Medical Library

Adjustment for gas exchange threshold enhances precision of heart rate-derived VO2 estimates during heavy exercise.

Overestimates of oxygen uptake (VO2) are derived from the heart rate reserve - VO2 reserve (HRR-VO2R) model. We tested the hypothesis that adjusting for differences above and below gas exchange threshold (HRR-GET model) would tighten the precision of HR-derived VO2 estimates during heavy exercise. Seven men and 7 women of various VO2 max levels, on 2 separate days, cycled for 6 min at intensities equal to power at GET, 15% the difference between GET and VO2 max (15% above), and at 30% above GET. A second bout at 15% above GET (15% above (bout 2)) after 3 min of recovery was performed to assess estimates during interval training. Actual VO2 was compared with estimates derived from the HRR-VO2R and the HRR-GET. VO2 values were summed over the 6 min duration of data collection (6 min LO2) and compared with Bland-Altman plots. HRR-VO2R yielded 6 min LO2 (+/-2 SD) overestimates of 2.0 (+/-2.5), 1.9 (+/-2.7), and 1.3 (+/-3.3) for GET, 15% over, and 30% over, respectively, whereas corresponding 6 min LO2 difference values for the HRR-GET model were -0.42 (+/-1.6), -0.23 (+/-1.1), and -0.55 (+/-1.8), respectively. For 15% above (bout 2), the 6 min LO2 difference for HRR-VO2R was 1.8 (+/-2.9), whereas the difference for HRR-GET was 0.17 (+/-1.4). The 6 min LO2 values relative to the subjects\’ VO2 max did not vary (r = 0.05 to 0.36); therefore, fitness level did not affect estimates. Sex did not affect accuracy of either estimate model (sex X estimate model interaction, p > 0.95). We observed accurate estimates from the HRR-GET model during heavy exercise.

Pettitt RW, Symons JD, Taylor JE, Eisenman PA, White AT.

California State University, Fresno, 5275 North Campus Drive M/S SG28, Fresno, CA 93740, USA.

Impact of metformin on peak aerobic capacity.

Individually, exercise and the drug metformin have been shown to prevent or delay type 2 diabetes. Metformin mildly inhibits complex I of the electron transport system and may impact aerobic capacity in people exercising while taking metformin. The purpose of the study was to evaluate the effects of metformin on maximal aerobic capacity in healthy individuals without mitochondrial dysfunction. Seventeen healthy, normal-weight men (n = 11) and women (n = 6) participated in a double-blind, placebo-controlled, cross-over design. Peak aerobic capacity was measured twice using a continuous, incrementally graded protocol; once after 7-9 d of metformin (final dose = 2000 mg/d) and once with placebo, with 1 week between tests. The order of the conditions was counterbalanced. Peak oxygen uptake (VO2 peak), heart rate (HR), ventilation (VE), respiratory exchange ratio (RER), rating of perceived exertion (RPE), and test duration were compared across conditions using paired t tests with the R statistical program. VO2 peak (-2.7%), peak heart rate (-2.0%), peak ventilation (-6.2%), peak RER (-3.0%), and exercise duration (-4.1%) were all reduced slightly, but significantly, with metformin (all p < 0.05). There was no effect of metformin on RPE or ventilatory breakpoint. Correlations between the decrement in VO2 peak and any of the other outcome variables were weak (r2 < 0.20) and not significant. Short-term treatment with metformin has statistically significant, but physiologically subtle, effects that reduce key outcomes related to maximal exercise capacity. Whether this small but consistent effect is manifested in people with insulin resistance or diabetes who already have some degree of mitochondrial dysfunction remains to be determined.

Braun B, Eze P, Stephens BR, Hagobian TA, Sharoff CG, Chipkin SR, Goldstein B.

Energy Metabolism Laboratory, Department of Kinesiology, School of Public Health and Health Sciences, 107 Totman Building, University of Massachusetts, Amherst, MA 01003, USA.

Reliability of electromyographic and force measures during prone isometric back extension in subjects with and without low back pain.

Maximal voluntary isometric activations (MVIA) are frequently used as inputs for models attempting to predict muscle force and as normalization values in studies assessing muscle function. However, pain may adversely affect maximal muscle activation. The purpose of this study was to assess reliability of MVIA force and electromyographic (EMG) activity during prone isometric back extension in subjects with and without low back pain (LBP). A novel sub-maximal method using the percentages of the estimated mass of the head-arms-trunk (HAT) segment was also investigated. Repeated measures on 20 male volunteers divided into an LBP (n = 10) and a control group (n = 10) were made on 4 occasions. Force and EMG activity were recorded bilaterally from upper lumbar erector spinae (ULES), lower lumbar erector spinae (LLES), and biceps femoris (BF). Subjects exerted a maximal extension effort against a harness assembly that was attached to a force transducer. Submaximal exertions were also performed with an additional resistance of 100%, 110%, 120%, 130%, 140%, 150%, 160%, and 170% of HAT. Mean MVIA forces were significantly (p &le; 0.05) lower in LBP vs. control. Intraclass correlation coefficients (ICC) for MVIA force, right and left ULES, and LLES EMG indicated high reliability in controls (R > 0.90), but were significantly less in LBP (R = 0.36-0.80). EMG of BF demonstrated excellent reliability across both groups (R > 0.90). The resistance at 100% HAT demonstrated the highest reliability for LBP patients, whereas higher percentages of HAT showed either similar or higher reliability for controls. Force output and back EMG activity are less reliable with LBP individuals and should be taken into consideration when testing.

Pitcher MJ, Behm DG, Mackinnon SN.

School of Human Kinetics and Recreation, Memorial University of Newfoundland, St. John’s, NL A1C 5S7, Canada.

Effect of dietary protein content during recovery from high-intensity cycling on subsequent performance and markers of stress, inflammation, and muscle damage in well-trained men.

Nutrition is an important aspect of recuperation for athletes during multi-day competition or hard training. Post-exercise carbohydrate is likely to improve recovery, but the effect of protein is equivocal. The objective of this study was to determine the effect of post-exercise dietary protein content imposed over a high-carbohydrate background on subsequent performance. Using a crossover design, 12 cyclists completed 3 high-intensity rides over 4 days. Day 1 comprised 2.5 h intervals, followed by repeat-sprint performance tests on days 2 (15 h post) and 4 (60 h post), interspersed with a rest day. During 4 h recovery on days 1 and 2, cyclists ingested either 1.4 g.kg-1.h-1 carbohydrate, 0.7 g.kg-1.h-1 protein and 0.26 g.kg-1.h-1 fat (protein-enriched) or 2.1 g.kg-1.h-1 carbohydrate, 0.1 g.kg-1.h-1 protein, and equal fat (control). At other times, cyclists ingested a standardized high-carbohydrate diet. Anabolism was gauged indirectly by nitrogen balance, stress and inflammation via cortisol and cytokines, skeletal-muscle membrane disruption by creatine kinase, and oxidative stress by malonyl dealdehyde. Sprint mean power was not clearly different on day 2 (0.0%; 95%CL: +/-3.9%), but on day 4 it was 4.1% higher (+/-4.1%) in the protein-enriched condition relative to control. Reduced creatine kinase was possible (26%; +/-30%) but effects on oxidative stress, inflammatory markers, and cortisol were inconclusive or trivial. Overnight nitrogen balance was positive in the protein-enriched condition on day 1 (249 +/- 70 mg N.kg FFM-1; mean +/- SD), but negative (-48 +/- 26 mg N.kg FFM-1) in the control condition. A nutritive effect of post-exercise protein content was not discernible short term (15 h), but a delayed performance benefit (60 h) was observed following protein-enriched high-carbohydrate ingestion.

Rowlands DS, Rössler K, Thorp RM, Graham DF, Timmons BW, Stannard SR, Tarnopolsky MA.

Institute of Food, Nutrition and Human Health, Massey University, New Zealand.

Central venous thrombosis in patients receiving long-term parenteral nutrition.

Long-term parenteral nutrition (PN) is administered to patients who are unable to use their gastrointestinal tract to absorb sufficient nutrients and water to maintain their nutritional status. Patients receiving long-term parenteral nutrition are at risk of numerous complications including thrombosis of the central venous catheter used to provide nutrition. Central venous access is essential to the successful delivery of long-term PN. One of the strategies to lessen the frequency of this complication is anticoagulation therapy with warfarin. The effect of warfarin in preventing this complication may be modified by vitamin K intake. Individuals with gastrointestinal failure may receive vitamin K from a variety of sources. This review summarizes the role of warfarin in preventing central venous access thrombosis. It also summarizes potential sources of vitamin K intake in home parenteral nutrition patients, examines the evidence for recommendations regarding vitamin K intake, and considers the potential impact of increased vitamin K intake on home PN patients, particularly on the prevention of central venous thrombosis.

Duerksen DR.

Department of Medicine, University of Manitoba, C5120 409 Tache Ave., Winnipeg, MB R2H 2A6.

Antioxidant supplemention in the treatment of skeletal muscle insulin resistance: potential mechanisms and clinical relevance.

The incidence of type 2 diabetes has increased dramatically over the past several decades and this trend is projected to continue into the foreseeable future. Skeletal muscle insulin resistance is thought to be a key development in the pathogenesis of type 2 diabetes. Given this fact, interventions that prevent or reverse impairments in skeletal muscle action can have profound effects on whole-body glucose homeostasis. Traditional approaches used in this regard include exercise, weight loss, and insulin-sensitizing drugs such as thiazolidinediones (TZDs). Although these interventions have proven effective in improving glucose homeostasis, there are adherence issues seen with lifestyle interventions and undesirable side effects have been reported with TZDs. With these points in mind, the development of alternative strategies to maintain or improve skeletal muscle insulin sensitivity is warranted. In this context, the purpose of the present review is to highlight the role of antioxidant compounds in the prevention and treatment of skeletal muscle insulin resistance. Specifically, we will briefly describe the mechanisms of insulin-stimulated skeletal muscle glucose uptake and the potential mediators of oxidative stress induced insulin resistance, highlight data suggesting that antioxidant compounds can have beneficial effects on skeletal muscle insulin action, and discuss potential mechanisms mediating this effect.

Wright D, Sutherland L.

Alberta Institute of Human Nutrition, 3-18b Ag/For Centre, University of Alberta, Edmonton, AB T6G 2P5.

Alcohol consumption: the good, the bad, and the indifferent.

Dietary ethanol (alcohol) is the most widely consumed drug worldwide. High levels of mortality, morbidity, and social malaise are associated with abuse of alcohol, and increasing numbers of women and youth are abusing alcohol. However, strong epidemiological data demonstrate a U- or J-shaped relationship between volume of alcohol consumed and all-cause mortality or disease burden. Moderate alcohol consumption is associated with a lower risk of all-cause mortality and disease burden than are abstinence and immoderate drinking. A brief review of the absorption, distribution, metabolism, and excretion of ethanol is provided with a discussion of the impact of gender differences. Potential mechanisms by which ethanol, ethanol metabolites, and (or) phytochemicals, as associated with different types of ethanol-containing beverages, are discussed in regards to the beneficial and detrimental impacts they may have on physiological system functioning and mortality or disease burden. Per capita consumption of ethanol-containing beverages varies across geo-political regions worldwide. A more recent research focus is the impact of consumption patterns on consumption volumes as they relate to disease and mortality. Certain drinking patterns moderate overall volume of ethanol consumption. Thus, an emerging approach to the study of alcohol consumption in populations is to consider both the volume and pattern of consumption as they relate to mortality and disease burden. Alcohol consumption patterns among athletes are discussed; physiological implications of alcohol abuse in this population are outlined. Current guidelines for the consumption of alcohol are reviewed. Alcohol consumption guidelines reflect the current scientific understanding of both the benefits of moderate alcohol consumption and the detriments of immoderate alcohol consumption.

Ferreira MP, Willoughby D.

Baylor University, 1312 S. 5th St., One Bear Place No. 97313, Waco, TX 76798, USA.

Home parenteral nutrition in advanced cancer: where are we?

Patients with advanced and incurable cancer are a compelling group. Questions and comments that these individuals and their families have may include: &ldquo;My daughter is expecting our first grandchild in 3 months - can I hope to see our new family member?&rdquo;; &ldquo;I can\’t keep any food down - is there anything I can do?&rdquo;; &ldquo;I am worried about losing so much weight, and feeling tired and weak - is there anything that may help?&rdquo;; &ldquo;Will I suffer a lot?&rdquo;. Indeed, the most pressing concerns of the patient relate to predictions about survival and control of symptoms. The clinician taking care of the patient may wonder what is the utility or futility of home parenteral nutrition (HPN) in both the individual with advanced cancer and in this population of patients at large, whether there is potential for harm such as increasing the burden of care or prolonging suffering, and how to optimize care and communication with the patient and their families. The nutrition scientist may want to know what the implications of advanced cancer are on nutrient requirements and utilization, whether there are markers that would differentiate between cachexia and simple starvation, and whether it is possible to use specific nutrients to modify the disease process. This review will provide insights into the understanding of the role of HPN in advanced cancer and opportunities for further investigation.

Mackenzie ML, Gramlich L.

Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, AB T6G 2P5, Canada.

F.y.eye.

McIlraith I.

Diagnostic atlas of common eyelid diseases, johnathan j. Dutton, gregg s. Gavre, alan d. Proia.

Boulos PR.