Biochemical Adaptations to Endurance Exercise in Skeletal Muscle

Exercise training and changes in skeletal muscle mitochondrial proteins: from blots to "omics"

Mitochondria are essential, membrane-enclosed organelles that consist of ∼1100 different proteins, which allow for many diverse functions critical to maintaining metabolism. Highly metabolic tissues, such as skeletal muscle, have a high mitochondrial content that increases with exercise training. The classic western blot technique has revealed training-induced increases in the relatively small number of individual mitochondrial proteins studied (∼5% of the >1100 proteins in MitoCarta), with some of these changes dependent on the training stimulus. Proteomic approaches have identified hundreds of additional mitochondrial proteins that respond to exercise training. There is, however, surprisingly little crossover in the mitochondrial proteins identified in the published human training studies. This suggests that to better understand the link between training-induced changes in mitochondrial proteins and metabolism, future studies need to move beyond maximizing protein detection to adopting methods that will increase the reliability of the changes in protein abundance observed.

[Mitochondrial biogenesis in hereditary optic neuropathies]

The article offers a review of mitochondrial biogenesis in hereditary optic neuropathies. It covers the mechanisms of mitochondrial biogenesis, factors affecting it and tools for mitochondrial turnover assessment.

Mitochondrial biogenesis in striated muscle

Mitochondrial biogenesis (synthesis) has been observed to occur in skeletal muscle in response to chronic use. It also occurs in cardiac muscle during growth and hypertrophy, and it may be impaired during the aging process. This review summarizes the literature on the processes of mitochondrial biogenesis at the biochemical and molecular levels, with particular reference to striated muscles. Mitochondrial biogenesis involves the expression of nuclear and mitochondrial genes and the coordination of these two genomes, the synthesis of proteins and phospholipids and their import into the organelle, and the incorporation of these lipids and proteins into their appropriate locations within the matrix, inner or outer membranes. The emphasis is on the regulation of these events, with information derived in part from other cellular systems. Although descriptions of mitochondrial content changes in heart and skeletal muscle during altered physiological states are plentiful, much work is needed at the molecular level to investigate the regulatory processes involved. A knowledge of biochemical and molecular biology techniques is essential for continued progress in the field. This is a promising area, and potential new avenues for future research are suggested.

Mitochondrial actaptations to chronic muscle use: Effect of iron deficiency

1. The effects of chronic muscle use on mitochondrial structure, enzymes and gene expression is reviewed. The role of iron deficiency in modulating this adaptation is discussed. 2. Chronic muscle use and disuse alter mitochondrial composition and affect mitochondrial subpopulations differentially. This has implications for an understanding of organelle assembly. 3. Iron deficiency decreases mitochondrial functional mass within muscle by reducing the level of heme and non-heme iron-containing components. This alters the metabolic response during exercise and results in a reduced endurance performance. 4. Both iron deficiency and chronic muscle use represent contrasting experimental models for the study of mitochondrial function and biogenesis.

Comparative analysis of myocardial enzyme activities of the energy-supplying metabolism in patients with dilative cardiomyopathies and valve diseases

We determined representative enzyme activities of glycogenolysis (glycogen phosphorylase) glycolysis (d-glyceraldehyde-3-phosphate dehydrogenase, GAPDH), beta oxidation of free fatty acids (1-3-hydroxyacyl CoA dehydrogenase, HADH), citric acid cycle (citrate synthase, CS), lactate fermentation (lactate dehydrogenase LDH), and creatine phosphate metabolism (creatine kinase, CK) in left ventricular samples of 36 patients to investigate if the metabolic capacities of the energy-supplying pathways are differently affected in different heart diseases. There were 17 patients with mitral valve diseases (MVD), 8 patients with aortic valve diseases (AVD), and 11 patients who suffered from dilative cardiomyopathies (DCM). The main metabolic characteristic on the level of enzymatic organization in patients with DCM was an increased ratio of GAPDH/HADH activities and a decreased ratio of HADH/CS activities compared to the valve-diseased patients. This result indicates that the capacity of glucose oxidation is enhanced at the expense of fatty acid metabolism in patients with DCM. Furthermore, we determined significantly lower myocardial CK activities in this group of patients, most probably reflecting a diminished content of myofibrils. Citrate synthase activity was lowest in patients with AVD. Although we cannot rule out that the impaired left ventricular function is in part responsible for the shift of the capacities of the energy-supplying metabolism in patients with DCM, we favor the assumption that it is a specific feature of this myocardial disease.

The effect of physical training in elderly subjects with special reference to energy-rich phosphagens and myoglobin in leg skeletal muscle

Energy-rich phosphagens and myoglobin were determined in leg skeletal muscles of seven, 61- to 80-year-old, apparently healthy male subjects. The study repeated after the participants had been exercising on an ergometer bicycle twice weekly for 6 weeks. Before training, myoglobin and all intramuscular energy-rich phosphagens were within the range recorded for a larger series of subjects of similar age. When re-examined after training the myoglobin level remained the same but creatine decreased significantly and the ratio between phosphocreatine and total creatine increased. A slight but significant rise was also observed for the ATP/ADP ratio. It is concluded that age-related changes of intramuscular phosphagens in elderly subjects in part might be due to physical inactivity.

Electro- and echocardiographic study of the left ventricle in man after training

Fourteen sedentary middle-aged men underwent a chest X-ray, a 12 lead ECG, a VCG, and an echocardiographic examination prior to and following 5 months of training a moderately severe intensity, on a cycle ergometer. No modification in the X-ray cardiac profile was observed following training. Some electrocardiographic (R wave amplitude in V5 and V6 and Sokolow index: SV1 + RV5 or V6) and vectorcardiographic (maximal QRS vector amplitude, maximal spatial QRS vector, and R wave amplitude) indices of left ventricular hypertrophy were slightly but significantly increased following training. The echocardiographic measurements in diastole (septal and posterior wall thickness, left ventricular internal diameter, and left ventricular mass) were unchanged after training. Results suggest that electrical changes may not provide adequate indications of left ventricular morphological modifications. The lack of echocardiographic evidences of left ventricular hypertrophy suggest that: (1) training does not necessarily induce left ventricular hypertrophy; (2) the large heart sometimes observed in athletes may be the result of a genetic factor or of a prolonged and very intensive training pursued since a very young age, over a number of years; and (3) left ventricular enlargement probably plays a minor role in the increase in aerobic capacity following training.

Specificity of metabolic and circulatory responses to arm or leg interval training

The purpose of this study was to evaluate metabolic and circulatory responses to interval training of legs or arms during steady-state, submaximal cycling. 15 college males cycled on a bicycle ergometer twice with arms (63 and 83 W) and twice with legs (100 and 125 W) before and following 5 weeks of daily interval training. Seven subjects trained with arm cycling and eight with leg cycling. Significant post-training decreases in submaximal oxygen consumption (VO2), heart rate (HR), and venous blood lactate (LA(V)) were noted when cycling with trained and untrained muscles with the magnitude of change significantly greater with trained muscles. These results indicate metabolic and circulatory adaptations to interval training that are mediated centrally and peripherally. With respect to HR, but not VO2, training a larger muscle mass (legs) produced a greater central but lesser peripheral effect whereas the opposite was true for the smaller arm muscles. The data also suggested that the peripheral adaptation involves a common mechanism controlling both HR and LA(V)) changes with a separate mechanism controlling VO2.

Capillary supply of the muscle fibre population in hindlimb muscles of the cat

Comparative analyses of the fibre content (FG, FOG, and SO fibres) and the capillary density (the number of capillaries surrounding individual fibres and the capillary/fibre ratio) were performed in hind limb muscles of the cat. Cross-sections from the tenuissimus, the biceps femoris, the lateral head (LG) and the medial head (MG) of the gastrocnemius and the soleus were cut in a cryostat. The sections were stained histochemically for the NADH2-diaphorase and alkaline (pH 9.4) actomyosin ATPase activity, which enables differentiation of different types of fibres. The endothelium of the capillaries was identified via staining for unspecific alkaline ATPase activity. The number of capillaries surrounding each individual muscle fibre had a positive correlation, first to the oxidative capacity and secondly to the average diameter of the fibres. The thin tenuissimus muscle did not differ in this respect from the thicker muscles. The highest proportion of SO fibres was found in the soleus and the MG muscles. FG fibres of two different types were dominating the fibre mass in the biceps femoris and the LG muscles, while the tenuissimus contained more FOG fibres than these muscles. In general the FG fibres had a larger diameter than the FOG and the SO fibres. The soleus and the MG muscles contained larger fibres than the other examined muscles. FG fibres were surrounded by fewer capillaries than FOG and SO fibres. The soleus and the MG muscles, with a higher percentage of SO fibres and also larger fibres, had the largest number of capillaries around the fibres and the highest capillary/fibre ratio.

Effect of endurance training on the capacity of red and white skeletal muscle of mouse to oxidize carboxyl-14C-labelled palmitate

Three groups of mice were trained for 1, 4 and 5 months according to different running programs on a motor driven treadmill and the fatty acid oxidation capacity (FAO) and the activities of some enzymes of energy metabolism (cytochrome c oxidase, malate dehydrogenase, triosephosphate dehydrogenase, and lactate dehydrogenase) were determined from m. quadriceps femoris (MQF). Endurance training increased the FAO [5-month training 4 days/week, 30 min/day 22% (p less than 0.05); 1-month training, 7 days/week, 150 min/day 37% (p less than 0.001); 4-month training, 5 days/week, 60 min/day 24% (p less than 0.05)]. The activities of cytochrome c oxidase and malate dehydrogenase increased approx. 30% (p less than 0.001) whereas triosephosphate dehydrogenase and lactate dehydrogenase activities were not prominently influenced by training. The predominantly red part of MQF of untrained animals oxidized palmitate four times faster than the predominantly white part. The activities of cytochrome c oxidase and malate dehydrogenase were two times higher showing pronounced FAO in the red part. Endurance training increased the FAO and activities of oxidative enzymes in the red and white parts and in the whole muscle relatively equally resulting in similar differences between the muscle types after training. The absolute increase in the FAO of the red muscle was, however, manyfold when compared in chemical units to the white muscle.

Quantitative measures of enzyme activities in type I and type II muscle fibres of man after training

The effect of 7 to 8 weeks of physical training on oxidative and glycolytic enzyme activities in the 2 major fibre types of human quadriceps femoris muscle has been investigated. 2 groups of 4 and 5 subjects respectively were trained at the same total work-load on a bicycle ergometer 3 days per week using interval exercise with maximal intensity (I.T.) or continuous exercise with submaximal intensity (C.T.). Succcinate dehydrogenase (SDH) and phosphofructokinase (PFK) activities were determined on crude homogenates of muscle biopsy samples and on pools of type I and type II fibres dissected from freeze-dried samples taken before and after training. Crude homogenate SDH activity increased to the same extent in both groups, average increases were 27.5% (I.T.) and 22% (C.T.) respectively. Only type I-SDH increased in the C.T. group (p less than 0.01), the average increase being 32%. On the other hand only type II-SDH increased in the I.T. group (p less than 0.01), with an average increase of 49%. No changes in PFK activity could be detected. The results of the present study emphasize the great adaptability in oxidative potential of both the two major human skeletal muscle fibre types and further that this adaptation seems to be related to the pattern of fibre recruitment during exercise.

Human muscle fiber types in power lifters, distance runners and untrained subjects

Muscle biopsies were taken from the vastus lateralis of 12 males: 5 control subjects, 4 power lifters and 3 distance runners. Three fiber "types" were distinguished by comparing serial sections for alkaline myofibrillar adenosine triphosphatase (ATPase) and succinic dehydrogenase (SDH) activities: 1. high ATPase and low SDH; fast-twitch-glycolytic (FG). 2. High ATPase and high SDH; fast-twitch-oxidative-glycolytic (FOG). 3. Low ATPase and high SDH; slow-twitch-oxidative (SO). In some cases the distinction between the FOG and FG classess was not clear and a group termed "transitional" was employed. A variation in percentage of fiber types and fiber area was found among individuals. The percentage of SO fibers varied from 19.6-60.1% within all 3 groups, with a mean of 40.5%. In the control group approximately 75% of the fibers were oxidative (FOG + SO). The major characteristics of the lifters were a decrease in the percentage of FOG fibers and a hypertrophy of FOG and FG fibers. The distance runners had a high percentage of oxidative fibers with few FG fibers. It is suggested that the fast-twitch fibers are mainly involved in the adaptation of muscle to exercise since the percentage of SO fibers varies greatly among individuals within and between the 3 groups studied.

Physical performance capacity of children in Norway. Part IV. The rate of growth in maximal aerobic power and the influence of improved physical education of children in a rural community - population parameters in a rural community

During a period of 4 years the annual increase of the physical performance of 31 boys and 34 girls was examined in a longitudinal study. In spite of the expected mean increase of the physical performance unsystematic annual variations of the increase of the maximal oxygen uptake related to body weight were observed. These variations can only be explained by the variations of the daily physical activity. The fact that in the longitudinal study a clear better performance over the years was observed than in a cross sectional study which was performed in the first year of the longitudinal study confirms this tendency. This can partly be explained by the improvement of the possibilities for physical activities in the community since the begin of the longitudinal study.

[Changes in serum proteins,-iron and -copper in swimmers before and after altitude training (author's transl)]

Fifteen male swimmers (mean age 19.3 +/- 2.1 years) were subjected to a standard 120 min swimming exercise test: a) before, and b) after 5 weeks of intensive training at middle altitude (2000 m). At rest, serum levels of alpha2-macroglobulin, transferrin and copper were elevated in swimmers as compared to untrained subjects. After the altitude training program, significant increases of the parameters of iron and copper metabolism, as well as of alpha2HS-glycoprotein and beta1A-globulin were observed. After the first exercise test (a), a significant rise in serum alpha1-acid glycoprotein, alpha1-antitrypsin, hemopexin, alpha2-macroglobulin, ceruloplasmin, transferrin, iron, copper and alpha2-HS-glycoprotein was noted. The same 120 min-exercise test after the altitude training (b) led to only small changes, especially as concerns the parameters of iron metabolism. The characteristic immediate and long-lasting changes in serum proteins and heavy metals in swimmers and the effects of training in middle altitude on the answer of the organism to swimming exercise with respect to the mentioned biochemical parameters are discussed.

Maximal steady state versus state of conditioning

Criteria for the identification of maximal steady state as related to state of conditioning were evaluated. 13 volunteers walker and/or ran during a series of 15 min tests on a treadmill. The speeds ranged from mild to exhaustive. Heart rate was monitored continuously; VO2 was determined from 6 min to 9 min; and venous blood was obtained at 10 min and 15 min for lactate analyses. Max VO2 was established for each subject. Subjects were classified on level of conditioning according to the quantity and quality of their activity record for the previous 6 months. The 10 min heart rate associated with a blood lactate level of 2.2 mM/L (MSSHR) was the best predictor of conditioning. The relative VO2 (% of max VO2) found with a 10 min blood lactate concentration of 2.2 mM/L (RMSSVO2) was almost as accurate as MSSHR in predicting state of conditioning. Changes in blood lactate levels between 10 min and 15 min were not significantly related to conditioning.

The effect of naftidrofuryl on the metabolic response to exercise in man

We have designed this investigation to determine whether naftidrofuryl has an effect upon metabolism in vivo in man. Five subjects were studied during and after steady exercise on a bicycle ergometer. On the first occasion they received naftidrofuryl (300 mg orally) 20-40 min before exercise; and on the second they exercised without the drug to provide control observations. Blood samples were taken for the estimation of glucose, pyruvate, lactate, glycerol, acetoacetate and 3-hydroxybutyrate. Exercise with naftidrofuryl caused a significantly greater rise in blood pyruvate concentration during the exercise and post-exercise period compared with the controls. Changes in glucose, lactate, glycerol and ketone-bodies were not significantly different from the control values. Lactate/pyruvate ratios were significantly reduced with naftidrofuryl during the post-exercise period. Exercise causes a rise in intracellular anaerobic metabolism with associated increases in blood lactate/pyruvate ratios. This is followed by enhanced oxidative capacity during the recovery period as adduced from falling lactate/pyruvate ratios. The greater decline in lactate/pyruvate ratios with naftidrofuryl during the post-exercise period is evidence that naftidrofuryl is able to enhance cellular oxidative activity in vivo in man. Further studies in clinical situations are therefore indicated.

Blood flow and tissue -pO2 in the trained and untrained gastrocnemius muscle of the anesthetized guinea pig

In 10 guinea pigs the gastrocnemius muscles on one side were tenotomised. By the tenotomy the daily work load of the gastorcnemius muscle was lowered in the operated leg ("untrained muscles") and increased in the control leg ("trained muscles"). Before and several weeks after the operation blood flow was measured in the lower legs (by segmental plethysmography) and oxygen pressure was measured in the gastrocnemius muscles (by micro-Pt-electrodes) of the anesthetized animals. 4 to 6 weeks after the operation statistically significant differences between the two extermities were noted: In the operated leg the mean pO2-value was 33%lower (P is less than 0.001) and the mean blood flow value 46% higher (P is less than 0.001). These differences could be explained by a reduced number of perfused capillaries in the untrained muscles (= non uniform blood flow distribution).