The influence of low resistance respiratory muscle training on pulmonary function and high intensity exercise performance.

Background/objectives: Respiratory muscle training (RMT) was recognized as an effective means to improve respiratory muscle (RM) strength and enhance exercise performance. The purpose of this study was to examine the effect of low-intensity RMT on RM strength, pulmonary function, and performance. Methods: Fourteen healthy active adults were assigned randomly to either a training or placebo group. The training group completed six weeks of RMT, which consisted of a first week, 1 set of 15 min/d, 5 d/wk at 10-25% of maximal inspiratory pressure (PImax), and the remaining 5 weeks, 2 sets of 15 min/d, 5 d/wk, at 30% PImax. The placebo group followed the same protocol but with almost no additional ventilatory resistance. Measurement of RM strength and endurance, spirometry, and endurance exercise performance were obtained before and after the RMT program. Results: In the training group, PImax (+14%) and maximal expiratory pressure (PEmax, +27%), forced vital capacity (FVC, +3.6%), maximal oxygen uptake (VO2max, +11%), and time to exhaustion (Tlim90%, +25%) increased significantly from baseline values (P < 0.05). No significant changes were observed in the placebo group. Also, no significant interaction in maximum voluntary ventilation (MVV12), minute ventilation (VE), and respiratory rate (RR) were detected. Conclusions: These data suggest that low-intensity RMT is an effective tool to improve RM strength, pulmonary elastic properties and endurance exercise performance.

Women's experiences of social support during pregnancy: a qualitative systematic review.

BACKGROUND: Social support during pregnancy can alleviate emotional and physical pressures, improving the well-being of mother and child. Understanding women's lived experiences and perceptions of social support during pregnancy is imperative to better support women. This systematic review explores and synthesises the qualitative research on women's experiences of social support during pregnancy. METHODS: Databases PubMed, CINAHL, MEDLINE, APA PsycInfo and Scopus were searched with no year limit. Eligible studies included pregnant women or women who were up to one year postpartum and were assessed on their experiences of social support during pregnancy. The data were synthesised using the thematic synthesis approach. RESULTS: Fourteen studies were included with data from 571 participating women across ten countries; two studies used focus groups, and 12 used interviews to collect their data. Four main themes were developed ('a variety of emotional support', 'tangible and intangible instrumental support', 'traditional rituals and spiritual support', and 'the all-encompassing natal home'), and six sub-themes ('female network connections', 'care and affection from the husband', 'dissatisfaction with relationships', 'financial support from the husband and family', 'practical support from family and friends', 'health information support'). CONCLUSIONS: This systematic review sheds light on women's experiences of social support during pregnancy. The results indicate a broad variety of emotional support experienced and valued by pregnant women from different sources. Additionally, women expressed satisfaction and dissatisfaction with tangible and intangible support forms. It was also highlighted that spirituality played an essential role in reducing stress and offering coping mechanisms for some, whereas spirituality increased stress levels for others.

Conceptualization of physical exercise and keeping fit by child wheelchair users and their parents.

AIM: To gain a better understanding of how children aged 6-18 years who use wheelchairs and their families conceptualized physical exercise and keeping fit. BACKGROUND: Disabled children with reduced mobility are commonly overweight and unfit. Nurse-led health screening programmes in schools commonly exclude disabled children if they cannot use standard weighing scales or stand against height measuring sticks. DESIGN: Qualitative interview study at two time points over 6 months with children who use wheelchairs and their families. METHODS: Framework analysis using the theory of planned behaviour. FINDINGS: Mainly physically active participants were recruited (24 children and 23 parents) 2013-2014. Despite engaging in high levels of physical exercise, children were assessed as fit but had elevated body fat and did not realize how fit they were or that they were slightly overweight and nor did their parents. Children enjoyed the social benefits of exercise. Unlike their parents, children confused the purpose and outcomes of physical exercise with therapy (e.g. physiotherapy) and incorrectly understood the effects of physical exercise on body function and strength, preventing stiffness, increasing stamina and reducing fatigue. A new model was developed to show children's misconceptions. CONCLUSIONS: Proactive parents can overcome barriers to enable their children to benefit from physical exercise. Professionals need to increase communication clarity to improve children's understanding of therapy compared with physical exercise outcomes. Inclusion of children who use wheelchairs in health education policy; routine health screening; physical education classes and teacher training requires improvement. Body composition measurement is recommended, for which nurses will need training.

Primary skeletal muscle cells cultured on gelatin bead microcarriers develop structural and biochemical features characteristic of adult skeletal muscle.

A primary skeletal muscle cell culture, in which myoblasts derived from newborn rabbit hindlimb muscles grow on gelatin bead microcarriers in suspension and differentiate into myotubes, has been established previously. In the course of differentiation and beginning spontaneous contractions, these multinucleated myotubes do not detach from their support. Here, we describe the development of the primary myotubes with respect to their ultrastructural differentiation. Scanning electron microscopy reveals that myotubes not only grow around the surface of one carrier bead but also attach themselves to neighboring carriers, forming bridges between carriers. Transmission electron microscopy demonstrates highly ordered myofibrils, T-tubules, and sarcoplasmic reticulum. The functionality of the contractile apparatus is evidenced by contractile activity that occurs spontaneously or can be elicited by electrostimulation. Creatine kinase activity increases steadily until day 20 of culture. Regarding the expression of isoforms of myosin heavy chains (MHC), we could demonstrate that from day 16 on, no non-adult MHC isoform mRNAs are present. Instead, on day 28 the myotubes express predominantly adult fast MHCIId/x mRNA and protein. This MHC pattern resembles that of fast muscles of adult rabbits. In contrast, primary myotubes grown on matrigel-covered culture dishes express substantial amounts of non-adult MHC protein even on day 21. To conclude, primary myotubes grown on microcarriers in their later stages exhibit many features of adult skeletal muscle and characteristics of fast type II fibers. Thus, the culture represents an excellent model of adult fast skeletal muscle, for example, when investigating molecular mechanisms of fast-to-slow fiber-type transformation.

Well-being, health and fitness of children who use wheelchairs: feasibility study protocol to develop child-centred 'keep-fit' exercise interventions.

AIM: To undertake the pre-clinical and modelling phases of the Medical Research Council complex intervention framework to underpin development of child-centred 'keep-fit', exercise and physical activity interventions for children and young people who use wheelchairs. BACKGROUND: Children who use wheelchairs face many barriers to participation in physical activity, which compromises fitness, obesity, well-being and health. 'Keep-fit' programmes that are child-centred and engaging are urgently required to enhance participation of disabled children and their families as part of a healthy lifestyle. Nurses will likely be important in promoting and monitoring 'keep-fit' intervention(s) when implemented in the community. DESIGN: Mixed-method (including economic analysis) feasibility study to capture child and family preferences and keep-fit needs and to determine outcome measures for a 'keep-fit' intervention. METHODS: The study comprises three stages. Stage 1 includes a mixed-method systematic review of effectiveness, cost effectiveness and key stakeholder views and experiences of keep-fit interventions, followed by qualitative interviews with children, young people and their parents to explore preferences and motivations for physical activity. Stage 2 will identify standardized outcome measures and test their application with children who use wheelchairs to obtain baseline fitness data. Options for an exercise-based keep-fit intervention will then be designed based on Stage 1 and 2 findings. In stage 3, we will present intervention options for feedback and further refinement to children and parents/carers in focus groups. (Project funded October 2012). DISCUSSION: At completion, this study will lead to the design of the intervention and a protocol to test its efficacy.

'Keep fit' exercise interventions to improve health, fitness and well-being of children and young people who use wheelchairs: mixed-method systematic review protocol.

AIM: This mixed-method systematic review aims to establish the current evidence base for 'keep fit', exercise or physical activity interventions for children and young people who use wheelchairs. BACKGROUND: Nurses have a vital health promotion, motivational and monitoring role in optimizing the health and well-being of disabled children. Children with mobility impairments are prone to have low participation levels in physical activity, which reduces fitness and well-being. Effective physical activity interventions that are fun and engaging for children are required to promote habitual participation as part of a healthy lifestyle. Previous intervention programmes have been trialled, but little is known about the most effective types of exercise to improve the fitness of young wheelchair users. DESIGN: Mixed-method design using Cochrane systematic processes. Evidence regarding physiological and psychological effectiveness, health economics, user perspectives and service evaluations will be included and analysed under distinct streams. METHODS: The project was funded from October 2012. Multiple databases will be searched using search strings combining relevant medical subheadings and intervention-specific terms. Articles will also be identified from ancestral references and by approaching authors to identify unpublished work. Only studies or reports evaluating the effectiveness, participation experiences or cost of a physical activity programme will be included. Separate analyses will be performed for each data stream, including a meta-analysis if sufficient homogeneity exists and thematic analyses. Findings across streams will be synthesized in an overarching narrative summary. DISCUSSION: Evidence from the first systematic review of this type will inform development of effective child-centred physical activity interventions and their evaluation.

A retrospective comparison of the biceps femoris long head muscle structure in athletes with and without hamstring strain injury history.

INTRODUCTION: Hamstring strain injuries (HSI) and re-injuries are endemic in high-speed running sports. The biceps femoris long head (BFlh) is the most frequently injured muscle among the hamstrings. Structural parameters of the hamstring muscle are stated to be susceptible to strain injuries at this location. This retrospective study targeted comparing the BFlh's structural parameters between previously injured and uninjured athletes. METHODS: Nineteen male athletes with previous BFlh strain injury history and nineteen athletes without former lower extremity injury history were included in this study. Fascicle length, mid-muscle belly and distal musculotendinous (MTJ) passive stiffnesses of the biceps femoris long head (BFlh) were examined via b-mode panoramic ultrasound scanning and ultrasound-based shear-wave elastography. Parameter comparisons of both legs within and between athletes with and without injury history were performed. RESULTS: Comparison of the BFlh fascicle length between the injured leg of the injured group and the legs of the controls revealed a trend to shorter fascicle lengths in the injured leg (p = 0.067, d = -0.62). However, the mid-muscle belly passive stiffness of the BFlh was significantly higher in the injured legs (p = 0.009, d = 0.7) compared with the controls. Additionally, the distal MTJ stiffness was much higher in the previously injured legs compared with controls (p < 0.001, d = 1.6). CONCLUSIONS: Outcomes support the importance of BFlh properties related to stiffness, and fascicle length for injury susceptibility in athletes. Future prospective studies should determine whether the higher stiffness in the injured athletes is a cause or consequence of the HSI. Physical therapy and rehabilitation programmes after HSI should focus on BFlh muscle properties i.e., elasticity and fascicle length for reducing re-injury and increasing sports performance.

Adaptive metabolic response to 4 weeks of sugar-sweetened beverage consumption in healthy, lightly active individuals and chronic high glucose availability in primary human myotubes.

PURPOSE: Chronic sugar-sweetened beverage (SSB) consumption is associated with obesity and type 2 diabetes mellitus (T2DM). Hyperglycaemia contributes to metabolic alterations observed in T2DM, such as reduced oxidative capacity and elevated glycolytic and lipogenic enzyme expressions in skeletal muscle tissue. We aimed to investigate the metabolic alterations induced by SSB supplementation in healthy individuals and to compare these with the effects of chronic hyperglycaemia on primary muscle cell cultures. METHODS: Lightly active, healthy, lean subjects (n = 11) with sporadic soft drink consumption underwent a 4-week SSB supplementation (140 ± 15 g/day, ~2 g glucose/kg body weight/day, glucose syrup). Before and after the intervention, body composition, respiratory exchange ratio (RER), insulin sensitivity, muscle metabolic gene and protein expression were assessed. Adaptive responses to hyperglycaemia (7 days, 15 mM) were tested in primary human myotubes. RESULTS: SSB supplementation increased fat mass (+1.0 kg, P < 0.05), fasting RER (+0.12, P < 0.05), fasting glucose (+0.3 mmol/L, P < 0.05) and muscle GAPDH mRNA expressions (+0.94 AU, P < 0.05). PGC1α mRNA was reduced (-0.20 AU, P < 0.05). Trends were found for insulin resistance (+0.16 mU/L, P = 0.09), and MondoA protein levels (+1.58 AU, P = 0.08). Primary myotubes showed elevations in GAPDH, ACC, MondoA and TXNIP protein expressions (P < 0.05). CONCLUSION: Four weeks of SSB supplementation in healthy individuals shifted substrate metabolism towards carbohydrates, increasing glycolytic and lipogenic gene expression and reducing mitochondrial markers. Glucose-sensing protein MondoA might contribute to this shift, although further in vivo evidence is needed to corroborate this.

Differential effects of repeated inspiratory and limb muscle loading on effort perception in patients with obstructive sleep apnea and healthy males.

Obstructive sleep apnea (OSA) is characterized by collapse of the upper airways during sleep. The contribution of alterations in effort perception is not understood. This study investigated the response of inspiratory and quadriceps muscles to repetitive loading on effort perception in OSA patients, pre and post continuous positive airway pressure (CPAP) treatment, and in healthy individuals. Twenty-one OSA patients and 40 healthy participants completed protocols for repetitive inspiratory and leg muscle loading combined with intermittent rating of perceived exertion (RPE 14-somewhat hard/hard) to assess effort sensitivity. Electromyography, inspiratory pressure and isometric force were measured. OSA patients reported higher fatiguability of respiratory and leg muscles than controls. OSA patients revealed lower effort sensitivity in the leg muscles compared with controls, while repetitive loading led to a decline in force production. In the respiratory system, OSA patients revealed similar effort sensitivity at baseline compared with controls, but a large reduction in effort sensitivity after loading. Baseline effort sensitivity was correlated with apnea-hypopnea index (AHI). After CPAP treatment, OSA patients revealed a decreased baseline effort sensitivity with a missing loading response. Effort sensitivity was differentially affected in the respiratory and leg systems with outcomes of CPAP treatment suggesting a full reversibility. Outcomes suggest that reversible adaptive response of effort perception in the respiratory system might contribute to the severity of OSA.

Influence of motor imagery training on hip abductor muscle strength and bilateral transfer effect.

Motor imagery training could be an important treatment of reduced muscle function in patients and injured athletes. In this study, we investigated the efficacy of imagery training on maximal force production in a larger muscle group (hip abductors) and potential bilateral transfer effects. Healthy participants (n = 77) took part in two experimental studies using two imagery protocols (∼30 min/day, 5 days/week for 2 weeks) compared either with no practice (study 1), or with isometric exercise training (study 2). Maximal hip abduction isometric torque, electromyography amplitudes (trained and untrained limbs), handgrip strength, right shoulder abduction (strength and electromyography), and imagery capability were measured before and after the intervention. Post intervention, motor imagery groups of both studies exhibited significant increase in hip abductors strength (∼8%, trained side) and improved imagery capability. Further results showed that imagery training induced bilateral transfer effects on muscle strength and electromyography amplitude of hip abductors. Motor imagery training was effective in creating functional improvements in limb muscles of trained and untrained sides.

Rugby Players Exhibit Stiffer Biceps Femoris, Lower Biceps Femoris Fascicle Length to Knee Extensors, and Knee Flexors to Extensors Muscle Volume Ratios Than Active Controls.

PURPOSE: This study aimed to determine if hamstring-strain-injury risk factors related to muscle structure and morphology differed between rugby union players and controls. METHODS: The biceps femoris long head (BFlh) fascicle length and passive muscle stiffness and relative and absolute muscle volume of knee flexors (KF) and extensors (KE) were measured in 21 male subelite rugby players and 21 male physically active nonathletes. RESULTS: BFlh fascicle length was significantly longer (mean difference [MD] = 1.6 [1.7] cm) and BFlh passive muscle stiffness was significantly higher in rugby players (MD = 7.8 [14.8] kPa). The absolute BFlh (MD = 71.9 [73.3] cm3), KF (MD = 332.3 [337.2] cm3), and KE (MD = 956.3 [557.4] cm3) muscle volumes were also significantly higher in rugby players. There were no significant differences in the relative BFlh and KF muscle volumes. The relative KE muscle volumes were significantly higher in rugby players (MD = 2.3 [3.7] cm3/kg). However, the percentage BFlh fascicle length:KE (MD = -0.1% [0.1%]), BFlh/KE (MD = -0.9% [1.9%]), and KF:KE (MD = -4.9% [5.9%]) muscle volume ratios were significantly lower in the rugby players. BFlh muscle volume significantly correlated with BFlh fascicle length (r = .59, r2 = .35) and passive muscle stiffness (r = .46, r2 = .21). CONCLUSION: Future prospective studies should examine whether there are threshold values in BFlh passive muscle stiffness and BFlh fascicle length:KE, BFlh:KE, and KF:KE muscle volume ratios for predicting hamstring strain injuries.

Gene regulation mediating fiber-type transformation in skeletal muscle cells is partly glucose- and ChREBP-dependent.

Adaptations in the oxidative capacity of skeletal muscle cells can occur under several physiological or pathological conditions. We investigated the effect of increasing extracellular glucose concentration on the expression of markers of energy metabolism in primary skeletal muscle cells and the C2C12 muscle cell line. Growth of myotubes in 25mM glucose (high glucose, HG) compared with 5.55mM led to increases in the expression and activity of glyceraldehyde-3-phosphate dehydrogenase (GAPDH), a marker of glycolytic energy metabolism, while oxidative markers peroxisome proliferator-activated receptor γ coactivator 1α and citrate synthase decreased. HG induced metabolic adaptations as are seen during a slow-to-fast fiber transformation. Furthermore, HG increased fast myosin heavy chain (MHC) IId/x but did not change slow MHCI/ß expression. Protein phosphatase 2A (PP2A) was shown to mediate the effects of HG on GAPDH and MHCIId/x. Carbohydrate response element-binding protein (ChREBP), a glucose-dependent transcription factor downstream of PP2A, partially mediated the effects of glucose on metabolic markers. The glucose-induced increase in PP2A activity was associated with an increase in p38 mitogen-activated protein kinase activity, which presumably mediates the increase in MHCIId/x promoter activity. Liver X receptor, another possible mediator of glucose effects, induced only an incomplete metabolic shift, mainly increasing the expression of the glycolytic marker. Taken together, HG induces a partial slow-to-fast transformation comprising metabolic enzymes together with an increased expression of MHCIId/x. This work demonstrates a functional role for ChREBP in determining the metabolic type of muscle fibers and highlights the importance of glucose as a signaling molecule in muscle.

Alterations in biceps femoris long head fascicle length, Eccentric hamstring strength qualities and single-leg hop distance throughout the ninety minutes of TSAFT90 simulated football match.

INTRODUCTION: Football matches show higher hamstring strain injuries (HSIs) than football training. The occurrence of HSIs increases in the last fifteen minutes of both halves of football matches and shows an incremental trend towards the end of the ninety minutes. OBJECTIVES: This study aimed to examine football-specific fatigue-induced alterations in risk factors of the HSIs, including biceps femoris long head fascicle length via ultrasonography (BFlh FL), single-leg hop distance, hamstrings' maximal eccentric strength, and single-leg hamstring bridge test (SLHB) performance. METHODOLOGY: During ninety minutes of the TSAFT90 football simulation, the BFlh FL and single-leg hop distance were measured three times (before, at half-time and after 90 minutes of simulated match-play), and maximal hamstrings eccentric strength and SLHB test scores were recorded twice (before and after simulated match-play) for both legs in physically active participants (n = 15). RESULTS: Maximal eccentric hamstrings' strength (dominant leg (D): p < 0.001, Hedges' (adjusted) g effect size = -0.969; non-dominant leg (ND): p < 0.001, g = -0.929) and the SLHB performance (D: p < 0.001, g = -1.249; ND: p < 0.001, g = -1.108) showed large decrements immediately after the TSAFT90 intervention. There were no significant alterations in the BFlh FL, and the single-leg hop distance. CONCLUSIONS: Maximal eccentric strength and the SLHB performance of hamstrings are reduced after 90 minutes of simulated football match-play. Practitioners may consider focusing on improving eccentric strength and the SLHB performance. Future studies should examine alterations in the BFlh fascicles' dynamic lengthening and shortening ability during a football match.

Taste perception and implicit attitude toward sweet related to body mass index and soft drink supplementation.

These studies examined the differences in sweet taste perception and implicit attitude toward sweet between normal-weight and overweight/obese adults; and tested the effects of soft drink consumption on sweet taste, explicit preference and implicit attitude toward sweet in normal-weight subjects. In study 1, normal-weight (n = 22) and overweight/obese (n = 11) adults were assessed for sweet taste intensity and pleasantness. Implicit attitude toward sweet was assessed by implicit association test (IAT). In study 2, normal-weight, lightly active adults (n = 12) underwent one month soft drink supplementation (≈760 ml/day). This increased their daily carbohydrate intake by 2.1 ± 0.2g/kg body weight. Sweet taste perception, explicit preference and implicit attitudes to sweet were assessed. In both studies salty taste was also assessed as a contrasting perception. Overweight/obese subjects perceived sweet and salty tastes as less intense (-23% and -19%, respectively) and reported higher IAT scores for sweet than normal-weight controls (2.1-fold). The supplementation changed sweet intensity/pleasantness ratings and it increased explicit preference (2.3-fold) for sweet in a subgroup of initial sucrose-dislikers. In conclusion, overweight/obese individuals are more implicitly attracted to sweet. One month of soft drink supplementation changed sweet taste perception of normal-weight subjects.

Plasma Interleukin-10 and Cholesterol Levels May Inform about Interdependences between Fitness and Fatness in Healthy Individuals.

Relationships between demographic, anthropometric, inflammatory, lipid and glucose tolerance markers in connection with the fat but fit paradigm were investigated by supervised and unsupervised learning. Data from 81 apparently healthy participants (87% females) were used to generate four classes of fatness and fitness. Principal Component Analysis (PCA) revealed that the principal component was preponderantly composed of glucose tolerance parameters. IL-10 and high-density lipoprotein, low-density lipoprotein (LDL), and total cholesterol, along with body mass index (BMI), were the most important features according to Random Forest based recursive feature elimination. Decision Tree classification showed that these play a key role into assigning each individual in one of the four classes, with 70% accuracy, and acceptable classification agreement, κ = 0.54. However, the best classifier with 88% accuracy and κ = 0.79 was the Naïve Bayes. LDL and BMI partially mediated the relationship between fitness and fatness. Although unsupervised learning showed that the glucose tolerance cluster explains the highest quote of the variance, supervised learning revealed that the importance of IL-10, cholesterol levels and BMI was greater than the glucose tolerance PCA cluster. These results suggest that fitness and fatness may be interconnected by anti-inflammatory responses and cholesterol levels. Randomized controlled trials are needed to confirm these preliminary outcomes.

Heterogeneous effects of eccentric training and nordic hamstring exercise on the biceps femoris fascicle length based on ultrasound assessment and extrapolation methods: A systematic review of randomised controlled trials with meta-analyses.

OBJECTIVE: To systematically review the effects of eccentric training based on biceps femoris fascicle length using ultrasound assessment and extrapolation methods. DESIGN: Systematic review and meta-analysis of randomised controlled trials. DATA SOURCES: CENTRAL, CINAHL Plus with full text, PubMed and OpenGrey databases were searched on 6 July 2021. ELIGIBILITY CRITERIA FOR SELECTING STUDIES: Randomised controlled trials (RCTs) lasting at least four weeks and presenting data about biceps femoris (BF) fascicle length (FL) as an outcome. METHOD: Searching databases, screening studies, performing risk of bias assessments and determining the level of evidence (LoE) for each meta-analysis were applied during the study. PRISMA 2020 statement and Cochrane Handbook for Systematic Reviews of Interventions were used as the guidelines of this systematic review. RESULTS: Eight randomised controlled trials included in meta-analyses. Based on the very low and low LoE, eccentric training has small (g = 0.29, 95% CI [-0.26, 0.85]), moderate (g = 0.72, 95% CI [0.17, 1.28]) and large (g = 2.20, 95% CI [0.99, 3.41]) effect sizes (ES) based on manual linear extrapolation (MLE), panoramic ultrasound scanning and trigonometric equation methods, respectively. Similarly, Nordic hamstring exercise (NHE) has small (g = 0.23 [-1.02, 1.47]), small (g = 0.38, 95% CI [-0.50, 1.27]) and large (g = 1.98, 95% CI [0.52, 3.44]) ES based on the MLE, panoramic ultrasound scanning and trigonometric equation methods, respectively. CONCLUSION: ES of eccentric training, including NHE, vary between the MLE, panoramic ultrasound scanning, and equation methods. The relevant scientific community should have a consensus on measurement standards of the BF FL measurements. Further studies can be conducted to compare the effects of eccentric training based on the ultrasound assessment and extrapolation methods.

Carrots for the donkey: Influence of evaluative conditioning and training on self-paced exercise intensity and delay discounting of exercise in healthy adults.

To choose exercise over alternative behaviours, subjective reward evaluation of the potential choices is a principal step in decision making. However, the selection of exercise intensity might integrate acute visceral responses (i.e. pleasant or unpleasant feelings) and motives related to goals (i.e. enjoyment, competition, health). To understand the factors determining the selection of exercise in its intensity and evaluation as a modality, we conducted a study combining exercise training and evaluative conditioning. Evaluative conditioning was performed by using a novel technique using a primary reinforcer (sweetness) as the unconditioned stimulus and physical strain i.e. heart rate elevation as the conditioned stimulus during interval training, using a randomized control design (N = 58). Pre, post-three weeks interval training w/o conditioning, and after 4 weeks follow-up, participants were tested on self-paced speed selection on treadmill measuring heart rate, subjective pleasantness, and effort levels, as well as delay-discounting of exercise and food rewards. Results revealed that the selection of exercise intensity was significantly increased by adaptation to training and evaluative conditioning, revealing the importance of visceral factors as well as learned expected rewards. Delay discounting rates of self-paced exercise were transiently reduced by training but not affected by evaluative conditioning. In conclusion, exercise decisions are suggested to separate the decision-making process into a modality-specific cognitive evaluation of exercise, and an exercise intensity selection based on acute visceral experience integrating effort, pleasantness, and learned rewards.

Passive mechanical forces upregulate the fast myosin heavy chain IId/x via integrin and p38 MAP kinase activation in a primary muscle cell culture.

We have studied the mechanism by which a previously described primary muscle culture growing on microcarriers predominantly expresses fast myosin heavy chain (MHC) IId/x. We have measured MHC IId/x mRNA and protein levels, mRNA of MHC I and markers of muscle metabolism, insulin-like growth factor (IGF)-1 and mechano-growth factor (MGF) transcripts, indicators of the activation of the Akt-mammalian target of rapamycin (mTOR) axis, the p38-, ERK1/2-, and JNK-mitogen-activated protein kinase (MAP) kinase pathways, and of protein phosphatase PP2A, and we have assessed the involvement of integrin. By placing the culture flasks on a rotary shaker, we induce a continuous motion of the culture medium in which the carrier-myotube aggregates are suspended. This motion exerts passive forces on the myotubes that are decisive for the predominance of MHC II expression. These forces act via integrin, which transduces the mechanical signal into activation of PP2A and of p38 MAP-Kinase. The latter presumably is directly responsible for a drastic upregulation of MHC IId/x, whereas MHC I and metabolic markers remain unaffected. At the same time, despite an elevated level of IGF-1 transcription under passive forces, the IGF-1 receptor-Akt-mTOR axis is switched off as evident from the lack of an effect of inhibition of the IGF-1 receptor and from the PP2A-mediated low degree of phosphorylation of Akt and 4E-BP1. Similarly, the ERK1/2- and JNK-MAP kinase pathways are repressed. We conclude that passive stretch exerted on the myotubes by the rotary fluid motion induces a rather selective upregulation of fast MHC II, which goes along with a mild muscle hypertrophy as judged from the amount of protein per cell and is caused by p38 MAP kinase activity elevated via integrin sensing. The direct link between passive stretch and MHC II expression constitutes a novel mechanism, which is expected to become effective physiologically under passive stretch and eccentric contractions of skeletal muscles.

High-intensity exercise and carbohydrate-reduced energy-restricted diet in obese individuals.

Continuous high glycemic load and inactivity challenge glucose homeostasis and fat oxidation. Hyperglycemia and high intramuscular glucose levels mediate insulin resistance, a precursor state of type 2 diabetes. The aim was to investigate whether a carbohydrate (CHO)-reduced diet combined with high-intensity interval training (HIIT) enhances the beneficial effects of the diet alone on insulin sensitivity and fat oxidation in obese individuals. Nineteen obese subjects underwent 14 days of CHO-reduced and energy-restricted diet. Ten of them combined the diet with HIIT (4 min bouts at 90% VO(2peak) up to 10 times, 3 times a week). Oral glucose insulin sensitivity (OGIS) increased significantly in both groups; [diet-exercise (DE) group: pre 377 ± 70, post 396 ± 68 mL min(-1) m(-2); diet (D) group: pre 365 ± 91, post 404 ± 87 mL min(-1) m(-2); P < 0.001]. Fasting respiratory exchange ratio (RER) decreased significantly in both groups (DE group: pre 0.91 ± 0.06, post 0.88 ± 0.06; D group: pre 0.92 ± 0.07, post 0.86 ± 0.07; P = 0.002). VO(2peak) increased significantly in the DE group (pre 27 ± 5, post 32 ± 6 mL kg(-1) min(-1); P < 0.001), but not in the D group (pre 26 ± 9, post 26 ± 8 mL kg(-1) min(-1)). Lean mass and resistin were preserved only in the DE group (P < 0.05). Fourteen days of CHO-reduced diet improved OGIS and fat oxidation (RER) in obese subjects. The energy-balanced HIIT did not further enhance these parameters, but increased aerobic capacity (VO(2peak)) and preserved lean mass and resistin.

Different roles of H-ras for regulation of myosin heavy chain promoters in satellite cell-derived muscle cell culture during proliferation and differentiation.

The effect of constitutively activated proto-oncogene H-ras (H-rasQ61L) on the regulation of myosin heavy chain (MHC) promoter activities was investigated in rabbit satellite cell-derived muscle cell culture during the proliferation stage and early and later stages of differentiation, respectively. During proliferation, overexpression of H-rasQ61L did not affect basal level of activity of the slow MHCI/beta or the fast MHCIId/x promoter luciferase reporter gene construct in transient transfection assays. By contrast, H-rasQ61L affected both MHC promoter activities during differentiation, and this effect changes from inactivation after 2 days to activation after 4 days of differentiation. The activating effect of H-rasQ61L on both MHC promoters after 4 days of differentiation was significantly reduced by LY-294002, a specific inhibitor of the phosphoinositol-3-kinase (PI3K), a downstream target of Ras. Furthermore, the protein kinase Akt (protein kinase B), a downstream target of PI3k, was activated 4 days after initiation of differentiation in myotubes overexpressing H-rasQ61L. By contrast, inhibition of another Ras downstream pathway, mitogen-activated protein kinase kinase 1/2-extracellular signal-regulated protein kinase 1/2 (MKK1/2-ERK1/2-MAPK), increased activities of both MHC promoters, indicating a suppressive role of this pathway. Moreover, the Ras-PI3K-Akt signaling pathway is involved in the activation of MHCI/beta and IId/x promoters in a later stage of differentiation of muscle cells, presumably by a known inhibiting effect of activated Akt on the MKK1/2-ERK1/2-MAPK pathway. The experiments demonstrate that during differentiation of muscle cells activated H-ras is an important regulator of MHC isoform promoter function with opposite effects during early and later stages.