than in RR+RX (P = 0.03 and P = 0.01, respectively), indicating a less pronounced activation of hypertrophy signaling in XX. Glycogen utilization during sprint exercise varied across ACTN3 genotypes in type II fibers (P = 0.03) but not in type I fibers (P = 0.38). The present results are in accordance with findings from the KO mice and reinforce the hypothesis that ACTN3 genotype-associated differences in muscle mass and glycogen utilization provide a mechanistic explanation for the modulation of human performance by the ACTN3 genotype.