Showing papers on "Exercise physiology published in 2005"

Exercise-induced increase in muscle insulin sensitivity

Abstract: Exercise/muscle contraction activates glucose transport. The increase in muscle glucose transport induced by exercise is independent of insulin. As the acute effect of exercise on glucose transport...

Effects of caffeine ingestion on rating of perceived exertion during and after exercise: a meta-analysis.

Abstract: The purpose of this study was to use the meta-analytic approach to examine the effects of caffeine ingestion on ratings of perceived exertion (RPE) Twenty-one studies with 109 effect sizes (ESs) met the inclusion criteria Coding incorporated RPE scores obtained both during constant load exercise (n=89) and upon termination of exhausting exercise (n=20) In addition, when reported, the exercise performance ES was also computed (n=16) In comparison to placebo, caffeine reduced RPE during exercise by 56% (95% CI (confidence interval), -45% to -67%), with an equivalent RPE ES of -047 (95% CI, -035 to -059) These values were significantly greater (P<005) than RPE obtained at the end of exercise (RPE % change, 001%; 95% CI, -19 to 20%; RPE ES, 000, 95% CI, -017 to 017) In addition, caffeine improved exercise performance by 112% (95% CI; 46-178%) Regression analysis revealed that RPE obtained during exercise could account for approximately 29% of the variance in the improvement in exercise performance The results demonstrate that caffeine reduces RPE during exercise and this may partly explain the subsequent ergogenic effects of caffeine on performance

Characterization of inflammatory responses to eccentric exercise in humans.

Abstract: Eccentric exercise commonly results in muscle damage. The primary sequence of events leading to exercise-induced muscle damage is believed to involve initial mechanical disruption of sarcomeres, followed by impaired excitation-contraction coupling and calcium signaling, and finally, activation of calcium-sensitive degradation pathways. Muscle damage is characterized by ultrastructural changes to muscle architecture, increased muscle proteins and enzymes in the bloodstream, loss of muscular strength and range of motion and muscle soreness. The inflammatory response to exercise-induced muscle damage is characterized by leukocyte infiltration and production of pro-inflammatory cytokines within damaged muscle tissue, systemic release of leukocytes and cytokines, in addition to alterations in leukocyte receptor expression and functional activity. Current evidence suggests that inflammatory responses to muscle damage are dependent on the type of eccentric exercise, previous eccentric loading (repeated bouts), age and gender. Circulating neutrophil counts and systemic cytokine responses are greater after eccentric exercise using a large muscle mass (e.g. downhill running, eccentric cycling) than after other types of eccentric exercise involving a smaller muscle mass. After an initial bout of eccentric exercise, circulating leukocyte counts and cell surface receptor expression are attenuated. Leukocyte and cytokine responses to eccentric exercise are impaired in elderly individuals, while cellular infiltration into skeletal muscle is greater in human females than males after eccentric exercise. Whether alterations in intracellular calcium homeostasis influence inflammatory responses to muscle damage is uncertain. Furthermore, the effects of antioxidant supplements are variable, and the limited data available indicates that anti-inflammatory drugs largely have no influence on inflammatory responses to eccentric exercise. In this review, we compare local versus systemic inflammatory responses, and discuss some of the possible mechanisms regulating the inflammatory responses to exercise-induced muscle damage in humans.

Prediction of energy expenditure from heart rate monitoring during submaximal exercise

Abstract: The aims of this study were to quantify the effects of factors such as mode of exercise, body composition and training on the relationship between heart rate and physical activity energy expenditure (measured in kJ · min−1) and to develop prediction equations for energy expenditure from heart rate. Regularly exercising individuals (n = 115; age 18 – 45 years, body mass 47 – 120 kg) underwent a test for maximal oxygen uptake ([Vdot]O2max test), using incremental protocols on either a cycle ergometer or treadmill; [Vdot]O2max ranged from 27 to 81 ml · kg−1 · min−1. The participants then completed three steady-state exercise stages on either the treadmill (10 min) or the cycle ergometer (15 min) at 35%, 62% and 80% of [Vdot]O2max, corresponding to 57%, 77% and 90% of maximal heart rate. Heart rate and respiratory exchange ratio data were collected during each stage. A mixed-model analysis identified gender, heart rate, weight, [Vdot]2max and age as factors that best predicted the relationship between heart...

Plasma cytokine changes in relation to exercise intensity and muscle damage

Abstract: The purpose of this study was to compare the effects of exercise intensity and exercise-induced muscle damage on changes in anti-inflammatory cytokines and other inflammatory mediators. Nine well-trained male runners completed three different exercise trials on separate occasions: ( 1) level treadmill running at 60% VO2max (moderate-intensity trial) for 60 min; (2) level treadmill running at 85% VO2max (high-intensity trial) for 60 min; (3) downhill treadmill running ( - 10% gradient) at 60% VO2 max (downhill running trial) for 45 min. Blood was sampled before, immediately after and 1 h after exercise. Plasma was analyzed for interleukin-1 receptor antagonist (IL-1ra), IL-4, IL-5, IL-10, IL-12p40, IL-13, monocyte chemotactic protein-1 (MCP-1), prostaglandin E-2, leukotriene B-4 and heat shock protein 70 (HSP70). The plasma concentrations of IL-1ra, IL-12p40, MCP-1 and HSP70 increased significantly (P< 0.05) after all three trials. Plasma prostaglandin E-2 concentration increased significantly after the downhill running and high-intensity trials, while plasma IL-10 concentration increased significantly only after the high-intensity trial. IL-4 and leukotriene B4 did not increase significantly after exercise. Plasma IL-1ra and IL-10 concentrations were significantly higher ( P< 0.05) after the high-intensity trial than after both the moderate-intensity and downhill running trials. Therefore, following exercise up to 1 h duration, exercise intensity appears to have a greater effect on anti-inflammatory cytokine production than exercise-induced muscle damage.

Changes in cardiorespiratory fitness and coronary heart disease risk factors following 24 wk of moderate- or high-intensity exercise of equal energy cost

Abstract: This study was designed to investigate the effect of exercise intensity on cardiorespiratory fitness and coronary heart disease risk factors. Maximum oxygen consumption (Vo(2 max)), lipid, lipoprotein, and fibrinogen concentrations were measured in 64 previously sedentary men before random allocation to a nonexercise control group, a moderate-intensity exercise group (three 400-kcal sessions per week at 60% of Vo(2 max)), or a high-intensity exercise group (three 400-kcal sessions per week at 80% of Vo(2 max)). Subjects were instructed to maintain their normal dietary habits, and training heart rates were represcribed after monthly fitness tests. Forty-two men finished the study. After 24 wk, Vo(2 max) increased by 0.38 +/- 0.14 l/min in the moderate-intensity group and by 0.55 +/- 0.27 l/min in the high-intensity group. Repeated-measures analysis of variance identified a significant interaction between monthly Vo(2 max) score and exercise group (F = 3.37, P < 0.05), indicating that Vo(2 max) responded differently to moderate- and high-intensity exercise. Trend analysis showed that total cholesterol, low-density lipoprotein cholesterol, non-high-density lipoprotein cholesterol, and fibrinogen concentrations changed favorably across control, moderate-intensity, and high-intensity groups. However, significant changes in total cholesterol (-0.55 +/- 0.81 mmol/l), low-density lipoprotein cholesterol (-0.52 +/- 0.80 mmol/l), and non-high-density lipoprotein cholesterol (-0.54 +/- 0.86 mmol/l) were only observed in the high-intensity group (all P < 0.05 vs. controls). These data suggest that high-intensity training is more effective in improving cardiorespiratory fitness than moderate-intensity training of equal energy cost. These data also suggest that changes in coronary heart disease risk factors are influenced by exercise intensity.

Effects of acute exercise on mood and well-being in patients with major depressive disorder.

Abstract: Purpose: This study was designed to determine if a single bout of moderate-intensity aerobic exercise would improve mood and well-being in 40 (15 male, 25 female) individuals who were receiving treatment for major depressive disorder (MDD). Methods: All participants were randomly assigned to exercise at 60-70% of age-predicted maximal heart rate for 30 min or to a 30-min period of quiet rest. Participants completed both the Profile of Mood States (POMS) and Subjective Exercise Experiences Scale (SEES) as indicators of mood 5 min before, and 5, 30, and 60 min following their experimental condition. Results: Both groups reported similar reductions in measures of psychological distress, depression, confusion, fatigue, tension, and anger. Only the exercise group, however, reported a significant increase in positive well-being and vigor scores. Conclusion: Although 30 min of either moderate-intensity treadmill exercise or quiet rest is sufficient to improve the mood and well-being of patients with MDD, exercise appears to have a greater effect on the positively valenced states measured.

Skeletal muscle adaptation: training twice every second day vs. training once daily

Abstract: Low muscle glycogen content has been demonstrated to enhance transcription of a number of genes involved in training adaptation. These results made us speculate that training at a low muscle glycog...

Exercise and the stress system.

Abstract: Exercise represents a physical stress that challenges homeostasis. In response to this stressor, autonomic nervous system and the hypothalamic-pituitary-adrenal axis are known to react and to participate in the maintenance of homeostasis. This includes elevation of cortisol and cathecholamines in plasma. However, sustained physical conditioning in highly trained athletes is associated with a decreased hypothalamic-pituitary-adrenal response to exercise. On the other hand, highly trained athletes exhibit a chronic mild hypercortisolism at baseline that may be an adaptive change to chronic exercise. In addition the proinflammatory cytokine IL-6 is also activated. Moreover, exercise stimulates the secretion of GH and prolactin, and may influence the type of immunity by stimulating TH2 response profile. Besides, the stress of exercise inhibits the gonadal function, through the production of glucocorticoids and cathecholamines, as well as through activation of the CRH neurons. Nowadays, apart from the beneficial effects of exercise, there is increasing incidence of exercise-related short- and long- term consequences, especially concerning the female athlete that many authors describe as the so-called "exercise-related female reproductive dysfunction". These consequences include amenorrhea, infertility, eating disorders, osteoporosis, coronary heart disease and euthyroid "sick" syndrome. The mechanisms involved in the pathogenesis of the above disorders are discussed in this review.

Elevations in core and muscle temperature impairs repeated sprint performance

Abstract: Aim: The present study investigated the effects of hyperthermia on intermittent exercise and repeated sprint performance. Methods: Seven men completed 40 min of intermittent cycling comprising of 15 s exercise (306 ± 22 W) and 15 s rest periods (0 W) followed by 5 × 15 s maximal sprints on a cycle ergometer in normal (∼20 °C, control) and hot (40 °C, hyperthermia) environments. Results: Completion of the intermittent protocol in the heat elevated core and muscle temperatures (39.5 ± 0.2 °C; 40.2 ± 0.4 °C), heart rate (178 ± 11 beats min−1), rating of perceived exertion (RPE) (18 ± 1) and noradrenaline (38.9 ± 13.2 μmol l−1) (all P < 0.05). During the first sprint (n = 6), both peak and mean power output were similar across the environmental conditions. However, mean power over the last four sprints declined to a larger extent during hyperthermia compared with the control trial (P < 0.05). Consequently, average mean power output during the five sprints was lower in hyperthermia (558.0 ± 146.9 W) compared with control (617.5 ± 122.6 W; P < 0.05). Power output during the repeated sprints was reduced by hyperthermia despite an elevated muscle temperature that should promote sprint performance. Venous plasma potassium concentrations (H; 5.3 ± 0.8 mmol l−1 vs. C; 6.3 ± 1.0 mmol l−1, P = 0.06) and muscle lactate levels (H; 76.6 ± 24.3 mmol kg−1 dry weight vs. C; 108.8 ± 20.1 mmol kg−1 dry weight) were lower following the hyperthermic sprints compared to control. Conclusion: Although an elevated muscle temperature is expected to promote sprint performance, power output during the repeated sprints was reduced by hyperthermia. The impaired performance does not seem to relate to the accumulation of recognized metabolic fatigue agents and we, therefore, suggest that it may relate to the influence of high core temperature on the function of the central nervous system.

Resistance Exercise Dosage in Older Adults: Single‐ Versus Multiset Effects on Physical Performance and Body Composition

Abstract: OBJECTIVES: To determine whether variation in resistance exercise volume affects muscle function and physical performance response in older adults. DESIGN: A randomized trial with subjects assigned to a single-set (1-SET) or three-set (3-SET) exercise group. SETTING: An exercise facility at the University of Queensland. PARTICIPANTS: Twenty-eight community-dwelling men and women aged 65 to 78. INTERVENTION: Progressive resistance training consisting of seven exercises targeting the major muscle groups of the upper and lower body performed on exercise machines twice weekly for 20 weeks at eight-repetition maximum (RM) intensity. MEASUREMENTS: Muscle function included isotonic muscle strength (1-RM) of the seven exercises, isokinetic and isometric knee extensor strength, and muscle endurance for the chest press and leg press exercises. Physical performance included timed chair rise, usual and fast 6-m walk, 6-m backwards walk, 400-m walk, floor rise to standing, and stair climbing ability. In addition, body composition was determined using dual energy x-ray absorptiometry. RESULTS: Isotonic muscle strength increased in both exercise groups for all seven exercises (P<.01), with the gain in the 3-SET group greater (P<.05) for the seated row, triceps extension, and knee extension (analysis of covariance). Similarly, muscle endurance gains were greater for the 3-SET than the 1-SET group (P<.01), with no significant difference between groups for isokinetic and isometric knee extensor strength. Both groups improved (P<.05) in the chair rise (1-SET, 10.1%; 3-SET, 13.6%), 6-m backwards walk (1-SET, 14.3%; 3-SET, 14.8%), 400-m walk (1-SET, 3.8%; 3-SET, 7.4%), and stair climbing test (1-SET, 7.7%; 3-SET, 6.4%), with the only difference between groups for the 400-m walk (P<.05). There was no difference between groups for change in body composition. CONCLUSION: Resistance training consisting of only single-set exercises is sufficient to significantly enhance muscle function and physical performance, although muscle strength and endurance gains are greater with higher-volume work. These findings have application in designing time-efficient exercise regimens to enhance neuromuscular function in older adults.

Influence of exercise order on the number of repetitions performed and perceived exertion during resistance exercises.

Abstract: The purpose of this study was to investigate the influence of different resistance exercise orders on the number of repetitions performed to failure and on the ratings of perceived exertion (RPE) in trained women. Twenty-three women with a minimum of 2 years of resistance training experience volunteered to participate in the study (age, 24.2 +/- 4.5 years; weight, 56.9 +/- 4.7 kg; height, 162.3 +/- 5.9 cm; percent body fat, 18.2 +/- 2.9%; body mass index, 22.2 +/- 2 kg x m(-2)). Data were collected in 2 phases: (a) determination of a 1 repetition maximum (1RM) for the leg-press (LP), bench press (BP), leg extension (LE), seated machine shoulder press (SP), leg curl (LC), and seated machine triceps extension (TE); and (b) execution of 3 sets, with 2-minute rest intervals between sets and exercises, until fatigue using 80% of 1RM in 2 exercise sequences of the exact opposite order--Sequence A: BP, SP, TE, LP, LE, and LC, and Sequence B: LC, LE, LP, TE, SP, and BP. The RPE (Borg CR-10) was accessed immediately after each sequence and analyzed using a Wilcoxon test. A 2-way analysis of variance with repeated measurements, followed by a post hoc Fisher least significant difference test where indicated was used to analyze the number of repetitions per set of each exercise during the 2 sequences. The RPE was not significantly different between the sequences. The mean number of repetitions per set was always less when an exercise was performed later in the exercise sequence. The data indicate that in trained women, performance of both large- and small-muscle group exercises is affected by exercise sequence.

Comparison between leg and arm eccentric exercises of the same relative intensity on indices of muscle damage.

Abstract: Many exercise models have demonstrated associations between eccentric muscle actions and muscle damage. However, the magnitude of muscle damage varies among the models. It appears that responses to eccentric exercise are different between leg and arm muscles but this has not been systematically clarified. This study compared leg and arm eccentric exercises of the same relative intensity for indices of muscle damage. Eleven healthy untrained males [Age: 21.2 (1.0) years, Height: 179.4 (3.0) cm, Weight: 78.4 (3.1) kg] performed a sub-maximal eccentric exercise of the knee extensors (LEGS) and the elbow flexors (ARMS), separately. Both LEGS and ARMS consisted of six sets of 12 repetitions with an intensity corresponding to 75% of the predetermined maximal eccentric peak torque (EPT) of each muscle. Range of motion (ROM), delayed onset muscle soreness (DOMS), serum creatine kinase (CK) and lactate dehydrogenase (LDH) activities, myoglobin (Mb) concentration, and muscle strength [EPT and isometric peak torque (IPT)] were assessed before and 24, 48, 72, and 96 h following exercise. Significant (P < 0.05) changes in DOMS and ROM were observed up to 96 h after both exercise bouts, and the magnitude of the change was similar between LEGS and ARMS. Increases in CK and Mb were significantly (P < 0.05) larger after ARMS than LEGS at 72 and 96 h post-exercise. EPT and IPT were significantly (P < 0.05) lower than the baseline up to 96 h post-exercise for ARMS but were fully recovered by 96 h post-exercise for LEGS. Decreases in muscle strength were significantly (p < 0.05) larger following ARMS than LEGS at 48, 72, and 96 h post-exercise for EPT, and from 24 h to 96 h post-exercise for IPT. These results suggest that the magnitude of muscle damage is greater and the recovery of muscle function was slower after eccentric exercise of arm elbow flexors than the knee extensors.

The Decline in Blood Glucose Levels Is Less With Intermittent High-Intensity Compared With Moderate Exercise in Individuals With Type 1 Diabetes

Abstract: OBJECTIVE —To compare the response of blood glucose levels to intermittent high-intensity exercise (IHE) and moderate-intensity exercise (MOD) in individuals with type 1 diabetes. RESEARCH DESIGN AND METHODS —Seven healthy individuals with type 1 diabetes were tested on two separate occasions, during which either a 30-min MOD or IHE protocol was performed. MOD consisted of continuous exercise at 40% Vo 2peak , while the IHE protocol involved a combination of continuous exercise at 40% Vo 2peak interspersed with 4-s sprints performed every 2 min to simulate the activity patterns of team sports. RESULTS —Both exercise protocols resulted in a decline in blood glucose levels. However, the decline was greater with MOD (−4.4 ± 1.2 mmol/l) compared with IHE (−2.9 ± 0.8 mmol/l; P P P P P CONCLUSIONS —The decline in blood glucose levels is less with IHE compared with MOD during both exercise and recovery in individuals with type 1 diabetes.

Effects of intra-session concurrent endurance and strength training sequence on aerobic performance and capacity.

Abstract: Aim: To examine the effects of the sequencing order of individualised intermittent endurance training combined with muscular strengthening on aerobic performance and capacity. Methods: Forty eight male sport students (mean (SD) age 21.4 (1.3) years) were divided into five homogeneous groups according to their maximal aerobic speeds ( v V˙o 2 max). Four groups participated in various training programmes for 12 weeks (two sessions a week) as follows: E (n = 10), running endurance training; S (n = 9), strength circuit training; E+S (n = 10) and S+E (n = 10) combined the two programmes in a different order during the same training session. Group C (n = 9) served as a control. All the subjects were evaluated before (T0) and after (T1) the training period using four tests: (1) a 4 km time trial running test; (2) an incremental track test to estimate v V˙o 2 max; (3) a time to exhaustion test (t lim ) at 100% v V˙o 2 max; (4) a maximal cycling laboratory test to assess V˙o 2 max. Results: Training produced significant improvements in performance and aerobic capacity in the 4 km time trial with interaction effect (p v V˙o 2 max (p 2 max (ml/kg 0.75 /min) (p lim and the second ventilatory threshold (%V˙o 2 max). Conclusions: Circuit training immediately after individualised endurance training in the same session (E+S) produced greater improvement in the 4 km time trial and aerobic capacity than the opposite order or each of the training programmes performed separately.

Comparison of forearm blood flow responses to incremental handgrip and cycle ergometer exercise: relative contribution of nitric oxide.

Abstract: The contribution of endothelium-derived nitric oxide (NO) to exercise hyperaemia remains controversial. Disparate findings may, in part, be explained by different shear stress stimuli as a result of different types of exercise. We have directly compared forearm blood flow (FBF) responses to incremental handgrip and cycle ergometer exercise in 14 subjects (age +/-s.e.m.) using a novel software system which calculates conduit artery blood flow continuously across the cardiac cycle by synchronising automated edge-detection and wall tracking of high resolution B-mode arterial ultrasound images and Doppler waveform envelope analysis. Monomethyl arginine (L-NMMA) was infused during repeat bouts of each incremental exercise test to assess the contribution of NO to hyperaemic responses. During handgrip, mean FBF increased with workload (P < 0.01) whereas FBF decreased at lower cycle workloads (P < 0.05), before increasing at 120 W (P < 0.001). Differences in these patterns of mean FBF response to different exercise modalities were due to the influence of retrograde diastolic flow during cycling, which had a relatively larger impact on mean flows at lower workloads. Retrograde diastolic flow was negligible during handgrip. Although mean FBF was lower in response to cycling than handgrip exercise, the impact of L-NMMA was significant during the cycle modality only (P < 0.05), possibly reflecting the importance of an oscillatory antegrade/retrograde flow pattern on shear stress-mediated release of NO from the endothelium. In conclusion, different types of exercise present different haemodynamic stimuli to the endothelium, which may result in differential effects of shear stress on the vasculature.

Acute Muscle Stretching Inhibits Muscle Strength Endurance Performance

Abstract: Since strength and muscular strength endurance are linked, it is possible that the inhibitory influence that prior stretching has on strength can also extend to the reduction of muscle strength endurance. To date, however, studies measuring muscle strength endurance poststretching have been criticized because of problems with their reliability. The purpose of this study was twofold: both the muscle strength endurance performance after acute static stretching exercises and the repeatability of those differences were measured. Two separate experiments were conducted. In experiment 1, the knee-flexion muscle strength endurance exercise was measured by exercise performed at 60 and 40% of body weight following either a no-stretching or stretching regimen. In experiment 2, using a test-retest protocol, a knee-flexion muscle strength endurance exercise was performed at 50% body weight on 4 different days, with 2 tests following a no-stretching regimen (RNS) and 2 tests following a stretching regimen (RST). For experiment 1, when exercise was performed at 60% of body weight, stretching significantly (p < 0.05) reduced muscle strength endurance by 24%, and at 40% of body weight, it was reduced by 9%. For experiment 2, reliability was high (RNS, intraclass correlation = 0.94; RST, intraclass correlation = 0.97). Stretching also significantly (p < 0.05) reduced muscle strength endurance by 28%. Therefore, it is recommended that heavy static stretching exercises of a muscle group be avoided prior to any performances requiring maximal muscle strength endurance.

Determinants of exercise capacity in patients with type 2 diabetes.

Abstract: OBJECTIVE —Type 2 diabetes is associated with reduced exercise capacity, but the cause of this association is unclear. We sought the associations of impaired exercise capacity in type 2 diabetes. RESEARCH DESIGN AND METHODS —Subclinical left ventricular (LV) dysfunction was sought from myocardial strain rate and the basal segmental diastolic velocity (Em) of each wall in 170 patients with type 2 diabetes (aged 56 ± 10 years, 91 men), good quality echocardiographic images, and negative exercise echocardiograms. The same measurements were made in 56 control subjects (aged 53 ± 10 years, 29 men). Exercise capacity was calculated in metabolic equivalents, and heart rate recovery (HRR) was measured as the heart rate difference between peak and 1 min after exercise. In subjects with type 2 diabetes, exercise capacity was correlated with clinical, therapeutic, biochemical, and echocardiographic variables, and significant independent associations were sought using a multiple linear regression model. RESULTS —Exercise capacity, strain rate, Em, and HRR were significantly reduced in type 2 diabetes. Exercise capacity was associated with age ( r = −0.37, P < 0.001), male sex ( r = 0.26, P = 0.001), BMI ( r = −0.19, P = 0.012), HbA1c (A1C; r = −0.22, P = 0.009), Em ( r = 0.43, P < 0.001), HRR ( r = 0.42, P < 0.001), diabetes duration ( r = −0.18, P = 0.021), and hypertension history ( r = −0.28, P < 0.001). Age ( P < 0.001), male sex ( P = 0.007), BMI ( P = 0.001), Em ( P = 0.032), HRR ( P = 0.013), and A1C ( P = 0.0007) were independent predictors of exercise capacity. CONCLUSIONS —Reduced exercise capacity in patients with type 2 diabetes is associated with diabetes control, subclinical LV dysfunction, and impaired HRR.

Malonyl-CoA and carnitine in regulation of fat oxidation in human skeletal muscle during exercise

Abstract: Intracellular mechanisms regulating fat oxidation were investigated in human skeletal muscle during exercise. Eight young, healthy, moderately trained men performed bicycle exercise (60 min, 65% pe...

Impact of cardiac rehabilitation on the exercise function of children with serious congenital heart disease

Abstract: Objectives. The exercise capacity of children with congenital heart disease (CHD) is often depressed. This depression is thought to be attributable to (1) residual hemodynamic defects and (2) deconditioning secondary to physical inactivity. We hypothesized that this latter component would be ameliorated by a formal cardiac rehabilitation program designed specifically for children. The objective of this study was to characterize the effect of a cardiac rehabilitation program on the exercise performance of children with CHD and to define the physiologic mechanisms that might account for any improvements that are observed. Methods. Nineteen patients with CHD who were referred for exercise testing and found to have a peak oxygen consumption (VO2) and/or peak work rate Results. Improvements were found in 15 of 16 patients. Peak VO2 rose from 26.4 ± 9.1 to 30.7 ± 9.2 mL/kg per min; peak work rate from 93 ± 32 to 106 ± 34 W, and the ventilatory anaerobic threshold from 14.2 ± 4.8 to 17.4 ± 4.5 mL/kg per min. The peak heart rate and peak respiratory exchange ratio did not change, suggesting that the improvements were not attributable merely to an increased effort. In contrast, the peak oxygen pulse rose significantly, from 7.6 ± 2.8 to 9.7 ± 4.1 mL/beat, an improvement that can be attributed only to an increase in stroke volume and/or oxygen extraction at peak exercise. No patient experienced rehabilitation-related complications. Conclusion. Cardiac rehabilitation can improve the exercise performance of children with CHD. This improvement is mediated by an increase in stroke volume and/or oxygen extraction during exercise. Routine use of formal cardiac rehabilitation may greatly reduce the morbidity of complex CHD.

A signalling role for muscle glycogen in the regulation of pace during prolonged exercise

Abstract: Introduction: In this study we examined the pacing strategy and the end muscle glycogen contents in eight cyclists, once when they were carbohydrate loaded and once when they were non-loaded. Methods: Cyclists completed 2 hours of cycling at ∼73% of maximum oxygen consumption, which included five sprints at 100% of peak sustained power output every 20 minutes, followed immediately by a 1 hour time trial. Muscle biopsies were performed before and immediately after exercise, while blood samples were taken during the 2 hour steady state rides and immediately after exercise. Results: Carbohydrate loading improved mean power output during the 1 hour time trial (mean (SEM) 219 (17) v 233 (15) W; p v 20 (3) mmol/kg w/w), despite significantly different starting values and time trial performances (36.55 (1.47) v 38.14 (1.27) km/h; p Conclusions: As seven subjects completed the time trials with the same end exercise muscle glycogen concentrations, diet induced changes in pacing strategies during the time trials in these subjects may have resulted from integrated feedback from the periphery, perhaps from glycogen content in exercising muscles.

Prescribing exercise at varied levels of intensity and frequency: a randomized trial.

Abstract: Background Regular physical activity produces beneficial effects on health, but the exercise prescription needed to improve cardiovascular disease risk factors in free-living sedentary individuals remains unclear. Methods Sedentary adults (N = 492, 64.0% women) were randomized to 1 of 4 exercise-counseling conditions or to a physician advice comparison group. The duration (30 minutes) and type (walking) of exercise were held constant, while exercise intensity and frequency were manipulated to form 4 exercise prescriptions: moderate intensity–low frequency, moderate intensity–high frequency (HiF), hard intensity (HardI)–low frequency, and HardI-HiF. Comparison group participants received physician advice and written materials regarding recommended levels of exercise for health. Outcomes included 6- and 24-month changes in cardiorespiratory fitness (maximum oxygen consumption), high-density lipoprotein cholesterol (HDL-C) level, and the total cholesterol–HDL-C ratio. Results At 6 months, the HardI-HiF, HardI–low-frequency, and moderate-intensity–HiF conditions demonstrated significant increases in maximum oxygen consumption ( P P P P P P = .57) or total cholesterol–HDL-C ratio ( P = .64) were observed. Conclusions Exercise counseling with a prescription for walking at either a HardI or a HiF produced significant long-term improvements in cardiorespiratory fitness. More exercise or the combination of HardI plus HiF exercise may provide additional benefits, including larger fitness changes and improved lipid profiles.

Effect of exercise, training, and glycogen availability on IL-6 receptor expression in human skeletal muscle

Abstract: The cytokine interleukin-6 (IL-6) exerts it actions via the IL-6 receptor (IL-6R) in conjunction with the ubiquitously expressed gp130 receptor. IL-6 is tightly regulated in response to exercise, being affected by factors such as exercise intensity and duration, as well as energy availability. Although the IL-6 response to exercise has been extensively studied, little is known about the regulation of the IL-6R response. In the present study, we aimed to investigate the effect of exercise, training, and glycogen availability, factors known to affect IL-6, on the regulation of gene expression of the IL-6R in human skeletal muscle. Human subjects performed either 10 wk of training with an acute exercise bout before and after the training period, or a low-glycogen vs. normal-glycogen acute exercise trial. The IL-6R mRNA response was evaluated in both trials. In response to acute exercise, an increase in IL-6R mRNA levels was observed. Neither training nor intramuscular glycogen levels had an effect on the IL-6R mRNA response to exercise. However, after 10 wk of training, the skeletal muscle expressed a higher mRNA level of IL-6R compared with before training. The present study demonstrated that the IL-6R gene expression levels in skeletal muscle are increased in response to acute exercise, a response that is very well conserved, being affected by neither training status nor intramuscular glycogen levels, as opposed to IL-6. However, after the training period, IL-6R mRNA production was increased in skeletal muscle, suggesting a sensitization of skeletal muscle to IL-6 at rest.

Is exercise effective for weight loss with ad libitum diet? Energy balance, compensation, and gender differences.

Abstract: Exercise generally results in less weight loss than expected and it is frequently observed that men and women do not respond equally to exercise for weight loss. This may be caused by differences in compensation by other components of energy balance or to differences in the energy expenditure of exercise observed between genders.

Fasted‐state skeletal muscle protein synthesis after resistance exercise is altered with training

Abstract: The purpose of the present investigation was to determine how fasted-state protein synthesis was affected, acutely, by resistance training. Eight men (24.8+/-1.7 years, body mass index=23.2+/-1.0 kg m-2; means+/-s.e.m.) undertook an 8 week programme of unilateral resistance exercise training (3 sessions week-1, progression from two to four sets; intensity was 80% of the subjects' single repetition maximum (1RM): knee extension and leg press). Following training, subjects underwent two primed constant infusions of l-[ring-13C6]phenylalanine to determine mixed and myofibrillar muscle protein synthesis (MPS) at rest and 12 h after an acute bout of resistance exercise at the same exercise intensity--each leg 80% of 1RM. Biopsies (vastus lateralis) were taken to measure incorporation of labelled phenylalanine into mixed and myofibrillar skeletal muscle proteins and yield fractional MPS. Training resulted in significant dynamic strength gains that were greater (P<0.001) in the trained leg. Hypertrophy of type IIa and IIx fibres (P<0.05) was observed following training. After training, resting mixed MPS rate was elevated (+48%; P<0.05). Acutely, resistance exercise stimulated mixed MPS only in the untrained leg (P<0.05). Myofibrillar MPS was unchanged at rest following training (P=0.61). Myofibrillar MPS increased after resistance exercise (P<0.05), but was not different between the trained and untrained legs (P=0.36). We observed divergent changes in resting mixed versus myofibrillar protein synthesis with training. In addition, resistance training modified the acute response of MPS to resistance exercise by dampening the increased synthesis of non-myofibrillar proteins while maintaining the synthesis of myofibrillar proteins.

Exercise training and inspiratory muscle training in patients with bronchiectasis

Abstract: Background: Bronchiectasis is a chronic suppurative lung disease often characterised by airflow obstruction and hyperinflation, and leading to decreased exercise tolerance and reduced health status. The role of pulmonary rehabilitation (PR) and inspiratory muscle training (IMT) has not been investigated in this group of patients. Methods: Thirty two patients with idiopathic bronchiectasis were randomly allocated to one of three groups: PR plus sham IMT (PR-SHAM), PR plus targeted IMT (PR-IMT), or control. All patients (except the control group) underwent an 8 week training programme of either PR or PR plus targeted IMT. Exercise training during PR was performed three times weekly at 80% of the peak heart rate. IMT was performed at home for 15 minutes twice daily over the 8 week period. Results: PR-SHAM and PR-IMT resulted in significant increases in the incremental shuttle walking test of 96.7 metres (95% confidence interval (CI) 59.6 to 133.7) and 124.5 metres (95% CI 63.2 to 185.9), respectively, and in endurance exercise capacity of 174.9% (95% CI 34.7 to 426.1) and 205.7% (95% CI 31.6 to 310.6). There were no statistically significant differences in the improvements in exercise between the two groups. Significant improvements in inspiratory muscle strength were also observed both in the PR-IMT group (21.4 cm H2O increase, 95% CI 9.3 to 33.4; p = 0.008) and the PR-SHAM group (12.0 cm H2O increase, 95% CI 1.1 to 22.9; p = 0.04), the magnitude of which were also similar (p = 0.220). Improvements in exercise capacity were maintained in the PR-IMT group 3 months after training, but not in the PR-SHAM group. Conclusion: PR is effective in improving exercise tolerance in bronchiectasis but there is no additional advantage of simultaneous IMT. IMT may, however, be important in the longevity of the training effects.