Characterizing the effects of muscle-specific GSK3α/ß reduction on murine muscle contractility and metabolism in female mice.

Dysregulation of skeletal muscle morphology and metabolism is associated with chronic diseases such as obesity and type 2 diabetes. The enzyme glycogen synthase kinase 3 (GSK3) is highly involved in skeletal muscle physiology and metabolism, acting as a negative regulator of muscle size, strength, adaptive thermogenesis, and glucose homeostasis. Correspondingly, we have shown that partial knockdown (∼40%) of GSK3 specifically in skeletal muscle increases lean mass, reduces fat mass, and activates muscle-based adaptive thermogenesis via sarco(endo)plasmic reticulum Ca2+ (SERCA) uncoupling in male mice. However, the effects of GSK3 knockdown in female mice have yet to be investigated. Here, we examined the effects of muscle-specific GSK3 knockdown on body composition, muscle size and strength, and whole body metabolism in female C57BL/6J mice. Our results show that GSK3 content is higher in the female soleus versus the male soleus; however, there were no differences in the extensor digitorum longus (EDL). Furthermore, muscle-specific GSK3 knockdown did not alter body composition in female mice, nor did it alter daily energy expenditure, glucose/insulin tolerance, mitochondrial respiration, or the expression of the SERCA uncouplers sarcolipin and neuronatin. We also did not find any differences in soleus muscle size, strength, or fatigue resistance. In the EDL, we found that an increase in absolute and specific force production, but there were no differences in fatigability. Therefore, our study highlights sex differences in the response to genetic reduction of gsk3, with most of the effects previously observed in male mice being absent in females.NEW & NOTEWORTHY Here we show that partial GSK3 knockdown has minimal effects on whole body metabolism and muscle contractility in female mice. This is partly inconsistent with previous results found in male mice, which reveal a potential influence of biological sex.

Low-dose lithium supplementation promotes adipose tissue browning and sarco(endo)plasmic reticulum Ca2+ ATPase uncoupling in muscle.

Sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) uncoupling in skeletal muscle and mitochondrial uncoupling via uncoupling protein 1 (UCP1) in brown/beige adipose tissue are two mechanisms implicated in energy expenditure. Here, we investigated the effects of glycogen synthase kinase 3 (GSK3) inhibition via lithium chloride (LiCl) treatment on SERCA uncoupling in skeletal muscle and UCP1 expression in adipose. C2C12 and 3T3-L1 cells treated with LiCl had increased SERCA uncoupling and UCP1 protein levels, respectively, ultimately raising cellular respiration; however, this was only observed when LiCl treatment occurred throughout differentiation. In vivo, LiCl treatment (10 mg/kg/day) increased food intake in chow-fed diet and high-fat diet (HFD; 60% kcal)-fed male mice without increasing body mass-a result attributed to elevated daily energy expenditure. In soleus muscle, we determined that LiCl treatment promoted SERCA uncoupling via increased expression of SERCA uncouplers, sarcolipin and/or neuronatin, under chow-fed and HFD-fed conditions. We attribute these effects to the GSK3 inhibition observed with LiCl treatment as partial muscle-specific GSK3 knockdown produced similar effects. In adipose, LiCl treatment inhibited GSK3 in inguinal white adipose tissue (iWAT) but not in brown adipose tissue under chow-fed conditions, which led to an increase in UCP1 in iWAT and a beiging-like effect with a multilocular phenotype. We did not observe this beiging-like effect and increase in UCP1 in mice fed a HFD, as LiCl could not overcome the ensuing overactivation of GSK3. Nonetheless, our study establishes novel regulatory links between GSK3 and SERCA uncoupling in muscle and GSK3 and UCP1 and beiging in iWAT.

Low-dose lithium feeding increases the SERCA2a-to-phospholamban ratio, improving SERCA function in murine left ventricles.

NEW FINDINGS: What is the central question of this study? Inhibition of glycogen synthase kinase-3 (GSK3) has been shown to improve cardiac SERCA2a function. Lithium can inhibit GSK3, but therapeutic doses used in treating bipolar disorder can have toxic effects. It has not been determined whether subtherapeutic doses of lithium can improve cardiac SERCA function. What is the main finding and its importance? Using left ventricles from wild-type mice, we found that subtherapeutic lithium feeding for 6 weeks decreased GSK3 activity and increased cardiac SERCA function compared with control-fed mice. These findings warrant the investigation of low-dose lithium feeding in preclinical models of cardiomyopathy and heart failure to determine the therapeutic benefit of GSK3 inhibition. ABSTRACT: The sarco(endo)plasmic reticulum Ca2+ -ATPase (SERCA) pump is responsible for regulating calcium (Ca2+ ) within myocytes, with SERCA2a being the dominant isoform in cardiomyocytes. Its inhibitor, phospholamban (PLN), acts by decreasing the affinity of SERCA for Ca2+ . Changes in the SERCA2a:PLN ratio can cause Ca2+ dysregulation often seen in patients with dilated cardiomyopathy and heart failure. The enzyme glycogen synthase kinase-3 (GSK3) is known to downregulate SERCA function by decreasing the SERCA2a:PLN ratio. In this study, we sought to determine whether feeding mice low-dose lithium, a natural GSK3 inhibitor, would improve left ventricular SERCA function by altering the SERCA2a:PLN ratio. To this end, male wild-type C57BL/6J mice were fed low-dose lithium via drinking water (10 mg kg-1  day-1 LiCl for 6 weeks) and left ventricles were harvested. GSK3 activity was significantly reduced in LiCl-fed versus control-fed mice. The apparent affinity of SERCA for Ca2+ was also increased (pCa50 ; control, 6.09 ± 0.03 versus LiCl, 6.26 ± 0.04, P < 0.0001) along with a 2.0-fold increase in SERCA2a:PLN ratio in LiCl-fed versus control-fed mice. These findings suggest that low-dose lithium supplementation can improve SERCA function by increasing the SERCA2a:PLN ratio. Future studies in murine preclinical models will determine whether GSK3 inhibition via low-dose lithium could be a potential therapeutic strategy for dilated cardiomyopathy and heart failure.

Low dose lithium supplementation activates Wnt/ß-catenin signalling and increases bone OPG/RANKL ratio in mice.

Lithium, a well-known inhibitor of glycogen synthase kinase-3ß (GSK3ß), can improve bone formation by activating the Wnt/ß-catenin signalling pathway. However, most studies have used higher doses of lithium, which potentially have adverse effects. Herein, we report that low dose lithium supplementation (10 mg/kg/d for 6 weeks) in mice results in a serum lithium concentration of 0.02 mM significantly inhibiting GSK3ß while activating Wnt/ß-catenin in bone. In turn, we observed a significant increase in the expression of osteoprotegerin (OPG), with unaltered expression of nuclear-factor kß ligand (RANKL), ultimately leading to a significant increase in the OPG/RANKL ratio. Altogether, our findings provide initial evidence that low dose lithium supplementation can promote the signalling pathways associated with bone formation.

Increases in skeletal muscle ATGL and its inhibitor G0S2 following 8 weeks of endurance training in metabolically different rat skeletal muscles.

Adipose triglyceride lipase (ATGL) catalyzes the rate-limiting removal of the first fatty acid from a triglyceride. ATGL is activated by comparative gene identification-58 and inhibited by G(0)/G(1) switch gene-2 protein (G0S2). Research in other tissues and cell culture indicates that inhibition is dependent on relative G0S2-to-ATGL protein content. G0S2 may also have several roles within mitochondria; however, this has yet to be observed in skeletal muscle. The purpose of this study was to determine if muscle G0S2 relative to ATGL content would decrease to facilitate intramuscular lipolysis following endurance training. Male Sprague-Dawley rats (n = 10; age 51-53 days old) were progressively treadmill trained at a 10% incline for 8 wk ending with 25 m/min for 1 h compared with control. Sciatic nerve stimulation for hind-limb muscle contraction (and lipolysis) was administered for 30 min to one leg, leaving the opposing leg as a resting control. Soleus (SOL), red gastrocnemius (RG), and white gastrocnemius were excised from both legs following stimulation or control. ATGL protein increased in all trained muscles. Unexpectedly, G0S2 protein was greater in the trained SOL and RG. In RG-isolated mitochondria, G0S2 also increased with training, yet mitochondrial G0S2 content was unaltered with acute contraction; therefore, any role of G0S2 in the mitochondria does not appear to be acutely mediated by content alone. In summary, G0S2 increased with training in oxidative muscles and mitochondria but not following acute contraction, suggesting that inhibition is not through relative G0S2-to-ATGL content but through more complicated intracellular mechanisms.

Pyruvate dehydrogenase kinase-4 contributes to the recirculation of gluconeogenic precursors during postexercise glycogen recovery.

During recovery from glycogen-depleting exercise, there is a shift from carbohydrate oxidation to glycogen resynthesis. The activity of the pyruvate dehydrogenase (PDH) complex may decrease to reduce oxidation of carbohydrates in favor of increasing gluconeogenic recycling of carbohydrate-derived substrates for this process. The precise mechanism behind this has yet to be elucidated; however, research examining mRNA content has suggested that the less-abundant pyruvate dehydrogenase kinase-4 (PDK4) may reduce PDH activation during exercise recovery. To investigate this, skeletal muscle and liver of wild-type (WT) and PDK4-knockout (PDK4-KO) mice were analyzed at rest (Rest), after exercise to exhaustion (Exh), and after 2 h of recovery with ad libitum feeding (Rec). Although there were no differences in exercise tolerance between genotypes, caloric consumption was doubled by PDK4-KO mice during Rec. Because of this, PDK4-KO mice at Rec supercompensated muscle glycogen to 120% of resting stores. Therefore, an extra group of PDK4-KO mice were pair-fed (PF) with WT mice during Rec for comparison. PF mice fully replenished muscle glycogen but recovered only 50% of liver glycogen stores. Concentrations of muscle lactate and alanine were also lower in PF than in WT mice, indicating that this decrease may lead to a potential reduction of recycled gluconeogenic substrates, due to oxidation of their carbohydrate precursors in skeletal muscle, leading to observed reductions in hepatic glucose and glycogen concentrations. Because of the impairments seen in PF PDK4-KO mice, these results suggest a role for PDK4 in regulating the PDH complex in muscle and promoting gluconeogenic precursor recirculation during recovery from exhaustive exercise.

Skeletal muscle PLIN proteins, ATGL and CGI-58, interactions at rest and following stimulated contraction.

Evidence indicates that skeletal muscle lipid droplet-associated proteins (PLINs) regulate lipolysis through protein-protein interactions on the lipid droplet surface. In adipocytes, PLIN1 is thought to regulate lipolysis by directly interacting with comparative gene identification-58 (CGI-58), an activator of adipose triglyceride lipase (ATGL). Upon lipolytic stimulation, PLIN1 is phosphorylated, releasing CGI-58 to fully activate ATGL and initiate triglyceride breakdown. The absence of PLIN1 in skeletal muscle leads us to believe that other PLIN family members undertake this role. Our purpose was to examine interactions between PLIN2, PLIN3, and PLIN5, with ATGL and its coactivator CGI-58 at rest and following contraction. Isolated rat solei were incubated for 30 min at rest or during 30 min of intermittent tetanic stimulation [150-ms volleys at 60 Hz with a train rate of 20 tetani/min (25°C)] to maximally stimulate intramuscular lipid breakdown. Results show that the interaction between ATGL and CGI-58 increased 128% following contraction (P = 0.041). Further, ATGL interacts with PLIN2, PLIN3, and PLIN5 at rest and following contraction. The PLIN2-ATGL interaction decreased significantly by 21% following stimulation (P = 0.013). Both PLIN3 and PLIN5 coprecipitated with CGI-58 at rest and following contraction, while there was no detectable interaction between PLIN2 and CGI-58 in either condition. Therefore, our findings indicate that in skeletal muscle, during contraction-induced muscle lipolysis, ATGL and CGI-58 strongly associate and that the PLIN proteins work together to regulate lipolysis, in part, by preventing ATGL and CGI-58 interactions at rest.

Maternal high fat feeding does not have long-lasting effects on body composition and bone health in female and male Wistar rat offspring at young adulthood.

High fat diets adversely affect body composition, bone mineral and strength, and alter bone fatty acid composition. It is unclear if maternal high fat (HF) feeding permanently alters offspring body composition and bone health. Female rats were fed control (CON) or HF diet for 10 weeks, bred, and continued their diets throughout pregnancy and lactation. Male and female offspring were studied at weaning and 3 months, following consumption of CON diet. At weaning, but not 3 months of age, male and female offspring from dams fed HF diet had lower lean mass and higher fat and bone mass, and higher femur bone mineral density (females only) than offspring of dams fed CON diet. Male and female offspring femurs from dams fed HF diet had higher monounsaturates and lower n6 polyunsaturates at weaning than offspring from dams fed CON diet, where females from dams fed HF diet had higher saturates and lower n6 polyunsaturates at 3 months of age. There were no differences in strength of femurs or lumbar vertebrae at 3 months of age in either male or female offspring. In conclusion, maternal HF feeding did not permanently affect body composition and bone health at young adulthood in offspring.

Changes in Body Mass, Physical Activity, and Dietary Intake during the COVID-19 Pandemic Lockdowns in Canadian University Students.

This study examined changes in body mass and body mass index (BMI), physical activity, and dietary intake in Canadian university students during the first year of the COVID-19 pandemic. Two self-reported recall surveys were conducted: after the first lockdown in September 2020 (T1) and following the second lockdown in March 2021 (T2). Eligible participants were full-time undergraduate students attending a Canadian university and residing in Canada during the first year of the pandemic. At T1, 510 students (99 male, 411 female) completed the survey, and of those, 135 (32 males, 103 females) completed the survey at T2 (73% attrition). At both T1 and T2, most participants were 18-24 years of age (93% and 90%, respectively), Caucasian (73% and 78%, respectively), and resided in the province of Ontario (79% and 80%, respectively). Body mass increased from T1 to T2 (+0.91 ± 3.89 kg t(132) = -2.7, p = 0.008). BMI also increased from T1 to T2 (+0.30 ± 1.33 kg/m2 [t(130) = -2.5, p = 0.012), with a greater number of participants within the overweight range (19.8% versus 24.4%, respectively). At T1, 38% of the participants reported a decrease in physical activity, while the number of students reporting a decrease in activity increased to 56% at T2. Dietary energy intake decreased from 1678 ± 958 kcal/day at T1 to 1565 ± 842 kcal/day at T2 [c2(1) = 7.2, p = 0.007]. Diet quality also decreased, with participants not meeting the recommended daily allowance for essential macro and micronutrients. A decrease was observed in daily servings of fruits (-27%, p < 0.001), vegetables (-72%, p < 0.001), and grains (-68%, p < 0.001). In conclusion, despite a small decrease in dietary energy intake, a modest weight gain occurred during the first year of the COVID-19 pandemic in this cohort of Canadian university students, which was potentially related to decreased physical activity and diet quality.

Correction: Klentrou et al. Circulating Levels of Bone Markers after Short-Term Intense Training with Increased Dairy Consumption in Adolescent Female Athletes. Children 2021, 8, 961.

There was an error in the original publication [...].

Beyond its Psychiatric Use: The Benefits of Low-dose Lithium Supplementation.

Lithium is most well-known for its mood-stabilizing effects in the treatment of bipolar disorder. Due to its narrow therapeutic window (0.5-1.2 mM serum concentration), there is a stigma associated with lithium treatment and the adverse effects that can occur at therapeutic doses. However, several studies have indicated that doses of lithium under the predetermined therapeutic dose used in bipolar disorder treatment may have beneficial effects not only in the brain but across the body. Currently, literature shows that low-dose lithium (≤0.5 mM) may be beneficial for cardiovascular, musculoskeletal, metabolic, and cognitive function, as well as inflammatory and antioxidant processes of the aging body. There is also some evidence of low-dose lithium exerting a similar and sometimes synergistic effect on these systems. This review summarizes these findings with a focus on low-dose lithium's potential benefits on the aging process and age-related diseases of these systems, such as cardiovascular disease, osteoporosis, sarcopenia, obesity and type 2 diabetes, Alzheimer's disease, and the chronic low-grade inflammatory state known as inflammaging. Although lithium's actions have been widely studied in the brain, the study of the potential benefits of lithium, particularly at a low dose, is still relatively novel. Therefore, this review aims to provide possible mechanistic insights for future research in this field.

Low-Dose Lithium Supplementation Influences GSK3ß Activity in a Brain Region Specific Manner in C57BL6 Male Mice.

BACKGROUND: Lithium, a commonly used treatment for bipolar disorder, has been shown to have neuroprotective effects for other conditions including Alzheimer's disease via the inhibition of the enzyme glycogen synthase kinase-3 (GSK3). However, dose-dependent adverse effects of lithium are well-documented, highlighting the need to determine if low doses of lithium can reliably reduce GSK3 activity. OBJECTIVE: The purpose of this study was to evaluate the effects of a low-dose lithium supplementation on GSK3 activity in the brain of an early, diet-induced Alzheimer's disease model. METHODS: Male C57BL/6J mice were divided into either a 6-week or 12-week study. In the 6-week study, mice were fed a chow diet or a chow diet with lithium-supplemented drinking water (10 mg/kg/day) for 6 weeks. Alternatively, in the 12-week study, mice were fed a chow diet, a high-fat diet (HFD), or a HFD with lithium-supplemented drinking water for 12 weeks. Prefrontal cortex and hippocampal tissues were collected for analysis. RESULTS: Results demonstrated reduced GSK3 activity in the prefrontal cortex as early as 6 weeks of lithium supplementation, in the absence of inhibitory phosphorylation changes. Further, lithium supplementation in an obese model reduced prefrontal cortex GSK3 activity as well as improved insulin sensitivity. CONCLUSION: Collectively, these data provide evidence for low-dose lithium supplementation to inhibit GSK3 activity in the brain. Moreover, these results indicate that GSK3 activity can be inhibited despite any changes in phosphorylation. These findings contribute to an overall greater understanding of low-dose lithium's ability to influence GSK3 activity in the brain and its potential as an Alzheimer's disease prophylactic.

Subcellular localization of skeletal muscle lipid droplets and PLIN family proteins OXPAT and ADRP at rest and following contraction in rat soleus muscle.

Skeletal muscle lipid droplet-associated proteins (PLINs) are thought to regulate lipolysis through protein-protein interactions on the lipid droplet surface. In adipocytes, PLIN2 [adipocyte differentiation-related protein (ADRP)] is found only on lipid droplets, while PLIN5 (OXPAT, expressed only in oxidative tissues) is found both on and off the lipid droplet and may be recruited to lipid droplet membranes when needed. Our purpose was to determine whether PLIN5 is recruited to lipid droplets with contraction and to investigate the myocellular location and colocalization of lipid droplets, PLIN2, and PLIN5. Rat solei were isolated, and following a 30-min equilibration period, they were assigned to one of two groups: 1) 30 min of resting incubation and 2) 30 min of stimulation (n = 10 each). Immunofluorescence microscopy was used to determine subcellular content, distribution, and colocalization of lipid droplets, PLIN2, and PLIN5. There was a main effect for lower lipid and PLIN2 content in stimulated compared with rested muscles (P < 0.05). Lipid droplet distribution declined exponentially from the sarcolemma to the fiber center in the rested muscles (P = 0.001, r(2) = 0.99) and linearly in stimulated muscles (slope = -0.0023 ± 0.0006, P < 0.001, r(2) = 0.93). PLIN2 distribution declined exponentially from the sarcolemma to the fiber center in both rested and stimulated muscles (P < 0.0001, r(2) = 0.99 rest; P = 0.0004, r(2) = 0.98 stimulated), while PLIN5 distribution declined linearly (slope = -0.0085 ± 0.0009, P < 0.0001, r(2) = 0.94 rest; slope=-0.0078 ± 0.0010, P = 0.0003, r(2) = 0.91 stimulated). PLIN5-lipid droplets colocalized at rest with no difference poststimulation (P = 0.47; rest r(2) = 0.55 ± 0.02, stimulated r(2) = 0.58 ± 0.03). PLIN2-lipid droplets colocalized at rest with no difference poststimulation (P = 0.48; rest r(2) = 0.66 ± 0.02, stimulated r(2) = 0.65 ± 0.02). Contrary to our hypothesis, these results show that PLIN5 is not recruited to lipid droplets with contraction in isolated skeletal muscle.

Muscle cellular properties in the ice hockey player: a model for investigating overtraining?

In this study, we hypothesized that athletes involved in 5-6 months of sprint-type training would display higher levels of proteins and processes involved in muscle energy supply and utilization. Tissue was sampled from the vastus lateralis of 13 elite ice hockey players (peak oxygen consumption = 51.8 ± 1.3 mL·kg(-1)·min(-1); mean ± standard error) at the end of a season (POST) and compared with samples from 8 controls (peak oxygen consumption = 45.5 ± 1.4 mL·kg(-1)·min(-1)) (CON). Compared with CON, higher activities were observed in POST (p < 0.05) only for succinic dehydrogenase (3.32 ± 0.16 mol·(mg protein)(-1)·min(-1) vs. 4.10 ± 0.11 mol·(mg protein)(-1)·min(-1)) and hexokinase (0.73 ± 0.05 mol·(mg protein)(-1)·min(-1) vs. 0.90 ± 0.05mol·(mg protein)(-1)·min(-1)) but not for phosphorylase, phosphofructokinase, and creatine phosphokinase. No differences were found in Na(+),K(+)-ATPase concentration (ß(max): 262 ± 36 pmol·(g wet weight)(-1) vs. 275 ± 27 pmol·(g wet weight)(-1)) and the maximal activity of the sarcoplasmic reticulum Ca(2+)-ATPase (98.1 ± 6.1 µmol·(g protein)(-1)·min(-1) vs. 102 ± 3.3 µmol·(g protein)(-1)·min(-1)). Cross-sectional area was lower (p < 0.05) in POST but only for the type IIA fibres (6312 ± 684 µm(2) vs. 5512 ± 335 µm(2)), while the number of capillary counts per fibre and the capillary to fibre area ratio were generally higher (p < 0.05). These findings suggest that elite trained ice hockey players display elevations only in support of glucose-based aerobic metabolism that occur in the absence of alterations in excitation-contraction processes.

Intensified training in adolescent female athletes: a crossover study of Greek yogurt effects on indices of recovery.

Background: During a period of intensified exercise (e.g. training/identification camps), often undertaken by competitive youth athletes, the maintenance of muscle function and peak performance can become challenging due to an accumulation of fatigue. The provision of post-exercise dairy protein in adults has been previously shown to accelerate recovery; however, its efficacy in youth athletes is currently unknown. Therefore, the purpose of this study was to examine the effects of increased dairy protein consumption with plain Greek yogurt (GY) on performance and recovery indices during an intensified soccer training camp in adolescent female soccer players. Methods: Thirteen players (14.3 ± 1.3 years) participated in a randomized, double blinded, crossover design study where they received 3 servings/day of either GY (~115 kcal, 17 g protein, ~11.5 g carbohydrates) or an isoenergetic carbohydrate control (CHO, ~115 kcal, 0.04 g protein, ~28.6 g carbohydrates) during two 5-day soccer-specific training camps. Performance was assessed before and after each training camp. Fasted, morning, creatine kinase (CK), insulin-like growth factor-1 (IGF-1), C-reactive protein (CRP), interleukin 6 (IL6), interleukin 10 (IL10) and tumor necrosis factor-α (TNFα) were measured in plasma pre- and post-training. Results: Training led to decrements in counter-movement jump (p = 0.01), broad jump (p = 0.04) and aerobic capacity (p = 0.006), with no effect of GY. A significant increase in anti-inflammatory cytokine IL10 was observed from pre- to post-training in GY (+26% [p = 0.008]) but not in CHO (p = 0.89). CRP and CK increased (+65% [p = 0.005] and +119% [p ≤ 0.001], respectively), while IGF-1 decreased (-34% [p ≤ 0.001]) from pre- to post-training with no difference between conditions. Conclusions: These results demonstrate that consumption of GY did not offer any added recovery benefit with respect to measures of performance and in the attenuation of exercise-induced muscle damage above that achieved with energy-matched carbohydrate in this group of young female soccer players. However, regular consumption of GY may assist with the acute anti-inflammatory response during periods of intensified training in adolescent athletes.

Creatine O'Clock: Does Timing of Ingestion Really Influence Muscle Mass and Performance?

It is well-established that creatine supplementation augments the gains in muscle mass and performance during periods of resistance training. However, whether the timing of creatine ingestion influences these physical and physiological adaptations is unclear. Muscle contractions increase blood flow and possibly creatine transport kinetics which has led some to speculate that creatine in close proximity to resistance training sessions may lead to superior improvements in muscle mass and performance. Furthermore, creatine co-ingested with carbohydrates or a mixture of carbohydrates and protein that alter insulin enhance creatine uptake. The purpose of this narrative review is to (i) discuss the purported mechanisms and variables that possibly justify creatine timing strategies, (ii) to critically evaluate research examining the strategic ingestion of creatine during a resistance training program, and (iii) provide future research directions pertaining to creatine timing.

Effects of Creatine Supplementation on Brain Function and Health.

While the vast majority of research involving creatine supplementation has focused on skeletal muscle, there is a small body of accumulating research that has focused on creatine and the brain. Preliminary studies indicate that creatine supplementation (and guanidinoacetic acid; GAA) has the ability to increase brain creatine content in humans. Furthermore, creatine has shown some promise for attenuating symptoms of concussion, mild traumatic brain injury and depression but its effect on neurodegenerative diseases appears to be lacking. The purpose of this narrative review is to summarize the current body of research pertaining to creatine supplementation on total creatine and phophorylcreatine (PCr) content, explore GAA as an alternative or adjunct to creatine supplementation on brain creatine uptake, assess the impact of creatine on cognition with a focus on sleep deprivation, discuss the effects of creatine supplementation on a variety of neurological and mental health conditions, and outline recent advances on creatine supplementation as a neuroprotective supplement following traumatic brain injury or concussion.

Correction: McKinlay et al. Effects of Post-Exercise Whey Protein Consumption on Recovery Indices in Adolescent Swimmers. Int. J. Environ. Res. Public Health 2020, 17, 7761.

The authors of "Effects of Post-Exercise Whey Protein Consumption on Recovery Indices in Adolescent Swimmers" report an error in Table 1 of their article [...].

Sarco(endo)plasmic reticulum Ca2+-ATPase function is impaired in skeletal and cardiac muscles from young DBA/2J mdx mice.

The DBA/2J (D2) mdx mouse is a more severe model of Duchenne muscular dystrophy when compared to the traditional C57BL/10 (C57) mdx mouse. Here, we questioned whether sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) function would differ in muscles from young D2 and C57 mdx mice. Both D2 and C57 mdx mice exhibited signs of impaired Ca2+ uptake in the gastrocnemius, diaphragm, and left ventricle; however, the level of impairment was more severe in D2 mdx mice. Reductions in maximal SERCA activity were also more prominent in the D2 mdx gastrocnemius and diaphragm when compared to those from C57 mdx mice; however, there were no differences detected in the left ventricle. Across all muscles, D2 mdx mice had the highest levels of oxidative stress as indicated by protein nitrosylation and/or nitration. In conclusion, our study shows that SERCA function is more impaired in young D2 mdx mice compared with age-matched C57 mdx mice.

Circulating Levels of Bone Markers after Short-Term Intense Training with Increased Dairy Consumption in Adolescent Female Athletes.

Thirteen female adolescent soccer players (14.3 ± 1.3 years) participated in a cross-over, double-blind trial examining the effects of Greek yogurt (GY) consumption on bone biomarkers during 5 days of intense soccer training. The study took place over two intervention weeks, which consisted of a pre-training assessment day, 5 training days, and a post-training assessment day. Participants completed the GY condition and a carbohydrate isocaloric placebo control pudding condition (CHO) in random order, 4 weeks apart. Morning, fasted, resting blood samples were collected pre- and post-training in each condition. Total osteocalcin (tOC), undercarboxylated osteocalcin (unOC), C-terminal telopeptide of type 1 collagen (CTX), osteoprotegerin (OPG), and receptor activator nuclear factor kappa-ß ligand (RANKL) were measured in serum. The results showed no effects for time (pre- to post-training) or condition, and no interaction for tOC, CTX, OPG, RANKL, and the OPG/RANKL ratio. A time-by-condition interaction (p = 0.011) was observed in unOC, reflecting a post-training decrease in the GY, but not the CHO condition (-26% vs. -3%, respectively). However, relative unOC (% of tOC) decreased post-training (-16%), with no differences between conditions. These findings suggest that short-term high-impact intense training had no direct catabolic impact on bone metabolism, with GY adding no benefit beyond that of the isocaloric CHO control pudding.