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Background: We investigated the impact of 1) passive heating (PH) induced by single and intermittent/prolonged hot-water immersion (HWI) and 2) the duration of PH, on muscle contractile function under the unfatigued state, and during the development of muscle fatigue. Methods: Twelve young males volunteered for this study consisting of two phases: single phase (SP) followed by intermittent/prolonged phase (IPP), with both phases including two conditions (i.e., four trials in total) performed randomly: control passive sitting (CON) and HWI (44-45°C; water up to the waist level). SP-HWI included one continuous 45-min bath (from 15 to 60 min). IPP-HWI included an initial 45-min bath (from 15 to 60 min) followed by eight additional 15-min baths interspaced with 15-min breaks at room temperature between 75 and 300 min. Intramuscular (Tmu; measured in the vastus lateralis muscle) and rectal (Trec) temperatures were determined. Neuromuscular testing (performed in the knee extensors and flexors) was performed at baseline and 60 min later during SP, and at baseline, 60, 90, 150 and 300 min after baseline during IPP. A fatiguing protocol (100 electrical stimulations of the knee extensors) was performed after the last neuromuscular testing of each trial. Results: HWI increased Tmu and Trec to 38°C-38.5°C (p < 0.05) during both SP and IPP. Under the unfatigued state, HWI did not affect electrically induced torques at 20 Hz (P20) and 100 Hz (P100). However, it induced a shift towards a faster contractile profile during both SP and IPP, as evidenced by a decreased P20/P100 ratio (p < 0.05) and an improved muscle relaxation (i.e., reduced half-relaxation time and increased rate of torque relaxation; p < 0.05). Despite a reduced voluntary activation (i.e., -2.63% ± 4.19% after SP-HWI and -5.73% ± 4.31% after IPP-HWI; condition effect: p < 0.001), HWI did not impair maximal isokinetic and isometric contraction torques. During the fatiguing protocol, fatigue index and the, This study was supported by a grant from the Swedish Research Council for Sports Sciences (P2020-0119 to TC) and by Institutional funds from Örebro University.

Track cycling entails a challenging progression from the youth categories to elite competition. Hence, this study aimed to investigate the importance of early performance and various publicly available performance indicators in predicting the success of male and female cyclists across different track disciplines. Additionally, the study enriches the findings by incorporating interviews with international-level coaches and athletes. A retrospective analysis of data from UCI track cycling databases was conducted, supplemented by interviews with international-level coaches and athletes. The success rate for highly ranked junior track cyclists was found to be less than 20%, with a majority of these athletes specializing in sprint events, regardless of gender. The study indicated that the UCI ranking and points earned during the season were not reliable indicators for distinguishing future success (p < 0.05). From the interviews, we identified three main themes: (1) trends in career success from the youth to elite categories, (2) performance markers as predictors of future success, and (3) the challenges and time involved in reaching elite categories. Junior category performance alone may not be the sole indicator of future success in track cycling. However, integrating performance analyses with practitioners and athletes’ perspectives enables a deeper understanding of the results and the developmental context.

The original version of this article unfortunately contained a mistake. Affiliation details for author Tomas Venckunas were incorrectly given as Department of Life Sciences, Research Centre for Musculoskeletal Science and Sports Medicine, Manchester Metropolitan University, John Dalton Building, Chester Street, Manchester M1 5GD, UK but should have been Lithuanian Sports University, Kaunas, Lithuania.

BACKGROUND: Proliferating cancer cells shift their metabolism towards glycolysis, even in the presence of oxygen, to especially generate glycolytic intermediates as substrates for anabolic reactions. We hypothesize that a similar metabolic remodelling occurs during skeletal muscle hypertrophy. METHODS: We used mass spectrometry in hypertrophying C2C12 myotubes in vitro and plantaris mouse muscle in vivo and assessed metabolomic changes and the incorporation of the [U-13C6]glucose tracer. We performed enzyme inhibition of the key serine synthesis pathway enzyme phosphoglycerate dehydrogenase (Phgdh) for further mechanistic analysis and conducted a systematic review to align any changes in metabolomics during muscle growth with published findings. Finally, the UK Biobank was used to link the findings to population level. RESULTS: The metabolomics analysis in myotubes revealed insulin-like growth factor-1 (IGF-1)-induced altered metabolite concentrations in anabolic pathways such as pentose phosphate (ribose-5-phosphate/ribulose-5-phosphate: +40%; P = 0.01) and serine synthesis pathway (serine: -36.8%; P = 0.009). Like the hypertrophy stimulation with IGF-1 in myotubes in vitro, the concentration of the dipeptide l-carnosine was decreased by 26.6% (P = 0.001) during skeletal muscle growth in vivo. However, phosphorylated sugar (glucose-6-phosphate, fructose-6-phosphate or glucose-1-phosphate) decreased by 32.2% (P = 0.004) in the overloaded muscle in vivo while increasing in the IGF-1-stimulated myotubes in vitro. The systematic review revealed that 10 metabolites linked to muscle hypertrophy were directly associated with glycolysis and its interconnected anabolic pathways. We demonstrated that labelled carbon from [U-13C6]glucose is increasingly incorporated by ~13% (P = 0.001) into the non-essential amino acids in hypertrophying myotubes, which is accompanied by an increased depletion of media serine (P = 0.006). The inhibition of Phgdh suppressed muscle protein synt

Background: We investigated the impact of moderate muscle cooling induced by single and intermittent/prolonged cold-water immersions (CWI) on muscle force and contractility in unfatigued state and during the development of fatigue resulting from electrically induced contractions. Methods: Twelve young males participated in this study consisting of two phases [single phase (SP) followed by intermittent/prolonged phase (IPP)], with both phases including two conditions (i.e., four trials in total) performed randomly: control passive sitting (CON) and cold-water immersions (10°C). SP-CWI included one 45 min-bath (from 15 to 60 min). IPP-CWI included three baths (45 min-bath from 15 to 60 min, and 15 min-baths from 165 to 180 min and from 255 to 270 min), with participants sitting at room temperature the rest of the time until 300 min. Blood pressure and intramuscular (Tmu) temperature were assessed, and neuromuscular testing was performed at baseline and 60 min after baseline during SP, and at baseline, 60, 90, 150 and 300 min after baseline during IPP. A fatiguing protocol (100 electrical stimulations) was performed after the last neuromuscular testing of each trial. Results: In unfatigued state, SP-CWI and IPP-CWI reduced electrically induced torque at 100 Hz (P100) but not at 20 Hz (P20), and increased P20/P100 ratio. The changes from baseline for P100 and P20/P100 ratio were lower in IPP-CWI than SP-CWI. Both cold-water immersion conditions slowed down muscle contraction and relaxation, and reduced maximal isokinetic contraction torque, but the changes from baseline were lower after IPP-CWI than SP-CWI. cold-water immersions did not impair maximal voluntary isometric contraction. During the fatiguing protocol, torque fatigue index and the changes in muscle contractile properties were larger after IPP-CWI than SP-CWI, but were in the same range as after CON conditions. The differences of muscle contractile function between SP-CWI and IPP-CWI were accompanied by a low, Funding agency:Swedish Research Council for Sports Sciences P2020-0119

Introduction In athletes, exposure to cold during winter sports may impair physical performance. Severe muscle cooling appears to reduce maximal force and induces a shift towards a slower contractile profile. However, whether moderate muscle cooling and the duration of cooling affect muscle contractile profile (assessed from electrically evoked torque at low and high frequencies) and maximal voluntary force (isometric and isokinetic contractions) remains to be clarified. Therefore, the aim of this study was to investigate the impact of acute and prolonged cooling on electrically evoked torque and maximal voluntary contraction torque in young males. Methods Twelve active males (27.2 ± 6.6 years old) were recruited for this study, consisting of 2 phases: acute and prolonged exposures. During each phase, participants were randomly exposed to cold water immersion (CWI, 10°C, up to the iliac crest) or passive resting (PR). Exposure to CWI was either continuous during 45min (acute CWI, A-CWI) or intermittent during a period of 300min [prolonged CWI (P-CWI) including immersions between baseline to 45min, 165 to 180min, and 255 to 270min]. Muscle (Tmu, average across 1, 2 and 3cm depth) and rectal (Trec) temperatures were assessed using thermo-sensors. Transcutaneous electrical stimulation of the quadriceps muscle was performed to determine torques at low (20 Hz: P20) and high (100 Hz: P100) frequencies, and P20/P100 ratio was calculated. Maximal voluntary isometric torque of the knee extensors (MVIC), as well as peak isokinetic torques (90°/s) of knee extensors (KE-IsoC) and flexors (KF-isoC) were determined. Neuromuscular tests were performed at baseline (BL) and 60min after BL during acute exposure, and at BL, 60, 90, 150 and 300min after BL during prolonged exposure. Results Trec did not change after A-CWI while it was reduced (0.8 ± 0.4°C, p<0.001) after P-CWI compared to BL. Tmu decreased during A-CWI and P-CWI compared to BL (6.1 ± 2.2°C and 4.6 ± 1.1°C, respecti

The effects of genetic polymorphisms on muscle structure and function remain elusive. The present study tested for possible associations of 16 polymorphisms (across ten candidate genes) with fittness and skeletal muscle phenotypes in 17- to 37-year-old healthy Caucasian male endurance (n = 86), power/strength (n = 75) and team athletes (n = 60), and non-athletes (n = 218). Skeletal muscle function was measured with eight performance tests covering multiple aspects of muscular fitness. Along with body mass and height, the upper arm and limb girths, and maximal oxygen uptake were measured. Genotyping was conducted on DNA extracted from blood. Of the 16 polymorphisms studied, nine (spanning seven candidate genes and four gene families/signalling pathways) were independently associated with at least one skeletal muscle fitness measure (size or function, or both) measure and explained up to 4.1% of its variation. Five of the studied polymorphisms (activin- and adreno-receptors, as well as myosine light chain kinase 1) in a group of one to three combined with body height, age and/or group explained up to 20.4% of the variation of muscle function. ACVR1B (rs2854464) contributed 2.0-3.6% to explain up to 14.6% of limb proximal girths. The G allele (genotypes AG and GG) of the ACVR1B (rs2854464) polymorphism was significantly overrepresented among team (60.4%) and power (62.0%) athletes compared to controls (52.3%) and endurance athletes (39.2%), and G allele was also most consistently/frequently associated with muscle size and power. Overall, the investigated polymorphisms determined up to 4.1% of the variability of muscular fitness in healthy young humans.

Methionine restriction (MR) reduces inflammation and increases longevity. We studied the effects of MR (0.17% kCal methionine, 10% kCal fat) and MR + high-fat diet (HFD) (0.17% methionine, 45% kCal fat) and overload-induced hypertrophy on inflammation, angiogenesis and mitochondrial activity in the hind-limb muscle in 10- and 26-month-old male C57BL/6J mice. Plasma IL-6 concentrations were higher in old compared to young mice. M. plantaris hypertrophy was accompanied by increased p-Akt, without a significant change in Akt and VEGF levels. In young mice on a HFD or MR + HFD diet the SDH activity was higher than in those from mice on other diets, irrespective of overload. There were no significant differences in total NAD concentration in the m. gastrocnemius. MR enhanced the skeletal muscle hypertrophic response in old age that was accompanied with an increase in p-Akt without significant changes in muscle oxidative capacity, low-grade systemic inflammation, NAD, VEGF or Akt levels.