Kynurenine aminotransferase isoforms display fiber-type specific expression in young and old human skeletal muscle.

Conversion of kynurenine (KYN) to kynurenic acid (KYNA) is the main pathway for free tryptophan degradation in skeletal muscle and has emerged as an important mechanism of how exercise is linked to promotion of mental health. Metabolism of KYN to KYNA mainly depends on the expression of kynurenine aminotransferases (KATs) that is under control of the mitochondria biogenesis regulator PGC-1α. We therefore hypothesized that expression of KATs would vary between muscle fibers that differ in mitochondrial content, i.e. oxidative type I vs more glycolytic type II muscle fibers. Moreover, we tested the hypothesis that KAT expression differs with age. Single muscle fibers were isolated from biopsies taken from the vastus lateralis muscle in young and old healthy subjects. In young and old subjects the abundance of KAT I, KAT III and KAT IV was greater in Type I than Type II fibers without age-dependent difference in the KAT isoform expressions. The link to mitochondrial content was further seen as the expression of KAT IV correlated to mitochondrial cytochrome c oxidase IV (COX IV) abundance in both fiber types. In conclusion, we describe for the first time the expression pattern of KAT isoforms with respect to specific fiber types and age in human skeletal muscle.

Acute effects of very low-volume high-intensity interval training on muscular fatigue and serum testosterone level vary according to age and training status.

PURPOSE: To compare the acute physiological responses of three different very low-volume cycling sessions (6 × 5 s, 3 × 30 s, and 3 × 60 s) and their dependence on age and training status. METHODS: Subjects were untrained young men (mean ± SD; age 22.3 ± 4.6 years, VO2peak 42.4 ± 5.5 ml/kg/min, n = 10), older untrained men (69.9 ± 6.3 years, 26.5 ± 7.6 ml/kg/min, n = 11), and endurance-trained cyclists (26.4 ± 9.4 years, 55.4 ± 6.6 ml/kg/min, n = 10). Maximal voluntary contraction (MVC) and electrically stimulated knee extension torque, and low-frequency fatigue, as ratio of stimulation torques at 20-100 Hz (P20/100), were measured only 24 h after exercise. Serum testosterone (Te) and blood lactate concentrations were measured only 1 h after exercise. RESULTS: All protocols increased the blood lactate concentration and decreased MVC and P20/100 in young men, but especially young untrained men. In old untrained men, 6 × 5 s decreased P20/100 but not MVC. Te increased after 3 × 30 s and 3 × 60 s in young untrained men and after 3 × 60 s in older untrained men. The increase in Te correlated with responses of blood lactate concentration, MVC, and P20/100 only in old untrained men. CONCLUSIONS: As little as 6 × 5 s all-out cycling induced fatigue in young and old untrained and endurance-trained cyclists. Slightly higher-volume sessions with longer intervals, however, suppressed contractile function more markedly and also transiently increased serum testosterone concentration in untrained men.

Sex-specific reliability and multidimensional stability of responses to tests assessing neuromuscular function.

The objective of this study was to estimate sex-specific effects in the test-retest cross-reliability of peripheral and central changes in nonlinear and linear measures of a surface electromyography signal during a brief (5 second) and sustained (2minute) isometric maximal voluntary contraction, combined with superimposed electrical stimulation involving the ankle plantar flexors over five identical trials. In this study, we repeated the testing protocol used in our previous study of 10 women (age 20.9, SD=0.3 years) (Bernecke et al., 2015) in a group of 10 men (age 21.2, SD=0.4 years). Despite the central (sex effect; p<0.05, ηp2>0.71, SP>70%) and peripheral fatigability (sex effect; p<0.01, ηp2>0.8, SP>90%) during sustained isometric maximal voluntary contraction, and lower reliability for central activation ratio during brief (intraclass correlation coefficient [ICC]=0.95 for men and ICC=0.82 for women) and sustained maximal voluntary contraction (ICC>0.82 for men and ICC>0.66 for women) over ankle plantar flexors expressed in women more than in men, all the ICCs of all indices measured by tests assessing neuromuscular function across the five identical test-retest trials were found as meaningful (correlation significance of p<0.05 was reached) and no significant differences were found between trials for any of the measured variables. In conclusion, the present study demonstrated greater central and peripheral fatigue for female participants following sustained (2minute) isometric maximal voluntary contraction of the plantar flexor muscles for all repeated trials and indicated an acceptable agreement between measurements of the characteristic variables made using the three different devices (dynamometry, electrical stimulation, and surface electromyography) over time for both sexes.

Effect of sprint cycling and stretch-shortening cycle exercises on the neuromuscular, immune and stress indicators in young men.

Selection of optimal physical load is essential for desired adaptation including health benefits. We hypothesized that neuromuscular, immune and stress indicators will be higher after energy demanding sprint interval exercise (SIE) than to mechanically demanding stretch-shortening cycle exercise (SSE). The main aim of this study was to assess and compare the kinetics of blood brain-derived neurotrophic factor (BDNF), norepinephrine (NE) and cortisol (as stress indicators) and proinflammatory (IL-6) and anti-inflammatory (IL-10) cytokines within 24 hours after metabolically demanding SIE and after muscle damage inducing SSE. Twenty healthy physically active young men randomly assigned to two equal groups to complete 12 bouts of 5 s stationary cycling sprints every 3 min (SIE) or 200 drop-jumps with 30 s interval between each jump (SSE), respectively. Quadriceps muscle maximal voluntary contraction torque and voluntary activation and soreness were measured and blood samples collected before and 2 min, 1 hour, 12 hours and 24 hours after the SIE and SSE. The BDNF, cortisol, IL-6 and NE levels increased more at 2 min after SIE than SSE (P < 0.05); however, the IL-10 level did not differ between SIE and SSE. BDNF and cortisol levels were decreased at 24 h after both SIE and especially after SSE. The higher was the initial BDNF level, the greater was its decrease at 24 h after both type of exercise. Before exercise BDNF level correlated closely with the change in central fatigue (decrease in voluntary activation) after both SIE and SSE. We thus conclude that both metabolically demanding SIE and muscle damage inflicting SSE induced long-lasting decrease in circulating BDNF which may not promote brain health. The level of circulating BDNF, but not cortisol, IL-6, IL-10 or NE, was associated with changes in central motor fatigue.

Single muscle fibre contractile properties differ between body-builders, power athletes and control subjects.

NEW FINDINGS: What is the central question of this study? Do the contractile properties of single muscle fibres differ between body-builders, power athletes and control subjects? What is the main finding and its importance? Peak power normalized for muscle fibre volume in power athletes is higher than in control subjects. Compared with control subjects, maximal isometric tension (normalized for muscle fibre cross-sectional area) is lower in body-builders. Although this difference may be caused in part by an apparent negative effect of hypertrophy, these results indicate that the training history of power athletes may increase muscle fibre quality, whereas body-building may be detrimental. We compared muscle fibre contractile properties of biopsies taken from the vastus lateralis of 12 body-builders (BBs; low- to moderate-intensity high-volume resistance training), six power athletes (PAs; high-intensity, low-volume combined with aerobic training) and 14 control subjects (Cs). Maximal isotonic contractions were performed in single muscle fibres, typed with SDS-PAGE. Fibre cross-sectional area was 67 and 88% (P < 0.01) larger in BBs than in PAs and Cs, respectively, with no significant difference in fibre cross-sectional area between PAs and Cs. Fibres of BBs and PAs developed a higher maximal isometric tension (32 and 50%, respectively, P < 0.01) than those of Cs. The specific tension of BB fibres was 62 and 41% lower than that of PA and C fibres (P < 0.05), respectively. Irrespective of fibre type, the peak power (PP) of PA fibres was 58% higher than that of BB fibres (P < 0.05), whereas BB fibres, despite considerable hypertrophy, had similar PP to the C fibres. This work suggests that high-intensity, low-volume resistance training with aerobic exercise improves PP, while low- to moderate-intensity high-volume resistance training does not affect PP and results in a reduction in specific tension. We postulate that the decrease in specific tension is caused by differences in myofibrillar density and/or post-translational modifications of contractile proteins.

The effect of plyometric training on central and peripheral fatigue in boys.

The aim of this study was to investigate the effect of high-intensity plyometric training (PT) on central and peripheral fatigue during exercise performed at maximal intensity in prepubertal boys. The boys (n=13, age 10.3+/-0.3 years) performed continuous 2-min maximal voluntary contractions (MVC) before and after 16 high-intensity PT sessions (two training sessions per week, 30 jumps in each session, 20 s between jumps). The greatest effect of PT was on excitation-contraction coupling: twitch force increased by 323.2+/-210.8% and the height of a counter-movement jump increased by 36.7+/-11.7%, whereas quadriceps femoris (QF) muscle voluntary activation index, central activation ratio and MVC did not change significantly after PT. The thickness of QF increased by 8.8+/-7.9% after PT. Central fatigue increased significantly by about 15-20% after PT, whereas peripheral fatigue decreased significantly by about 10% during the 2-min MVC. Central fatigue and peripheral fatigue during the 2-min MVC were inversely related before PT, but this relationship disappeared after PT.

Prolonged muscle damage depends on force variability.

Skeletal muscle damage frequently occurs after eccentric exercise, however, the relationship between intraindividual variability of eccentric exercise and skeletal muscle damage is not clear yet. The aim of the study was to test the hypothesis that prolonged decrease in skeletal muscle force depends on intraindividual variability of eccentric exercise. Eleven healthy men were asked to perform knee eccentric extension of 10 series with 12 repetitions (EE) with maximal intensity at 160 degrees/s. The maximal voluntary knee extension isometric torque (MVC) of the quadriceps muscle and isokinetic concentric torque (IT) at 30 degrees/s of knee angles were established before and 2 min, 60 min, 24 h and 14 days after EE. At 24 h and 48 h after EE muscle soreness and creatine kinase activity before and at 48 h after EE were calculated. The intraindividual variability of EE and autocorrelation coefficient of EE were calculated. We observed a significant decrease in MVC and IT after EE. The maximal isokinetic torque shifted to longer muscle length after EE. It was concluded that longer lasting (within 14 days) indirect symptoms of exercise induced muscle damage (decrease in muscle force) are closely related to variability of EE.

Electron beam computed tomography screening of the coronary arteries: experience with 3,263 patients at Walter Reed Army Medical Center.

The U.S. Department of Defense desires to reduce the impact of coronary atherosclerosis on its active duty, retired, and dependent populations. Electron beam computed tomography (EBCT) is currently the best way to noninvasively image the coronary arteries directly. Between August 1997 and February 1999, a total of 3,263 patients were scanned by EBCT in the Radiology Department at Walter Reed Army Medical Center. Scans were performed on 2,415 men (74%) and 848 women (26%). The most common age group was 50 to 54 years (25%). Coronary calcification was found in approximately half of the patients (46%), and the magnitude of the score was strongly associated with age and male gender. Average scores increased exponentially with age, doubling every 7 years. In men, average scores ranged from 17 units in those aged 35 to 39 years to 842 in those older than 70 years old. In women, average scores ranged from 1 in those 35 to 39 years to 162 in those older than 70 years. Significant numbers of patients fell into the high-risk categories, with 8% of men in their 40s, 20% of men in their 50s, 33% of men in their 60s, and 49% of men in their 70s with high scores. Scores of more than 400 units were seen in 368 patients (8%) overall. There is a large amount of coronary calcium present in military personnel and their dependents, in patterns that are consistent with previous studies. Many patients had very high scores that are consistent with advanced coronary artery disease. EBCT should play a central role in the identification of occult calcific atherosclerosis of the coronary arteries in military, retired, and dependent patients.

Do conventional risk factors predict subclinical coronary artery disease? Results from the Prospective Army Coronary Calcium Project.

BACKGROUND: Recent guidelines recommend against the routine use of coronary artery calcification (CAC) detection because the additive value over clinical prediction tools is uncertain. We compared CAC, with use of electron-beam computed tomography (EBCT), with clinical and serologic coronary risk factors for the identification of patients with increased coronary heart disease risk. METHODS AND RESULTS: We studied 630 active-duty US Army personnel (39-45 years old) without known coronary artery disease (CAD) who were undergoing a routine physical examination as required by regulations. Each participant underwent clinical and serologic risk factor screening and EBCT. The cohort (mean age 42 +/- 2 years, 82% male) had a low predicted risk of coronary events (mean 5-year Framingham risk index [FRI] 1.6% +/- 1.2%). The prevalence of coronary calcification was 17.6% (male 20.6%, female 4.3%). Significant univariate correlates of CAC were total and low-density lipoprotein [LDL] cholesterol, triglycerides, systolic blood pressure, and body mass index. However, only LDL cholesterol was independently associated with CAC. There was a significant but weak relationship between CAC and the Framingham risk index (FRI) (receiver-operator characteristic [ROC] curve area 0.62 +/- 0.03, P <.001), which was not different from the relationship between CAC and LDL cholesterol alone (ROC curve area 0.61 +/- 0.03, P <.001). The prevalence of any CAC in men increased slightly across increasing quartiles of FRI: 17.0%, 20.8%, 33.0%, and 29.2% (P =.033). Other risk factors (family history, homocysteine, insulin, lipoprotein[a], and fibrinogen) were not related to CAC. CONCLUSIONS: In this age-homogeneous, low-risk screening cohort, conventional coronary risk factors significantly underestimated the presence of premature, subclinical calcified coronary atherosclerosis. These data support the potential of CAC detection as an anatomic, plaque-burden diagnostic test to identify patients who may require more intensive risk-reduction therapies, independent of predicted clinical risk.

Rationale and design of the Prospective Army Coronary Calcium (PACC) Study: utility of electron beam computed tomography as a screening test for coronary artery disease and as an intervention for risk factor modification among young, asymptomatic, active-duty United States Army Personnel.

BACKGROUND: Screening for coronary artery calcium with electron beam computed tomography (EBCT) has potential diagnostic and prognostic implications. Most prior research on this technology has been done on selected, high-risk populations. The goal of the Prospective Army Coronary Calcium (PACC) study is to determine the utility of EBCT for the detection of coronary calcium as a screening test for coronary artery disease and as an intervention for risk factor modification among young, asymptomatic, active-duty personnel undergoing the United States Army's Cardiovascular Screening Program. METHODS AND RESULTS: Three study designs will be used to address the objectives of this investigation: (1) a cross-sectional study of 2000 unselected, consecutive participants to determine the prevalence and extent of coronary calcification in the 40- to 45-year-old Army population, (2) a randomized, controlled trial with a 2 x 2 factorial design involving 1000 participants to assess the impact of EBCT information on several dimensions of patient behavior, with and without intensive risk factor case management, and (3) a prospective cohort study of 2000 participants followed for at least 5 years to establish the relation between coronary calcification and cardiovascular events in an unselected, "low-risk" (by conventional standards) Army population. CONCLUSIONS: We present a review of the literature on the clinical utility of EBCT, with a focus on the limited research in young, asymptomatic populations. The details of the PACC study (begun in October1998) are presented. The results of the PACC study will determine the clinical utility of EBCT in young, asymptomatic patients.

The radiologic evaluation of acute abdominal pain of intestinal origin. A clinical approach.

The patient with acute abdominal pain presents the attending physician with a wide and varied gamut of diagnostic possibilities. Prompt and accurate diagnosis is essential for the proper care and management of these acutely ill patients. Diagnostic radiology is often an integral part of the emergent evaluation of these patients. This article focuses on some of the key plain-film findings in the patients suffering from acute abdominal pain of intestinal causes and reviews the radiologic evaluation of several major abdominal conditions such as acute appendicitis, diverticulitis, inflammatory bowel disease, bowel ischemia, and infarction.