Christos S. Katsanos

Differential stimulation of muscle protein synthesis in elderly humans following isocaloric ingestion of amino acids or whey protein

To counteract the debilitating progression of sarcopenia, a protein supplement should provide an energetically efficient anabolic stimulus. We quantified net muscle protein synthesis in healthy elderly individuals (65-79 yrs) following ingestion of an isocaloric intact whey protein supplement (WY; n=8) or an essential amino acid supplement (EAA; n=7). Femoral arterio-venous blood samples and vastus lateralis muscle biopsy samples were obtained during a primed, constant infusion of L-[ring-2H5]phenylalanine. Net phenylalanine uptake and mixed muscle fractional synthetic rate (FSR) were calculated during the post-absorptive period and for 3.5 h following ingestion of 15 g EAA or 15 g whey. After accounting for the residual increase in the intracellular phenylalanine pool, net post-prandial phenylalanine uptake was 53.4+/-9.7 mg phe leg-1 (EAA) and 21.7+/-4.6 mg phe leg-1 (WY), (P<0.05). Postabsorptive FSR values were 0.056+/-0.004% h-1 (EAA) and 0.049+/-0.006% h-1 (WY), (P>0.05). Both supplements stimulated FSR (P<0.05), but the increase was greatest in the EAA group with values of 0.088+/-0.011% h-1 (EAA) and 0.066+/-0.004% h-1 (WY), (P<0.05). While both EAA and WY supplements stimulated muscle protein synthesis, EAAs may provide a more energetically efficient nutritional supplement for elderly individuals.

Blood glucose threshold and the metabolic responses to incremental exercise tests with and without prior lactic acidosis induction

This study compared the metabolic–ventilatory responses and the glycemic threshold identified during lactate minimum (LM) and individual anaerobic threshold (IAT) tests. In addition, the ability to determine the anaerobic power, aerobic–anaerobic transition (Trans) (e.g. ventilatory threshold; VT) and the maximal oxygen consumption (V̇O2max) all within a single incremental treadmill test (IT) was investigated. Fifteen physically fit men [25.9 (5.5)xa0years; 77.4 (6.5)xa0kg] performed the following: test 1, IT for IAT; and test 2, LM: 30-s Wingate test followed by 8xa0min rest and then an IT that was the same as test 1. Blood lactate concentration [lac], glucose concentration [gluc], pH, PO2, PCO2, base excess (BE) and ventilatory variables were measured. At the beginning of the IT for LM, the ventilation, PO2 and V̇O2 were higher and the pH, BE and PCO2 were lower in relation to IAT (P<0.05), while no differences were observed after reaching LM intensity during IT. Moreover, the Trans could be identified by [lac] (IAT, LM), minute ventilation [V̇E; VT identified during IAT protocol (VT–IAT) and VT identified during LM protocol (VT–LM)], and [gluc] (IGT, GM) during the IT for IAT and LM. The velocities (kilometers per hour) corresponding to IAT (12.6±1.6), VT–IAT (12.5±1.7), IGT (12.6±1.6), LM (12.5±1.5), VT–LM (12.3±1.5), and GM (12.6±1.9) were not different from each other and the LM and IAT protocols resulted in the similar V̇O2max. We concluded that: (1) after reaching the LM the metabolic responses during IT are similar to IAT; (2) performing a Wingate test prior to an IT does not interfere with the Trans and V̇O2max attainment; (3) and the IGT and GM can predict the Trans.

Acute effects of premeal versus postmeal exercise on postprandial hypertriglyceridemia.

ObjectiveThe objective of this study was to examine the effects of the timing of exercise relative to the consumption of a fat-rich meal (81% fat) on postprandial hypertriglyceridemia. DesignA single bout of exercise was either completed 30 minutes before the fat meal (EM trial) or initiated 90 minutes after the fat meal (ME trial). A third trial, fat meal only, served as a control (CON trial). The trials performed in a random order, and venous blood samples were drawn before and 1.5, 3.5, 5.5, and 7.5 hours after the meal for the determination of triglycerides, glycerol, insulin, glucose, and free fatty acids. ParticipantsTen untrained healthy males 25.2 ± 0.9 years old (mean ± SE) with maximal oxygen uptake (VO2max) of 46.6 ± 3.0 mL · kg−1 · min−1. InterventionWalking exercise performed at 50% VO2max for 90 minutes. Main Outcome MeasurePostprandial hypertriglyceridemia, which was quantified by calculating the area under the triglycerides curve over the 7.5-hour postprandial period. ResultsThe mean incremental area under the curve (total area adjusted to baseline) describing postprandial hypertriglyceridemia was lower both in the EM trial (3.16 ± 0.99 mmol · L−1 · 8 h) and in the ME trial (2.96 ± 0.69 mmol · L−1 · 8 h) compared with CON trial (6.18 ± 1.10 mmol · L−1 · 8 h; P < 0.05). The corresponding areas under the curve describing the postprandial insulinemia were not different between trials (ME: 38.56 ± 8.36 uIU · mL−1 · 8 h; EM: 21.65 ± 3.80 uIU · mL−1 · 8 h; CON: 25.06 ± 5.15 uIU · mL−1 · 8 h; P > 0.05). ConclusionA single bout of moderate intensity exercise decreases postprandial hypertriglyceridemia irrespective of the timing of the exercise relative to a high-fat meal.

Prescribing aerobic exercise for the regulation of postprandial lipid metabolism : Current research and recommendations

Prolonged presence of elevated plasma triglycerides (TGs) during the postprandial period has been suggested to increase the risk for coronary artery disease. Aerobic exercise attenuates postprandial lipaemia and this has generally been described as a short-term effect of the exercise. Effects of exercise on postprandial lipaemia have mostly been investigated, and documented, with large exercise-induced energy expenditures (i.e. 1000 kcal). The exact mechanisms involved in the attenuation of postprandial lipaemia with exercise are not completely understood, but it appears that at least two mechanisms are involved: a decrease in TG secretion by the liver and an increase in plasma TG clearance by the muscle. Changes in the metabolism of other lipids, such as those in high-density lipoprotein cholesterol, have been documented only when the exercise is performed some hours before the fat meal. Although factors such as the physical fitness and percentage body fat of an individual are likely to also be involved, the most important factors determining the magnitude of the attenuation in postprandial lipaemia appear to be the magnitude of the exercise-induced energy expenditure and the intensity of exercise. To date, the evidence suggests that healthy individuals can generally induce favourable changes in postprandial lipaemia with aerobic exercise that: (i) is completed during the period extending from 16 hours before a meal through 1.5 hours after a meal; (ii) is of moderate intensity; and (iii) results in an energy expenditure of approximately 500 kcal (or more).

Muscle Protein Synthesis and Balance Responsiveness to Essential Amino Acids Ingestion in the Presence of Elevated Plasma Free Fatty Acid Concentrations

CONTEXTnElevated plasma free fatty acid (FFA) concentrations are observed under various clinical circumstances and are associated with impaired glucose disposal in skeletal muscle.nnnOBJECTIVEnThe aim of the study was to determine the effects of elevated plasma FFA concentrations on the response of protein synthesis and balance in muscle after essential amino acids (EAAs) ingestion.nnnDESIGNnLeg protein kinetics were determined in young healthy individuals before and after the ingestion of EAAs at 10 h after the initiation of either lipid (Liposyn/heparin+EAA) or saline (saline+EAA) infusions.nnnRESULTSnPlasma insulin responses where higher (P <0.05) in the Liposyn/heparin+EAA group than the saline+EAA group both before (14 +/- 4 vs. 6 +/- 1 microIU . ml(-1)) and after (1038 +/- 257 vs. 280 +/- 87 microIU . ml(-1) . 210 min(-1)) the EAA ingestion. After the EAA ingestion, the rates of both leg phenylalanine disappearance (Rd; nmol . min(-1) . kg lean leg mass(-1)) and muscle proteins fractional synthesis (FSR; % . h(-1)) increased (P <0.05) in both the Liposyn/heparin+EAA and saline+EAA groups, but these changes were not different between the two groups (Rd, 102 +/- 32 vs. 118 +/- 34; FSR, 0.014 +/- 0.005 vs. 0.018 +/- 0.007; P > 0.05). Although the leg phenylalanine rate of appearance (Ra; nmol . min(-1) . kg lean leg mass(-1)) was lower (381 +/- 47 vs. 518 +/- 40) and the balance was greater (-109 +/- 20 vs. -172 +/- 17) in the Liposyn/heparin+EAA group compared to the saline+EAA group before the EAA ingestion (P <0.05), the changes in both of these parameters were not different between groups after the EAA ingestion (P > 0.05).nnnCONCLUSIONSnElevated plasma FFA concentrations do not interfere with the response of muscle protein synthesis and balance to a bolus ingestion of EAAs.

Lipid-induced insulin resistance in the liver: Role of exercise

Hepatic lipid accumulation may be a result of one or several of the following factors: increased delivery of adipose tissue or dietary fatty acids to the liver, increased de novo synthesis of fatty acids in the liver, decreased rate of hepatic fatty-acid oxidation, or decreased rate in the exit of fatty acids from the liver in the form of triglycerides. Delivery of fatty acids to the liver appears to be the most potent mechanism for hepatic lipid accumulation. Hepatic lipid accumulation is linked to the development of hepatic insulin resistance, which is demonstrated by the impaired suppression of hepatic glucose output by insulin. Current evidence suggests that defects associated with the molecular mechanisms responsible for the propagation of the insulin signal in the liver cells are responsible for the impaired insulin effect and that these defects can develop secondary to lipid accumulation in the liver. Hepatic lipid accumulation appears to affect the activity of phosphatidylinositol 3-kinase, which has a central role in mediating the insulin action in hepatocytes. Generally, exercise has been shown to enhance the insulin action in the liver. Although an exercise-related mechanistic link between attenuation in hepatic lipid accumulation and enhancement in insulin action in the liver has not been described yet, the benefits of exercise on hepatic insulin action may relate to the potential effects of exercise on regulating/preventing hepatic lipid accumulation. However, direct effects of exercise on insulin action in the liver, independent of any effects on hepatic lipid metabolism, cannot currently be excluded. Further research is needed to evaluate the relative importance of exercise in the treatment of hepatic insulin resistance, specifically as it relates to lipid accumulation in the liver.

Reliability of heart rate responses at given ratings of perceived exertion in cycling and walking.

Eleven healthy men (M age = 27 years, SD = 4) completed three cycling and three walking trials in an alternating order. During each trial, participants were allowed, within 3 min, to adjust the work rate to correspond to given rating of perceived exertion (RPE) values according to the following order: RPE 11, 13, and 15. For cycling as well as walking, at each RPE there were no significant differences between mean heart rate responses across the three trials (p > .05). Mode-specific estimates for heart rate intraclass correlation coefficient and coefficient of variation ranged between .80 and .91, and 5.6% and 8.3%, respectively. This study provides absolute reliability estimates for heart rate responses when using RPE in a production format and suggests there may be RPE- (and mode) specific practice requirements for achieving a reliable heart rate response at a given RPE.

Energy Expenditure Relative to Perceived Exertion: Stationary Cycling versus Treadmill Walking

Various exercise modes have been compared with regard to their potential to maximize energy expenditure (EE) and elicit a sufficient cardiovascular stimulus. Evidence indicates that the rate of EE is greater in some exercise modes than others (Kravitz, Robergs, Heyward, Wagner, & Powers, 1997; Thomas, Ziogas, Smith, Zhang, & Londeree, 1995; Zeni, Hofman, & Clifford, 1996). Recent evidence suggests that when exercise is performed at a given percentage of maximal oxygen uptake (V0 2 max; Thomas et aI., 1995), rating of perceived exertion (RPE; Thomas et aI., 1995; Zeni et aI., 1996), or self-selected intensity(Kravitzet al., 1997), treadmill running appears to elicit a higher V0 2 and EE than cycling. Treadmill walking has received less attention despite its growing popularity. Walking is convenient, does not require any specific skill, and can provide a sufficient stimulus to achieve fitness and health goals (Spelman, Pate, Macera, & Ward, 1993). Although there is a considerable number of studies in the literature related to EE ofcycling and walking, relativelyfew studies have compared these two modes ofexercise. When such studies were conducted, they were based on equivalent percentages of V0 2 max (Miles, Critz, & Knowlton, 1980) or comparable relative heart rates (Thomas, Feiock, & Araujo, 1989). Many exercising individuals, however, establish and monitor their exercise intensity based on a subjective parameter such as perceived effort. It would be reasonable, therefore, to try to compare the

Deliberate Imagery Practice

Abstract Eleven healthy men (M age = 27 years, SD = 4) completed three cycling and three walking trials in an alternating order. During each trial, participants were allowed, within 3 min, to adjust the work rate to correspond to given rating of perceived exertion (RPE) values according to the following order: RPE 11, 13, and 15. For cycling as well as walking, at each RPE there were no significant differences between mean heart rate responses across the three trials (p > .05). Mode-specific estimates for heart rate intraclass correlation coefficient and coefficient of variation ranged between .80 and .91, and 5.6% and 8.3%, respectively. This study provides absolute reliability estimates for heart rate responses when using RPE in a production format and suggests there may be RPE- (and mode) specific practice requirements for achieving a reliable heart rate response at a given RPE.