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1.
BMJ Open Sport Exerc Med ; 7(4): e001170, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-34745647

RESUMO

Exercising women report three to six times more ACL tears than men, which happen, in the majority of cases, with a non-contact mechanism. This sex disparity has, in part, been attributed to the differences in reproductive hormone profiles between men and women. Many studies have shown that anterior knee (AK) laxity and the rate of non-contact ACL injuries vary across the menstrual cycle, but these data are inconsistent. Similarly, several studies have investigated the potential protective effect of hormonal contraceptives on non-contact ACL injuries, but their conclusions are also variable. The purpose of this systematic review and meta-analysis is to, identify, evaluate and summarise the effects of endogenous and exogenous ovarian hormones on AK laxity (primary outcome) and the occurrence of non-contact ACL injuries (secondary outcome) in women. We will perform a systematic search for all observational studies conducted on this topic. Studies will be retrieved by searching electronic databases, clinical trial registers, author's personal files and cross-referencing selected studies. Risk of bias will be assessed using the Newcastle Ottawa Quality Assessment Scale for Cohort and Case-Control Studies. Certainty in the cumulative evidence will be assessed using the Grading of Recommendations Assessment, Development and Evaluation approach. The meta-analyses will use a Bayesian approach to address specific research questions in a more intuitive and probabilistic manner. This review is registered on the international database of prospectively registered systematic reviews (PROSPERO; CRD42021252365).

2.
Eur J Nutr ; 2021 Nov 11.
Artigo em Inglês | MEDLINE | ID: mdl-34766208

RESUMO

PURPOSE: This study aimed to assess the effects of consuming a very-low-energy placebo breakfast on subsequent appetite and lunch energy intake. METHODS: Fourteen healthy males consumed water-only (WAT), very-low-energy, viscous placebo (containing water, low-calorie flavoured squash, and xanthan gum; ~ 16 kcal; PLA), and whole-food (~ 573 kcal; FOOD) breakfasts in a randomised order. Subjects were blinded to the energy content of PLA and specific study aims. Venous blood samples were collected pre-breakfast, 60- and 180-min post-breakfast to assess plasma acylated ghrelin and peptide tyrosine tyrosine concentrations. Subjective appetite was measured regularly, and energy intake was assessed at an ad libitum lunch meal 195-min post-breakfast. RESULTS: Lunch energy intake was lower during FOOD compared to WAT (P < 0.05), with no further differences between trials (P ≥ 0.132). Cumulative energy intake (breakfast plus lunch) was lower during PLA (1078 ± 274 kcal) and WAT (1093 ± 249 kcal), compared to FOOD (1554 ± 301 kcal; P < 0.001). Total area under the curve (AUC) for hunger, desire to eat and prospective food consumption were lower, and fullness was greater during PLA and FOOD compared to WAT (P < 0.05). AUC for hunger was lower during FOOD compared to PLA (P < 0.05). During FOOD, acylated ghrelin was suppressed compared to PLA and WAT at 60 min (P < 0.05), with no other hormonal differences between trials (P ≥ 0.071). CONCLUSION: Consuming a very-low-energy placebo breakfast does not alter energy intake at lunch but may reduce cumulative energy intake across breakfast and lunch and attenuate elevations in subjective appetite associated with breakfast omission. TRIAL REGISTRATION: NCT04735783, 2nd February 2021, retrospectively registered.

4.
Exerc Sport Sci Rev ; 2021 Oct 13.
Artigo em Inglês | MEDLINE | ID: mdl-34669626

RESUMO

ABSTRACT: Best-practice guidance and management of pregnant and postpartum elite athletes and women in arduous occupations is limited by the lack of high-quality evidence available within these populations. We have summarised the adaptations and implications of pregnancy and childbirth; proposed a novel integrative concept to address these changes; and made recommendations to progress research in this area.

5.
Amino Acids ; 53(11): 1763-1766, 2021 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-34676442

RESUMO

We evaluated whether insulin could stimulate ß-alanine uptake by skeletal muscle cells in vitro. Mouse myoblasts (C2C12) (n = 3 wells per condition) were cultured with ß-alanine (350 or 700 µmol·L-1), with insulin (100 µU·mL-1) either added to the media or not. Insulin stimulated the ß-alanine uptake at the lower (350 µmol·L-1) but not higher (700 µmol·L-1) ß-alanine concentration in culture medium, indicating that transporter saturation might blunt the stimulatory effects of insulin.

6.
Int J Sport Nutr Exerc Metab ; : 1-8, 2021 Sep 03.
Artigo em Inglês | MEDLINE | ID: mdl-34480008

RESUMO

This study determined the influence of a high- (HI) versus low-intensity (LI) cycling warm-up on blood acid-base responses and exercise capacity following ingestion of sodium bicarbonate (SB; 0.3 g/kg body mass) or a placebo (PLA; maltodextrin) 3 hr prior to warm-up. Twelve men (21 ± 2 years, 79.2 ± 3.6 kg body mass, and maximum power output [Wmax] 318 ± 36 W) completed a familiarization and four double-blind trials in a counterbalanced order: HI warm-up with SB, HI warm-up with PLA, LI warm-up with SB, and LI warm-up with PLA. LI warm-up was 15 min at 60% Wmax, while the HI warm-up (typical of elites) featured LI followed by 2 × 30 s (3-min break) at Wmax, finishing 30 min prior to a cycling capacity test at 110% Wmax. Blood bicarbonate and lactate were measured throughout. SB supplementation increased blood bicarbonate (+6.4 mmol/L; 95% confidence interval, CI [5.7, 7.1]) prior to greater reductions with HI warm-up (-3.8 mmol/L; 95% CI [-5.8, -1.8]). However, during the 30-min recovery, blood bicarbonate rebounded and increased in all conditions, with concentrations ∼5.3 mmol/L greater with SB supplementation (p < .001). Blood bicarbonate significantly declined during the cycling capacity test at 110%Wmax with greater reductions following SB supplementation (-2.4 mmol/L; 95% CI [-3.8, -0.90]). Aligned with these results, SB supplementation increased total work done during the cycling capacity test at 110% Wmax (+8.5 kJ; 95% CI [3.6, 13.4], ∼19% increase) with no significant main effect of warm-up intensity (+0.0 kJ; 95% CI [-5.0, 5.0]). Collectively, the results demonstrate that SB supplementation can improve HI cycling capacity irrespective of prior warm-up intensity, likely due to blood alkalosis.

7.
Artigo em Inglês | MEDLINE | ID: mdl-34492385

RESUMO

Freshwater turtles found in higher latitudes can experience extreme challenges to acid-base homeostasis while overwintering, due to a combination of cold temperatures along with the potential for environmental hypoxia. Histidine-containing dipeptides (HCDs; carnosine, anserine and balenine) may facilitate pH regulation in response to these challenges, through their role as pH buffers. We measured the HCD content of three tissues (liver, cardiac and skeletal muscle) from the anoxia-tolerant painted turtle (C. picta bellii) acclimated to either 3 or 20 °C. HCDs were detected in all tissues, with the highest content shown in the skeletal muscle. Turtles acclimated to 3 °C had more HCD in their skeletal muscle than those acclimated to 20 °C (carnosine = 20.8 ± 4.5 vs 12.5 ± 5.9 mmol·kg DM-1; ES = 1.59 (95%CI: 0.16-3.00), P = 0.013). The higher HCD content shown in the skeletal muscle of the cold-acclimated turtles suggests a role in acid-base regulation in response to physiological challenges associated with living in the cold, with the increase possibly related to the temperature sensitivity of carnosine's dissociation constant.

8.
Free Radic Biol Med ; 175: 65-79, 2021 11 01.
Artigo em Inglês | MEDLINE | ID: mdl-34455039

RESUMO

Type 2 diabetes is characterised by failure to control glucose homeostasis, with numerous diabetic complications attributable to the resulting exposure of cells and tissues to chronic elevated concentrations of glucose and fatty acids. This, in part, results from formation of advanced glycation and advanced lipidation end-products that are able to modify protein, lipid, or DNA structure, and disrupt normal cellular function. Herein we used mass spectrometry to identify proteins modified by two such adduction events in serum of individuals with obesity, type 2 diabetes, and gestational diabetes, along with similar analyses of human and mouse skeletal muscle cells and mouse pancreatic islets exposed to glucolipotoxic stress. We also report that carnosine, a histidine containing dipeptide, prevented 65-90% of 4-hydroxynonenal and 3-nitrotyrosine adduction events, and that this in turn preserved mitochondrial function and protected stimulus-secretion coupling in cells exposed to metabolic stress. Carnosine therefore offers significant therapeutic potential against metabolic diseases.


Assuntos
Carnosina , Complicações do Diabetes , Diabetes Mellitus Tipo 2 , Animais , Carnosina/farmacologia , Diabetes Mellitus Tipo 2/tratamento farmacológico , Produtos Finais de Glicação Avançada/metabolismo , Camundongos , Estresse Oxidativo , Carbonilação Proteica
9.
Adv Nutr ; 12(6): 2216-2231, 2021 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-34333586

RESUMO

There is growing evidence that supplementation with carnosine, or its rate-limiting precursor ß-alanine, can ameliorate aspects of metabolic dysregulation that occur in diabetes and its related conditions. The purpose of this systematic review and meta-analysis was to evaluate the effect of carnosine or ß-alanine supplementation on markers of glycemic control and insulin resistance in humans and animals. We performed a systematic search of 6 electronic databases up to 31 December 2020. Primary outcomes were changes in 1) fasting glucose, 2) glycated hemoglobin (HbA1c), and 3) 2-h glucose following a glucose-tolerance test. A set of additional outcomes included fasting insulin and homeostatic model assessment of ß-cell function (HOMA-ß) and insulin resistance (HOMA-IR). We assessed risk of bias using the Cochrane risk of bias (RoB) 2.0 (human studies) and the Systematic Review Center for Laboratory Animal Experimentation (SYRCLE) RoB (animal studies) tools; and used the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach to assess certainty. We used Bayesian hierarchical random-effects models, with informative priors for human data and noninformative priors for animal data. Inferences were made on posterior samples generated by Hamiltonian Markov Chain Monte Carlo using 90% credible intervals (90% CrI) and calculated probabilities. Twenty studies (n = 4 human, n = 16 rodent) were included, providing data for 2 primary outcomes (fasting glucose and HbA1c) and 3 additional outcomes (fasting insulin, HOMA-ß, and HOMA-IR). The model provides evidence that supplementation decreases fasting glucose [humans: mean difference (MD)0.5 = -0.95 mmol · L-1 (90% CrI: -2.1, 0.08); rodent: MD0.5 = -2.26 mmol · L-1 (90% CrI: -4.03, -0.44)], HbA1c [humans: MD0.5 = -0.91% (90% CrI: -1.46, -0.39); rodents: MD0.5 = -1.05% (90% CrI: -1.64, -0.52)], HOMA-IR [humans: standardized mean difference (SMD)0.5 = -0.41 (90% CrI: -0.82, -0.07); rodents: SMD0.5 = -0.63 (90% CrI: -1.98, 0.65)], and fasting insulin [humans: SMD0.5 = -0.41 (90% CrI: -0.77, -0.07)]. GRADE assessment showed our certainty in the effect estimate of each outcome to be moderate (human outcomes) or very low (rodent outcomes). Supplementation with carnosine or ß-alanine may reduce fasting glucose, HbA1c, and HOMA-IR in humans and rodents, and fasting insulin in humans; both compounds show potential as therapeutics to improve glycemic control and insulin resistance. This review was registered at PROSPERO as CRD42020191588.

10.
Biochim Biophys Acta Mol Cell Res ; 1868(11): 119117, 2021 10.
Artigo em Inglês | MEDLINE | ID: mdl-34384791

RESUMO

Carnosine is a naturally occurring dipeptide found in meat. Alternatively it can be formed through synthesis from the amino acids, ß-alanine and L-histidine. Carnosine has long been advocated for use as an anti-oxidant and anti-glycating agent to facilitate healthy ageing, and there have also been reports of it having anti-proliferative effects that have beneficial actions against the development of a number of different cancers. Carnosine is able to undertake multiple molecular processes, and it's mechanism of action therefore remains controversial - both in healthy tissues and those associated with cancer or metabolic diseases. Here we review current understanding of its mechanistic role in different physiological contexts, and how this relates to cancer. Carnosine turns over rapidly in the body due to the presence of both serum and tissue carnosinase enzymes however, so its use as a dietary supplement would require ingestion of multiple daily doses. Strategies are therefore being developed that are based upon either resistance of carnosine analogs to enzymatic turnover, or else ß-alanine supplementation, and the development of these potential therapeutic agents is discussed.


Assuntos
Antineoplásicos/farmacologia , Carnosina/farmacologia , Homeostase/efeitos dos fármacos , Humanos
11.
Eur J Sport Sci ; : 1-10, 2021 Jun 22.
Artigo em Inglês | MEDLINE | ID: mdl-34092191

RESUMO

This study investigated the effect of beta-alanine supplementation on short-duration sprints and final 4-km simulated uphill cycling time-trial performance during a comprehensive and novel exercise protocol representative of the demands of road-race cycling, and determined if changes were related to increases in muscle carnosine content. Seventeen cyclists (age 38 ± 9 y, height 1.76 ± 0.07 m, body mass 71.4 ± 8.8 kg, V̇O2max 52.4 ± 8.3 ml·kg-1·min-1) participated in this placebo-controlled, double-blind study. Cyclists undertook a prolonged intermittent cycling protocol lasting 125 min, with a 10-s sprint every 20 min, finishing with a 4-km time-trial at 5% simulated incline. Participants completed two familiarization sessions, and two main sessions, one pre-supplementation and one post-supplementation following 28 days of 6.4 g·day-1 of beta-alanine (N=11) or placebo (N=6; maltodextrin). Muscle biopsies obtained pre- and post-supplementation were analysed for muscle carnosine content. There were no main effects on sprint performance throughout the intermittent cycling test (all P>0.05). There was no group (P=0.69), time (P=0.50) or group x time interaction (P=0.26) on time-to-complete the 4-km time-trial. Time-to-completion did not change from pre- to post-supplementation for BA (-19.2 ± 45.6 s, P=0.43) or PL (+2.8 ± 31.6 s, P=0.99). Beta-alanine supplementation increased muscle carnosine content from pre- to post-supplementation (+9.4 ± 4.0 mmol·kg-1dm; P<0.0001) but was not related to performance changes (r=0.320, P=0.37). Chronic beta-alanine supplementation increased muscle carnosine content but did not improve short-duration sprint performance throughout simulated road race cycling, nor 4-km uphill time-trial performance conducted at the end of this cycling test.Highlights Performance during prolonged cycling events often depends on the ability to maintain an increased power output during higher intensity periods. Thus, cyclists are likely heavily dependent on their ability to resist fatigue during these periods of high-intensity activity.Meta-analytical data show beta-alanine to be an effective supplement to improve exercise outcomes, but little work exists on its efficacy during dynamic actions that are common during prolonged cycling.Beta-alanine supplementation increased muscle carnosine content but did not generate improvements in the performance of high-intensity cycling (10-s sprints or 4-km uphill time-trial) during a simulated road race cycling protocol.These data suggest that short duration sprints (≤10 s) and longer duration (>10 min) high-intensity activity throughout endurance cycling may not be improved with beta-alanine supplementation despite increases in muscle carnosine content.

12.
Int J Sport Nutr Exerc Metab ; 31(4): 305-313, 2021 Jun 07.
Artigo em Inglês | MEDLINE | ID: mdl-34098531

RESUMO

Currently, little is known about the extent of interindividual variability in response to beta-alanine (BA) supplementation, nor what proportion of said variability can be attributed to external factors or to the intervention itself (intervention response). To investigate this, individual participant data on the effect of BA supplementation on a high-intensity cycling capacity test (CCT110%) were meta-analyzed. Changes in time to exhaustion (TTE) and muscle carnosine were the primary and secondary outcomes. Multilevel distributional Bayesian models were used to estimate the mean and SD of BA and placebo group change scores. The relative sizes of group SDs were used to infer whether observed variation in change scores were due to intervention or non-intervention-related effects. Six eligible studies were identified, and individual data were obtained from four of these. Analyses showed a group effect of BA supplementation on TTE (7.7, 95% credible interval [CrI] [1.3, 14.3] s) and muscle carnosine (18.1, 95% CrI [14.5, 21.9] mmol/kg DM). A large intervention response variation was identified for muscle carnosine (σIR = 5.8, 95% CrI [4.2, 7.4] mmol/kg DM) while equivalent change score SDs were shown for TTE in both the placebo (16.1, 95% CrI [13.0, 21.3] s) and BA (15.9, 95% CrI [13.0, 20.0] s) conditions, with the probability that SD was greater in placebo being 0.64. In conclusion, the similarity in observed change score SDs between groups for TTE indicates the source of variation is common to both groups, and therefore unrelated to the supplement itself, likely originating instead from external factors such as nutritional intake, sleep patterns, or training status.


Assuntos
Ciclismo/fisiologia , Carnosina/metabolismo , Suplementos Nutricionais , Tolerância ao Exercício/fisiologia , Músculo Esquelético/metabolismo , beta-Alanina/administração & dosagem , Teorema de Bayes , Viés , Método Duplo-Cego , Humanos , Ensaios Clínicos Controlados Aleatórios como Assunto , Fenômenos Fisiológicos da Nutrição Esportiva , Fatores de Tempo
13.
Redox Biol ; 44: 102016, 2021 08.
Artigo em Inglês | MEDLINE | ID: mdl-34038814

RESUMO

Histidine-containing dipeptides (HCDs) are abundantly expressed in striated muscles. Although important properties have been ascribed to HCDs, including H+ buffering, regulation of Ca2+ transients and protection against oxidative stress, it remains unknown whether they play relevant functions in vivo. To investigate the in vivo roles of HCDs, we developed the first carnosine synthase knockout (CARNS1-/-) rat strain to investigate the impact of an absence of HCDs on skeletal and cardiac muscle function. Male wild-type (WT) and knockout rats (4 months-old) were used. Skeletal muscle function was assessed by an exercise tolerance test, contractile function in situ and muscle buffering capacity in vitro. Cardiac function was assessed in vivo by echocardiography and cardiac electrical activity by electrocardiography. Cardiomyocyte contractile function was assessed in isolated cardiomyocytes by measuring sarcomere contractility, along with the determination of Ca2+ transient. Markers of oxidative stress, mitochondrial function and expression of proteins were also evaluated in cardiac muscle. Animals were supplemented with carnosine (1.8% in drinking water for 12 weeks) in an attempt to rescue tissue HCDs levels and function. CARNS1-/- resulted in the complete absence of carnosine and anserine, but it did not affect exercise capacity, skeletal muscle force production, fatigability or buffering capacity in vitro, indicating that these are not essential for pH regulation and function in skeletal muscle. In cardiac muscle, however, CARNS1-/- resulted in a significant impairment of contractile function, which was confirmed both in vivo and ex vivo in isolated sarcomeres. Impaired systolic and diastolic dysfunction were accompanied by reduced intracellular Ca2+ peaks and slowed Ca2+ removal, but not by increased markers of oxidative stress or impaired mitochondrial respiration. No relevant increases in muscle carnosine content were observed after carnosine supplementation. Results show that a primary function of HCDs in cardiac muscle is the regulation of Ca2+ handling and excitation-contraction coupling.


Assuntos
Carnosina , Dipeptídeos , Animais , Anserina , Histidina , Masculino , Músculo Esquelético , Miócitos Cardíacos , Ratos
14.
Front Physiol ; 12: 653060, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-34017264

RESUMO

Objective: Disuse atrophy (DA) describes inactivity-induced skeletal muscle loss, through incompletely defined mechanisms. An intriguing observation is that individual muscles exhibit differing degrees of atrophy, despite exhibiting similar anatomical function/locations. We aimed to develop an innovative experimental paradigm to investigate Atrophy Resistant tibialis anterior (TA) and Atrophy Susceptible medial gastrocnemius (MG) muscles (aRaS) with a future view of uncovering central mechanisms. Method: Seven healthy young men (22 ± 1 year) underwent 15 days unilateral leg immobilisation (ULI). Participants had a single leg immobilised using a knee brace and air-boot to fix the leg (75° knee flexion) and ankle in place. Dual-energy X-ray absorptiometry (DXA), MRI and ultrasound scans of the lower leg were taken before and after the immobilisation period to determine changes in muscle mass. Techniques were developed for conchotome and microneedle TA/MG muscle biopsies following immobilisation (both limbs), and preliminary fibre typing analyses was conducted. Results: TA/MG muscles displayed comparable fibre type distribution of predominantly type I fibres (TA 67 ± 7%, MG 63 ± 5%). Following 15 days immobilisation, MG muscle volume (-2.8 ± 1.4%, p < 0.05) and muscle thickness decreased (-12.9 ± 1.6%, p < 0.01), with a positive correlation between changes in muscle volume and thickness (R2 = 0.31, p = 0.038). Importantly, both TA muscle volume and thickness remained unchanged. Conclusion: The use of this unique "aRaS" paradigm provides an effective and convenient means by which to study the mechanistic basis of divergent DA susceptibility in humans, which may facilitate new mechanistic insights, and by extension, mitigation of skeletal muscle atrophy during human DA.

15.
Physiol Rep ; 9(10): e14799, 2021 05.
Artigo em Inglês | MEDLINE | ID: mdl-34042295

RESUMO

The development of safe and practical strategies to prevent weakening of bone tissue is vital, yet attempts to achieve this have been hindered by a lack of understanding of the short-term (days-weeks) physiology of bone collagen turnover. To address this, we have developed a method to quantify bone collagen synthesis in vivo, using deuterium oxide (D2 O) tracer incorporation techniques combined with gas chromatography pyrolysis isotope-ratio mass spectrometry (GC-pyrolysis-IRMS). Forty-six male and female rats from a selectively bred model ingested D2 O for 3 weeks. Femur diaphyses (FEM), tibia proximal (T-PRO), and distal (T-DIS) epiphyses-metaphyses and tibia mid-shaft diaphyses (T-MID) were obtained from all rats after necropsy. After demineralisation, collagen proteins were isolated and hydrolysed and collagen fractional synthetic rates (FSRs) determined by incorporation of deuterium into protein-bound alanine via GC-pyrolysis-IRMS. The collagen FSR for the FEM (0.131 ± 0.078%/day; 95% CI [0.106-0.156]) was greater than the FSR at T-MID (0.055 ± 0.049%/day; 95% CI [0.040-0.070]; p < 0.001). The T-PRO site had the highest FSR (0.203 ± 0.123%/day; 95% CI [0.166-0.241]) and T-DIS the lowest (0.027 ± 0.015%/day; 95% CI [0.022-0.031]). The three tibial sites exhibited different FSRs (p < 0.001). Herein, we have developed a sensitive method to quantify in vivo bone collagen synthesis and identified site-specific rates of synthesis, which could be applicable to studies of human bone collagen turnover.

16.
Am J Physiol Regul Integr Comp Physiol ; 320(6): R824-R832, 2021 06 01.
Artigo em Inglês | MEDLINE | ID: mdl-33789445

RESUMO

To examine the role of chronic (in)activity on muscle carnosine (MCarn) and how chronic (in)activity affects MCarn responses to ß-alanine supplementation in spinal cord-injured athletes, 16 male athletes with paraplegia were randomized (2:1 ratio) to receive ß-alanine (n = 11) or placebo (PL, n = 5). They consumed 6.4 g/day of ß-alanine or PL for 28 days. Muscle biopsies of the active deltoid and the inactive vastus lateralis (VL) were taken before and after supplementation. MCarn in the VL was also compared with the VL of a group of individuals without paraplegia (n = 15). MCarn was quantified in whole muscle and in pools of individual fibers by high-performance liquid chromatography. MCarn was higher in chronically inactive VL vs. well-trained deltoid (32.0 ± 12.0 vs. 20.5 ± 6.1 mmol/kg DM; P = 0.018). MCarn was higher in inactive vs. active VL (32.0 ± 12.0 vs. 21.2 ± 7.5 mmol/kg DM; P = 0.011). In type-I fibers, MCarn was significantly higher in the inactive VL than in the active deltoid (38.3 ± 4.7 vs. 27.3 ± 11.8 mmol/kg DM, P = 0.014). MCarn increased similarly between inactive VL and active deltoid in the ß-alanine group (VL: 68.9 ± 55.1%, P = 0.0002; deltoid: 90.5 ± 51.4%, P < 0.0001), with no changes in the PL group. MCarn content was higher in the inactive VL than in the active deltoid and the active VL, but this is probably a consequence of fiber type shift (type I to type II) that occurs with chronic inactivity. Chronically inactive muscle showed an increase in MCarn after BA supplementation equally to the active muscle, suggesting that carnosine accretion following ß-alanine supplementation is not influenced by muscle inactivity.


Assuntos
Carnosina/metabolismo , Homeostase/fisiologia , Músculo Esquelético/fisiopatologia , Traumatismos da Medula Espinal/fisiopatologia , Medula Espinal/fisiopatologia , Atletas , Suplementos Nutricionais , Humanos , Medula Espinal/efeitos dos fármacos , beta-Alanina/administração & dosagem , beta-Alanina/farmacologia
17.
J Sports Sci ; 39(11): 1295-1301, 2021 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-33491594

RESUMO

The availability of dietary beta-alanine (BA) is the limiting factor in carnosine synthesis within human muscle due to its low intramuscular concentration and substrate affinity. Carnosine can accept hydrogen ions (H+), making it an important intramuscular buffer against exercise-induced acidosis. Metabolite accumulation rate increases when exercising in hypoxic conditions, thus an increased carnosine concentration could attenuate H+ build-up when exercising in hypoxic conditions. This study examined the effects of BA supplementation on high intensity cycling capacity in normoxia and hypoxia. In a double-blind design, nineteen males were matched into a BA group (n = 10; 6.4 g·d-1) or a placebo group (PLA; n = 9) and supplemented for 28 days, carrying out two pre- and two post-supplementation cycling capacity trials at 110% of powermax, one in normoxia and one in hypoxia (15.5% O2). Hypoxia led to a 9.1% reduction in exercise capacity, but BA supplementation had no significant effect on exercise capacity in normoxia or hypoxia (P > 0.05). Blood lactate accumulation showed a significant trial x time interaction post-supplementation (P = 0.016), although this was not significantly different between groups. BA supplementation did not increase high intensity cycling capacity in normoxia, nor did it improve cycling capacity in hypoxia even though exercise capacity was reduced under hypoxic conditions.


Assuntos
Ciclismo/fisiologia , Carnosina/biossíntese , Suplementos Nutricionais , Hipóxia/metabolismo , Músculo Esquelético/metabolismo , beta-Alanina/metabolismo , Acidose Láctica/sangue , Análise de Variância , Método Duplo-Cego , Teste de Esforço , Tolerância ao Exercício/fisiologia , Humanos , Hidrogênio/metabolismo , Masculino , Substâncias para Melhoria do Desempenho/administração & dosagem , Substâncias para Melhoria do Desempenho/metabolismo , Placebos , Método Simples-Cego , Adulto Jovem , beta-Alanina/administração & dosagem
18.
Bone ; 145: 115864, 2021 04.
Artigo em Inglês | MEDLINE | ID: mdl-33508495

RESUMO

There is a need to further understand the impact of the menstrual cycle and phase of combined oral contraceptive (COC) use on the pre-analytical variability of markers of bone metabolism in order to improve standardisation procedures for clinical practice and research. The aim of this study was to assess bone metabolism marker concentrations across the menstrual cycle and phases of COC use. Carboxy-terminal cross-linking telopeptide of type I collagen (ß-CTX), procollagen type 1 N propeptide (P1NP) and Bone alkaline phosphatase (Bone ALP) concentrations were assessed in eumenorrheic women (n = 14) during the early follicular, ovulatory and mid-luteal phases of the menstrual cycle and in COC (Microgynon®) (n = 14) users on day 2-3 of pill consumption (PC1), day 15-16 pill consumption (PC2) and day 3-4 of the pill free interval (PFI). ß-CTX was significantly (-16%) lower at PC2 compared to PC1 (P = 0.015) in COC users and was not affected by menstrual cycle phase (P > 0.05). P1NP and Bone ALP were not significantly different across either menstrual cycle phase or phase of COC use (all P > 0.05). There was no difference in pooled bone marker concentrations between eumenorrheic women and COC users (P > 0.05). In contrast to some previous studies, this study showed that bone marker concentrations do not significantly fluctuate across the menstrual cycle. Furthermore, bone resorption markers are significantly affected by phase of COC use, although bone formation markers do not significantly vary by COC phase. Therefore, the phase of COC use should be considered in clinical practice and research when assessing markers of bone metabolism as this can impact circulating concentrations of bone metabolic markers yet is not currently considered in existing guidelines for best practice.


Assuntos
Anticoncepcionais Orais Combinados , Ciclo Menstrual , Osso e Ossos , Colágeno Tipo I , Feminino , Humanos , Fase Luteal
19.
Med Sci Sports Exerc ; 53(5): 1079-1088, 2021 05 01.
Artigo em Inglês | MEDLINE | ID: mdl-33148972

RESUMO

PURPOSE: This study aimed to describe the kinetics of carnosine washout in human skeletal muscle over 16 wk. METHODS: Carnosine washout kinetics were studied in 15 young, physically active omnivorous men randomly assigned to take 6.4 g·d-1 of ß-alanine (n = 11) or placebo (n = 4) for 8 wk. Muscle carnosine content (M-Carn) was determined before (PRE), immediately after (POST), and 4, 8, 12, and 16 wk after supplementation. High-intensity exercise tests were performed at these same time points. Linear and exponential models were fitted to the washout data, and the leave-one-out method was used to select the model with the best fit for M-Carn decay data. Repeated-measures correlation analysis was used to assess the association between changes in M-Carn and changes in performance. RESULTS: M-Carn increased from PRE to POST in the ß-alanine group only (+91.1% ± 29.1%; placebo, +0.04% ± 10.1%; P < 0.0001). M-Carn started to decrease after cessation of ß-alanine supplementation and continued to decrease until week 16 (POST4, +59% ± 40%; POST8, +35% ± 39%; POST12, +18% ± 32%; POST16, -3% ± 24% of PRE M-Carn). From week 12 onward, M-Carn was no longer statistically different from PRE. Both linear and exponential models displayed very similar fit and could be used to describe carnosine washout, although the linear model presented a slightly better fit. The decay in M-Carn was mirrored by a similar decay in high-intensity exercise tolerance; M-Carn was moderately and significantly correlated with total mechanical work done (r = 0.505; P = 0.032) and time to exhaustion (r = 0.72; P < 0.001). CONCLUSIONS: Carnosine washout takes 12-16 wk to complete, and it can be described either by linear or exponential curves. Changes in M-Carn seem to be mirrored by changes in high-intensity exercise tolerance. This information can be used to optimize ß-alanine supplementation strategies.


Assuntos
Carnosina/metabolismo , Tolerância ao Exercício/fisiologia , Exercício Físico/fisiologia , Músculo Esquelético/metabolismo , beta-Alanina/administração & dosagem , Adulto , Suplementos Nutricionais , Teste de Esforço , Humanos , Modelos Lineares , Masculino , Fatores de Tempo , Adulto Jovem
20.
Sports Med ; 51(3): 391-403, 2021 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-33346900

RESUMO

Endurance athletes expend large amounts of energy in prolonged high-intensity exercise and, due to the weight-sensitive nature of most endurance sports, often practice periods of dietary restriction. The Female Athlete Triad and Relative Energy Deficiency in Sport models consider endurance athletes at high-risk for suffering from low energy availability and associated health complications, including an increased chance of bone stress injury. Several studies have examined the effects of low energy availability on various parameters of bone structure and markers of bone (re)modelling; however, there are differences in findings and research methods and critical summaries are lacking. It is difficult for athletes to reduce energy expenditure or increase energy intake (to restore energy availability) in an environment where performance is a priority. Development of an alternative tool to help protect bone health would be beneficial. High-impact exercise can be highly osteogenic and energy efficient; however, at present, it is rarely utilized to promote bone health in endurance athletes. Therefore, with a view to reducing the prevalence of bone stress injury, the objectives of this review are to evaluate the effects of low energy availability on bone health in endurance athletes and explore whether a high-impact exercise intervention may help to prevent those effects from occurring.


Assuntos
Densidade Óssea , Síndrome da Tríade da Mulher Atleta , Atletas , Ingestão de Energia , Metabolismo Energético , Feminino , Humanos , Estado Nutricional
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