Effects of endurance training status and sex difference on Na+, K+-pump mRNA expression, content and maximal activity in human skeletal muscle

Aim: This study investigated the effects of endurance training status and sex differences on skeletal muscle Na⁺,K⁺-pump mRNA expression, content and activity. Methods: Forty-five endurance-trained males (ETM), 11 recreationally active males (RAM), and nine recreationally active females (RAF) underwent a vastus lateralis muscle biopsy. Muscle was analysed for Na⁺,K⁺-pump α1, α2, α3, β1, β2 and β3 isoform mRNA expression (real-time reverse transcription-polymerase chain reaction), content ([³H]-ouabain-binding site) and maximal activity (3-O-methylfluorescein phosphatase, 3-O-MFPase). Results: ETM demonstrated lower α1, α3, β2 and β3 mRNA expression by 74%, 62%, 70% and 82%, respectively, than RAM (P < 0.04). In contrast, [³H]-ouabain binding and 3-O-MFPase activity were each higher in ETM than in RAM, by 16% (P < 0.03). RAM demonstrated a 230% and 364% higher α3 and b3 mRNA expression than RAF, respectively (P < 0.05), but no significant sex differences were found for α1, α2, β1 or β2 mRNA, [³H]-ouabain binding  or 3-O-MFPase activity. No significant correlation was found between years of endurance training and either [³H]-ouabain binding or 3-O-MFPase activity. Significant but weak correlations were found between the number of training hours per week and 3-O-MFPase activity (r = 0.31, P < 0.02) and between incremental exercise V O_2(peak) and both   [³H]-ouabain binding (r = 0.33, P < 0.01) and 3-O-MFPase activity (r = 0.28, P < 0.03). Conclusions: Isoform-specific differences in Na⁺,K⁺-pump mRNA expression were found with both training status and sex differences, but only training status influenced Na⁺,K⁺-pump content and maximal activity in human skeletal muscle.

UCP3 protein expression is lower in type I, IIa and IIx muscle fiber types of endurance-trained compared to untrained subjects

Uncoupling protein 3 (UCP3) is a muscle mitochondrial protein believed to uncouple the respiratory chain, producing heat and reducing aerobic ATP production. Our aim was to quantify and compare the UCP3 protein levels in type I, IIa and IIx skeletal muscle fibers of endurance-trained (Tr) and healthy untrained (UTr) individuals. UCP3 protein content was quantified using Western blot and immunofluorescence. Skeletal muscle fiber type was determined by both an enzymatic ATPase stain and immunofluorescence. UCP3 protein expression measured in skeletal muscle biopsies was 46% lower ( P=0.01) in the Tr compared to the UTr group. UCP3 protein expression in the different muscle fibers was expressed as follows; IIx>IIa>I in the fibers for both groups ( P<0.0167) but was lower in all fiber types of the Tr when compared to the UTr subjects ( P<0.001). Our results show that training status did not change the skeletal muscle fiber hierarchical UCP3 protein expression in the different fiber types. However, it affected UCP3 content more in type I and type IIa than in the type IIx muscle fibers. We suggest that this decrease may be in relation to the relative improvement in the antioxidant defense systems of the skeletal muscle fibers and that it might, as a consequence, participate in the training induced improvement in mechanical efficiency.

Effects of aerobic training on pyruvate dehydrogenase and pyruvate dehydrogenase kinase in human skeletal muscle

This study examined the effects of short- and long-term aerobic training on the stable up-regulation of pyruvate dehydrogenase (PDH) and PDH kinase (PDK) in human skeletal muscle. We hypothesized that 8 weeks, but not 1 week, of aerobic training would increase total PDH (PDHt) and PDK activities compared to pretraining, and this would be detectable at the level of gene transcription (mRNA) and/or gene translation (protein). Resting muscle biopsies were taken before and after 1 and 8 weeks of aerobic cycle exercise training. PDHt and PDK activities, and their respective protein and mRNA expression, did not differ after 1 week of aerobic training. PDHt activity increased 31% after 8 weeks and this may be partially due to a 1.3-fold increase in PDH-E₁α protein expression. PDK activity approximately doubled after 8 weeks of aerobic training and this was attributed to a 1.3-fold increase in PDK2 isoform protein expression. Similar to 1 week, no changes were observed at the mRNA level after 8 weeks of training. These findings  suggest that aerobically trained human skeletal muscle has an increased maximal capacity to utilize carbohydrates, evident by increased PDHt, but increased metabolic control sensitivity to pyruvate through increased contribution of PDK2 to total PDK activity.

Interaction of contractile activity and training history on mRNA abundance in skeletal muscle from trained athletes

Skeletal muscle displays enormous plasticity to respond to contractile activity with muscle from strength- (ST) and endurance-trained (ET) athletes representing diverse states of the adaptation continuum. Training adaptation can be viewed as the accumulation of specific proteins. Hence, the altered gene expression that allows for changes in protein concentration is of major importance for any training adaptation. Accordingly, the aim of the present study was to quantify acute subcellular responses in muscle to habitual and unfamiliar exercise. After 24-h diet/exercise control, 13 male subjects (7 ST and 6 ET) performed a random order of either resistance (8 x 5 maximal leg extensions) or endurance exercise (1 h of cycling at 70% peak O2 uptake). Muscle biopsies were taken from vastus lateralis at rest and 3 h after exercise. Gene expression was analyzed using real-time PCR with changes normalized relative to preexercise values. After cycling exercise, peroxisome proliferator-activated receptor- coactivator-1 (ET 8.5-fold, ST 10-fold, P < 0.001), pyruvate dehydrogenase kinase-4 (PDK-4; ET 26-fold, ST 39-fold), vascular endothelial growth factor (VEGF; ET 4.5-fold, ST 4-fold), and muscle atrophy F-box protein (MAFbx) (ET 2-fold, ST 0.4-fold) mRNA increased in both groups, whereas MyoD (3-fold), myogenin (0.9-fold), and myostatin (2-fold) mRNA increased in ET but not in ST (P < 0.05). After resistance exercise PDK-4 (7-fold, P < 0.01) and MyoD (0.7-fold) increased, whereas MAFbx (0.7-fold) and myostatin (0.6-fold) decreased in ET but not in ST. We conclude that prior training history can modify the acute gene responses in skeletal muscle to subsequent exercise.

Effects of Alcohol and Training on Exercise Performance and Muscle Recovery Biochemistry in the Brown Anole (Anolis sagrei)

Contrary to previous research, training may improve exercise performance in a lizard, the brown anole. A brief, two-week training period resulted in increased performance speed and distance before exhaustion in trained lizards. Trained lizards were also able to more effectively use leg glycogen stores, however each of these improvements were not found in lizards treated with alcohol. Liver glycogen concentrations were also lower in alcohol-treated lizards, and patterns of liver glycogen concentrations during recovery indicate some hepatic lactate gluconeogenesis.

Acute signalling responses to intense endurance training commenced with low or normal muscle glycogen

We have previously demonstrated that well-trained subjects who completed a 3 week training programme in which selected high-intensity interval training (HIT) sessions were commenced with low muscle glycogen content increased the maximal activities of several oxidative enzymes that promote endurance adaptations to a greater extent than subjects who began all training sessions with normal glycogen levels. The aim of the present study was to investigate acute skeletal muscle signalling responses to a single bout of HIT commenced with low or normal muscle glycogen stores in an attempt to elucidate potential mechanism(s) that might underlie our previous observations. Six endurance-trained cyclists/triathletes performed a 100 min ride at ∼70% peak O₂ uptake (AT) on day 1 and HIT (8 × 5 min work bouts at maximal self-selected effort with 1 min rest) 24 h later (HIGH). Another six subjects, matched for fitness and training history, performed AT on day 1 then 1–2 h later, HIT (LOW). Muscle biopsies were taken before and after HIT. Muscle glycogen concentration was higher in HIGH versus LOW before the HIT (390 ± 28 versus 256 ± 67 μmol (g dry wt)⁻¹). After HIT, glycogen levels were reduced in both groups (P < 0.05) but HIGH was elevated compared with LOW (229 ± 29 versus 124 ± 41 μmol (g dry wt)−1; P < 0.05). Phosphorylation of 5'AMP-activated protein kinase (AMPK) increased after HIT, but the magnitude of increase was greater in LOW (P < 0.05). Despite the augmented AMPK response in LOW after HIT, selected downstream AMPK substrates were similar between groups. Phosphorylation of p38 mitogen-activated protein kinase (p38 MAPK) was unchanged for both groups before and after the HIT training sessions. We conclude that despite a greater activation AMPK phosphorylation when HIT was commenced with low compared with normal muscle glycogen availability, the localization and phosphorylation state of selected downstream targets of AMPK were similar in response to the two interventions.

Active recovery, training status, muscle metabolism and repeated sprint performance

This thesis found that light exercise between repeated sprints improved performance in a subsequent bout. This was attributed to a reduction in potentially fatiguing by-products within the muscle and an increased aerobic metabolism in the second sprint.

Neurophysiological responses after short-term strength training of the biceps brachii muscle

The neural adaptations that mediate the increase in strength in the early phase of a strength training program are not well understood; however, changes in neural drive and corticospinal excitability have been hypothesized. To determine the neural adaptations to strength training, we used transcranial magnetic stimulation (TMS) to compare the effect of strength training of the right elbow flexor muscles on the functional properties of the corticospinal pathway. Motorevoked potentials (MEPs) were recorded from the right biceps brachii (BB) muscle from 23 individuals (training group; n = 13 and control group; n = 10) before and after 4 weeks of progressive overload strength training at 80% of 1-repetition maximum (1 RM). The TMS was delivered at 10% of the root mean square electromyographic signal (rmsEMG) obtained from a maximal voluntary contraction (MVC) at intensities of 5% of stimulator output below active motor threshold (AMT) until saturation of the MEP (MEP maxl. Strength training resulted in a 28% (p = 0.0001) increase in 1 RM strength, and this was accompanied by a 53% increase (p = 0.05) in the amplitude of the MEP at AMT; 33% (p = 0.05) increase in MEP at 20% above AMT, and a 38% increase at MEPmax (p = 0.04). There were no significant differences in the estimated slope (p = 0.4 7) or peak slope of the stimulus-response curve for the left primary motor cortex (M1) after strength training (p = 0.61). These results demonstrate that heavy-load isotonic strength training alters neural transmission via the corticospinal pathway projecting to the motoneurons controlling BB and in part underpin the strength changes observed in this study.

Circuit resistance training in chronic heart failure improves skeletal muscle mitochondrial ATP production rate—A randomized controlled trial

Background : We aimed to determine the role of skeletal muscle mitochondrial ATP production rate (MAPR) in relation to exercise tolerance after resistance training (RT) in chronic heart failure (CHF).

Methods and Results : Thirteen CHF patients (New York Heart Association functional class 2.3 ± 0.5; Left ventricular ejection fraction 26 ± 8%; age 70 ± 8 years) underwent testing for peak total body oxygen consumption (VO_2peak), and resting vastus lateralis muscle biopsy. Patients were then randomly allocated to 11 weeks of RT (n = 7), or continuance of usual care (C; n = 6), after which testing was repeated. Muscle samples were analyzed for MAPR, metabolic enzyme activity, and capillary density. VO_2peak and MAPR in the presence of the pyruvate and malate (P+M) substrate combination, representing carbohydrate metabolism, increased in RT (P < .05) and decreased in C (P < .05), with a significant difference between groups (VO_2peak, P = .005; MAPR, P = .03). There was a strong correlation between the change in MAPR and the change in peak total body oxygen consumption (VO_2peak) over the study (r = 0.875; P < .0001), the change in MAPR accounting for 70% of the change in VO_2peak.

Conclusions : These findings suggest that mitochondrial ATP production is a major determinant of aerobic capacity in CHF patients and can be favorably altered by muscle strengthening exercise.