Significance of skeletal muscle properties on fitness, long-term physical training and serum lipids

Effects of endurance training on serum lipids

BACKGROUND AND AIMS

Physical activity is recommended as part of the lifestyle modification for the treatment of hyperlipidemia, however, the literature reports heterogeneous quantitative effects of exercise on serum lipids. We therefore reviewed the effects of aerobic exercise on serum lipids with special focus on the training effectiveness.

METHODS

Data regarding effects of endurance training (ET) on total Cholesterol (TC), LDL-Cholesterol (LDL-C), HDL-Cholesterol (HDL-C) and triglycerides (TG) were evaluated in a selective literature search. To account for the observed heterogeneity of the training interventions, studies were analyzed according to effectiveness (duration, intensity, frequency) of training.

RESULTS

Unselected training intervention studies did not exert significant effects on serum LDL-C but showed minor positive effects on HDL-C and TG. Effective endurance training - defined as endurance training performed by an intensity of 65-75% of the heart rate reserve (corresponding to 75-85% maximum heart rate or 65-80% VO_2max) for a duration of 40-50min per training unit on 3-4days/week over a period of 26-40weeks showed improvement of serum lipids. Effective training lowered TC by -3.75% (p=0.0006), LDL-C by -4.76% (p=0.0015), TG by -8.24% (p=0.0004) and increased HDL-C by +4.43% (p=0.0061).

CONCLUSION

The analysis suggests that a minimum exercise threshold is necessary to produce effects on serum lipids. Overall, the quantitative effect of physical activity on serum lipids is small.

The beneficial effects of aerobic and concurrent training on metabolic profile and body composition after detraining: a 1-year follow-up in postmenopausal women

BACKGROUND/OBJECTIVES

Aerobic and concurrent training (CT, aerobic and strength training) improves body composition and metabolic profile; however, it is not known whether these positive outcomes acquired after aerobic or CT are maintained long term (⩾6 months) after program interruption in postmenopausal women. This study investigated the changes in total and appendicular body composition, bone mineral density and metabolic profile following 16 weeks of aerobic or CT, and through 6 months and 1 year of detraining in postmenopausal women.

SUBJECTS/METHODS

In total, 60 postmenopausal women were divided into the following groups: aerobic (AT), aerobic plus strength training (CT) and control group (CG), and 31 participants were assessed for the 1 year follow-up. Body composition and bone mineral density were evaluated by dual-energy X-ray absorptiometry (DXA), and total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, triacylglycerol, glucose, insulin, leptin, adiponectin and plasminogen activator inhibitor-1 (PAI-1) were assessed.

RESULTS

There were main effects of time for arm fat mass, arm lean mass and trunk lean mass (P<0.05). There was a statistical difference between AT and CG for leg fat mass and percentage of fat (P<0.05). After 6 months of detraining, leg lean mass decreased in relation to post-intervention, and there was a statistically significant interaction for total and appendicular lean mass (P<0.05). There were differences between CT and CG in glucose and between AT and CG in glucose and triacylglycerol (P<0.05).

CONCLUSIONS

A duration of 16 weeks of aerobic or CT improved total and appendicular body composition and metabolic profile but after 6 months of detraining, leg lean mass returned to the values obtained pre-training in CT.

The low-fitness phenotype as a risk factor: more than just being sedentary?

Higher levels of fitness are associated with reduced risk of a wide variety of illnesses and chronic conditions. For cardiovascular disease (CVD) and many metabolic conditions, the fitness-morbidity/mortality curve is not linear but curvilinear, with lower levels of fitness being associated with significantly higher levels of risk compared to moderate and high levels of fitness. We have a very poor understanding of what the low fit phenotype represents as it is clearly more than just low physical activity levels. For example, there are likely some metabolic disadvantaged individuals with intrinsically low fitness and low oxidative capacity that are also prone to being sedentary due to easy fatigability. For these individuals, there exists a worse case scenario of a sedentary lifestyle superimposed on metabolically disadvantaged muscle resulting in the exaggerated CVD and metabolic risk. There is clearly a need for more work exploring the risk associated with low fitness and developing strategies to address the risk of low fitness. For example, we need to (i) define the mechanisms responsible for the exceptional risk associated with being low fit, (ii) identify best physical activity programs for reversing low fitness, (iii) examine whether exercise training nonresponders receive health benefits from exercise training despite the failure to improve fitness, and (iv) explore methods to identify individuals with the "low fit" phenotype without conducting a maximal exercise test. Individuals in the low fit category typically account for the majority of accumulated metabolic/CVD events, thus reducing this risk in this category would have substantial public health and clinical payoff.

Effect of intermittent hypoxic training on HIF gene expression in human skeletal muscle and leukocytes

Intermittent hypoxic exposure with exercise training is based on the assumption that brief exposure to hypoxia is sufficient to induce beneficial muscular adaptations mediated via hypoxia-inducible transcription factors (HIF). We previously demonstrated (Mounier et al. Med Sci Sports Exerc 38:1410-1417, 2006) that leukocytes respond to hypoxia with a marked inter-individual variability in HIF-1alpha mRNA. This study compared the effects of 3 weeks of intermittent hypoxic training on hif gene expression in both skeletal muscle and leukocytes. Male endurance athletes (n = 19) were divided into an Intermittent Hypoxic Exposure group (IHE) and a Normoxic Training group (NT) with each group following a similar 3-week exercise training program. After training, the amount of HIF-1alpha mRNA in muscle decreased only in IHE group (-24.7%, P < 0.05) whereas it remained unchanged in leukocytes in both groups. The levels of vEGF(121) and vEGF(165) mRNA in skeletal muscle increased significantly after training only in the NT group (+82.5%, P < 0.05 for vEGF(121); +41.2%, P < 0.05 for vEGF(165)). In leukocytes, only the IHE group showed a significant change in vEGF(165) (-28.2%, P < 0.05). The significant decrease in HIF-1alpha mRNA in skeletal muscle after hypoxic training suggests that transcriptional and post-transcriptional regulations of the hif-1alpha gene are different in muscle and leukocytes.

Modulation of apolipoprotein A1 and B, adiponectin, ghrelin, and growth hormone concentrations by plant sterols and exercise in previously sedentary humans

Plant sterols combined with exercise beneficially alter lipid levels in hypercholesterolemic adults. The effect of this combination therapy on other indicators of coronary heart disease risk, however, has yet to be determined. The objective of this trial was to investigate the effect of plant sterols and exercise, alone and in combination, on levels of apolipoprotein (apo) A1 and B, adiponectin, ghrelin, and growth hormone in previously sedentary hypercholesterolemic adults. In an 8 week, parallel-arm trial, 84 subjects were randomized to 1 of 4 groups: combination, exercise, plant sterols, or control. Body mass decreased by 1.1% (p < 0.01) and 0.9% (p < 0.05) in the combination and exercise group, respectively. Low-density lipoprotein cholesterol levels decreased (p < 0.01) by 0.30 mmol/L in the combination group and by 0.49 mmol/L in the plant sterol group. High-density lipoprotein cholesterol levels increased by 7.5% and 9.5% (p < 0.01) in the combination and exercise groups, respectively. Plant sterols increased (p < 0.05) adiponectin levels by 16%. No change in apoA1, apoB, ghrelin, or growth hormone levels were noted in any intervention group. ApoA1 was correlated with high-density lipoprotein cholesterol (r = 0.33, p = 0.01), whereas apoB was weakly related to low-density lipoprotein cholesterol levels (r = 0.13, p = 0.002). Adiponectin was associated with body mass index (r = -0.10, p = 0.006) and high-density lipoprotein cholesterol (r = 0.17, p = 0.0003). These findings suggest that plant sterols can increase adiponectin levels, thereby possibly reducing the risk of future coronary heart disease.

Lipids, lipoproteins, and peroxisome proliferator activated receptor-delta

Peroxisome proliferator activated receptors (PPARs) are nuclear receptors activated by small, lipophilic compounds. Typically resident on nuclear DNA, full activation requires heterodimer formation with retinoid X receptor and ligand binding, leading to modulation in the expression of hundreds of genes. Of the 3 described forms, (PPAR-alpha, PPAR-gamma, and PPAR-delta), PPAR-delta has been the least investigated. Preclinical in vitro data show that activation of PPAR-delta, like PPAR-alpha, results in enhancement of fatty acid oxidation, leading to increased energy production in the form of adenosine triphosphate and of energy uncoupling. Microarray data in preclinical models suggest substantial PPAR-delta expression in skeletal muscle. Exercise, which induces upregulation of PPAR-delta in muscle tissue, leads to an increased requirement for an external or serum derived triacylglycerol energy source. This suggests that upregulation of skeletal muscle PPAR-delta would influence lipoprotein composition, this being the major source of combustible substrate. In the first human study using a PPAR-delta agonist, experimental data obtained with GW 501516 (a highly specific PPAR-delta agonist) suggested that upregulated enzymes critical to fatty acid oxidation in human cells enhanced fatty acid and beta-oxidation in skeletal muscle.

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.

METHODS

To quantify interactions among cellular and skeletal muscle metabolic adaptations, and to predict metabolic responses to exercise after periods of altered loading states, we develop a computational model of skeletal muscle metabolism. The governing model equations - with parameters characterizing chronic loading/unloading states- were solved numerically to simulate metabolic responses to moderate intensity exercise (WR < or = 40% VO2 max).

RESULTS

Model simulations showed that carbohydrate oxidation was 8.5% greater in chronically unloaded muscle compared with the loaded muscle (0.69 vs. 0.63 mmol/min), while fat oxidation was 7% higher in chronically loaded muscle (0.14 vs. 0.13 mmol/min), during exercise. Muscle oxygen uptake (VO2) and blood flow (Q) response times were 29% and 44% shorter in chronically loaded muscle (0.4 vs. 0.56 min for VO2 and 0.25 vs. 0.45 min for Q).

CONCLUSION

The present model can be applied to test complex hypotheses during exercise involving the integration and control of metabolic processes at various organizational levels (cellular to tissue) in individuals who have undergone periods of chronic loading or unloading.

Exercise training reverses downregulation of HSP70 and antioxidant enzymes in porcine skeletal muscle after chronic coronary artery occlusion

Oxidative stress is associated with muscle fatigue and weakness in skeletal muscle of ischemic heart disease patients. Recently, it was found that endurance training elevates protective heat shock proteins (HSPs) and antioxidant enzymes in skeletal muscle in healthy subjects and antioxidant enzymes in heart failure patients. However, it is unknown whether coronary ischemia and mild infarct without heart failure contributes to impairment of stress proteins and whether exercise training reverses those effects. We tested the hypothesis that exercise training would reverse alterations in muscle TNF-α, oxidative stress, HSP70, SOD (Mn-SOD, Cu,Zn-SOD), glutathione peroxidase (GPX), and catalase (CAT) due to chronic coronary occlusion of the left circumflex (CCO). Yucatan swine were divided into three groups ( n = 6 each): sedentary with CCO (SCO); 12 wk of treadmill exercise training following CCO (ECO); and sham surgery controls (sham). Forelimb muscle mass-to-body mass ratio decreased by 27% with SCO but recovered with ECO. Exercise training reduced muscle TNF-α and oxidative stress (4-hydroxynonenal adducts) caused by CCO. HSP70 levels decreased with CCO (−45%), but were higher with exercise training (+348%). Mn-SOD activity, Mn-SOD protein expression, and Cu,Zn-SOD activity levels were higher in ECO than SCO by 72, 82, and 112%, respectively. GPX activity was 177% greater in ECO than in SCO. CAT trended higher ( P = 0.059) in ECO compared with SCO. These data indicate that exercise training following onset of coronary artery occlusion results in recovery of critical stress proteins and reduces oxidative stress.

Triglyceride:high-density lipoprotein cholesterol effects in healthy subjects administered a peroxisome proliferator activated receptor delta agonist

OBJECTIVE

Exercise increases fatty acid oxidation (FAO), improves serum high density lipoprotein cholesterol (HDLc) and triglycerides (TG), and upregulates skeletal muscle peroxisome proliferator activated receptor (PPAR)delta expression. In parallel, PPARdelta agonist-upregulated FAO would induce fatty-acid uptake (via peripheral lipolysis), and influence HDLc and TG-rich lipoprotein particle metabolism, as suggested in preclinical models.

METHODS AND RESULTS

Healthy volunteers were allocated placebo (n=6) or PPARdelta agonist (GW501516) at 2.5 mg (n=9) or 10 mg (n=9), orally, once-daily for 2 weeks while hospitalized and sedentary. Standard lipid/lipoproteins were measured and in vivo fat feeding studies were conducted. Human skeletal muscle cells were treated with GW501516 in vitro and evaluated for lipid-related gene expression and FAO. Serum TG trended downwards (P=0.08, 10 mg), whereas TG clearance post fat-feeding improved with drug (P=0.02). HDLc was enhanced in both treatment groups (2.5 mg P=0.004, 10 mg P<0.001) when compared with the decrease in the placebo group (-11.5+/-1.6%, P=0.002). These findings complimented in vitro cell culture results whereby GW501516 induced FAO and upregulated CPT1 and CD36 expression, in addition to a 2-fold increase in ABCA1 (P=0.002). However, LpL expression remained unchanged.

CONCLUSIONS

This is the first report of a PPARdelta agonist administered to man. In this small study, GW501516 significantly influenced HDLc and TGs in healthy volunteers. Enhanced in vivo serum fat clearance, and the first demonstrated in vitro upregulation in human skeletal muscle fat utilization and ABCA1 expression, suggests peripheral fat utilization and lipidation as potential mechanisms toward these HDL:TG effects.

Effect of physical activity and muscle morphology on endothelial function and arterial stiffness

Physically active persons have a reduced risk of atherosclerotic disease. Arterial stiffness and endothelial dysfunction are important risk factors for cardiovascular disease. A high proportion of type I (slow-twitch) muscle fibers in skeletal muscle is associated with a favorable cardiovascular risk profile. We tested physical activity and muscle fiber-type distribution as determinants of endothelial function and arterial stiffness in middle-aged men. Fifty-four men (median age 58) who underwent a muscle biopsy in 1984 were re-studied in 2003. Aortic pulse wave velocity (PWV) and pulse wave reflection were assessed by applanation tonometry. Endothelial function was tested by examining the effects of salbutamol and nitroglycerin on pulse wave reflection. In multiple regression analyses aortic PWV (R2=0.51) correlated positively with age (P=0.017), BMI (P=0.001), and systolic blood pressure (P=0.004). A high augmentation index (R2=0.33) was associated with smoking (P<0.001), high LDL cholesterol (P=0.02), and elevated diastolic blood pressure (P=0.03). Impaired endothelial function (R2=0.37) was associated with high age (P=0.04), high LDL cholesterol (P=0.017), high triglycerides (P=0.027), and high physical activity (P=0.005). Muscle fiber-type distribution is not a determinant of arterial stiffness or endothelial function. Impaired endothelial function was observed in physically active men, underlining the need for further research.

Muscle fiber-type distribution as a predictor of blood pressure: a 19-year follow-up study

The known association between physical activity and low blood pressure may be influenced by inherited characteristics. Skeletal muscle consists of type I (slow-twitch) and type II (fast-twitch) muscle fibers, with proportions highly variable between individuals and mostly determined by genetic factors. A high percentage of type I fibers (type I%) has been associated with low blood pressure in cross-sectional studies. We investigated whether type I percentage predicts future blood pressure levels and explains part of the association between physical activity and blood pressure. At baseline, in 1984, muscle fiber-type distribution, physical activity, and body mass index (BMI) were determined in 64 healthy men (age, 32 to 58 years). At follow-up, in 2003, blood pressure, physical activity, and BMI were determined in these men. In subjects without antihypertensive medication (n=43), type I percentage accounted for 5%/18% of the variation in systolic/diastolic blood pressure. A high type I percentage predicted, independent of both baseline (in 1984) and follow-up (in 2003), physical activity, BMI, and low systolic and diastolic blood pressure. Adjusted for all baseline covariates, a 20-unit higher type I percentage predicted a 11.6-mm Hg lower systolic blood pressure (P=0.018) and a 5.0-mm Hg lower diastolic blood pressure (P=0.018). High levels of physical activity in 1984 predicted low diastolic blood pressure, but this association was lost when type I percentage was included into the model. A high proportion of type I fibers in skeletal muscle is an independent predictor of low blood pressure and explains part of the known association between high levels of physical activity and low blood pressure.

Do blood cells mimic gene expression profile alterations known to occur in muscular adaptation to endurance training ?

Exercise is known to upregulate mRNA synthesis for carnitine palmitoyl transferase1 (CPT1) and possibly also other mitochondrial carnitine acyltransferases in muscle tissue. The aim of this study was to test whether such an adaptation of oxidative metabolism in skeletal muscle is a systemic process and consequently, also affects other cells. Messenger RNA levels of five genes [carnitine palmitoyl transferases 1 and 2 (CPT1 and CPT2), carnitine acetyltransferase (CRAT), carnitine palmitoyltransferase 2 (CPT2), microsomal carnitine palmitoyltransferase (GRP58) and organic cation transporter (OCTN2)] were determined with quantitative real time polymerase chain reaction (PCR) in blood cells and in muscle biopsy samples from six cross country skiers before and 6 months after a high volume/low intensity exercise training, when training had elicited a significantly slower rate of lactate accumulation. Quantitative real time PCR showed that levels of mRNA in blood cells correlated significantly (CPT1B: P< 0.001) with those in muscle tissue from the same donors. After 6-months training, there was a 15-fold upregulation of CPT1B mRNA, a six to ninefold increase of CRAT mRNA, of CPT2 mRNA, GRP58 mRNA, and of OCTN2 mRNA. The observation of a concordant stimulation of CPT1, CPT2, CRAT, GRP58 and OCTN2 transcription in blood cells and muscle tissue after 6-month-endurance training leads the hypothesis of a common stimulation mechanism other than direct mechanical stress or local chemical environment, but rather humoral factors.

Glutathione: its implications for animal health, meat quality, and health benefits of consumers

There has been an increasing focus on the role of antioxidants for human health. This review outlines associations of the most predominant antioxidant, glutathione (GSH), in the body and some ageing-related diseases. Strategies to replete GSH, particularly developing animal-source food products, are discussed. Potentials to alter GSH content in the animal’s body and its possible effects on health are also explored.

Training and detraining effects of a combined-strength and aerobic exercise program on blood lipids in patients with coronary artery disease

PURPOSE

The aim of this study was to investigate training and detraining effects on blood lipids and apolipoproteins induced by a specific program that combined strength and aerobic exercise in patients with coronary artery disease (CAD).

METHODS

For this study, 14 patients participated in a supervised 8-month training program composed of two strength sessions (60% of 1 repetition maximum) and two aerobic training sessions (60%-85% of maximum heart rate), and 13 patients served as a control group. Blood samples for total cholesterol (TC), triglycerides (TG), high-density lipoprotein cholesterol (HDL-C), apolipoproteins A1 (apo-A1) and B (apo-B), and lipoprotein (a) (Lp[a]) were obtained along with muscular strength at the beginning of the study, after 4 and 8 months of training and after 3 months of detraining.

RESULTS

The patients in the intervention group showed favorable alterations after 8 months of training (TC, -9.4; TG, -18.6; HDL-C, 5.2; apo-A1, 11.2%; P <.05), but these were reversed after 3 months of detraining (TC, +3.7; TG, 16.1; HDL-C, -3.6; apo-A1, -5.5%). In addition, body strength also improved after training (27.8%) but reversed (-12.9%) after detraining (P <.05). The patients in the control group did not experience any significant alterations.

CONCLUSIONS

The results indicate that an 8-month training program combining strength and aerobic exercise induces favorable muscular and biochemical adaptations, on TC, TG, HDL-C, and apo-A1 levels, protecting patients with CAD. After 3 months of detraining, however, the favorable adaptations were reversed, underscoring the need of uninterrupted exercise throughout life.

Effects of low intensity aerobic training on skeletal muscle capillary and blood lipoprotein profiles

The effects of low intensity endurance training on skeletal muscle capillary density and serum lipoprotein levels were studied in 11 non-obese men (18-25 years). The subjects performed a 6-week training regimen (60 min, 5 times per week) at the lactate threshold (LT). Capillary density was determined in biopsy specimens obtained from the vastus lateralis muscle before and after the training. The number of capillaries per fiber (cap/fiber ratio) before training was 1.97 +/- 0.47, and increased to 2.49 +/- 0.69 after training (p < 0.05). The maximal oxygen uptake (VO2 max) and LT- VO2 increased significantly by 5% (p < 0.01) and 27% (p < 0.01), respectively, whereas no change was observed in body weight. Low density lipoprotein cholesterol (LDL-C) tended to decrease (p = 0.06). The change in the cap/fiber ratio correlated inversely with the change in the ratio of LDL-C to high density lipoprotein cholesterol (HDL-C) (r = -0.61, p < 0.05). It was also, positively associated with the change in HDL2-C (r = 0.82, p < 0.01) and inversely associated with the change in HDL3-C (r = -0.63, p < 0.05). The change in LT- VO2 was inversely associated with the change in LDL-C (r = -0.62, r < 0.05). These results indicate that low intensity training increases capillary density in skeletal muscle, which may explain in part the changes in the lipoprotein profiles.

Effect of resistance exercise on postprandial lipemia

The purpose of this study was to examine the effect of resistance exercise on postprandial lipemia. Fourteen young men and women participated in each of three treatments: 1) control (Con), 2) resistance exercise (RE), and 3) aerobic exercise (AE) estimated to have an energy expenditure (EE) equal that for RE. Each trial consisted of performing a treatment on day 1 and ingesting a fat-tolerance test meal 16 h later (day 2). Resting metabolic rate and fat oxidation were measured at baseline and at 3 and 6 h postprandial on day 2. Blood was collected at baseline and at 0.5, 1, 2, 3, 4, 5, and 6 h after meal ingestion. RE and AE were similar in EE [1.7 +/- 0.1 vs. 1.6 +/- 0.1 (SE) MJ, respectively], as measured by using the Cosmed K4b(2). Baseline triglycerides (TG) were significantly lower after RE than after Con (19%) and AE (21%). Furthermore, the area under the postprandial response curve for TG, adjusted for baseline differences, was significantly lower after RE than after Con (14%) and AE (18%). Resting fat oxidation was significantly greater after RE than after Con (21%) and AE (28%). These results indicate that resistance exercise lowers baseline and postprandial TG, and increases resting fat oxidation, 16 h after exercise.

Exercise training and blood lipids in hyperlipidemic and normolipidemic adults: a meta-analysis of randomized, controlled trials

OBJECTIVE

To determine the effectiveness of exercise training (aerobic and resistance) in modifying blood lipids, and to determine the most effective training programme with regard to duration, intensity and frequency for optimizing the blood lipid profile.

DESIGN

Trials were identified by a systematic search of Medline, Embase, Science Citation Index (SCI), published reviews and the references of relevant trials. The inclusion criteria were limited to randomized, controlled trials of aerobic and resistance exercise training which were conducted over a minimum of four weeks and involved measurement of one or more of the following: total cholesterol (TC), high density lipoprotein (HIDL-C), low density lipoprotein (LDL-C) and triglycerides (TG).

SUBJECTS

A total of 31 trials ( 1833 hyperlipidemic and normolipidemic participants) were included.

RESULTS

Aerobic exercise training resulted in small but statistically significant decreases of 0.10 mmol/L (95% CI: 0.02, 0.18). 0.10 (95% CI: 0.02, 0.19), 0.08 mmol/L (95% CI: 0.02, 0.14), for TC, LDL-C, and TG, respectively, with an increase in HDL-C of 0.05 mmol/L (95% CI: 0.02, 0.08). Comparisons between the intensities of the aerobic exercise programmes produced inconsistent results; but more frequent exercise did not appear to result in greater improvements to the lipid profile than exercise three times per week. The evidence for the effect of resistance exercise training was inconclusive.

CONCLUSIONS

Caution is required when drawing firm conclusions from this study given the significant heterogeneity with comparisons. However, the results appear to indicate that aerobic exercise training produced small but favourable modifications to blood lipids in previously sedentary adults.