Phosphocreatine Stores Research Articles

Nanoencapsulation of creatine: Unlocking hydrophilic bioactive potential through double emulsification by solvent diffusion

AbstractNanotechnology has emerged as a pivotal tool in pharmaceutical research, driving the development of innovative techniques to enhance drug distribution within the body by finely tuning the biopharmaceutical properties of various drugs. Among these techniques, encapsulating biologically active substances in polymeric nanoparticles has garnered significant attention. However, achieving high encapsulation efficiency for hydrophilic molecules remains a formidable challenge, despite their growing importance in treating diverse diseases such as cancer, where nucleic acids, peptides, proteins, and smaller hydrophilic molecules are key players. While some studies have reported improvements in encapsulating hydrophilic drugs, notable examples, like the solid/oil/water ion‐pairing method and the use of calcium phosphate, have shown promise in enhancing encapsulation efficiency for different drugs. Nonetheless, the challenge of preparing aqueous core nanoparticles capable of encapsulating a high percentage of water‐soluble actives persists. Creatine monohydrate, a bioactive compound widely consumed by athletes for its role in increasing muscular phosphocreatine stores, presents an intriguing case. Despite its insolubility in organic media, creatine exhibits limited aqueous solubility, rendering it a suitable candidate for encapsulation in polymeric nanoparticles to improve its aqueous solubility and gastrointestinal absorption. In this study, we aim to produce polymeric nanoparticles containing creatine monohydrate utilizing the double emulsification (W/O/W) method. This promising and efficient approach holds the potential to significantly enhance the aqueous solubility and gastrointestinal absorption of creatine, thereby broadening its clinical application spectrum. Leveraging nanotechnology in this context offers an innovative and potentially impactful strategy to augment the therapeutic efficacy of creatine.

The Top 5 Can't-Miss Sport Supplements.

Background/Objectives: Sports supplements have become popular among fitness enthusiasts for enhancing the adaptive response to exercise. This review analyzes five of the most effective ergogenic aids: creatine, beta-alanine, nitrates, caffeine, and protein. Methods: We conducted a narrative review of the literature with a focus on the sport supplements with the most robust evidence for efficacy and safety. Results: Creatine, one of the most studied ergogenic aids, increases phosphocreatine stores in skeletal muscles, improving ATP production during high-intensity exercises like sprinting and weightlifting. Studies show creatine supplementation enhances skeletal muscle mass, strength/power, and muscular endurance. The typical dosage is 3-5 g per day and is safe for long-term use. Beta-alanine, when combined with the amino acid histidine, elevates intramuscular carnosine, which acts as a buffer in skeletal muscles and delays fatigue during high-intensity exercise by neutralizing hydrogen ions. Individuals usually take 2-6 g daily in divided doses to minimize paresthesia. Research shows significant performance improvements in activities lasting 1-4 min. Nitrates, found in beetroot juice, enhance aerobic performance by increasing oxygen delivery to muscles, enhancing endurance, and reducing oxygen cost during exercise. The recommended dosage is approximately 500 milligrams taken 2-3 h before exercise. Caffeine, a central nervous system stimulant, reduces perceived pain while enhancing focus and alertness. Effective doses range from 3 to 6 milligrams per kilogram of body weight, typically consumed an hour before exercise. Protein supplementation supports muscle repair, growth, and recovery, especially after resistance training. The recommended intake for exercise-trained men and women varies depending on their specific goals. Concluions: In summary, creatine, beta-alanine, nitrates, caffeine, and protein are the best ergogenic aids, with strong evidence supporting their efficacy and safety.

A slow V̇O2 on-response allows to comfortably adopt aerobically unaffordable walking and running speeds in short stairs ascending.

The aim of this paper is to investigate the mechanical and metabolic reasons of the spontaneous gait/speed choice of ascending short flight of stairs, where walking on every step or running on every other step are frequently interchangeable options. Twenty-four subjects' kinematics, oxygen uptake (V̇O2), ventilation and heart rate were sampled during climbing one and two flights of stairs while using the two gaits. Although motor acts were very short in time (5-22 s), metabolic kinetics, extending in the successive 250 s after the end of climbing, consistently reflected the (equivalent of the) needed mechanical energy and allowed to compare the two ascent choices: despite a 250% higher mechanical power associated to running, measured V̇O2, ventilation and heart rate peaked only at +25% with respect to walking, and in both gaits at a much lower values than V̇O2max despite of predictions based on previous gradient locomotion studies. Mechanical work and metabolic cost of transport, as expected, showed similar increase (+25%) in running. For stairs up to 4.8 m tall (30 steps at 53% gradient), running makes us consuming slightly more calories than walking, and in both gaits at no discomfort at all. The cardio-respiratory-metabolic responses similarly delay and damp the replenishing of phosphocreatine stores, which were much faster depleted during the impulsive, highly powered mechanical event, with almost overlapping time courses. Such a discrepancy between mechanical and metabolic dynamics allows to afford almost-to-very anaerobic climbs and to interchangeably decide whether to walk or run up a short flight of stairs.

Hypoxia and Sprint Swimming Performance of Juvenile Striped Bass,Morone saxatilis

Annual hypoxia in the Chesapeake Bay has expanded to the point where Darwinian fitness of juvenile striped bass (Morone saxatilis) may depend on their ability to perform in low-oxygen environments. The locomotion they use in predator/prey dynamics relies primarily on white (type II) muscle that is powered by anaerobic metabolic pathways and has generally been thought to be immune to aquatic hypoxia. We tested the sprint performance of 15 juvenile striped bass twice under acute hypoxia (20% air saturation [AS]) 5 wk apart and once under normoxia (>85% AS) in between. Average sprint performance was lower under the first hypoxia exposure than in normoxia and increased in the second hypoxia test relative to the first. The rank order of individual sprint performance was significantly repeatable when comparing the two hypoxia tests but not when compared with sprint performance measured under normoxic conditions. The maximum sprint performance of each individual was also significantly repeatable within a given day. Thus, sprint performance of striped bass is reduced under hypoxia, is phenotypically plastic, and improves with repetitive hypoxia exposures but is unrelated to relative sprint performance under normoxia. Since energy to fuel a sprint comes from existing ATP and creatine phosphate stores, the decline in sprint performance probably reflects reduced function of a part of the reflex chain leading from detection of aversive stimuli to activation of the muscle used to power the escape response.

Metabolic Responses to Weight Lifting

Metabolic Responses to Weight Lifting

“Panoptic Differential Training: Bio-Dynamics Approach for Sprint Time Trial Cycling Performance” – A Critical Perspective

Background: Intensity of the exercise mostly determines the dominant metabolic pathway for energy. In a sprint cycling 1km time trial, the dominant metabolic pathway must be ATP hydrolysis and glycolysis. Phosphocreatine (PCr) hydrolysis and Anaerobic Glycolysis lead to lactate and H+ accumulation in sarcolemmal cytosol, interfering the muscle contraction leading to fatigue and reduction of power output. To resist fatigue and to continue the high power output throughout the cycling sprint, the lactate flux is an essential phenomenon apart from the regeneration of the ATP. The appearance of H+ and lactate is simultaneous with high intensity exercise, hence the co transport of lactate-H+ is essential and the training should target both the systems to resist fatigue and sustain the cycling sprint power output at maximum throughout the time trial. Biodynamic Implications: Resting ATP and PCr stores of muscle seems less responsive to training and hence strengthening lactate transfer and oxidation appear better alternative along with more concentration on early oxidative phosphorylation. Monocarboxylate Transporter (MCT) isoforms like MCT1 and MCT4 expression should be increased to increase the lactate transport. Load of pH gradient along with lactate flux to be targeted during the training. MCTs also facilitate the H+ efflux and prevent the decrements in intracellular pH. Training Implications: High intensity training has significant influence on the status of both MCT1 and MCT4 ranging from 18% to 120%, though inter individual differences have been observed. Slow endurance training, like sub maximal sprint repetitions increases MCT1 and MCT4 expression leading to lactate uptake and oxidation. With the increase in sustaines sprints without much lactate accumulation during the initial seconds improves oxidative enzymal expression significantly. An acute high intensity sprint form of exercise could reduce the MCT1 expression considerably wherein high expression of H+ is seen in the myocyctes. . Recommendation: very high intensity sprint cycling in repetition need to be reduced to the minimum to avoid excess accumulation of H+. Instead differential training like repetitions of sub maximal runs with initial forty seconds of high intensity sprint cycling followed by sub maximal sprinting for

Effects of 6 weeks of aerobic exercise combined with conjugated linoleic acid on the physical working capacity at fatigue threshold.

The purpose of this study was to examine the effects of conjugated linoleic acid (CLA) supplementation in conjunction with 6 weeks of aerobic exercise training on the physical working capacity at the fatigue threshold (PWCFT), timed sit-ups, and the standing long jump. Thirty-three untrained to moderately trained men (mean ± SD; age = 21.6 ± 2.8 years) participated in this double-blind, placebo-controlled study and were randomly assigned to either a CLA (Clarinol A-80; n = 17) or placebo (PLA; sunflower oil; n = 16) group. Before and after 6 weeks of aerobic training (50% VO2peak for 30 minutes, twice per week) and supplementation (8 ml CLA or PLA per day), each subject completed an incremental cycle ergometer test to exhaustion to determine the PWCFT, maximal number of sit-ups in 1 minute, and the standing long jump. There were no differences (all p ≥ 0.23) between the CLA and PLA groups for the analysis of covariance-adjusted posttest mean values for PWCFT, sit-ups, or standing long jump. The PWCFT increased from pre- to posttraining in the CLA (p = 0.003) and PLA (p = 0.003) groups. There were no differences (p > 0.05) from pre- to posttraining for sit-ups and standing long jump in either the CLA or PLA groups. There was no effect of CLA on the training-induced increases in PWCFT, nor were there any effects of CLA or aerobic training on the maximum number of sit-ups or standing long jump. Thus, CLA had no ergogenic benefits on this model of aerobic training-induced improvements in neuromuscular fatigue, or on field tests of muscle endurance and power.

The effects of creatine loading on oxygen uptake kinetics during heavy exercise

The kinetics of oxygen uptake during the rest to exercise transition are thought to be modulated by intracellular metabolic processes. Evidence suggests that increased phosphocreatine stores may impact the kinetics of VO2, namely, slowing kinetics due to the now increased ATP buffering capacity. Thus, the purpose of this study was to test the hypothesis that creatine loading would induce slowed VO2 kinetics during heavy leg cycling. Four (N=4) subjects completed three separate exercise bouts of heavy (supra‐lactate threshold) exercise both prior to and following a creatine loading regimen. VO2 was measured continuously at the mouth during exercise and recovery for each bout. During the on‐transition, the total amplitude was reduced following creatine loading (Atot: Control 1.22±0.26 vs Creatine 0.97±0.20 L/min, p = 0.03). The time constant during the off‐transition was also slower during the creatine trials (Tau: Control 36.4±9.3 vs Creatine 53.3±7.6 sec, p = 0.02). These findings suggest that an increase in the temporal buffering capacity of phosphocreatine reduces the on‐transient VO2 as well as, slowing the recovery kinetics of VO2.

Blood Flow Restriction: How Does It Work?

Blood Flow Restriction: How Does It Work?

Effects Of Ramadan Fasting On Repeated Sprint Ability In Young Children

Ramadan is a period of daylight abstention from solid or liquid nutrients. Although Ramadan fast starts from early adolescence, previous studies have focused mainly on health- and/or endurance performance-related aspects of the Ramadan participation in adult Muslims. Children are mostly engaged in multiple-sprint sports (e.g. soccer, basketball, tennis). To date, however, the effects of Ramadan on the ability to reproduce sprint performance in the young population are unclear. PURPOSE: To investigate the impact of the Ramadan fast on the ability of young children to perform repeated running sprints. METHODS: Sixteen young children (age: 12.4±1.6 years) performed 6 × 15 m sprints in alternating directions interspersed with 15 s of passive recovery. This procedure was conducted at the same time of the day (between 1 and 2 pm) one week before Ramadan (BR), during Ramadan after 7 and 25 days (DR1 and DR2, respectively) and two weeks after (AR) Ramadan. RESULTS: There were significant sprint number (P<0.001) and test session (P<0.01) main effects on sprint times but there was no interaction between these two factors. The sum of the six sprint times differed (P=0.02) across test sessions. Compared with BR (18.19±0.41s), total sprint times lengthened during Ramadan (DR1: 18.48±0.39s; P>0.05 and DR2: 18.65±0.39s; P=0.05) and remained significantly elevated by AR (18.62±0.46s; P<0.05). Initial sprint performance (2.93±0.07, 2.96±0.06, 2.97±0.05 and 2.96±0.06s BR, DR1, DR2 and AR, respectively) and sprint decrement score (3.7±0.9, 4.1±0.6, 4.7±0.4 and 4.8±0.6 BR, DR1, DR2 and AR, respectively) did not change throughout the study. CONCLUSION: In a group of young children, mean sprint performance during from repeated sprinting was altered toward the end of the Ramadan month and this effect persisted for at least two weeks, while fatigue resistance was not affected. Pending confirmatory research, this reduced ability of young children to repeat running sprints may be linked to limitations in energy supply including an altered glycolytic capacity or a slower replenishment of muscle creatine phosphate stores.

Can the use of creatine supplementation attenuate muscle loss in cachexia and wasting?

Weight loss and low BMI due to an underlying illness have been associated with increased mortality, reduced functional capacity, and diminished quality of life. There is a need for well tolerated, long-term approaches to maintain body weight in patients with cachexia or wasting. The purpose of this review is to highlight the scientific and clinical evidence derived from the recent literature investigating the rationale for and potential medical use of creatine supplementation in patients with cachexia or wasting. Some studies have demonstrated that supplementation with creatine can increase creatine reserves in skeletal muscle and increase muscle mass and performance in various disease states that affect muscle size and function. The mechanisms underlying these effects are not clear. It has been suggested that creatine supplementation may increase intramuscular phosphocreatine stores and promote more rapid recovery of adenosine triphosphate levels following exercise, thus allowing users to exercise for longer periods or at higher intensity levels. Other hypothesized mechanisms include attenuation of proinflammatory cytokines, stimulation of satellite cell proliferation and upregulation of genes that promote protein synthesis and cell repair. Creatine is a generally well tolerated, low-cost, over-the-counter nutritional supplement that shows potential in improving lean body mass and functionality in patients with wasting diseases. However, placebo-controlled studies have shown variable effects, with improvements in some and not in others. Additional studies with longer follow-up are required to identify the populations that might benefit most from creatine supplementation.

Early Beneficial Effects of Bone Marrow-Derived Mesenchymal Stem Cells Overexpressing Akt on Cardiac Metabolism After Myocardial Infarction

Administration of mesenchymal stem cells (MSCs) is an effective therapy to repair cardiac damage after myocardial infarction (MI) in experimental models. However, the mechanisms of action still need to be elucidated. Our group has recently suggested that MSCs mediate their therapeutic effects primarily via paracrine cytoprotective action. Furthermore, we have shown that MSCs overexpressing Akt1 (Akt-MSCs) exert even greater cytoprotection than unmodified MSCs. So far, little has been reported on the metabolic characteristics of infarcted hearts treated with stem cells. Here, we hypothesize that Akt-MSC administration may influence the metabolic processes involved in cardiac adaptation and repair after MI. MI was performed in rats randomized in four groups: sham group and animals treated with control MSCs, Akt-MSCs, or phosphate-buffered saline (PBS). High energy metabolism and basal 2-deoxy-glucose (2-DG) uptake were evaluated on isolated hearts using phosphorus-31 nuclear magnetic resonance spectroscopy at 72 hours and 2 weeks after MI. Treatment with Akt-MSCs spared phosphocreatine stores and significantly limited the increase in 2-DG uptake in the residual intact myocardium compared with the PBS- or the MSC-treated animals. Furthermore, Akt-MSC-treated hearts had normal pH, whereas low pH was measured in the PBS and MSC groups. Correlative analysis indicated that functional recovery after MI was inversely related to the rate of 2-DG uptake. We conclude that administration of MSCs overexpressing Akt at the time of infarction results in preservation of normal metabolism and pH in the surviving myocardium.

The phosphocreatine–creatine kinase system helps to shape muscle cells and keep them healthy and alive

The phosphocreatine–creatine kinase system helps to shape muscle cells and keep them healthy and alive

The lampricide 3-trifluoromethyl-4-nitrophenol (TFM) interferes with intermediary metabolism and glucose homeostasis, but not with ion balance, in larval sea lamprey (Petromyzon marinus)

Although treatment of streams with the lampricide 3-trifluoromethyl-4-nitrophenol (TFM) has been highly effective for sea lamprey (Petromyzon marinus) population control in the Great Lakes, little is known about its mechanism(s) of toxicity. We investigated two hypotheses of TFM toxicity in larval sea lamprey exposed to TFM for 12 h. The first was that TFM interferes with oxidative ATP production by mitochondria, causing depletion of fuel stores in the body. The second was that TFM interferes with gill-mediated ion exchange, which eventually causes circulatory collapse. While exposure of larvae to TFM (2 mg·L–1) did not disturb tissue ATP stores, it led to a sustained 60% reduction in phosphocreatine (PCr) after 6 h. This was accompanied by 6- to 10-fold increases in plasma and tissue lactate, which persisted through 12 h. By 12 h, plasma glucose was nearly depleted in the five surviving lamprey, but TFM caused no appreciable changes in plasma Cl–, haematocrit, haemoglobin, or ammonia concentration. We conclude that TFM-mediated gill damage and ionic failure are not underlying mechanisms of TFM toxicity. Rather, TFM likely interferes with oxidative ATP production, leading to reduced tissue PCr stores and eventually profound hypoglycaemia that starves the nervous system of glucose, causing death.

Tribute to P. L. Lutz: cardiac performance and cardiovascular regulation during anoxia/hypoxia in freshwater turtles

Freshwater turtles overwintering in ice-covered ponds in North America may be exposed to prolonged anoxia, and survive this hostile environment by metabolic depression. Here, we review their cardiovascular function and regulation, with particular emphasis on the factors limiting cardiac performance. The pronounced anoxia tolerance of the turtle heart is based on the ability to match energy consumption with the low anaerobic ATP production during anoxia. Together with a well-developed temporal and spatial energy buffering by creatine kinase, this allows for cellular energy charge to remain high during anoxia. Furthermore, the turtle heart is well adapted to handle the adverse effects of free phosphate arising when phosphocreatine stores are used. Anoxia causes tenfold reductions in heart rate and blood flows that match the metabolic depression, and blood pressure is largely maintained through increased systemic vascular resistance. Depression of the heart rate is not driven by the autonomic nervous system and seems to arise from direct effects of oxygen lack and the associated hyperkalaemia and acidosis on the cardiac pacemaker. These intra- and extracellular changes also affect cardiac contractility, and both acidosis and hyperkalaemia severely depress cardiac contractility. However, increased levels of adrenaline and calcium may, at least partially, salvage cardiac function under prolonged periods of anoxia.

Creatine Monohydrate as a Therapeutic Aid in Muscular Dystrophy

In recent years, dietary supplementation with creatine has been shown to enhance neuromuscular function in several diseases. Recent studies have suggested that creatine can be beneficial in patients with muscular dystrophy and other mitochondrial cytopathies, and may attenuate sarcopenia and facilitate rehabilitation of disuse atrophy. Though the mechanisms are still unknown, creatine has been shown to decrease cytoplasmic Ca2+ levels and increase intramuscular and cerebral phosphocreatine stores, providing potential musculoskeletal and neuroprotective effects.

Effects Of A Short Duration Creatine Loading Protocol On A 1 Minute Anaerobic Cycling Test

A typical Creatine (Cr) loading protocol of 20g/day for 5 days has been shown to increase muscle Cr and Phosphocreatine (PCr) by 20–50% and to improve strength, power, sprint performance, and work performed during multiple sets of maximal effort. Evidence also indicates that PCr stores are elevated within 2 days of Cr supplementation but little information exists concerning exercise performance following 2 days of supplementation. The purpose of this study was to determine if a short duration 2 day creatine loading protocol would enhance exercise performance during a 1 minute anaerobic cycling test. Twenty-two active volunteer males were randomly assigned in a double-blind fashion to either an experimental (creatine monohydrate) group or placebo (maltodextrin) group for 5 full days. Doses were taken four times a day at evenly spaced intervals. To simulate a high intensity bout of exercise subjects performed a 1 minute anaerobic cycling test; before supplementation, following 2 days and again following 5 days of supplementation. Lactate measurements were taken at 1, 3, and 5 minutes post exercise. Results: Peak power significantly increased by 7.1% following 2 days and 9.9% following 5 days of supplementation. There was also a significant 6.38% increase in total work after 2 days and 10.35 % increase in total work after 5 days. There were no significant differences in any of the measurements for the placebo group after 2 or 5 days. The rate of power decline (measured in 5 sec intervals) and post exercise blood lactates were not significantly different following 2 or 5 days of Cr supplementation in either group. These results suggest that 2 days of Cr supplementation similar to a 5 day protocol in active males is effective in increasing peak power output and total work in high intensity anaerobic exercise lasting up to 1 minute in duration.

Acetyl group availability influences phosphocreatine degradation even during intense muscle contraction

We previously established that activation of the pyruvate dehydrogenase complex (PDC) using dichloroacetate (DCA) reduced the reliance on substrate-level phosphorylation (SLP) at the onset of exercise, with normal and reduced blood flow. PDC activation also reduced fatigue development during contraction with reduced blood flow. Since these observations, several studies have re-evaluated our observations. One study demonstrated a performance benefit without a reduction in SLP, raising a question mark over PDC's role in the regulation of ATP regeneration and our interpretation of fatigue mechanisms. Using a model of muscle contraction similar to the conflicting study (i.e. tetanic rather than twitch stimulation), we re-examined this question. Using canine skeletal muscle, one group was infused with saline while the other was pretreated with 300 mg (kg body mass)(-1) DCA. Muscle biopsies were taken at rest, peak tension (1 min) and after 6 min of tetanic electrical stimulation (75 ms on-925 ms off per second) and blood flow was limited to 25% of normal values observed during contraction. DCA reduced phosphocreatine (PCr) degradation by 40% during the first minute of contraction, but did not prevent the almost complete depletion of PCr stores at 6 min, while muscle fatigue did not differ between the two groups. During intermittent tetanic stimulation PCr degradation was 75% greater than with our previous 3 Hz twitch contraction protocol, despite a similar rate of oxygen consumption at 6 min. Thus, in the present study enhanced acetyl group availability altered the time course of PCr utilization but did not prevent the decline towards depletion. Consistent with our earlier conclusions, DCA pretreatment reduces muscle fatigue only when SLP is attenuated. The present study and our met-analysis indicates that enhanced acetyl group availability results in a readily measurable reduction in SLP when the initial rate of PCr utilization is approximately 1 mmol (kg dry mass)(-1) s(-1) or less (depending on intrinsic mitochondrial capacity). When measured early during an uninterrupted period of muscle contraction, acetyl group availability is likely to influence SLP under any condition where mitochondria are responsible for a significant proportion of ATP regeneration.

Increased uncoupling protein 3 content does not affect mitochondrial function in human skeletal muscle in vivo

Phosphocreatine (PCr) resynthesis rate following intense anoxic contraction can be used as a sensitive index of in vivo mitochondrial function. We examined the effect of a diet-induced increase in uncoupling protein 3 (UCP3) expression on postexercise PCr resynthesis in skeletal muscle. Nine healthy male volunteers undertook 20 one-legged maximal voluntary contractions with limb blood flow occluded to deplete muscle PCr stores. Exercise was performed following 7 days consumption of low-fat (LF) or high-fat (HF) diets. Immediately following exercise, blood flow was reinstated, and muscle was sampled after 20, 60, and 120 seconds of recovery. Mitochondrial coupling was assessed by determining the rate of PCr resynthesis during recovery. The HF diet increased UCP3 protein content by approximately 44% compared with the LF diet. However, this HF diet–induced increase in UCP3 expression was not associated with any changes in the rate of muscle PCr resynthesis during conditions of maximal flux through oxidative phosphorylation. Muscle acetylcarnitine, free-creatine, and lactate concentrations during recovery were unaffected by the HF diet. Taken together, our findings demonstrate that increasing muscle UCP3 expression does not diminish the rate of PCr resynthesis, allowing us to conclude that the primary role of UCP3 in humans is not uncoupling.

Increased uncoupling protein 3 content does not affect mitochondrial function in human skeletal muscle in vivo.

Phosphocreatine (PCr) resynthesis rate following intense anoxic contraction can be used as a sensitive index of in vivo mitochondrial function. We examined the effect of a diet-induced increase in uncoupling protein 3 (UCP3) expression on postexercise PCr resynthesis in skeletal muscle. Nine healthy male volunteers undertook 20 one-legged maximal voluntary contractions with limb blood flow occluded to deplete muscle PCr stores. Exercise was performed following 7 days consumption of low-fat (LF) or high-fat (HF) diets. Immediately following exercise, blood flow was reinstated, and muscle was sampled after 20, 60, and 120 seconds of recovery. Mitochondrial coupling was assessed by determining the rate of PCr resynthesis during recovery. The HF diet increased UCP3 protein content by approximately 44% compared with the LF diet. However, this HF diet-induced increase in UCP3 expression was not associated with any changes in the rate of muscle PCr resynthesis during conditions of maximal flux through oxidative phosphorylation. Muscle acetylcarnitine, free-creatine, and lactate concentrations during recovery were unaffected by the HF diet. Taken together, our findings demonstrate that increasing muscle UCP3 expression does not diminish the rate of PCr resynthesis, allowing us to conclude that the primary role of UCP3 in humans is not uncoupling.