Age and aerobic exercise training effects on whole body and muscle protein metabolism

Aging in humans is associated with loss of lean body mass, but the causes are incompletely defined. Lean tissue mass and function depend on continuous rebuilding of proteins. We tested the hypotheses that whole body and mixed muscle protein metabolism declines with age in men and women and that aerobic exercise training would partly reverse this decline. Seventy-eight healthy, previously untrained men and women aged 19-87 yr were studied before and after 4 mo of bicycle training (up to 45 min at 80% peak heart rate, 3-4 days/wk) or control (flexibility) activity. At the whole body level, protein breakdown (measured as [13C]leucine and [15N]phenylalanine flux), Leu oxidation, and protein synthesis (nonoxidative Leu disposal) declined with age at a rate of 4-5% per decade (P < 0.001). Fat-free mass was closely correlated with protein turnover and declined 3% per decade (P < 0.001), but even after covariate adjustment for fat-free mass, the decline in protein turnover with age remained significant. There were no differences between men and women after adjustment for fat-free mass. Mixed muscle protein synthesis also declined with age 3.5% per decade (P < 0.05). Exercise training improved aerobic capacity 9% overall (P < 0.01), and mixed muscle protein synthesis increased 22% (P < 0.05), with no effect of age on the training response for either variable. Fat-free mass, whole body protein turnover, and resting metabolic rate were unchanged by training. We conclude that rates of whole body and muscle protein metabolism decline with age in men and women, thus indicating that there is a progressive decline in the body's remodeling processes with aging. This study also demonstrates that aerobic exercise can enhance muscle protein synthesis irrespective of age.     

Regulation of fuel metabolism by preexercise muscle glycogen content and exercise intensity.

To date, the results of studies that have examined the effects of altering preexercise muscle glycogen content and exercise intensity on endogenous carbohydrate oxidation are equivocal. Differences in the training status of subjects between investigations may, in part, explain these inconsistent findings. Accordingly, we determined the relative effects of exercise intensity and carbohydrate availability on patterns of fuel utilization in the same subjects who performed a random order of four 60-min rides, two at 45% and two at 70% of peak O(2) uptake (Vo(2 peak)), after exercise-diet intervention to manipulate muscle glycogen content. Preexercise muscle glycogen content was 596 +/- 43 and 202 +/- 21 mmol/kg dry mass (P < 0.001) for high-glycogen (HG) and low-glycogen (LG) conditions, respectively. Respiratory exchange ratio was higher for HG than LG during exercise at both 45% (0.85 +/- 0.01 vs. 0.74 +/- 0.01; P < 0.001) and 70% (0.90 +/- 0.01 vs. 0.79 +/- 0.01; P < 0.001) of Vo(2 peak). The contribution of whole body muscle glycogen oxidation to energy expenditure differed between LG and HG for exercise at both 45% (5 +/- 2 vs. 45 +/- 5%; P < 0.001) and 70% (25 +/- 3 vs. 60 +/- 3%; P < 0.001) of Vo(2 peak). Yet, despite marked differences in preexercise muscle glycogen content and its subsequent utilization, rates of plasma glucose disappearance were similar under all conditions. We conclude that, in moderately trained individuals, muscle glycogen availability (low vs. high) does not influence rates of plasma glucose disposal during either low- or moderate-intensity exercise.     

The adaptations in muscle architecture following whole body vibration training

Objective:This study aims to investigate the effect of 8-week whole-body vibration (WBV) added to conventional training on muscular architecture, dynamic muscle strength and physical performance compared to controls in young basketball players.Methods:Sixteen young basketball players between the ages of 14-16 years were randomly assigned to whole body vibration group (VG) or control group (CG). Both groups were trained with a conventional program. Pennation angle (PeA), fascicle length and muscle thickness of Rectus Femoris (RF) and Vastus lateralis were measured by ultrasonography. Isokinetic dynamic muscle testing at 180 °/s and 60°/s, squat jump (SJ) and flexibility were evaluated before and after 8 weeks of training programs. Primary outcome measure was the fascicle length.Results:Fascicle length of RF, SJ height and flexibility increased significantly within VG compared to pretraining (p<0.05). SJ height increased in VG compared to CG significantly following training (p<0.05). PeA, fascicle length, muscle thicknesses, strength and flexibility did not differ between groups.Conclusion:Eight weeks of WBV training improved fascicle length of RF, SJ height, and flexibility compared to pre-training. Addition of WBV to conventional training did not cause improvement in muscle architecture, strength and flexibility compared to conventional training alone.     

Diastolic dysfunction and intraventricular dyssynchrony are restored by low intensity exercise training in obese men

The aim of this study was to evaluate the impact of a low-intensity training program on subclinical cardiac dysfunction and on dyssynchrony in moderately obese middle aged men. Ten obese and 14 age-matched normal-weight men (BMI: 33.6 ± 1.0 and 24.2 ± 0.5 kg/m(2)) were included. Obese men participated in an 8-week low-intensity training program without concomitant diet. Cardiac function and myocardial synchrony were assessed by echocardiography with tissue Doppler imaging (TDI) and speckle tracking echocardiography (STE). At baseline, obese men showed diastolic dysfunction on standard echocardiography, lower strain values (systolic strain: 15.9 ± 0.9 vs. 18.8 ± 0.3%, diastolic strain rate: 0.81 ± 0.09 vs. 1.05 ± 0.06 s(-1)), and significant intraventricular dyssynchrony (systolic: 13.3 ± 2.1 vs. 5.4 ± 2.1 ms, diastolic: 17.4 ± 3.2 vs. 9.1 ± 2.1 ms) (P < 0.05 vs. controls for all variables). Training improved aerobic fitness, decreased systolic blood pressure and heart rate, and reduced fat mass without weight loss. Diastolic function, strain values (systolic strain: 17.4 ± 0.9%, diastolic strain rate: 0.96 ± 0.12 s(-1)) and intraventricular dyssynchrony (systolic: 3.3 ± 1.7 ms, diastolic: 5.5 ± 3.4 ms) improved significantly after training (P < 0.05 vs. baseline values for all variables), reaching levels similar to those of normal-weight men. In conclusion, in obese men, a short and easy-to-perform low intensity training program restored diastolic function and cardiac synchrony and improved body composition without weight loss.     

Modulation of whole body protein metabolism, during and after exercise, by variation of dietary protein

The aim of this study was to investigate dietaryprotein-induced changes in whole body leucine turnover and oxidationand in skeletal muscle branched chain 2-oxo acid dehydrogenase (BCOADH) activity, at rest and during exercise. Postabsorptive subjects receiveda primed constant infusion ofL-[1-¹³C,¹⁵N]leucinefor 6 h, after previous consumption of a high- (HP; 1.8 g · kg¹ · day¹,n = 8) or a low-protein diet (LP; 0.7 g · kg¹ · day¹,n = 8) for 7 days. The subjects werestudied at rest for 2 h, during 2-h exercise at 60% maximum oxygenconsumption, then again for 2 h at rest. Exercise induced a doubling ofboth leucine oxidation from 20 µmol · kg¹ · h¹and BCOADH percent activation from 7% in all subjects. Leucine oxidation was greater before (+46%) and during (+40%,P < 0.05) the first hour of exercisein subjects consuming the HP rather than the LP diet, but there was noadditional change in muscle BCOADH activity. The results suggest thatleucine oxidation was increased by previous ingestion of an HP diet,attributable to an increase in leucine availability rather than to astimulation of the skeletal muscle BCOADH activity.

     

Effects of whole body vibration on muscle contractile properties in exercise induced muscle damaged females

Determining muscle contractile properties following exercise is critical in understanding neuromuscular function. Following high intensity training, individuals often experience exercise induced muscle damage (EIMD). The purpose of this investigation was to determine the effect of whole-body vibration (WBV) on muscle contractile properties following EIMD. Twenty-seven females volunteered for 7 sessions and were randomly assigned to a treatment or control group. Muscle contractile properties were assessed via voluntary torque (VT), peak twitch torque (TT), time to reach peak torque, half relaxation time of twitch torque, percent activation (%ACT), rate of rise (RR), rate of decline (RD), mean and peak electromyography during maximum voluntary isometric contraction. Two testing sets were collected each day, consisting of pre measures followed by WBV or control and post measures. A mixed factor analysis of variance was conducted for each variable. %ACT measures found baseline being less than day 1 in both measures in the control group. TT was found to be greater in the control group compared to WBV group. TT and VT baseline measures were greater than all other time points. RR showed control group had higher values than WBV group. These results indicate that WBV following EIMD had some positive effects on muscle contractile properties.     

The effects of diet on muscle pH and metabolism during high intensity exercise

Five healthy male subjects exercised for 3 min at a workload equivalent to 100% VO2max on two separate occasions. Each exercise test was performed on an electrically braked cycle ergometer after a four-day period of dietary manipulation. During each of these periods subjects consumed either a low carbohydrate (3 +/- 0%, mean +/- SD), high fat (73 +/- 2%), high protein (24 +/- 3%) diet (FP) or a high carbohydrate (82 +/- 1%), low fat (8 +/- 1%) low protein (10 +/- 1%) diet (CHO). The diets were isoenergetic and were assigned in a randomised manner. Muscle biopsy samples (Vastus lateralis) were taken at rest prior to dietary manipulation, immediately prior to exercise and immediately post-exercise for measurement of pH, glycogen, glucose 6-phosphate, fructose 1,6-diphosphate, triose phosphates, lactate and glutamine content. Blood acid-base status and selected metabolites were measured in arterialised venous samples at rest prior to dietary manipulation, immediately prior to exercise and at pre-determined intervals during the post-exercise period. There was no differences between the two treatments in blood acid-base status at rest prior to dietary manipulation; immediately prior to exercise plasma pH (p less than 0.01), blood PCO2 (p less than 0.01), plasma bicarbonate (p less than 0.001) and blood base-excess (p less than 0.001) values were all lower on the FP treatment. There were no major differences in blood acid-base variables between the two diets during the post-exercise period.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of age and exercise training on lipid metabolism in Fischer-344 rats

The influence of training on fatty acid and glyceride synthesis by liver and adipose tissue homogenates of young and old Fischer-344 rats was examined. Four groups of rats (10 animals/group) were studied: young untrained, young trained, old untrained, and old trained. Training of each group was for 10 wk at 75% maximal O2 uptake. Young rats were killed at 6 mo of age and old rats were killed at 27 mo of age. Fatty acid synthesis was assessed by measuring the activities of acetyl-CoA carboxylase, fatty acid synthase, ATP citrate-lyase, "malic" enzyme, and glucose-6-phosphate dehydrogenase. Glyceride synthesis was evaluated by determining the rate of incorporation of [14C]glycerol 3-phosphate into lipids. In addition, lipoprotein lipase activity was measured in acetone-ether powders of adipose tissue from the four groups of rats. In liver, training had no effect on fatty acid or glyceride synthesis in either group. However, aging caused a significant decrease in the activities of four of the lipogenic enzymes but had no effect on glyceride synthesis. Training caused an increase in fatty acid synthase and glyceride synthesis in adipose tissue, and aging decreased lipoprotein lipase activity. It was concluded that training enhances the synthetic capacity of lipids by adipose tissue but that aging had a more profound effect in that the activities of the enzymes involved in these processes were lower in the old rats. Furthermore, the decreased activity of lipoprotein lipase in the older rats may explain the higher plasma triglyceride levels that were observed in these animals.     

Active muscle and whole body lactate kinetics after endurance training in men.

We evaluated the hypotheses that endurance training decreases arterial lactate concentration ([lactate](a)) during continuous exercise by decreasing net lactate release () and appearance rates (R(a)) and increasing metabolic clearance rate (MCR). Measurements were made at two intensities before [45 and 65% peak O(2) consumption (VO(2 peak))] and after training [65% pretraining VO(2 peak), same absolute workload (ABT), and 65% posttraining VO(2 peak), same relative intensity (RLT)]. Nine men (27.4 +/- 2.0 yr) trained for 9 wk on a cycle ergometer, 5 times/wk at 75% VO(2 peak). Compared with the 65% VO(2 peak) pretraining condition (4.75 +/- 0.4 mM), [lactate](a) decreased at ABT (41%) and RLT (21%) (P < 0.05). decreased at ABT but not at RLT. Leg lactate uptake and oxidation were unchanged at ABT but increased at RLT. MCR was unchanged at ABT but increased at RLT. We conclude that 1) active skeletal muscle is not solely responsible for elevated [lactate](a); and 2) training increases leg lactate clearance, decreases whole body and leg lactate production at a given moderate-intensity power output, and increases both whole body and leg lactate clearance at a high relative power output.     

A computational model of skeletal muscle metabolism linking cellular adaptations induced by altered loading states to metabolic responses during exercise

Background  

The alterations in skeletal muscle structure and function after prolonged periods of unloading are initiated by the chronic lack of mechanical stimulus of sufficient intensity, which is the result of a series of biochemical and metabolic interactions spanning from cellular to tissue/organ level. Reduced activation of skeletal muscle alters the gene expression of myosin heavy chain isoforms to meet the functional demands of reduced mechanical load, which results in muscle atrophy and reduced capacity to process fatty acids. In contrast, chronic loading results in the opposite pattern of adaptations.     

Changes in muscle mitochondrial lipid composition resulting from training and exhaustive exercise.

This study was undertaken to determine if the changes in mitochondrial structure and function that occur in muscle with exhaustive exercise could be caused by alterations in lipid composition of mitochondrial membranes. Further, the effect of training on lipid composition was studied to ascertain if lipid changes accompany the adaptation in the level of mitochondrial protein. Training decreased free fatty acids and triglycerides. Exhaustion of untrained animals resulted in increases of total phospholipid and phosphatidyl choline while exhaustion of trained rats caused a lowering of total phospholipid and phosphatidyl choline. Alterations in membrane lipid composition are most likely not the cause of changes in mitochondrial structure and function after exhaustive exercise since mitochondrial yield and lipid levels did not change in concert; i.e. muscle mitochondrial yield was decreased in both untrained and trained rats while total phospholipids were increased in untrained rats and decreased in trained rats as a result of exhaustive exercise. Although the physiological significance of the effects observed remains to be determined, this study does demonstrate that the lipid composition of mitochondria is not a constant parameter but can change in response to a chronic (training) or acute (exhaustive exercise) physiological condition.     

不同强度有氧运动对大鼠脂代谢的影响

通过对不同强度有氧运动时大鼠脂代谢相关指标进行测试,发现规律的、周期性的、适宜的有氧运动对维持机体健康有益.     

Endurance exercise training blunts the deleterious effect of high-fat feeding on whole body efficiency

We recently showed that a week-long, high-fat diet reduced whole body exercise efficiency in sedentary men by >10% (Edwards LM, Murray AJ, Holloway CJ, Carter EE, Kemp GJ, Codreanu I, Brooker H, Tyler DJ, Robbins PA, Clarke K. FASEB J 25: 1088-1096, 2011). To test if a similar dietary regime would blunt whole body efficiency in endurance-trained men and, as a consequence, hinder aerobic exercise performance, 16 endurance-trained men were given a short-term, high-fat (70% kcal from fat) and a moderate carbohydrate (50% kcal from carbohydrate) diet, in random order. Efficiency was assessed during a standardized exercise task on a cycle ergometer, with aerobic performance assessed during a 1-h time trial and mitochondrial function later measured using (31)P-magnetic resonance spectroscopy. The subjects then underwent a 2-wk wash-out period, before the study was repeated with the diets crossed over. Muscle biopsies, for mitochondrial protein analysis, were taken at the start of the study and on the 5th day of each diet. Plasma fatty acids were 60% higher on the high-fat diet compared with moderate carbohydrate diet (P < 0.05). However, there was no change in whole body efficiency and no change in mitochondrial function. Endurance exercise performance was significantly reduced (P < 0.01), most probably due to glycogen depletion. Neither diet led to changes in citrate synthase, ATP synthase, or mitochondrial uncoupling protein 3. We conclude that prior exercise training blunts the deleterious effect of short-term, high-fat feeding on whole body efficiency.     

Cutaneous vasoconstrictor response to whole body skin cooling is altered by time of day.

To test for a diurnal difference in the vasoconstrictor control of the cutaneous circulation, we performed whole body skin cooling (water-perfused suits) at 0600 (AM) and 1600 (PM). After whole body skin temperature (T(sk)) was controlled at 35 degrees C for 10 min, it was progressively lowered to 32 degrees C over 18-20 min. Skin blood flow (SkBF) was monitored by laser-Doppler flowmetry at three control sites and at a site that had been pretreated with bretylium by iontophoresis to block noradrenergic vasoconstriction. After whole body skin cooling, maximal cutaneous vascular conductance (CVC) was measured by locally warming the sites of SkBF measurement to 42 degrees C for 30 min. Before whole body skin cooling, sublingual temperature (T(or)) in the PM was significantly higher than that in the AM (P < 0.05), but CVC, expressed as a percentage of maximal CVC (%CVC(max)), was not statistically different between AM and PM. During whole body skin cooling, %CVC(max) levels at bretylium-treated sites in AM or PM were not significantly reduced from baseline. In the PM, %CVC(max) at control sites fell significantly at T(sk) of 34.3 +/- 0.01 degrees C and lower (P < 0.05). In contrast, in the AM %CVC(max) at control sites was not significantly reduced from baseline until T(sk) reached 32.3 +/- 0.01 degrees C and lower (P < 0.05). Furthermore, the decrease in %CVC(max) in the PM was significantly greater than that in AM at T(sk) of 33.3 +/- 0.01 degrees C and lower (P < 0.05). Integrative analysis of the CVC response with respect to both T(or) and T(sk) showed that the cutaneous vasoconstrictor response was shifted to higher internal temperatures in the PM. These findings suggest that during whole body skin cooling the reflex control of the cutaneous vasoconstrictor system is shifted to a higher internal temperature in the PM. Furthermore, the slope of the relationship between CVC and T(sk) is steeper in the PM compared with that in the AM.     

Predictable adaptations by skeletal muscle mitochondria to different exercise training workloads

1. Mitochondria were isolated according to their cellular location within the fibers of pooled gastrocnemius and plantaris muscle of the rat. This procedure yields two populations of mitochondria which display different biochemical properties. 2. The adaptive response of these mitochondria populations to the chronic exposure to different elevated energy demands (different modes of exercise training) was investigated. 3. The observed changes in mitochondrial protein content and cytochrome oxidase activity in the respective mitochondria population suggests that each population is capable of independent adaptations. 4. The adaptive response of each mitochondria population, furthermore, was predictable with respect to the metabolic energy demand of the exercise training workload.     

Effect of exercise training on insulin binding and glucose metabolism in mouse soleus muscle

Training stimulates glucose uptake and metabolism by muscles independent of a rise in serum glucose. Whether this increased insulin action is associated with enhanced insulin binding in muscles is unknown. We studied the effect of 6 weeks of treadmill running on insulin binding, uptake of 2-deoxy-D-glucose, glycolysis, and glycogenesis by the soleus muscle of Swiss Webster mice. Training was progressively increased. The in vitro studies using intact soleus preparations were done 48 h after the last exercise bout. Training increased insulin binding, insulin-stimulated uptake of 2-deoxy-D-glucose, and glycogenesis but not glycolysis in the soleus. Our data suggest that the enhanced glucose uptake and metabolism in muscles induced by exercise training are associated with an increase in insulin binding.