Glycaemic Control in Athletes

Substituting sedentary time with sleep or physical activity and subsequent weight-loss maintenance

OBJECTIVE

In this study, the associations between the substitution of sedentary time with sleep or physical activity at different intensities and subsequent weight-loss maintenance were examined.

METHODS

This prospective study included 1152 adults from the NoHoW trial who had achieved a successful weight loss of ≥5% during the 12 months prior to baseline and had BMI ≥25 kg/m² before losing weight. Physical activity and sleep were objectively measured during a 14-day period at baseline. Change in body weight was included as the primary outcome. Secondary outcomes were changes in body fat percentage and waist circumference. Cardiometabolic variables were included as exploratory outcomes.

RESULTS

Using isotemporal substitution models, no associations were found between activity substitutions and changes in body weight or waist circumference. However, the substitution of sedentary behavior with moderate-to-vigorous physical activity was associated with a decrease in body fat percentage during the first 6 months of the trial (-0.33% per 30 minutes higher moderate-to-vigorous physical activity [95% CI: -0.60% to -0.07%], p = 0.013).

CONCLUSIONS

Sedentary behavior had little or no influence on subsequent weight-loss maintenance, but during the early stages of a weight-loss maintenance program, substituting sedentary behavior with moderate-to-vigorous physical activity may prevent a gain in body fat percentage.

Blood Metabolomics Analysis Identifies Differential Serum Metabolites in Elite and Sub-elite Swimmers

Objective: Metabolites in body fluids, such as lactate, glucose, and creatinine, have been measured by conventional methods to evaluate physical function and performance or athletic status. The objectives of the current study were to explore the novel metabolite biomarkers in professional swimmers with different competition levels using nuclear magnetic resonance (NMR) metabolomics, and try to establish a model to identify the athletic status or predict the competitive potential.

Methods: Serum samples were collected from 103 elite and 84 sub-elite level Chinese professional swimmers, and were profiled by NMR analysis.

Results: Out of the thirty-six serum metabolites profiled, ten were associated with the athletic status of swimmers (with p < 0.05). When compared with sub-elite swimmers, elite swimmers had higher levels of high-density lipoprotein (HDL), unsaturated fatty acid, lactic acid, and methanol. Elite swimmers had lower levels of isoleucine, 3-hydroxybutyric acid, acetoacetate, glutamine, glycine, and α-glucose. A model with four metabolites, including HDL, glutamine, methanol, and α-glucose, was established to predict athletic status by adjusting with different covariates. The area under the curve (AUC) of the best model was 0.904 (95% CI: 0.862-0.947), with a sensitivity and specificity of 75.5 and 90.2%, respectively.

Conclusion: We have identified ten metabolite biomarkers with differentially expressed levels between elite and sub-elite swimmers, the differences could result from genetic or sports level between the two cohorts. A model with four metabolites has successfully differentiated professional swimmers with different competitive levels.

Acute Changes in Heart Rate Variability to Glucose and Fructose Supplementation in Healthy Individuals: A Double-Blind Randomized Crossover Placebo-Controlled Trial

Simple Summary

In this study, we investigated the cardio-autonomic stress responses to the ingestion of liquid glucose, fructose, a combination thereof and a placebo in healthy individuals at rest. The cardio-autonomic response was more pronounced in all groups with carbohydrates compared to placebo indicating an increased cardio-autonomic stress response resulting in a reduced heart-rate variability. When investigating different levels of blood glucose, the findings showed a significant decline in heart-rate variability with increasing blood glucose levels. This was also seen with severely low levels of blood glucose. The speed of how quick blood glucose increased and decreased also impacted the cardio-autonomic response which further deteriorated heart-rate variability. These findings indicate that healthy human’s autonomic system responds quickly to changes in their blood glucose.

Abstract

Background: It is unknown how different types of carbohydrates alter the cardio-autonomic system in healthy individuals. Therefore, the aim of this study was to investigate how heart-rate variability changes to single dose ingestion of glucose, fructose, glucose and fructose, and an artificial sweetener (sucralose). Methods: In a double-blind randomized crossover placebo-controlled setting, 15 participants received all study-specific substances in liquid form. During each 2-h visit, venous blood glucose was measured in a 5-min interval while heart-rate variability was measured continuously via Holter-electrocardiograph. Results: Ingestion of different types of carbohydrates and sucralose showed significant differences for heart rate (p < 0.001), SDNN (p < 0.008), RMSSD (p < 0.001), pNN50 (p < 0.001) and blood pressure (p < 0.001). Different glucose levels significantly altered parameters of heart-rate variability and blood pressure (all p < 0.001), while the rate of change in blood glucose led to changes in heart rate variability, but not in heart rate (p = 0.25) or blood pressure (p = 0.99). Conclusions: Ingestion of different types of carbohydrates lead to reductions in heart-rate variability compared to a placebo. Blood glucose values above or below 70–90 mg/dL decreased heart rate variability while this was also seen for rapid glucose changes, yet not as pronounced. Healthy individuals should be conscious about carbohydrate intake while maintaining blood glucose levels between 70–90 mg/dL.

Genomic Characterization of the Istrian Shorthaired Hound

Istrian shorthaired hound is an old indigenous Croatian dog breed with historical traces of its origin, which date back to the 14th century. Due to its intelligence and great hunting abilities, it is considered an excellent hunting dog. Despite its ancient origin, there is no data on genetic diversity, population structure, and degree of inbreeding that could be used for advanced management and conservation of this breed. Our study aimed to provide a high-resolution population structure of the Istrian shorthaired hound using a 220K HD SNP array, to compare the obtained data with the genealogical records and to place the breed in a broader context of world dog populations. Relatively high population size and low inbreeding coefficient estimated from genealogical data indicate a preserved genetic diversity in this breed. The principle component analysis, the NeighborNet network, and TreeMix were used to determine the genetic relationship between the Istrian shorthaired hound and other breeds. The Istrian shorthaired hound was found to be genetically related to Italian hunting dogs sharing the same branch with the Segugio Italiano a Pelo Raso and Segugio Italiano a Pelo Forte. The ADMIXTURE analysis indicated that the Istrian shorthaired hound could be involved in the development of some other hunting dog breeds. The estimated effective population size (Ne) based on SNP data was similar to Ne calculated from genealogical data indicating the absence of bottlenecks and well-balanced use of breeding animals. The low genomic inbreeding coefficient, together with the higher number of short runs of homozygosity, observed in the Istrian shorthaired hound, confirms the ancient origin of the breed based on historical documents. The analysis of selective sweeps identified genomic regions with the strongest selection signals in the vicinity of the genes associated with cognitive performance and behavior. Genome analysis proved to be a useful tool for estimating population parameters and can be implemented in the conservation plan for this indigenous breed.

Ubiquinone Supplementation with 300 mg on Glycemic Control and Antioxidant Status in Athletes: A Randomized, Double-Blinded, Placebo-Controlled Trial

The aim of this study is to investigate the glycemic profile, oxidative stress, and antioxidant capacity in athletes after 12 weeks of ubiquinone supplementation. It was a double-blinded, randomized, parallel, placebo-controlled study. Thirty-one well-trained college athletes were randomly assigned to ubiquinone (300 mg/d, n = 17) or placebo group (n = 14). The glycemic profile [fasting glucose, glycated hemoglobin (HbA1c), homeostatic model assessment-insulin resistance (HOMA-IR), quantitative insulin sensitivity check index (QUICKI)], plasma and erythrocyte malondialdehyde (MDA), total antioxidant capacity (TAC), and ubiquinone status were measured. After supplementation, the plasma ubiquinone concentration was significantly increased (p < 0.05) and the level of erythrocyte MDA was significantly lower in the ubiquinone group than in the placebo group (p < 0.01). There was a significant correlation between white blood cell (WBC) ubiquinone and glycemic parameters [HbA1c, r = −0.46, p < 0.05; HOMA-IR, r = −0.67, p < 0.01; QUICKI, r = 0.67, p < 0.01]. In addition, athletes with higher WBC ubiquinone level (≥0.5 nmol/g) showed higher erythrocyte TAC and QUICKI and lower HOMA-IR. In conclusion, we demonstrated that athletes may show a better antioxidant capacity with higher ubiquinone status after 12 weeks of supplementation, which may further improve glycemic control.

Coenzyme Q10 status, glucose parameters, and antioxidative capacity in college athletes

BACKGROUND

Glycemia is related to energy production during exercise. Coenzyme Q10 is an antioxidant that participates in adenosine triphosphate synthesis in mitochondria. The aim of this study was to investigate the level of coenzyme Q10, glucose parameters, and antioxidant capacity in athletes.

METHODS

This study was designed as a cross-sectional study. Well-trained college athletes (n = 43) and age-gender matched healthy subjects (n = 25) were recruited from a college. The levels of glucose parameters, oxidative stress, antioxidant enzymes activity, Trolox equivalent antioxidant capacity (TAC), and coenzyme Q10 status were measured in the present study.

RESULTS

The athletes had a significantly lower level of white blood cells (WBC) coenzyme Q10 than the healthy subjects (0.34 ± 0.24 vs. 0.65 ± 0.43 nmol/g, p < 0.01); however, no significant difference was detected in plasma coenzyme Q10 between the two groups. Regarding the glucose parameters, the athletes had significantly higher values for HbA1c (5.5 ± 0.3 vs. 5.3 ± 0.3%, p < 0.05) and quantitative insulin sensitivity check index (QUICKI, 0.37 ± 0.03 vs. 0.34 ± 0.03, p < 0.05), and lower homeostatic model assessment-insulin resistance (HOMA-IR, 1.5 ± 0.8 vs. 2.9 ± 3.8, p < 0.05) than the healthy subjects. A higher level of TAC was found in the athletes (serum, 5.7 ± 0.3 vs. 5.4 ± 0.2 mM Trolox; erythrocyte, 10.5 ± 0.6 vs. 10.0 ± 0.5 mM Trolox, p < 0.05). In addition, WBC coenzyme Q10 status was significantly correlated with catalase activity (r = 0.56, p < 0.01), GPx activity (r = 0.56, p < 0.01), serum TAC (r = 0.54, p < 0.01), fasting glucose (β = - 1.10, p < 0.01), HbA1c (β = - 0.82, p < 0.01), HOMA-IR (β = - 1.81, p < 0.01), and QUICK (β = 0.08, p < 0.01).

CONCLUSIONS

Athletes may suffer from a marginal coenzyme Q10 deficiency, and the level was related to glycemic control and antioxidant capacity. Further interventional studies are needed to clarify an adequate dose of coenzyme Q10 supplementation in athletes to optimize their coenzyme Q10 status and athletic performance or recovery during exercise.

Biomarkers in Sports and Exercise: Tracking Health, Performance, and Recovery in Athletes

Lee, EC, Fragala, MS, Kavouras, SA, Queen, RM, Pryor, JL, and Casa, DJ. Biomarkers in sports and exercise: tracking health, performance, and recovery in athletes. J Strength Cond Res 31(10): 2920–2937, 2017—Biomarker discovery and validation is a critical aim of the medical and scientific community. Research into exercise and diet-related biomarkers aims to improve health, performance, and recovery in military personnel, athletes, and lay persons. Exercise physiology research has identified individual biomarkers for assessing health, performance, and recovery during exercise training. However, there are few recommendations for biomarker panels for tracking changes in individuals participating in physical activity and exercise training programs. Our approach was to review the current literature and recommend a collection of validated biomarkers in key categories of health, performance, and recovery that could be used for this purpose. We determined that a comprehensive performance set of biomarkers should include key markers of (a) nutrition and metabolic health, (b) hydration status, (c) muscle status, (d) endurance performance, (e) injury status and risk, and (f) inflammation. Our review will help coaches, clinical sport professionals, researchers, and athletes better understand how to comprehensively monitor physiologic changes, as they design training cycles that elicit maximal improvements in performance while minimizing overtraining and injury risk.

Irisin: A Potential Link between Physical Exercise and Metabolism-An Observational Study in Differently Trained Subjects, from Elite Athletes to Sedentary People

We compared irisin levels among groups of differently trained healthy individuals to explore the role of irisin as a physiological linker between exercise and metabolic health. Irisin and biochemical parameters of glucose and lipid metabolism were assessed in 70 healthy volunteers stratified for sport performance level into four groups: (1) 20 elite athletes of national level, (2) 20 subelite athletes of local level, (3) 20 recreational athletes, and (4) 10 sedentary subjects. All biochemical parameters were within the ranges of normality. Fasting glucose, HOMA-IR, and total cholesterol levels were inversely related to the degree of physical activity. HbA1c was higher in elite athletes compared to all the other groups (p < 0.01). A U-shaped relation between free fatty acids and the degree of physical activity was observed. All groups showed similar plasma irisin levels. After correction for the degree of insulin resistance (irisin/HOMA-IR), elite athletes showed higher levels compared to sedentary and recreational subjects (p < 0.01 and p < 0.05, resp.). In addition, the number of metabolic parameters correlated with irisin increased at increasing the training status. Our study suggests a correlation between sport performance, insulin sensitivity, and irisin levels. Irisin may be one potential mediator of the beneficial effects of exercise on metabolic profile.

Controlling sources of preanalytical variability in doping samples: challenges and solutions

The use of illicit substances and methods contravenes the ethics of sports and may be associated with side effects. Antidoping testing is an essential tool for preventing or limiting the consequences of cheating in sports. As for conventional laboratory testing, major emphasis has been placed on analytical quality, overlooking the inherent risks that may arise from analysis of unsuitable doping samples. The adherence to scrupulous criteria for collection, handling, transportation and storage of samples, especially blood and urine samples, is essential. The leading preanalytical variables that influence doping sample quality include biological variability, sample collection, venous stasis, spurious hemolysis and presence of other interfering substances, sample manipulation and degradation, and inappropriate conditions for transportation and storage. This article provides a personal overview about the current challenges in preanalytical management of doping samples, as well as potential solutions for preventing the negative impact of preanalytical variables on sample quality and test results.

Insulin sensitivity and β-cell function estimated by HOMA2 model in sprint-trained athletes aged 20-90 years vs endurance runners and untrained participants

There are no studies available that portray insulin sensitivity and β-cell function in ageing sprint-trained athletes. We compared male young and master sprint-trained athletes to endurance-trained and untrained individuals. We hypothesised that ageing sprint-trained athletes would preserve insulin sensitivity and β-cell function at a level similar to that of endurance-trained peers and better than in untrained individuals. We showed the associations between age and parameters derived from the updated Homeostasis Model Assessment (HOMA2 model) in 52 sprint-trained track and field athletes (aged 20-90 years), 85 endurance runners (20-80 years) and 55 untrained individuals (20-70 years). Fasting glucose, fasting insulin, insulin sensitivity and β-cell function were not associated with age in sprint-trained athletes. These variables remained relatively stable across a wide range of age and comparable to those observed in endurance-trained athletes. In contrast, the untrained group showed considerable age-related increase in fasting insulin and β-cell activity and a strong decrease in insulin sensitivity compared to both athletic groups. HOMA2 parameters were significantly related to maximal oxygen in the combined group of participants. In summary, chronic training based on a "sprint model" of physical activity, that contains mixed exercise, seems to be effective in maintaining normal insulin sensitivity with ageing.

Metabolic markers in sports medicine

Physical exercise induces adaptations in metabolism considered beneficial for health. Athletic performance is linked to adaptations, training, and correct nutrition in individuals with genetic traits that can facilitate such adaptations. Intense and continuous exercise, training, and competitions, however, can induce changes in the serum concentrations of numerous laboratory parameters. When these modifications, especially elevated laboratory levels, result outside the reference range, further examinations are ordered or participation in training and competition is discontinued or sports practice loses its appeal. In order to correctly interpret commonly used laboratory data, laboratory professionals and sport physicians need to know the behavior of laboratory parameters during and after practice and competition. We reviewed the literature on liver, kidney, muscle, heart, energy, and bone parameters in athletes with a view to increase the knowledge about clinical chemistry applied to sport and to stimulate studies in this field. In liver metabolism, the interpretation of serum aminotransferases concentration in athletes should consider the release of aspartate aminotransferase (AST) from muscle and of alanine aminotransferase (ALT) mainly from the liver, when bilirubin can be elevated because of continuous hemolysis, which is typical of exercise. Muscle metabolism parameters such as creatine kinase (CK) are typically increased after exercise. This parameter can be used to interpret the physiological release of CK from muscle, its altered release due to rhabdomyolysis, or incomplete recovery due to overreaching or trauma. Cardiac markers are released during exercise, and especially endurance training. Increases in these markers should not simply be interpreted as a signal of cardiac damage or wall stress but rather as a sign of regulation of myocardial adaptation. Renal function can be followed in athletes by measuring serum creatinine concentration, but it should be interpreted considering the athlete's body-mass index (BMI) and phase of the competitive season; use of cystatin C could be a reliable alternative to creatinine. Exercise and training induce adaptations in glucose metabolism which improve glucose utilization in athletes and are beneficial for reducing insulin insensitivity in nonathletes. Glucose metabolism differs slightly for different sports disciplines, as revealed in laboratory levels. Sport activities induce a blood lipid profile superior to that of sedentary subjects. There are few reports for a definitive conclusion, however. The differences between athletes and sedentary subjects are mainly due to high-density lipoprotein cholesterol (HDLC) concentrations in physically active individuals, although some differences among sport disciplines exist. The effect of sports on serum and urinary markers for bone metabolism is not univocal; further studies are needed to establish the real and effective influence of sport on bone turnover and especially to establish its beneficial effect.

A laboratory standpoint on the role of hemoglobin A1c for the diagnosis of diabetes in childhood: more doubts than certainties?

Lippi G, Targher G. A laboratory standpoint on the role of hemoglobin A1c for the diagnosis of diabetes in childhood: more doubts than certainties? The American Diabetes Association has recently included the measurement of hemoglobin A1c (A1c) among the criteria for diagnosing diabetes, so that this diagnostic strategy might also be extended in childhood and adolescence. Although the possibility of using A1c testing for screening and even diagnosing diabetes is highly appealing, A1c testing cannot be considered as yet the 'panacea' for a variety of reasons that include the suboptimal correlation with the mean blood glucose, the risk of misdiagnosis in children or adolescents with impaired renal function, iron-deficiency anemia and increased red blood cell turnover, the interference from hemoglobin variants, and the heterogeneous diagnostic performance among different populations. Additional limitations include the higher imprecision of most A1c assays (especially point-of-care testing devices) when compared with plasma glucose measurement, as well as the incremental cost deriving from routinely replacing plasma glucose with A1c determination. Taken together, the current limitations would suggest a certain degree of caution before recommending the widespread implementation of the A1c assay for diagnosing diabetes in childhood and adolescence. The potential clinical benefits (if any) of replacing blood glucose testing with A1c for diagnosing diabetes are still uncertain and will probably remain so until reliable cost-effective analyses are available.

Glycated hemoglobin (HbA1c): old dogmas, a new perspective?

The hemoglobin A1c (HbA1c) assay provides a reliable measure of chronic glycemia and correlates well with the risk of long-term diabetes complications, so that it is currently considered the test of choice for monitoring and chronic management of diabetes. Recently, HbA1c testing has been included within the diagnostic criteria recommended for diagnosis of diabetes in nonpregnant individuals by the American Diabetes Association (ADA). The emerging concept that HbA1c can be used rather than blood glucose in the diagnosis of diabetes is highly appealing for a variety of reasons, including less sensitivity to preanalytical variables, lower within subject biological variability, little to null interference from diurnal variations, acute stress and common drugs which are known to influence glucose metabolism, as well as the fact that one single measurement might provide information for both diagnosing diabetes and tracking glycemic control. On the other hand, the use of HbA1c for screening and diagnosing diabetes also carries some limitations, including the worse diagnostic performance in different populations (i.e., pregnancy, elderly and non-Hispanic blacks), the risk of overdiagnosis in subjects with iron deficiency anemia, in subjects genetically predisposed to hyperglycation, and in those with increased red blood cell turnover. There is also a higher risk of misdiagnosis in patients with end-stage renal disease and heavy alcohol consumption. Finally, HbA1c testing might be biased due to the interference from several hemoglobin variants, is characterized by a higher imprecision than blood glucose measurement, and is more expensive. This paper will critically summarize the potential advantages and limitations of HbA1c as a recommended test for diagnosing diabetes.

Discipline-specific insulin sensitivity in athletes

OBJECTIVE

Weight status and abnormal liver function are the two factors that influence whole-body insulin sensitivity. The main goal of the study was to compare insulin sensitivity in athletes (n=757) and physically active controls (n=670) in relation to the two factors.

METHODS

Homeostatic metabolic assessment for insulin resistance (HOMA-IR), weight status, and abnormal liver function (alanine aminotransferase and aspartate aminotransferase) were determined from 33 sports disciplines under morning fasted condition. This study was initiated in autumn 2006 and repeated in autumn 2007 (n=1508) to ensure consistency of all observations.

RESULTS

In general, HOMA-IR and blood pressure levels in athletes were significantly greater than those in physically active controls but varied widely with sport disciplines. Rowing and short-distance track athletes had significantly lower HOMA-IR values and archery and field-throwing athletes had significantly higher values than the control group. Intriguingly, athletes from 22 sports disciplines displayed significantly greater body mass index values above control values. Multiple regression analysis showed that, for non-athlete controls, body mass index was the only factor that contributed to the variations in HOMA-IR. For athletes, body mass index and alanine aminotransferase independently contributed to the variation of HOMA-IR.

CONCLUSION

This is the first report documenting HOMA-IR values in athletes from a broad range of sport disciplines. Weight status and abnormal liver function levels appear to be the major contributors predicting insulin sensitivity for the physically active population.