Effects of L-carnitine L-tartrate supplementation on muscle oxygenation responses to resistance exercise

Previous research has shown that L-carnitine L-tartrate (LCLT) supplementation beneficially affects markers of hypoxic stress following resistance exercise. However, the mechanism of this response is unclear. Therefore, the primary purpose of this study was to determine the effects of LCLT supplementation on muscle tissue oxygenation during and after multiple sets of squat exercise. Nine healthy, previously resistance-trained men (25.2 +/- 6.years, 91.2 +/- 10.2 kg, 180.2 +/- 6.3 cm) ingested 2 g.d of LCLT or an identical placebo for 23 days in a randomized, balanced, crossover, double-blind, placebo-controlled, repeated-measures study design. On day 21, forearm muscle oxygenation was measured during and after an upper arm occlusion protocol using near infrared spectroscopy (NIRS), which measures the balance of oxygen delivery in relation to oxygen consumption. On day 22, subjects performed 5 sets of 15 to 20 repetitions of squat exercise with corresponding measures of thigh muscle oxygenation, via NIRS, and serial blood draws. Compared to the placebo trial, muscle oxygenation was reduced in the LCLT trial during upper arm occlusion and following each set of resistance exercise. Despite reduced oxygenation, plasma malondealdehyde, a marker of membrane damage, was attenuated during the LCLT trial. There were no differences between trials in the vasoactive substance prostacyclin. In conclusion, because oxygen delivery was occluded during the forearm protocol, it is proposed that enhanced oxygen consumption mediated the reduced muscle oxygenation during the LCLT trial. Enhanced oxygen consumption would explain why hypoxic stress was attenuated with LCLT supplementation.     

The impact of cold-water immersion on power production in the vertical jump and the benefits of a dynamic exercise warm-up

The purpose of this study was to examine the influence of a cold treatment and a dynamic warm-up on lower body power in the form of a countermovement vertical jump (CMVJ). Nine physically active men, who were either current or ex-National Collegiate Athletic Association (NCAA) Division 1 athletes, consented to participate in the study. Using a balanced, randomized presentation and a within-subject design, each subject performed 4 environmental and warm-up protocols (i.e., ambient temperature without warm-up, ambient temperature with warm-up, cold without warm-up, or cold with warm-up). Two sets of 3 maximal effort CMVJs were performed on a force plate at each testing time point. For each protocol, the subjects completed a pretest set of CMVJ (pretreatment [PRE]), were then exposed to 1 of the 2 temperature treatments, completed another set of CMVJ (initial [IT]), then either went through a 15-minute warm-up, or were asked to sit in place. Then a final set of CMVJs was completed (posttreatment [PT]). The primary finding in this study was that warm-up was effective in offsetting the negative effects of cold exposure on CMVJ power. There was a significant main effect for Time (PRE > PT > IT), and there was a significant (p ≤ 0.05) main effect for Trial (AMB = AMBWU > COLDWU > COLD). Because athletic competitions happen in various colder climates, it is important to make sure that a proper warm-up be completed to maximize the athlete's power output. The results of this study demonstrate that when athletes are exposed to cold conditions, it is recommended that before practice or play, a dynamic warm-up be employed to optimize performance.     

Eggs distinctly modulate plasma carotenoid and lipoprotein subclasses in adult men following a carbohydrate-restricted diet

We previously reported that carbohydrate restriction (CR) (10–15% en) during a weight loss intervention lowered plasma triglycerides (TG) by 45% in male subjects (P<.001). However, those subjects with a higher intake of cholesterol provided by eggs (640 mg additional cholesterol, EGG group) had higher concentrations of high-density lipoprotein (HDL) cholesterol (P<.0001) than the individuals consuming lower amounts (0 mg of additional cholesterol, SUB group). The objectives of the present study were to evaluate whether CR and egg intake (1) modulate circulating carotenoids and (2) affect the concentrations of plasma apolipoproteins (apo), lipoprotein size and subfraction distribution. CR decreased the number of large and medium very low-density lipoprotein cholesterol subclasses (P<.001), while small low-density lipoprotein (LDL) were reduced (P<.001). In agreement with these observations, a decrease in apo B (P<.01) was observed. In addition, CR resulted in a 133% increase in apo C-II and a 65% decrease in apo C-III (P<.0001). Although an increase of the larger LDL subclass was observed for all subjects, the EGG group had a greater increase (P<.05). The EGG group also presented a higher number of large HDL particles (P<.01) compared to the SUB group. Regarding carotenoids, CR resulted in no changes in dietary or plasma α- or β-carotene and β-cryptoxanthin, while there was a significant reduction in both dietary and plasma lycopene (P<.001). In contrast, dietary lutein and zeaxanthin were increased during the intervention (P<.05). However, only those subjects from the EGG group presented higher concentrations of these two carotenoids in plasma, which were correlated with the higher concentrations of large LDL observed in the EGG group. These results indicate that CR favorably alters VLDL metabolism and apolipoprotein concentrations, while the components of the egg yolk favor the formation of larger LDL and HDL leading to an increase in plasma lutein and zeaxanthin.     

Four weeks of optimal load ballistic resistance training at the end of season attenuates declining jump performance of women volleyball players

Anecdotal and research evidence is that vertical jump performance declines over the competitive volleyball season. The purpose of this study was to evaluate whether a short period of ballistic resistance training would attenuate this loss. Fourteen collegiate women volleyball players were trained for 11 weeks with periodized traditional and ballistic resistance training. There was a 5.4% decrease (p < 0.05) in approach jump and reach height during the traditional training period (start of season to midseason), and a 5.3% increase (p < 0.05) during the ballistic training period (midseason to end of season), but values were not different from start to end of season. These changes in overall jump performance were reflective of changes in underlying neuromuscular performance variables: in particular, power output and peak velocity during loaded jump squats, countermovement jumps, and drop jumps. During the first 7 weeks of traditional heavy resistance training, it appears that the neuromuscular system is depressed, perhaps by the combination of training, game play, and skills practice precluding adequate recovery. Introduction of a novel training stimulus in the form of ballistic jump squats and reduction of heavy resistance training of the leg extensors stimulated a rebound in performance, in some cases to exceed the athlete's ability at the start of the season. Periodization of in-season training programs similar to that used in this study may provide volleyball players with good vertical jump performance for the crucial end-of-season games.     

Effect of pectin and amidated pectin on cholesterol homeostasis and cecal metabolism in rats fed a high-cholesterol diet

Two experiments were performed to compare the effect of pectin and its hydrophobic derivatives on homeostasis of cholesterol and cecal metabolism in male young rats. Control rats were fed a diet supplemented with palm fat and cholesterol (50 and 10 g/kg, respectively). Rats of other groups were fed the same diet containing citrus pectin or octadecylpectinamide (60 g/kg). Diets were fed for 4 weeks. In experiment I, pectinamide of lower degree of amidation (30 %) increased serum HDL cholesterol from 1.20 to 1.43 micromol/ml (p>0.05) at the expense of other cholesterol fractions. In experiment II, pectinamide of a higher degree of amidation (53 %) significantly decreased total serum cholesterol from 2.08 to 1.67 micromol/ml. Amidated pectins at both levels of substitution significantly decreased hepatic concentrations of cholesterol and fat. In both experiments the relative weight of cecum in the pectinamide group was significantly lower than in pectin group. The highest cecal concentrations of short-chain fatty acids (SCFA) were found in rats fed a diet with pectin (133.2 and 129.3 micromol/g in experiment I and II, respectively). In other groups, cecal SCFA was significantly (pectinamide groups) or non-significantly (controls) lower. In wet feces, SCFA concentrations were higher and butyrate molar proportions lower than in corresponding cecal contents. Pectinamide of a lower or higher degree of substitution significantly increased fecal content of cholesterol from 18.5 and 17.3 micromol/g in controls to 31.8 and 28.0 micromol/g, respectively. Corresponding concentrations of coprostanol were decreased. Effects of pectin on cholesterol homeostasis were absent or marginal. Histological examination revealed that hepatic tissue of control and pectin-fed rats was infiltrated with lipids. The Sudan black-positive material was absent in the liver of rats fed pectinamides. No pathological changes of liver tissue were apparent. In summary, hydrophobic amidated pectins significantly altered cholesterol homeostasis in rats and might be considered as a clinically effective hypocholesterolemic agent. Low cecal SCFA concentrations in rats fed pectinamides suggest that amidation of pectin had decreased its fermentability.     

Gender-based differences in the effect of dietary cholesterol in rats

Male and female rats were fed diets supplemented with cholesterol and palm fat at 10 and 50 g/kg, respectively; serum, hepatic tissue and faeces were analysed. Cholesterol supplementation significantly increased serum and hepatic cholesterol both in male and female rats. Male and female rats fed the cholesterol-containing diet differed significantly in serum cholesterol concentration (2.48 ??mol/mL vs 2.92 ??mol/mL), concentration of serum triacylglycerols, but not in hepatic cholesterol concentration. The serum and hepatic cholesterol concentrations correlated non-significantly in male rats (r=0.491; P=0.063) and significantly in female rats (r=0.818; P<0.001). Cholesterol supplementation non-significantly decreased relative expression of the hepatic LDL receptor gene and significantly increased relative expression of the hepatic cholesterol 7??-hydroxylase gene in rats of both genders. The faeces of control rats contained similar amounts of cholesterol and bile acids. Cholesterol supplementation increased cholesterol concentration 10 times in the faeces of male rats and 12 times in faeces of female rats. The corresponding increases of bile acid concentration were much lower (83% in male rats and 108% in female rats). It can be concluded that the effects of cholesterol supplementation were more pronounced in female than in male rats.     

Effects of stretching on upper-body muscular performance

The purpose of this investigation was to examine the influence of upper-body static stretching and dynamic stretching on upper-body muscular performance. Eleven healthy men, who were National Collegiate Athletic Association Division I track and field athletes (age, 19.6 +/- 1.7 years; body mass, 93.7 +/- 13.8 kg; height, 183.6 +/- 4.6 cm; bench press 1 repetition maximum [1RM], 106.2 +/- 23.0 kg), participated in this study. Over 4 sessions, subjects participated in 4 different stretching protocols (i.e., no stretching, static stretching, dynamic stretching, and combined static and dynamic stretching) in a balanced randomized order followed by 4 tests: 30% of 1 RM bench throw, isometric bench press, overhead medicine ball throw, and lateral medicine ball throw. Depending on the exercise, test peak power (Pmax), peak force (Fmax), peak acceleration (Amax), peak velocity (Vmax), and peak displacement (Dmax) were measured. There were no differences among stretch trials for Pmax, Fmax, Amax, Vmax, or Dmax for the bench throw or for Fmax for the isometric bench press. For the overhead medicine ball throw, there were no differences among stretch trials for Vmax or Dmax. For the lateral medicine ball throw, there was no difference in Vmax among stretch trials; however, Dmax was significantly larger (p 相似文献   

The effects of amino acid supplementation on muscular performance during resistance training overreaching

The purpose of this study was to examine the effects of amino acid supplementation on muscular strength, power, and high-intensity endurance during short-term resistance training overreaching. Seventeen resistance-trained men were randomly assigned to either an amino acid (AA) or placebo (P) group and underwent 4 weeks of total-body resistance training consisting of two 2-week phases of overreaching (phase 1: 3 x 8-12 repetitions maximum [RM], 8 exercises; phase 2: 5 x 3-5 RM, 5 exercises). Muscle strength, power, and high-intensity endurance were determined before (T1) and at the end of each training week (T2-T5). One repetition maximum squat and bench press decreased at T2 in P (5.2 and 3.4 kg, respectively) but not in AA, and significant increases in 1 RM squat and bench press were observed at T3-T5 in both groups. A decrease in the ballistic bench press peak power was observed at T3 in P but not AA. The fatigue index during the 20-repetition jump squat assessment did not change in the P group at T3 and T5 (fatigue index = 18.6 and 18.3%, respectively) whereas a trend for reduction was observed in the AA group (p = 0.06) at T3 (12.8%) but not T5 (15.2%; p = 0.12). These results indicate that the initial impact of high-volume resistance training overreaching reduces muscle strength and power, and it appears that these reductions are attenuated with amino acid supplementation. In addition, an initial high-volume, moderate-intensity phase of overreaching followed by a higher intensity, moderate-volume phase appears to be very effective for enhancing muscle strength in resistance-trained men.