Tyrosine for Mitigating Stress and Enhancing Performance in Healthy Adult Humans, a Rapid Evidence Assessment of the Literature.

BACKGROUND: Tyrosine, a precursor of catecholamine neurotransmitters, may help alleviate physical/cognitive performance decrements in humans under conditions of high physical/psychological stress. OBJECTIVE: Determine whether supplemental tyrosine mitigates stress-induced decrements in cognitive and/or physical performance in healthy individuals using Samueli Institute's Rapid Evidence Assessment of the Literature methodology. METHODS: Key databases (PubMed/MEDLINE, CINAHL, Embase, PsycInfo, and Agricola) were searched for randomized controlled trials from inception to October 2012. Scottish Intercollegiate Guidelines 50 criteria and Grading of Recommendation Assessment, Development, and Evaluation framework were used to assess the quality of individual studies and the overall literature pool, respectively. Controlled clinical trials were included later in the overall methodology. RESULTS: 10 randomized controlled trials and 4 controlled clinical trials met our inclusion criteria. On the basis of the available evidence, no recommendation could be made for the effect of tyrosine on physical performance under stressful physical conditions. However, a weak recommendation in favor of tyrosine was made for cognitive stress as all studies showed a positive effect. CONCLUSIONS: This review indicates that the available evidence is insufficient to make confident recommendations on the effectiveness of tyrosine for mitigating stress effects on physical/cognitive performance. However, tyrosine may benefit cognitive performance and is worthy of further study.

Warm-ups for military fitness testing: rapid evidence assessment of the literature.

INTRODUCTION: Warm-up exercises are commonly used before exercise as a method to physiologically prepare for strenuous physical activity. Various warm-up exercises are often implemented but without scientific merit and, at times, may be detrimental to performance. PURPOSE/OBJECTIVE: To date, no systematic reviews have examined the effectiveness of warm-up exercises for military physical fitness test (PFT) or combat fitness test (CFT). The purpose of this rapid evidence assessment of the literature was to examine the quantity, quality, and effectiveness of warm-up exercises for PFT and identify those that might increase PFT and/or CFT scores, as reported in the literature. METHODS: Literature searches of randomized controlled trials were performed across various databases from database inception to May 2011. Methodological quality of included studies was assessed using the Scottish Intercollegiate Guidelines Network (SIGN) 50 criteria for randomized controlled trial designs, and studies were individually described. Subject matter experts summarized the results applicable or generalizable to military testing. RESULTS: The search yielded a total of 1177 citations, with 37 fitting our inclusion criteria. Cardiovascular warm-ups increased sprint/running time, but dynamic stretching and dynamic warm-ups had the most positive outcome for the various exercise tests examined. Systematically, static stretching had no beneficial or detrimental effect on exercise performance but did improve range of movement exercises. CONCLUSIONS: Selected warm-up exercise may increase PFT and possibly CFT scores. Further research is needed to investigate the efficacy of dynamic stretching and dynamic warm-ups.

Relationship between Depressive Symptoms and Cardiovascular Disease Risk Factors in African American Individuals.

Objective. To examine the relationship between depressive symptoms and cardiovascular disease (CVD) risk factors in a group of African American individuals. Design. A nonrandom sample of 253 (age 43.7 ± 11.6 years; 37% male) African American individuals was recruited by advertisements. Data were obtained by validated questionnaires, anthropometric, blood pressure, and blood sample measurements. Results. Regression analyses were performed to assess the relationship between depressive symptoms and CVD risk factors controlling for socioeconomic status indicators. These analyses demonstrated that those with higher levels of depressive symptoms had larger waist-to-hip ratios, higher percent body fat, higher triglycerides, and were more likely to be smokers. Conclusions. It has been well documented that higher levels of depressive symptoms are associated with higher CVD risk. However, this evidence is derived primarily from samples of predominantly Caucasian individuals. The present investigation demonstrates that depressive symptoms are related to CVD risk factors in African American individuals.

Diagnostic criteria for metabolic syndrome: caucasians versus African-Americans.

BACKGROUND: Metabolic syndrome is a constellation of risk factors used to identify individuals at greatest risk for developing cardiovascular disease (CVD). Early diagnosis of CVD would benefit African-Americans (AA), who have a higher prevalence of and mortality rate from CVD compared to Caucasians (CA). Two definitions for metabolic syndrome were used to classify healthy CA and AA, and evaluate how other CVD risk factors [C-reactive protein (CRP), percent body fat, fitness level, insulin resistance, and non-high-density lipoprotein cholesterol (HDL-C)] changed metabolic syndrome classification. METHODS: Healthy AA (n = 97) and CA (n = 51) ranging from normal weight to obese, 18-45 years of age, with neither hypertension nor diabetes, were evaluated for cardiorespiratory fitness, height, weight, percent body fat, hip and waist circumference, blood pressure (BP), and fasting blood glucose, insulin, triglycerides, HDL, non-HDL-C, and CRP. Participants were classified as meeting the criteria for metabolic syndrome according to the National Cholesterol Education Program Adult Treatment Panel III 2004 (NCEP ATP III) and the International Diabetes Federation (IDF) definitions. RESULTS: Significant ethnic differences (P < 0.01) in classification were noted for both metabolic syndrome definitions (NCEP ATP III, CA = 16.7% vs. AA = 5.7%; IDF, CA = 23.5% vs. AA = 8.2%). Ethnic differences were eliminated when fitness level or percent body fat was included as a criterion. CONCLUSIONS: If diagnosis of metabolic syndrome is intended for early recognition of CVD risk and slowing CVD development, current definitions for metabolic syndrome will not capture healthy AA. Health-care providers may consider assessing percent body fat and participation in regular exercise, because these criteria would help identify AA at risk.

Cardiovascular fitness and risk factors of healthy African Americans and Caucasians.

BACKGROUND: African Americans have a higher prevalence of and mortality rates from cardiovascular disease than Caucasians. One important risk factor for cardiovascular disease is poor cardiovascular fitness. We quantified associations between fitness and related primary risk factors for cardiovascular disease in healthy African Americans and Caucasians. METHODS AND RESULTS: Participants included African American (n = 91) and Caucasian (n = 51) men and women aged 18 to 45 years with a body mass index less than 38 kg/m2, fasting blood glucose less than 126 mg/dL, and blood pressure less than 140/90 mm Hg. Fitness, waist and hip circumference, percent body fat, fasting blood glucose, insulin, lipid profiles, and C-reactive protein (CRP) were measured. The majority of African Americans (57.1%) were low-fair fitness (Caucasians, 31.4%), and only 20.8% were good/high fitness (Caucasians, 39.2%). The number of cardiovascular disease risk factors increased with decreasing fitness, and CRP was negatively associated with fitness in both groups. CONCLUSIONS: Low fitness may characterize apparently healthy African Americans as at risk for cardiovascular disease. Including fitness as a risk factor may improve early identification of at-risk African Americans. Importantly, prescribing exercise as medicine and promoting regular physical activity to improve fitness is essential among African Americans.

Should triglycerides and the triglycerides to high-density lipoprotein cholesterol ratio be used as surrogates for insulin resistance?

The aims of the present study were to examine whether triglycerides (TG) and the triglyceride to high-density lipoprotein cholesterol ratio (TG/HDL-C) could predict insulin resistance in healthy African Americans and whites. This cross-sectional study included 99 African American and 50 white men and women between 18 and 45 years of age with body mass indexes between 18.5 and 38.0 kg/m(2). Anthropometric measures were obtained; and overnight fasting blood was collected for TG, HDL-C, glucose, and insulin. Insulin resistance was defined by fasting insulin concentration of at least 13.13 microU/mL and homeostasis model assessment of insulin resistance (HOMA-IR) of at least 2.5. Receiver operating characteristic curves were used to analyze the data. African Americans and whites had comparable demographic and anthropometric measures. Fasting insulin was higher in African Americans (12.4 +/- 7.8 microU/mL) than whites (10.2 +/- 7.5 microU/mL), but HOMA-IR did not differ significantly (African Americans, 2.9 +/- 2.0; whites, 2.4 +/- 1.9). Triglycerides and TG/HDL-C were significantly lower in African Americans (TG, 68.2 +/- 43.3 mg/dL; TG/HDL-C, 1.8 +/- 2.1) compared with whites (TG, 105.4 +/- 55.2 mg/dL; TG/HDL-C, 2.8 +/- 1.8). Area under the receiver operating characteristic curves revealed that both TG and TG/HDL-C were acceptable markers of insulin resistance, as defined by fasting insulin concentration, in whites, 0.770 and 0.765, respectively, but poor predictors in African Americans, 0.633 and 0.651, respectively. Similarly, TG and TG/HDL-C were acceptable in predicting insulin resistance, as measured by HOMA-IR, in whites, 0.763 and 0.770, respectively, but poor in predicting HOMA-IR in African Americans, with areas of 0.625 and 0.639, respectively. In conclusion, the relationship between TG and TG/HDL-C with insulin resistance differs by ethnicity; and using TG and TG/HDL-C to predict insulin resistance in African Americans would not be appropriate.