The molecular bases of training adaptation

Cross-Education Related to the Ipsilateral Limb Activity on Monopedal Postural Control of the Contralateral Limb: A Review

Cross-education is the effect whereby the ipsilateral limb training generates contralateral effects as part of motor tasks requiring strength and skills. However, it is not yet known if cross-education applies to postural control which could be essential as part of human motricity. Hence, this review addresses the possible effects of acute and chronic unilateral exercises (i.e., fatiguing exercises and regularly repeated/training exercises, respectively) on the contralateral monopedal postural control. Evidence suggests that fatiguing exercises disturb the contralateral monopedal postural control. This disturbance emanates from spinal and supra-spinal alterations which provokes changes to the motor function of the contralateral limb and degrades its postural control. Unilateral training produces cross-education related to postural control, especially when it includes balance exercises, but this remains to be tested when it includes resistance exercises. Mechanistic explanations are proposed to explain how neurophysiological changes operate in the disturbance or improvement of the contralateral monopedal postural control after unilateral fatiguing exercises or training exercises (respectively) of the lower-limb.

AMPD1 C34T Polymorphism (rs17602729) Is Not Associated with Post-Exercise Changes of Body Weight, Body Composition, and Biochemical Parameters in Caucasian Females

Background: The C34T polymorphism (rs 17602729) in adenosine monophosphate deaminase 1 gene (AMPD1) is associated with muscular energy metabolism in exercise. However, the role of its potential modifying impact on exercise-induced changes in obesity related parameters is unknown. The aim of the study was to determine if the C34T polymorphism influences the effects of an exercise training. Methods: This study examines a group of one hundred and sixty-eight, young, non-obese Caucasian women in Poland who took part in a 12-week aerobic training program to determine the impact of allele and genotype distribution on training outcomes. Results: A two-way analysis of variance ANOVA was conducted assuming a dominant model by pooling rare homozygotes and heterozygotes (TT + CT, n = 79) and comparing against common homozygotes (CC, n = 89). Our results showed that the AMPD1 C34T polymorphism was not related with selected parameters in study group. After completing the 12-week training program, a wide array of parameters (body mass, body mass index, fat mass, free fat mass, total body water) were significantly changed in the study participants with the exception of AMPD1 genotypes, among whom no significant changes were observed. Conclusions: The results did not confirm that harboring the rs 17602729 T allele influences the effects of the training program.

Inter-Day Reliability and Changes of Surface Electromyography on Two Postural Muscles Throughout 12 Weeks of Hippotherapy on Patients with Cerebral Palsy: A Pilot Study

Cerebral palsy (CP) is an umbrella term covering a group of permanent developmental disorders of movement and posture characterized by highly variable clinical features. The aim of this study was to assess the short-term and mid-term effects of neurorehabilitation via hippotherapy on the contractile properties of two key postural muscles during functional sitting in such patients. Thirty-minute hippotherapy sessions were conducted biweekly for 12 weeks in 18 patients (18.1 ± 5.7 years old). Surface electromyography (EMG) was implemented bilaterally in rectus abdominis and adductor magnus. We quantitatively analyzed the amplitude of EMG signals in the time domain and its spectral characteristics in the frequency domain. EMGs were recorded at the beginning and end of each session on day one and at week six and week twelve. Statistical analysis revealed a substantial inter-day reliability of the EMG signals for both muscles, validating the methodological approach. To a lesser extent, while beyond the scope of the current study, quantitative changes suggested a more selective recruitment/contractile properties’ shift of the examined muscles. Exploring postural control during functional activities would contribute to understanding the relationship between structural impairment, activity performance and patient capabilities, allowing the design of neurorehabilitation programs aimed at improving postural and functional skills according to each individual’s needs. The present study provides basic quantitative data supporting the body of scientific evidence making hippotherapy an approach of choice for CP neurorehabilitation.

Primary defects in lipid handling and resistance to exercise in myotubes from obese donors with and without type 2 diabetes

Several studies have shown that human primary myotubes retain the metabolic characteristic of their donors in vitro. We have demonstrated, along with other researchers, a reduced lipid turnover and fat oxidation rate in myotubes derived from obese donors with and without type 2 diabetes (T2D). Because exercise is known to increase fat oxidative capacity in skeletal muscle, we investigated if in vitro exercise could restore primary defects in lipid handling in myotubes of obese individuals with and without T2D compared with lean nondiabetic donors. Primary myotubes cultures were derived from biopsies of lean, obese, and T2D subjects. One single bout of long-duration exercise was mimicked in vitro by electrical pulse stimulation (EPS) for 24 h. Lipid handling was measured using radiolabeled palmitate, metabolic gene expression by real-time qPCR, and proteins by Western blot. We first showed that myotubes from obese and T2D donors had increased uptake and incomplete oxidation of palmitate. This was associated with reduced mitochondrial respiratory chain complex II, III, and IV protein expression in myotubes from obese and T2D subjects. EPS stimulated palmitate oxidation in lean donors, while myotubes from obese and T2D donors were refractory to this effect. Interestingly, EPS increased total palmitate uptake in myotubes from lean donors while myotubes from T2D donors had a reduced rate of palmitate uptake into complex lipids and triacylglycerols. Novelty Myotubes from obese and T2D donors are characterized by primary defects in palmitic acid handling. Both obese and T2D myotubes are partially refractory to the beneficial effect of exercise on lipid handling.

Swimming Differentially Affects T2DM-Induced Skeletal Muscle ER Stress and Mitochondrial Dysfunction Related to MAM

PURPOSE

Mitochondrial dysfunction and endoplasmic reticulum stress (ERS) are associated with metabolic diseases such as obesity and Type 2 diabetes mellitus (T2DM). Mitochondria and ER are connected via mitochondria-associated membranes (MAM) that are involved in glucose homeostasis and insulin resistance. We postulated that exercise might positively benefit T2DM-induced ER and mitochondrial dysfunction that might be associated with MAM.

MATERIALS AND METHODS

Mice were fed a high-fat diet and injected with streptozotocin (STZ) to create T2DM models. Glucose tolerance, mitochondrial quality, MAM quality, and ERS were investigated in diabetic mice after six weeks of swimming.

RESULTS

Type 2 DM induced decreased MAM quantity, impaired mitochondrial quality, and deteriorated ERS in skeletal muscle that led to endoplasmic reticulum-associated degradation (ERAD). Swimming alleviated strong ERS caused by T2DM. Importantly, MAM quantity was positively associated with mitochondrial function and tended to negatively correlate with the ERS branch, ATF6. Moreover, both ATF6 branches of ERS and ERAD were positively associated with the pIRE1α branch of ERS.

CONCLUSION

Type 2 DM induced glucose intolerance, powerful ERS, and mitochondrial dysfunction associated with decreased amounts of MAM. Swimming improved glucose intolerance and selectively mitigated the ERS in skeletal muscle. Therefore, MAM quality and ATF6 might be novel and important targets for T2DM treatment. Endoplasmic reticulum stress might be an effective target of swimming to improve diabetes.

Shark liver oil consumption decreases contractility in EDL muscle of trained rats

Abstract Introduction: Professional and recreational athletes make daily use of nutritional supplements to improve physical performance. Polyunsaturated fatty acids (PUFAs) have been used in this sense. N-3 PUFA, particularly eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids are involved in important physiological functions and the benefits of supplementation are demonstrated in several types of users. Shark liver oil (SLO) is a natural source of n-3 PUFA. Objective: To evaluate the effect of supplementation with SLO on contractility of skeletal muscles with different metabolic characteristics, soleus and extensor digitorum longus (EDL) from rats submitted to eight weeks of interval training of progressive intensity on a motorized treadmill. In the supplemented group, animals were supplemented with SLO (1 g/kg) five times a week for eight weeks. Method: Contractile parameters as maximum isometric twitch force (Tmax), maximum speed of force development (+dF/dt), maximum speed of force decrease (-dF/dt), maximum tetanic force (Fmax) and resistance to fatigue were analyzed in isolated muscle. Results: Compared to the control group, EDL muscles from the supplemented group reduced Tmax at the first (10.82 ± 0.89 vs 14.30 ± 0.67 mN/mm2. p < 0.01) and second minutes of experimentation (9.85 ± 0.63 vs 13.12 ± 0.70 mN/mm2. p < 0.01). However, it increased resistance to fatigue (22.80 ± 0.97 vs 18.60 ± 0.51 seconds. p = 0.005). Conclusion: No difference was observed in the soleus muscle.

Exercise Modalities Improve Aversive Memory and Survival Rate in Aged Rats: Role of Hippocampal Epigenetic Modifications

We aimed to investigate the effects of aging and different exercise modalities on aversive memory and epigenetic landscapes at brain-derived neurotrophic factor, cFos, and DNA methyltransferase 3 alpha (Bdnf, cFos, and Dnmt3a, respectively) gene promoters in hippocampus of rats. Specifically, active epigenetic histone markers (H3K9ac, H3K4me3, and H4K8ac) and a repressive mark (H3K9me2) were evaluated. Adult and aged male Wistar rats (2 and 22 months old) were subjected to aerobic, acrobatic, resistance, or combined exercise modalities for 20 min, 3 times a week, during 12 weeks. Aging per se altered histone modifications at the promoters of Bdnf, cFos, and Dnmt3a. All exercise modalities improved both survival rate and aversive memory performance in aged animals (n = 7-10). Exercise altered hippocampal epigenetic marks in an age- and modality-dependent manner (n = 4-5). Aerobic and resistance modalities attenuated age-induced effects on hippocampal Bdnf promoter H3K4me3. Besides, exercise modalities which improved memory performance in aged rats were able to modify H3K9ac or H3K4me3 at the cFos promoter, which could increase gene transcription. Our results highlight biological mechanisms which support the efficacy of all tested exercise modalities attenuating memory deficits induced by aging.

Perspectives and Determinants for Training-Intensity Distribution in Elite Endurance Athletes

Training-intensity distribution (TID), or the intensity of training and its distribution over time, has been considered an important determinant of the outcome of a training program in elite endurance athletes. The polarized and pyramidal TID, both characterized by a high amount of low-intensity training (below the first lactate or ventilatory threshold), but with different contributions of threshold training (between the first and second lactate or ventilatory threshold) and high-intensity training (above the second lactate or ventilatory threshold), have been reported most frequently in elite endurance athletes. However, the choice between these 2 TIDs is not straightforward. This article describes the historical, evolutionary, and physiological perspectives of the success of the polarized and pyramidal TID and proposes determinants that should be taken into account when choosing the most appropriate TID.

Combined Exercise Modulates Cortisol, Testosterone, and Immunoglobulin A Levels in Individuals Living With HIV/AIDS

BACKGROUND

Combined exercise (CE) has been recommended for individuals living with HIV/AIDS (ILWHA) under antiretroviral therapy. However, depending on the intensity and duration, physical exercise may occasionally increase inflammatory parameters and reduce immunological responses that if not reversed, cause health injury specifically in this population. Information about immunological and hormonal responses after CE in ILWHA has not been completely elucidated. Therefore, the aim is to verify the acute effects of CE on cortisol, testosterone, immunoglobulin A, and pro-inflammatory and anti-inflammatory cytokines over 24 hours in ILWHA.

METHODS

Noninfected individuals and ILWHA undergone 5 sessions of CE prior to the acute assessment session. Seventy-two hours after the last session, the subjects were submitted to one session of CE (aerobic exercise: 25 min at 60-70% reserve heart rate and resistance exercise: 3 sets of 15 maximum repetitions of 6 exercises). Saliva samples were collected before, immediately, 6 and 24 hours after CE.

RESULTS

CE reduced cortisol (6 h: 2.54 [0.58] vs 0.65 [0.22] pg·mL-1; P = .02), increased testosterone (all moments) and immunoglobulin A levels (24 h: 255.3 [44.7] vs 349.2 [41.9] μm·mL-1; P = .01) without significant difference in cytokines levels in ILWHA.

CONCLUSION

CE modulates cortisol, testosterone, and immunoglobulin A levels without the change in immunological parameters in ILWHA.

Native Whey Induces Similar Adaptation to Strength Training as Milk, despite Higher Levels of Leucine, in Elderly Individuals

BACKGROUND

Large amounts of protein (40 g) or supplementing suboptimal servings of protein with leucine are able to overcome the anabolic resistance in elderly muscle. Our aim was to compare the effects of supplementation of native whey, high in leucine, with milk on gains in muscle mass and strength during a period of strength training, in elderly individuals.

METHODS

In this double-blinded, randomized, controlled study, a total of 30 healthy men and women received two daily servings of 20 g of either milk protein or native whey, during an 11-week strength training intervention. Muscle strength, lean mass, m. vastus lateralis thickness, muscle fiber area, and resting and post-exercise phosphorylation of p70S6K, 4E-BP1, and eEF-2 were assessed prior to and after the intervention period.

RESULTS

Muscle mass and strength increased, by all measures applied in both groups (p < 0.001), with no differences between groups (p > 0.25). p70S6K phosphorylation increased (~1000%, p < 0.045) 2 h after exercise in the untrained and trained state, with no differences between supplements. Total and phosphorylated mTORC-1 decreased after training.

CONCLUSION

Supplementation with milk or native whey during an 11-week strength training period increased muscle mass and strength similarly in healthy elderly individuals.

Mechanisms of exercise-induced survival motor neuron expression in the skeletal muscle of spinal muscular atrophy-like mice

Key points

Spinal muscular atrophy (SMA) is a health‐ and life‐limiting neuromuscular disorder caused by a deficiency in survival motor neuron (SMN) protein.

While historically considered a motor neuron disease, current understanding of SMA emphasizes its systemic nature, which requires addressing affected peripheral tissues such as skeletal muscle in particular.

Chronic physical activity is beneficial for SMA patients, but the cellular and molecular mechanisms of exercise biology are largely undefined in SMA.

After a single bout of exercise, canonical responses such as skeletal muscle AMP‐activated protein kinase (AMPK), p38 mitogen‐activated protein kinase (p38) and peroxisome proliferator‐activated receptor γ coactivator 1α (PGC‐1α) activation were preserved in SMA‐like Smn^2B/− animals. Furthermore, molecules involved in SMN transcription were also altered following physical activity. Collectively, these changes were coincident with an increase in full‐length SMN transcription and corrective SMN pre‐mRNA splicing.

This study advances understanding of the exercise biology of SMA and highlights the AMPK–p38–PGC‐1α axis as a potential regulator of SMN expression in muscle.

Abstract

Chronic physical activity is safe and effective in spinal muscular atrophy (SMA) patients, but the underlying cellular events that drive physiological adaptations are undefined. We examined the effects of a single bout of exercise on molecular mechanisms associated with adaptive remodelling in the skeletal muscle of Smn^2B/− SMA‐like mice. Skeletal muscles were collected from healthy Smn^2B/+ mice and Smn^2B/− littermates at pre‐ (postnatal day (P) 9), early‐ (P13) and late‐ (P21) symptomatic stages to characterize SMA disease progression. Muscles were also collected from Smn^2B/− animals exercised to fatigue on a motorized treadmill. Intracellular signalling and gene expression were examined using western blotting, confocal immunofluorescence microscopy, real‐time quantitative PCR and endpoint PCR assays. Basal skeletal muscle AMP‐activated protein kinase (AMPK) and p38 mitogen‐activated protein kinase (p38) expression and activity were not affected by SMA‐like conditions. Canonical exercise responses such as AMPK, p38 and peroxisome proliferator‐activated receptor γ coactivator‐1α (PGC‐1α) activation were observed following a bout of exercise in Smn^2B/− animals. Furthermore, molecules involved in survival motor neuron (SMN) transcription, including protein kinase B (AKT) and extracellular signal‐regulated kinases (ERK)/ETS‐like gene 1 (ELK1), were altered following physical activity. Acute exercise was also able to mitigate aberrant proteolytic signalling in the skeletal muscle of Smn^2B/− mice. Collectively, these changes were coincident with an exercise‐evoked increase in full‐length SMN mRNA expression. This study advances our understanding of the exercise biology of SMA and highlights the AMPK–p38–PGC‐1α axis as a potential regulator of SMN expression alongside AKT and ERK/ELK1 signalling.

Spinal muscular atrophy (SMA) is a health‐ and life‐limiting neuromuscular disorder caused by a deficiency in survival motor neuron (SMN) protein.

While historically considered a motor neuron disease, current understanding of SMA emphasizes its systemic nature, which requires addressing affected peripheral tissues such as skeletal muscle in particular.

Chronic physical activity is beneficial for SMA patients, but the cellular and molecular mechanisms of exercise biology are largely undefined in SMA.

After a single bout of exercise, canonical responses such as skeletal muscle AMP‐activated protein kinase (AMPK), p38 mitogen‐activated protein kinase (p38) and peroxisome proliferator‐activated receptor γ coactivator 1α (PGC‐1α) activation were preserved in SMA‐like Smn^2B/− animals. Furthermore, molecules involved in SMN transcription were also altered following physical activity. Collectively, these changes were coincident with an increase in full‐length SMN transcription and corrective SMN pre‐mRNA splicing.

This study advances understanding of the exercise biology of SMA and highlights the AMPK–p38–PGC‐1α axis as a potential regulator of SMN expression in muscle.

No Difference between Spray Dried Milk and Native Whey Supplementation with Strength Training

Background

A rapid digestibility and high leucine content are considered important for maximal stimulation of muscle protein synthesis. Consequently, with these properties, native whey may hold greater anabolic potential than milk, when supplemented in combination with strength training. Our aim was to compare the effects of supplementation with milk or native whey, during a 12-wk strength training period, on gains in muscle mass and strength in young adults.

Methods

In this double-blinded, randomized, controlled study a total of 40 untrained young men and women received two daily servings of either milk or native whey containing 20 g of protein, during a 12-wk strength training intervention. Muscle strength, lean mass, thigh muscle cross-sectional area, m. vastus lateralis thickness and muscle fiber cross-sectional area were assessed before and after the training period. In addition, the acute phosphorylation of the anabolic kinases p70S6K, 4E-BP1 and eEF-2 in response to a standardized workout and supplementation was investigated before and after the 12-wk training period.

Results

Muscle mass and strength increased, by all measures applied (5%–16%, P < 0.001), with no differences between groups (P > 0.25). p70S6K phosphorylation increased (~1000%, P < 0.02) 2 h after exercise in the untrained and trained state, but no differences in anabolic signaling were observed between supplements (P > 0.40). No correlation between these acute measures and changes in muscle mass or strength were observed.

Conclusion

Supplementation with milk or native whey during a 12-wk strength training period did not differentially affect muscle mass and strength in young untrained individuals.

Sustained Muscle Deoxygenation vs. Sustained High VO2 During High-Intensity Interval Training in Sprint Canoe-Kayak

Recent data suggests that peripheral adaptations, i.e., the muscle ability to extract and use oxygen, may be a stronger predictor of canoe-kayak sprint performance compared to VO₂max or central adaptations. If maximizing the time near VO₂max during high-intensity interval training (HIIT) sessions is believed to optimize central adaptations, maximizing the time near maximal levels of muscle desaturation could represent a critical stimulus to optimize peripheral adaptations.

Purpose: Therefore, the purpose of this study was to assess the VO₂, muscle oxygenation and cardiac output responses to various HIIT sessions, and to determine which type of HIIT elicits the lowest muscle oxygenation and the longest cumulated time at low muscle O₂ saturation.

Methods: Thirteen well-trained canoe-kayak athletes performed an incremental test to determine VO₂max and peak power output (PPO), and 4 HIIT sessions (HIIT-15: 40x[15 s at 115%PPO, 15 s at 30%PPO]; HIIT-30: 20x[30 s at 115%PPO, 30 s at 30%PPO]; HIIT-60: 6x[1 min at 130%PPO, 3 min rest]; sprint interval training (SIT): 6x[30 s all-out, 3 min 30 rest]) on a canoe or kayak ergometer. Portable near-infrared spectroscopy monitors were placed on the Latissimus dorsi (LD), Biceps brachii (BB), and Vastus lateralis (VL) during every session to assess changes in muscle O₂ saturation (SmO₂, % of physiological range).

Results: HIIT-15 and HIIT-30 elicited a longer time >90%VO₂max (HIIT-15: 8.1 ± 6.2 min, HIIT-30: 6.8 ± 4.6 min), compared to SIT (1.7 ± 1.3 min, p = 0.006 and p = 0.035) but not HIIT-60 (4.1 ± 1.7 min). SIT and HIIT-60 elicited the lowest SmO₂ in the VL (SIT: 0 ± 1%, HIIT-60: 8 ± 9%) compared to HIIT-15 (26 ± 12%, p < 0.001 and p = 0.007) and HIIT-30 (25 ± 12%, p < 0.001 and p = 0.030). SIT produced the longest time at >90% of maximal deoxygenation in all 3 muscles, with effect sizes ranging from small to very large.

Conclusions: Short HIIT performed on a canoe/kayak ergometer elicits the longest time near VO₂max, potentially conducive to VO₂max improvements, but SIT is needed in order to maximize muscle deoxygenation during training, which would potentially conduct to greater peripheral adaptations.

Skeletal Muscle Fiber Adaptations Following Resistance Training Using Repetition Maximums or Relative Intensity

The purpose of the study was to compare the physiological responses of skeletal muscle to a resistance training (RT) program using repetition maximum (RM) or relative intensity (RI_SR). Fifteen well-trained males underwent RT 3 d·wk⁻¹ for 10 weeks in either an RM group (n = 8) or RI_SR group (n = 7). The RM group achieved a relative maximum each day, while the RI_SR group trained based on percentages. The RM group exercised until muscular failure on each exercise, while the RI_SR group did not reach muscular failure throughout the intervention. Percutaneous needle biopsies of the vastus lateralis were obtained pre-post the training intervention, along with ultrasonography measures. Dependent variables were: Fiber type-specific cross-sectional area (CSA); anatomical CSA (ACSA); muscle thickness (MT); mammalian target of rapamycin (mTOR); adenosine monophosphate protein kinase (AMPK); and myosin heavy chains (MHC) specific for type I (MHC1), type IIA (MHC2A), and type IIX (MHC2X). Mixed-design analysis of variance and effect size using Hedge’s g were used to assess within- and between-group alterations. RI_SR statistically increased type I CSA (p = 0.018, g = 0.56), type II CSA (p = 0.012, g = 0.81), ACSA (p = 0.002, g = 0.53), and MT (p < 0.001, g = 1.47). RI_SR also yielded a significant mTOR reduction (p = 0.031, g = −1.40). Conversely, RM statistically increased only MT (p = 0.003, g = 0.80). Between-group effect sizes supported RI_SR for type I CSA (g = 0.48), type II CSA (g = 0.50), ACSA (g = 1.03), MT (g = 0.72), MHC2X (g = 0.31), MHC2A (g = 0.87), and MHC1 (g = 0.59); with all other effects being of trivial magnitude (g < 0.20). Our results demonstrated greater adaptations in fiber size, whole-muscle size, and several key contractile proteins when using RI_SR compared to RM loading paradigms.

Epigenetic changes in healthy human skeletal muscle following exercise- a systematic review

Exercise training is continually challenging whole-body homeostasis, leading to improvements in performance and health. Adaptations to exercise training are complex and are influenced by both environmental and genetic factors. Epigenetic factors regulate gene expression in a tissue-specific manner and constitute a link between the genotype and the environment. Moreover, epigenetic factors are emerging as potential biomarkers that could predict the response to exercise training. This systematic review aimed to identify epigenetic changes that have been reported in skeletal muscle following exercise training in healthy populations. A literature search of five databases (PUBMED, MEDLINE, CINHAL, SCOPUS and SportDiscuss) was conducted in November 2018. Articles were included if they examined epigenetic modifications (DNA methylation, histone modifications and non-coding RNAs) in skeletal muscle, following either an acute bout of exercise, an exercise intervention in a pre/post design, or a case/control type of study. Twenty-two studies met the inclusion criteria. Several epigenetic markers including DNA methylation of genes known to be differentially expressed after exercise and myomiRs were reported to be modified after exercise. Several epigenetic marks were identified to be altered in response to exercise, with potential influence on skeletal muscle metabolism. However, whether these epigenetic marks play a role in the physiological impact of exercise is unclear. Exercise epigenetics is still a very young research field, and it is expected that in the future the causality of such changes will be elucidated via the utilization of emerging experimental models able to target the epigenome.

Skeletal muscle signaling responses to resistance exercise of the elbow extensors are not compromised by a preceding bout of aerobic exercise

The current study examined the effects of a preceding bout of aerobic exercise (AE) on subsequent molecular signaling to resistance exercise (RE) of the elbow extensors. Eleven men performed unilateral elbow-extensor AE (~45 min at 70% peak workload) followed by unilateral RE (4 × 7 maximal repetitions) for both arms. Thus, one arm performed AE+RE interspersed with 15 min recovery, whereas the other arm conducted RE alone. Muscle biopsies were taken from the triceps brachii of each arm immediately before (PRE) and 15 min (POST1) and 3 h (POST2) after RE. Molecular markers involved in translation initiation, protein breakdown, mechanosignaling, and ribosome biogenesis were analyzed. Peak power during RE was reduced by 24% (±19%) when preceded by AE ( P < 0.05). Increases in PGC1a and MuRF1 expression were greater from PRE to POST2 in AE+RE compared with RE (18- vs. 3.5- and 4- vs. 2-fold, respectively, interaction, P < 0.05). Myostatin mRNA decreased in both arms ( P < 0.05). Phosphorylation of AMPK (Thr172) increased (2.5-fold), and 4E-BP1 (Thr37/46) decreased (2.0-fold), after AE (interactions, P < 0.05). p70 S6K, yes-associated protein, and c-Jun NH2-terminal kinase phosphorylation were unaltered, whereas focal adhesion kinase decreased ~1.5-fold, and β1-integrin increased ~1.3- to 1.5-fold, (time effect, P < 0.05). Abundance of 45S pre-ribosomal (r)RNA (internally transcribed spacer, ITS) decreased (~30%) after AE (interaction, P < 0.05), whereas CMYC mRNA was greater in AE+RE compared with RE (12-fold, P < 0.05). POLR1B abundance increased after both AE+RE and RE. All together, our results suggest that a single bout of AE leads to an immediate decrease in signaling for translation initiation and ribosome biogenesis. Yet, this did not translate into altered RE-induced signaling during the 3-h postexercise recovery period.

Mito-nuclear interactions modify Drosophila exercise performance

Endurance exercise has received increasing attention as a broadly preventative measure against age-related disease and dysfunction. Improvement of mitochondrial quality by enhancement of mitochondrial turnover is thought to be among the important molecular mechanisms underpinning the benefits of exercise. Interactions between the mitochondrial and nuclear genomes are important components of the genetic basis for variation in longevity, fitness and the incidence of disease. Here, we examine the effects of replacing the mitochondrial genome (mtDNA) of several Drosophila strains with mtDNA from other strains, or from closely related species, on exercise performance. We find that mitochondria from flies selected for longevity increase the performance of flies from a parental strain. We also find evidence that mitochondria from other strains or species alter exercise performance, with examples of both beneficial and deleterious effects. These findings suggest that both the mitochondrial and nuclear genomes, as well as interactions between the two, contribute significantly to exercise capacity.

Dietary Nitrate and Physical Performance

Nitric oxide (NO) plays a plethora of important roles in the human body. Insufficient production of NO (for example, during older age and in various disease conditions) can adversely impact health and physical performance. In addition to its endogenous production through the oxidation of l-arginine, NO can be formed nonenzymatically via the reduction of nitrate and nitrite, and the storage of these anions can be augmented by the consumption of nitrate-rich foodstuffs such as green leafy vegetables. Recent studies indicate that dietary nitrate supplementation, administered most commonly in the form of beetroot juice, can ( a) improve muscle efficiency by reducing the O₂ cost of submaximal exercise and thereby improve endurance exercise performance and ( b) enhance skeletal muscle contractile function and thereby improve muscle power and sprint exercise performance. This review describes the physiological mechanisms potentially responsible for these effects, outlines the circumstances in which ergogenic effects are most likely to be evident, and discusses the effects of dietary nitrate supplementation on physical performance in a range of human populations.

Comparative Strength and Endurance Parameters of the Craniocervical and Cervicothoracic Extensors and Flexors in Females With and Without Idiopathic Neck Pain

Isometric strength and endurance performance of cervical flexor and extensor muscles were compared in women with (n = 30) and without (n = 30) idiopathic neck pain at the craniocervical and cervicothoracic axes. Strength and endurance time (time to task failure in seconds) at 50% maximal voluntary contraction were recorded in 4 directions (craniocervical flexion/extension and cervicothoracic flexion/extension) and 6 strength and endurance ratios were calculated. Participants in both groups were matched for body mass index. The idiopathic neck pain group demonstrated significantly less strength for the cervicothoracic flexors and extensors (1.58-4.7 N·m [12.4%-17.9%] less, P < .04) and significantly less endurance time for the cervicothoracic and craniocervical flexors (10.77-10.9 s [23.3%-27.5%] less, P < .03). The cervicothoracic extension to craniocervical flexion strength ratio was also lower in the idiopathic neck pain group (P = .01); however, no other strength or endurance ratio was significantly different between groups. This exploratory study suggests assessing specific performance parameters accounting for regional muscular differences in the upper and lower neck is potentially informative to understanding impairments in neck pain conditions, particularly as impairments may not be uniform across muscle groups.

MicroRNA suppression of stress-responsive NDRG2 during dexamethasone treatment in skeletal muscle cells

Background

MicroRNAs (miRNAs) are increasingly being identified as modulatory molecules for physiological and pathological processes in muscle. Here, we investigated whether miRNAs influenced the expression of the stress-responsive gene N-myc downstream-regulated gene 2 (Ndrg2) in skeletal muscle cells through the targeted degradation or translation inhibition of NDRG2 mRNA transcripts during basal or catabolic stress conditions.

Results

Three miRNAs, mmu-miR-23a-3p (miR-23a), mmu-miR-23b-3p (miR-23b) and mmu-miR-28-5p (miR-28), were identified using an in silico approach and confirmed to target the 3′ untranslated region of the mouse Ndrg2 gene through luciferase reporter assays. However, miR-23a, -23b or -28 overexpression had no influence on NDRG2 mRNA or protein levels up to 48 h post treatment in mouse C2C12 myotubes under basal conditions. Interestingly, a compensatory decrease in the endogenous levels of the miRNAs in response to each other’s overexpression was measured. Furthermore, dexamethasone, a catabolic stress agent that induces NDRG2 expression, decreased miR-23a and miR-23b endogenous levels at 24 h post treatment suggesting an interplay between these miRNAs and NDRG2 regulation under similar stress conditions. Accordingly, when overexpressed simultaneously, miR-23a, -23b and -28 attenuated the dexamethasone-induced increase of NDRG2 protein translation but did not affect Ndrg2 gene expression.

Conclusion

These findings highlight modulatory and co-regulatory roles for miR-23a, -23b and -28 and their novel regulation of NDRG2 during stress conditions in muscle.

Electronic supplementary material

The online version of this article (10.1186/s12860-019-0194-3) contains supplementary material, which is available to authorized users.

Molecular mechanisms relating to amino acid regulation of protein synthesis

Some amino acids (AA) act through several signalling pathways and mechanisms to mediate the control of gene expression at the translation level, and the regulation occurs, specifically, on the initiation and the signalling pathways for translation. The translation of mRNA to protein synthesis proceeds through the steps of initiation and elongation, and AA act as important feed-forward activators that are involved in many pathways, such as the sensing and the transportation of AA by cells, in these steps in many tissues of mammals. For the translation, phosphorylation of eukaryotic translation initiation factor 2α (eIF2α) is a critical molecule that controls the translation initiation and its functions can be regulated by some AA. Another control point in the mRNA binding step in the translation initiation is at the regulation by mammalian target of rapamycin, which requires a change of phosphorylation status of ribosomal protein S6. In fact, the change of phosphorylation status of ribosomal protein S6 might be involved in global protein synthesis. The present review summarises recent work on the molecular mechanisms of the regulation of protein synthesis by AA and highlights new findings.

Carbohydrate Availability and Physical Performance: Physiological Overview and Practical Recommendations

Strong evidence during the last few decades has highlighted the importance of nutrition for sport performance, the role of carbohydrates (CHO) being of special interest. Glycogen is currently not only considered an energy substrate but also a regulator of the signaling pathways that regulate exercise-induced adaptations. Thus, low or high CHO availabilities can result in both beneficial or negative results depending on the purpose. On the one hand, the depletion of glycogen levels is a limiting factor of performance during sessions in which high exercise intensities are required; therefore ensuring a high CHO availability before and during exercise is of major importance. A high CHO availability has also been positively related to the exercise-induced adaptations to resistance training. By contrast, a low CHO availability seems to promote endurance-exercise-induced adaptations such as mitochondrial biogenesis and enhanced lipolysis. In the present narrative review, we aim to provide a holistic overview of how CHO availability impacts physical performance as well as to provide practical recommendations on how training and nutrition might be combined to maximize performance. Attending to the existing evidence, no universal recommendations regarding CHO intake can be given to athletes as nutrition should be periodized according to training loads and objectives.

Eccentric Muscle Contractions: Risks and Benefits

Eccentric contractions, characterized by the lengthening of the muscle-tendon complex, present several unique features compared with other types of contractions, which may lead to unique adaptations. Due to its specific physiological and mechanical properties, there is an increasing interest in employing eccentric muscle work for rehabilitation and clinical purposes. However, unaccustomed eccentric exercise is known to cause muscle damage and delayed pain, commonly defined as “Delayed-Onset Muscular Soreness” (DOMS). To date, the most useful preventive strategy to avoid these adverse effects consists of repeating sessions involving submaximal eccentric contractions whose intensity is progressively increased over the training. Despite an increased number of investigations focusing on the eccentric contraction, a significant gap still remains in our understanding of the cellular and molecular mechanisms underlying the initial damage response and subsequent adaptations to eccentric exercise. Yet, unraveling the molecular basis of exercise-related muscle damage and soreness might help uncover the mechanistic basis of pathological conditions as myalgia or neuromuscular diseases. In addition, a better insight into the mechanisms governing eccentric training adaptations should provide invaluable information for designing therapeutic interventions and identifying potential therapeutic targets.

Circulating Tumor Necrosis Factor Alpha May Modulate the Short-Term Detraining Induced Muscle Mass Loss Following Prolonged Resistance Training

Introduction

Tumor necrosis factor alpha (TNFα) is a pro-inflammatory cytokine that has been shown to modulate muscle mass, and is responsive to exercise training. The effects of resistance training (RT) followed by a short period of detraining on muscle size, architecture and function in combination with circulating TNFα levels have not been previously investigated in a young, healthy population.

Methods

Sixteen participants (8 males and 8 females) were randomly assigned to a training group (TRA; age 20 ± 3 years, mass 76 ± 7 kg), whilst fourteen participants (7 males and 7 females) age 22 ± 2 years, mass 77 ± 6 kg were assigned to a control group (CON). Measures of vastus lateralis (VL) muscle size (normalized physiological cross-sectional area allometrically scaled to body mass; npCSA), architecture (fascicle length; L_F, pennation angle Pθ), strength (knee extensor maximal voluntary contraction; KE MVC), specific force, subcutaneous fat (SF) and circulating TNFα were assessed at baseline (BL), post 8 weeks RT (PT), and at two (DT1) and four (DT2) weeks of detraining.

Results

Pooled BL TNFα was 0.87 ± 0.28 pg/mL with no differences between groups. BL TNFα tended to be correlated with npCSA (p = 0.055) and KEMVC (p = 0.085) but not specific force (p = 0.671) or SF (p = 0.995). There were significant (p < 0.05) increases in npCSA compared to BL and CON in TRA at PT, DT1, and DT2, despite significant (p < 0.05) decreases in npCSA compared to PT at DT1 and DT2. There were significant (p < 0.05) increases in L_F, Pθ and KE MVC at PT but only L_F and torque at DT1. There were no significant (p > 0.05) changes in SF, specific force or TNFα at any time points. There was a significant correlation (p = 0.022, r = 0.57) between the relative changes in TNFα and npCSA at DT2 compared to PT.

Discussion

Neither RT nor a period of short term detraining altered the quality of muscle (i.e., specific force) despite changes in morphology and function. TNFα does not appear to have any impact on RT-induced gains in muscle size or function, however, TNFα may play a role in inflammatory-status mediated muscle mass loss during subsequent detraining in healthy adults.

Molecular and cellular adaptations to exercise training in skeletal muscle from cancer patients treated with chemotherapy

BACKGROUND

A growing body of evidence suggests that exercise training has beneficial effects in cancer patients. The aim of the present study was to investigate the molecular basis underlying these beneficial effects in skeletal muscle from cancer patients.

METHODS

We investigated expression of selected proteins involved in cellular processes known to orchestrate adaptation to exercise training by western blot. Skeletal muscle biopsies were sampled from ten cancer patients before and after 4-7 weeks of ongoing chemotherapy, and subsequently after 10 weeks of continued chemotherapy in combination with exercise training. Biopsies from ten healthy matched subjects served as reference.

RESULTS

The expression of the insulin-regulated glucose transporter, GLUT4, increased during chemotherapy and continued to increase during exercise training. A similar trend was observed for ACC, a key enzyme in the biosynthesis and oxidation of fatty acids, but we did not observe any changes in other regulators of substrate metabolism (AMPK and PDH) or mitochondrial proteins (Cyt-C, COX-IV, SDHA, and VDAC). Markers of proteasomal proteolysis (MURF1 and ATROGIN-1) decreased during chemotherapy, but did not change further during chemotherapy combined with exercise training. A similar pattern was observed for autophagy-related proteins such as ATG5, p62, and pULK1 Ser⁷⁵⁷, but not ULK1 and LC3BII/LC3BI. Phosphorylation of FOXO3a at Ser^318/321 did not change during chemotherapy, but decreased during exercise training. This could suggest that FOXO3a-mediated transcriptional regulation of MURF1 and ATROGIN-1 serves as a mechanism by which exercise training maintains proteolytic systems in skeletal muscle in cancer patients. Phosphorylation of proteins that regulate protein synthesis (mTOR at Ser²⁴⁴⁸ and 4EBP1 at Thr^37/46) increased during chemotherapy and leveled off during exercise training. Finally, chemotherapy tended to increase the number of satellite cells in type 1 fibers, without any further change during chemotherapy and exercise training. Conversely, the number of satellite cells in type 2 fibers did not change during chemotherapy, but increased during chemotherapy combined with exercise training.

CONCLUSIONS

Molecular signaling cascades involved in exercise training are disturbed during cancer and chemotherapy, and exercise training may prevent further disruption of these pathways.

TRIAL REGISTRATION

The study was approved by the local Scientific Ethics Committee of the Central Denmark Region (Project ID: M-2014-15-14; date of approval: 01/27/2014) and the Danish Data Protection Agency (case number 2007-58-0010; date of approval: 01/28/2015). The trial was registered at http//www.clinicaltrials.gov (registration number: NCT02192216; date of registration 07/17-2014).

Gene expression variability in human skeletal muscle transcriptome responses to acute resistance exercise

NEW FINDINGS

What is the central question of this study? Does exercise, independent of random error and within-subject variability, contribute to the variability in gene expression responses to an acute bout of resistance exercise? What is the main finding and its importance? A reanalysis of publicly available microarray data revealed that variability in observed gene expression responses for a subset of genes could be partially attributable to an effect of acute resistance exercise. These finding support the notion that individual responsiveness explains a portion of the variability in observed gene expression responses to acute resistance exercise.

ABSTRACT

The purpose of this study was to use publicly available transcriptomic data to determine whether variability in gene expression responses to an acute bout of acute resistance exercise (ARE) can be attributable to an effect of ARE per se. We examined microarray data from a previous study that collected skeletal muscle biopsies before and 24 h after ARE or a no-exercise time-matched control period (CTL). By subtracting the standard deviation in the observed responses to CTL from ARE, we determined that ARE contributed to the variability in the observed gene expression responses for many (∼31,000), but not all, transcripts included on the Affymetrix Human Genome chips. ARE had a large effect on variability in the observed gene expression responses in 1290 genes that was not attributed to any technical/biological variability associated with repeated measurements. Pathway analysis using WebGestalt revealed that several of these 1290 genes are involved in pathways known to regulate skeletal muscle adaptations to chronic resistance training. These results suggest that variability in the observed gene expression responses for a subset of genes could be partially attributable to an effect of ARE.

Mechanoresponsive self-growing hydrogels inspired by muscle training

Living tissues, such as muscle, autonomously grow and remodel themselves to adapt to their surrounding mechanical environment through metabolic processes. By contrast, typical synthetic materials cannot grow and reconstruct their structures once formed. We propose a strategy for developing “self-growing” polymeric materials that respond to repetitive mechanical stress through an effective mechanochemical transduction. Robust double-network hydrogels provided with a sustained monomer supply undergo self-growth, and the materials are substantially strengthened under repetitive loading through a structural destruction-reconstruction process. This strategy also endows the hydrogels with tailored functions at desired positions by mechanical stamping. This work may pave the way for the development of self-growing gel materials for applications such as soft robots and intelligent devices.

Short-term effects of the suboccipital muscle inhibition technique and cranio-cervical flexion exercise on hamstring flexibility, cranio-vertebral angle, and range of motion of the cervical spine in subjects with neck pain: A randomized controlled trial

BACKGROUND

Cervical spinal instability often leads to neck pain and forward head posture (FHP). To improve neck pain and FHP, both the suboccipital muscle inhibition (SMI) technique and cranio-cervical flexion exercise (CCFE) have been used. However, little is known regarding the validity of hamstring flexibility in neck pain subjects after CCFE as a treatment index, and comparison between the SMI technique and CCFE for neck pain treatment.

OBJECTIVE

This study aimed to determine the short-term effects of SMI technique and CCFE, which represent passive and active exercise programs, respectively, and whether these improve the straight leg raise (SLR) test results, popliteal angle (PA), cranio-vertebral angle (CVA), and cervical range of motion (CROM) and are equally effective in immediate enhancement of such measures in neck pain subjects.

METHODS

Twenty subjects with neck pain were randomly allocated to the SMI and CCFE groups (n= 10 each). The outcomes were evaluated via clinical evaluation and SLR, PA, CVA, and CROM measurement before and after intervention.

RESULTS

SLR test results, PA, CVA (sitting and standing), and CROM (flexion, extension, lateral flexion, and right and left rotations) after both interventions were significantly higher than those before the interventions (P< 0.05). The SLR test results (left), PA, and CVA (standing) after the SMI technique improved to levels similar to those observed after CCFE.

CONCLUSIONS

Both the SMI technique and CCFE improve SLR test results, PA, CVA, and CROM and are equally effective in immediate enhancement of the hamstring flexibility, CVA, and CROM in subjects with neck pain.

A physiological drop in pH decreases mitochondrial respiration, and HDAC and Akt signaling, in L6 myocytes

Exercise stimulates mitochondrial biogenesis and increases mitochondrial respiratory function and content. However, during high-intensity exercise muscle pH can decrease below pH 6.8 with a concomitant increase in lactate concentration. This drop in muscle pH is associated with reduced exercise-induced mitochondrial biogenesis, while increased lactate may act as a signaling molecule to affect mitochondrial biogenesis. Therefore, in this study we wished to determine the impact of altering pH and lactate concentration in L6 myotubes on genes and proteins known to be involved in mitochondrial biogenesis. We also examined mitochondrial respiration in response to these perturbations. Differentiated L6 myotubes were exposed to normal (pH 7.5)-, low (pH 7.0)-, or high (pH 8.0)-pH media with and without 20 mM sodium l-lactate for 1 and 6 h. Low pH and 20 mM sodium l-lactate resulted in decreased Akt (Ser473) and AMPK (T172) phosphorylation at 1 h compared with controls, while at 6 h the nuclear localization of histone deacetylase 5 (HDAC5) was decreased. When the pH was increased both Akt (Ser473) and AMPK (T172) phosphorylation was increased at 1 h. Overall increased lactate decreased the nuclear content of HDAC5 at 6 h. Exposure to both high- and low-pH media decreased basal mitochondrial respiration, ATP turnover, and maximum mitochondrial respiratory capacity. These data indicate that muscle pH affects several metabolic signaling pathways, including those required for mitochondrial function.

Concurrent Training for Sports Performance: The 2 Sides of the Medal

The classical work by Robert C. Hickson showed in 1980 that the addition of a resistance-training protocol to a predominantly aerobic program could lead to impaired leg-strength adaptations in comparison with a resistance-only training regimen. This interference phenomenon was later highlighted in many reports, including a meta-analysis. However, it seems that the interference effect has not been consistently reported, probably because of the complex interactions between training variables and methodological issues. On the other side of the medal, Dr Hickson et al subsequently (1986) reported that a strength-training mesocycle could be beneficial for endurance performance in running and cycling. In recent meta-analyses and review articles, it was demonstrated that such a training strategy could improve middle- and long-distance performance in many disciplines (running, cycling, cross-country skiing, and swimming). Notably, it appears that improvements in the energy cost of locomotion could be associated with these performance enhancements. Despite these benefits, it was also reported that strength training could represent a detrimental stimulus for endurance performance if an inappropriate training plan has been prepared. Taken together, these observations suggest that coaches and athletes should be careful when concurrent training seems imperative to meet the complex physiological requirements of their sport. This brief review presents a practical appraisal of concurrent training for sports performance. In addition, recommendations are provided so that practitioners can adapt their interventions based on the training objectives.

The Influence of Post-Exercise Cold-Water Immersion on Adaptive Responses to Exercise: A Review of the Literature

Post-exercise cold-water immersion (CWI) is used extensively in exercise training as a means to minimise fatigue and expedite recovery between sessions. However, debate exists around its merit in long-term training regimens. While an improvement in recovery following a single session of exercise may improve subsequent training quality and stimulus, reports have emerged suggesting CWI may attenuate long-term adaptations to exercise training. Recent developments in the understanding of the molecular mechanisms governing the adaptive response to exercise in human skeletal muscle have provided potential mechanistic insight into the effects of CWI on training adaptations. Preliminary evidence suggests that CWI may blunt resistance signalling pathways following a single exercise session, as well as attenuate key long-term resistance training adaptations such as strength and muscle mass. Conversely, CWI may augment endurance signalling pathways and the expression of genes key to mitochondrial biogenesis following a single endurance exercise session, but have little to no effect on the content of proteins key to mitochondrial biogenesis following long-term endurance training. This review explores current evidence regarding the underlying molecular mechanisms by which CWI may alter cellular signalling and the long-term adaptive response to exercise in human skeletal muscle.

The Relationships Between Internal and External Measures of Training Load and Intensity in Team Sports: A Meta-Analysis

BACKGROUND

The associations between internal and external measures of training load and intensity are important in understanding the training process and the validity of specific internal measures.

OBJECTIVES

We aimed to provide meta-analytic estimates of the relationships, as determined by a correlation coefficient, between internal and external measures of load and intensity during team-sport training and competition. A further aim was to examine the moderating effects of training mode on these relationships.

METHODS

We searched six electronic databases (Scopus, Web of Science, PubMed, MEDLINE, SPORTDiscus, CINAHL) for original research articles published up to September 2017. A Boolean search phrase was created to include search terms relevant to team-sport athletes (population; 37 keywords), internal load (dependent variable; 35 keywords), and external load (independent variable; 81 keywords). Articles were considered for meta-analysis when a correlation coefficient describing the association between at least one internal and one external measure of session load or intensity, measured in the time or frequency domain, was obtained from team-sport athletes during normal training or match-play (i.e., unstructured observational study). The final data sample included 122 estimates from 13 independent studies describing 15 unique relationships between three internal and nine external measures of load and intensity. This sample included 295 athletes and 10,418 individual session observations. Internal measures were session ratings of perceived exertion (sRPE), sRPE training load (sRPE-TL), and heart-rate-derived training impulse (TRIMP). External measures were total distance (TD), the distance covered at high and very high speeds (HSRD ≥ 13.1-15.0 km h^-1 and VHSRD ≥ 16.9-19.8 km h^-1, respectively), accelerometer load (AL), and the number of sustained impacts (Impacts > 2-5 G). Distinct training modes were identified as either mixed (reference condition), skills, metabolic, or neuromuscular. Separate random effects meta-analyses were conducted for each dataset (n = 15) to determine the pooled relationships between internal and external measures of load and intensity. The moderating effects of training mode were examined using random-effects meta-regression for datasets with at least ten estimates (n = 4). Magnitude-based inferences were used to interpret analyses outcomes.

RESULTS

During all training modes combined, the external load relationships for sRPE-TL were possibly very large with TD [r = 0.79; 90% confidence interval (CI) 0.74 to 0.83], possibly large with AL (r = 0.63; 90% CI 0.54 to 0.70) and Impacts (r = 0.57; 90% CI 0.47 to 0.64), and likely moderate with HSRD (r = 0.47; 90% CI 0.32 to 0.59). The relationship between TRIMP and AL was possibly large (r = 0.54; 90% CI 0.40 to 0.66). All other relationships were unclear or not possible to infer (r range 0.17-0.74, n = 10 datasets). Between-estimate heterogeneity [standard deviations (SDs) representing unexplained variation; τ] in the pooled internal-external relationships were trivial to extremely large for sRPE (τ range = 0.00-0.47), small to large for sRPE-TL (τ range = 0.07-0.31), and trivial to moderate for TRIMP (τ range= 0.00-0.17). The internal-external load relationships during mixed training were possibly very large for sRPE-TL with TD (r = 0.82; 90% CI 0.75 to 0.87) and AL (r = 0.81; 90% CI 0.74 to 0.86), and TRIMP with AL (r = 0.72; 90% CI 0.55 to 0.84), and possibly large for sRPE-TL with HSRD (r = 0.65; 90% CI 0.44 to 0.80). A reduction in these correlation magnitudes was evident for all other training modes (range of the change in r when compared with mixed training - 0.08 to - 0.58), with these differences being unclear to possibly large. Training mode explained 24-100% of the between-estimate variance in the internal-external load relationships.

CONCLUSION

Measures of internal load derived from perceived exertion and heart rate show consistently positive associations with running- and accelerometer-derived external loads and intensity during team-sport training and competition, but the magnitude and uncertainty of these relationships are measure and training mode dependent.

The Impact of Resistance Training on Swimming Performance: A Systematic Review

BACKGROUND

The majority of propulsive forces in swimming are produced from the upper body, with strong correlations between upper body strength and sprint performance. There are significant gaps in the literature relating to the impact of resistance training on swimming performance, specifically the transfer to swimming performance.

OBJECTIVE

The aims of this systematic literature review are to (1) explore the transfer of resistance-training modalities to swimming performance, and (2) examine the effects of resistance training on technical aspects of swimming.

METHODS

Four online databases were searched with the following inclusion criteria: (1) journal articles with outcome measures related to swimming performance, and (2) competitive swimmers participating in a structured resistance-training programme. Exclusion criteria were (1) participants with a mean age <16 years; (2) untrained, novice, masters and paraplegic swimmers; (3) triathletes and waterpolo players; (4) swimmers with injuries or illness; and (5) studies of starts and turns specifically. Data were extracted using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, and the Physiotherapy Evidence Database (PEDro) scale was applied.

RESULTS

For optimal transfer, specific, low-volume, high-velocity/force resistance-training programmes are optimal. Stroke length is best achieved through resistance training with low repetitions at a high velocity/force. Resisted swims are the most appropriate training modality for improving stroke rate.

CONCLUSION

Future research is needed with respect to the effects of long-term resistance-training interventions on both technical parameters of swimming and overall swimming performance. The results of such work will be highly informative for the scientific community, coaches and athletes.

Cross-Adaptation: Heat and Cold Adaptation to Improve Physiological and Cellular Responses to Hypoxia

To prepare for extremes of heat, cold or low partial pressures of oxygen (O₂), humans can undertake a period of acclimation or acclimatization to induce environment-specific adaptations, e.g. heat acclimation (HA), cold acclimation (CA), or altitude training. While these strategies are effective, they are not always feasible due to logistical impracticalities. Cross-adaptation is a term used to describe the phenomenon whereby alternative environmental interventions, e.g. HA or CA, may be a beneficial alternative to altitude interventions, providing physiological stress and inducing adaptations observable at altitude. HA can attenuate physiological strain at rest and during moderate-intensity exercise at altitude via adaptations allied to improved O₂ delivery to metabolically active tissue, likely following increases in plasma volume and reductions in body temperature. CA appears to improve physiological responses to altitude by attenuating the autonomic response to altitude. While no cross-acclimation-derived exercise performance/capacity data have been measured following CA, post-HA improvements in performance underpinned by aerobic metabolism, and therefore dependent on O₂ delivery at altitude, are likely. At a cellular level, heat shock protein responses to altitude are attenuated by prior HA, suggesting that an attenuation of the cellular stress response and therefore a reduced disruption to homeostasis at altitude has occurred. This process is known as cross-tolerance. The effects of CA on markers of cross-tolerance is an area requiring further investigation. Because much of the evidence relating to cross-adaptation to altitude has examined the benefits at moderate to high altitudes, future research examining responses at lower altitudes should be conducted, given that these environments are more frequently visited by athletes and workers. Mechanistic work to identify the specific physiological and cellular pathways responsible for cross-adaptation between heat and altitude, and between cold and altitude, is warranted, as is exploration of benefits across different populations and physical activity profiles.

Swifter, higher, stronger: What’s on the menu?

The exploits of elite athletes delight, frustrate, and confound us as they strive to reach their physiological, psychological, and biomechanical limits. We dissect nutritional approaches to optimal performance, showcasing the contribution of modern sports science to gold medals and world titles. Despite an enduring belief in a single, superior “athletic diet,” diversity in sports nutrition practices among successful athletes arises from the specificity of the metabolic demands of different sports and the periodization of training and competition goals. Pragmatic implementation of nutrition strategies in real-world scenarios and the prioritization of important strategies when nutrition themes are in conflict add to this variation. Lastly, differences in athlete practices both promote and reflect areas of controversy and disagreement among sports nutrition experts.

Bioactive food and exercise in chronic kidney disease: Targeting the mitochondria

Chronic kidney disease (CKD), which affects 10%-15% of the population, associates with a range of complications-such as cardiovascular disease, frailty, infections, muscle and bone disorders and premature ageing-that could be related to alterations of mitochondrial number, distribution, structure and function. As mitochondrial biogenesis, bioenergetics and the dynamic mitochondrial networks directly or indirectly regulate numerous intra- and extracellular functions, the mitochondria have emerged as an important target for interventions aiming at preventing or improving the treatment of complications in CKD. In this review, we discuss the possible role of bioactive food compounds and exercise in the modulation of the disturbed mitochondrial function in a uraemic milieu.

Muscle plasticity of aged subjects in response to electrical stimulation training and inversion and/or limitation of the sarcopenic process

This review addresses the possible structural and functional adaptations of the muscle function to neuromuscular electrical stimulation (NMES) training in frail and/or aged (without advanced chronic disease) subjects. Evidence suggests that the sarcopenic process and its structural and functional effects would be limited and/or reversed through NMES training using excito-motor currents (or direct currents). From a structural viewpoint, NMES helps reduce muscle atrophy. From a functional viewpoint, NMES enables the improvement of motor output (i.e., muscle strength), gait, balance and activities of daily living which enhances the quality of life of aged subjects. Muscle plasticity of aged subjects in response to NMES training turns out to be undeniable, although many mechanisms are not yet explained and deserve to be explore further. Mechanistic explanations as well as conceptual models are proposed to explain how muscle plasticity operates in aged subjects through NMES training. NMES could be seen as a clinically applicable training technique, safe and efficient among aged subjects and could be used more often as part of prevention of sarcopenia. Therapists and physical conditioners/trainers could exploit this new knowledge in their professional practice to improve life conditions (including the risk of fall) of frail and/or aged subjects.

Insulin inhibits autophagy signaling independent of counter-regulatory hormone levels, but does not affect the effects of exercise

Acute exercise increases autophagic signaling through ULK1 in human skeletal muscle during both anabolic and catabolic conditions. The aim of the present study was to investigate if changes in ULK1 Ser⁵⁵⁵ phosphorylation during exercise are reflected by changes in phosphorylation of a newly identified ULK1 substrate (ATG14 Ser²⁹), and to elucidate the involvement of circulatory hormones in regulation of autophagy in human skeletal muscle. We show that one hour of cycling exercise increases ATG14 Ser29 phosphorylation during both hyperinsulinemic euglycemic and euinsulinemic euglycemic conditions. This could suggest that counter-regulatory hormones stimulate autophagy in skeletal muscle, as circulating concentrations of these hormones are highly elevated during exercise. Furthermore, ATG14 Ser²⁹ correlated positively with ULK1 phosphorylation, suggesting that ULK1 Ser⁵⁵⁵ (activating site) phosphorylation reflects ULK1 kinase activity. In a separate series of experiments, we show that insulin stimulates ULK1 phosphorylation at Ser⁷⁵⁷ (inhibitory site) in both hypoglycemic and euglycemic conditions, suggesting that counter-regulatory hormones (such as epinephrine, norepinephrine, growth hormone and glucagon) have limited effects on autophagy signaling in human skeletal muscle. In conclusion, one hour of cycling exercise increases phosphorylation of ATG14 at Ser²⁹ in a pattern that mirrors ULK1 phosphorylation at Ser⁵⁵⁵. Moreover, insulin effects on autophagy signaling in human skeletal muscle are independent of hypoglycemic and euglycemic conditions.

High-Intensity Interval Training Performed by Young Athletes: A Systematic Review and Meta-Analysis

Background: High-intensity interval training (HIIT) is as a time-efficient alternative to moderate- or low-intensity continuous exercise for improving variables related to endurance and anaerobic performance in young and adolescent athletes.

Objectives: To assess original research about enhancement of endurance and anaerobic exercise performance in young and adolescent athletes performing HIIT.

Method: Relevant articles published in peer-reviewed journals were retrieved from the electronic databases PubMed and SPORTDiscus in December 2017. Inclusion criteria were: (i) controlled trials (HIIT vs. alternative training protocol) with pre-post design; (ii) healthy young athletes (≤18 years); (iii) assessing variables related to endurance and exercise performance. Hedges' g effect size (ES), and associated 95% confidence intervals were calculated for comparison of any outcome between experimental (HIIT) and alternative training protocol.

Results: Twenty four studies, involving 577 athletes (mean age: 15.5 ± 2.2 years), were included in this review. HIIT exerted no or small positive mean ES on peak oxygen uptake (VO_2peak), running performance, repeated sprint ability, jumping performance and submaximal heart rate. Although the mean ES for changes in VO_2peak with HIIT is small (mean g = 0.10±0.28), the average increase in VO_2peak from pre to post HIIT-interventions were 7.2 ± 6.9% vs. 4.3 ± 6.9% with any other alternative intervention. HIIT largely and positively affected running speed and oxygen consumption at various lactate- or ventilatory-based thresholds, as well as for sprint running performance. Calculations showed negative mean ES for change-of-direction ability (large), and peak blood lactate concentrations (small). Mean duration per training session for HIIT was shorter than for control interventions (28 ± 15 min vs. 38 ± 24 min).

Conclusion: The present findings suggest that young athletes performing HIIT may improve certain important variables related to aerobic, as well as anaerobic, performance. With HIIT, most variables related to endurance improved to a higher extent, compared to alternative training protocols. However, based on ES, HIIT did not show clear superiority to the alternative training protocols. Nevertheless, young athletes may benefit from HIIT as it requires less time per training session leaving more time for training sport specific skills.

Tailored exercise interventions to reduce fatigue in cancer survivors: study protocol of a randomized controlled trial

Background

Cancer-related fatigue (CRF) is a common and distressing symptom of cancer and/or cancer treatment that persists for years after treatment completion in approximately one third of cancer survivors. Exercise is beneficial for the management of CRF, and general exercise guidelines for cancer survivors are available. There are multiple potential pathways by which exercise improves CRF, and cancer survivors with CRF are diverse with respect to cancer type, treatments and experienced side effects. While the general exercise guidelines are likely sufficient for most cancer survivors, tailoring of exercise interventions may be more effective in those with persistent fatigue. The primary aim of this research is to investigate the effect of a traditional vs. tailored exercise intervention on CRF severity in cancer survivors with persistent CRF.

Methods/design

Cancer survivors (≥ 3 months and ≤ 5 years since primary treatment) who score ≤ 34 on the Functional Assessment of Chronic Illness Therapy Fatigue Scale (FACIT-F) will be randomly allocated to one of two parallel treatment arms: traditional (active control) and tailored exercise. Participants in the traditional exercise group will engage in aerobic and resistance exercise that is consistent with exercise guidelines for cancer survivors. The tailored exercise group will be prescribed an intervention designed to address individual deficits identified at baseline, such as loss of muscular strength, cardiorespiratory deconditioning or sleep disturbance. Participants will be assessed before and after the intervention for CRF severity and other patient-reported outcomes, neuromuscular function and fatigue in response to whole-body exercise, sleep quantity and quality, physical activity levels, cardiorespiratory fitness and blood biomarkers.

Discussion

To our knowledge, this will be the first study to compare the effects of a traditional vs. tailored exercise intervention on CRF severity in cancer survivors with persistent CRF. Using physiological, behavioural and patient-reported outcomes, this study will add to the current knowledge about both the factors contributing to CRF, and the potential reduction in CRF severity with an exercise intervention.

Trial registration

The study is registered at ClinicalTrials.gov (NCT03049384), February, 2017.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4668-z) contains supplementary material, which is available to authorized users.