Biomedical subjects

Kevin D Tipton

Publications and source records attributed to Kevin D Tipton.

12 recordsLinked to original sources

PubMed2006

Stimulation of net muscle protein synthesis by whey protein ingestion before and after exercise.

Timing of nutrient ingestion has been demonstrated to influence the anabolic response of muscle following exercise. Previously, we demonstrated that net amino acid uptake was greater when free essential amino acids plus carbohydrates were ingested before resistance exercise rather than following exercise. However, it is unclear if ingestion of whole proteins before exercise would stimulate a superior response compared with following exercise. This study was designed to examine the response of muscle protein balance to ingestion of whey proteins both before and following resistance exercise. Healthy volunteers were randomly assigned to one of two groups. A solution of whey proteins was consumed either immediately before exercise (PRE; n = 8) or immediately following exercise (POST; n = 9). Each subject performed 10 sets of 8 repetitions of leg extension exercise. Phenylalanine concentrations were measured in femoral arteriovenous samples to determine balance across the leg. Arterial amino acid concentrations were elevated by approximately 50%, and net amino acid balance switched from negative to positive following ingestion of proteins at either time. Amino acid uptake was not significantly different between PRE and POST when calculated from the beginning of exercise (67 +/- 22 and 27 +/- 10 for PRE and POST, respectively) or from the ingestion of each drink (60 +/- 17 and 63 +/- 15 for PRE and POST, respectively). Thus the response of net muscle protein balance to timing of intact protein ingestion does not respond as does that of the combination of free amino acids and carbohydrate.

Administration, Oral↗

PubMed2006

Promoting training adaptations through nutritional interventions.

Training and nutrition are highly interrelated in that optimal adaptation to the demands of repeated training sessions typically requires a diet that can sustain muscle energy reserves. As nutrient stores (i.e. muscle and liver glycogen) play a predominant role in the performance of prolonged, intense, intermittent exercise typical of the patterns of soccer match-play, and in the replenishment of energy reserves for subsequent training sessions, the extent to which acutely altering substrate availability might modify the training impulse has been a key research area among exercise physiologists and sport nutritionists for several decades. Although the major perturbations to cellular homeostasis and muscle substrate stores occur during exercise, the activation of several major signalling pathways important for chronic training adaptations take place during the first few hours of recovery, returning to baseline values within 24 h after exercise. This has led to the paradigm that many chronic training adaptations are generated by the cumulative effects of the transient events that occur during recovery from each (acute) exercise bout. Evidence is accumulating that nutrient supplementation can serve as a potent modulator of many of the acute responses to both endurance and resistance training. In this article, we review the molecular and cellular events that occur in skeletal muscle during exercise and subsequent recovery, and the potential for nutrient supplementation (e.g. carbohydrate, fat, protein) to affect many of the adaptive responses to training.

Adaptation, Physiological↗

PubMed2006

Milk ingestion stimulates net muscle protein synthesis following resistance exercise.

PURPOSE: Previous studies have examined the response of muscle protein to resistance exercise and nutrient ingestion. Net muscle protein synthesis results from the combination of resistance exercise and amino acid intake. No study has examined the response of muscle protein to ingestion of protein in the context of a food. This study was designed to determine the response of net muscle protein balance following resistance exercise to ingestion of nutrients as components of milk. METHOD: Three groups of volunteers ingested one of three milk drinks each: 237 g of fat-free milk (FM), 237 g of whole milk (WM), and 393 g of fat-free milk isocaloric with the WM (IM). Milk was ingested 1 h following a leg resistance exercise routine. Net muscle protein balance was determined by measuring amino acid balance across the leg. RESULTS: Arterial concentrations of representative amino acids increased in response to milk ingestion. Threonine balance and phenylalanine balance were both > 0 following milk ingestion. Net amino acid uptake for threonine was 2.8-fold greater (P < 0.05) for WM than for FM. Mean uptake of phenylalanine was 80 and 85% greater for WM and IM, respectively, than for FM, but not statistically different. Threonine uptake relative to ingested was significantly (P < 0.05) higher for WM (21 +/- 6%) than FM (11 +/- 5%), but not IM (12 +/- 3%). Mean phenylalanine uptake/ingested also was greatest for WM, but not significantly. CONCLUSIONS: Ingestion of milk following resistance exercise results in phenylalanine and threonine uptake, representative of net muscle protein synthesis. These results suggest that whole milk may have increased utilization of available amino acids for protein synthesis.

Administration, Oral↗

PubMed2005

Dietary protein intake impacts human skeletal muscle protein fractional synthetic rates after endurance exercise.

This investigation evaluated the physiological impact of different dietary protein intakes on skeletal muscle protein synthesis postexercise in endurance runners. Five endurance-trained, male runners participated in a randomized, crossover design diet intervention, where they consumed either a low (0.8 g/kg; LP)-, moderate (1.8 g/kg; MP)-, or high (3.6 g/kg; HP)-protein diet for 4 wk. Diets were designed to be eucaloric with carbohydrate, fat, and protein approximating 60, 30, and 10%; 55, 30, and 15%; and 40, 30, and 30% for LP, MP, and HP, respectively. Substrate oxidation was assessed via indirect calorimetry at 3 wk of the dietary interventions. Mixed-muscle protein fractional synthetic rate (FSR) was measured after an endurance run (75 min at 70% V(O2 peak)) using a primed, continuous infusion of [(2)H(5)]phenylalanine. Protein oxidation increased with increasing protein intake, with each trial being significantly different from the other (P < 0.01). FSR after exercise was significantly greater for LP (0.083%/h) and MP (0.078%/h) than for HP (0.052%/h; P < 0.05). There was no difference in FSR between LP and MP. This is the first investigation to establish that habitual dietary protein intake in humans modulates skeletal muscle protein synthesis after an endurance exercise bout. Future studies directed at mechanisms by which level of protein intake influences skeletal muscle turnover are needed.

Adult↗

PubMed2004

Incidence of associated events during the performance of invasive procedures in healthy human volunteers.

Metabolic investigations often utilize arteriovenous sampling and muscle biopsy. These investigations represent some risk to the subject. We examined 369 studies performed in the General Clinical Research Center between January 1994 and May 2003 for events related to femoral catheterization and muscle biopsies. Incidents were further examined by age (younger: 18-59 yr, n=133; and older: 60-76 yr, n=28). There were no clinically defined major complications associated with either procedure. The incidence of femoral catheter repositioning or reinsertion was higher in the older group (25.5 vs. 9.7%). There was no difference in the incidence of premature removal of catheters, ecchymosis or hematoma, or the persistence of pain after discharge. The occurrence of all incidents did not increase with multiple catheterizations. Muscle biopsy was associated with infrequent ecchymosis or hematoma in both groups (1.1 and 3.6% in younger and older groups, respectively). Both procedures entail a small likelihood of a vagallike response (3.3% overall), resulting in nausea, dizziness, and rarely a loss of consciousness. These results indicate that, in skilled hands and a defined clinical setting, the incidents associated with femoral catheterization and muscle biopsy in healthy volunteers are reasonable and largely controllable.

Adolescent↗

PubMed2004

Leg glucose and protein metabolism during an acute bout of resistance exercise in humans.

The present study investigated the responses of leg glucose and protein metabolism during an acute bout of resistance exercise. Seven subjects (5 men, 2 women) were studied at rest and during a strenuous lower body resistance exercise regimen consisting of approximately 8 sets of 10 repetitions of leg press at approximately 75% 1 repetition maximum and 8 sets of 8 repetitions of knee extensions at approximately 80% 1 repetition maximum. L-[ring-2H5]phenylalanine was infused throughout the study for measurement of phenylalanine rates of appearance, disappearance, protein synthesis, and protein breakdown across the leg. Femoral arterial and venous blood samples were collected at rest and during exercise for determination of leg blood flow, concentrations of glucose, lactate, alanine, glutamine, glutamate, leucine, and phenylalanine, and phenylalanine enrichments. Muscle biopsies were obtained at rest and immediately after exercise. Leg blood flow was nearly three times (P <0.009) higher and glucose uptake more than five times higher (P=0.009) during exercise than at rest. Leg lactate release was 86 times higher than rest during the exercise bout. Although whole body phenylalanine rate of appearance, an indicator of whole body protein breakdown, was reduced during exercise; leg phenylalanine rate of appearance, rate of disappearance, protein synthesis, and protein breakdown did not change. Arterial and venous alanine concentrations and glutamate uptake were significantly higher during exercise than at rest. We conclude that lower body resistance exercise potently stimulates leg glucose uptake and lactate release. In addition, muscle protein synthesis is not elevated during a bout of resistance exercise.

Adaptation, Physiological↗

PubMed2004

Protein and amino acids for athletes.

The main determinants of an athlete's protein needs are their training regime and habitual nutrient intake. Most athletes ingest sufficient protein in their habitual diet. Additional protein will confer only a minimal, albeit arguably important, additional advantage. Given sufficient energy intake, lean body mass can be maintained within a wide range of protein intakes. Since there is limited evidence for harmful effects of a high protein intake and there is a metabolic rationale for the efficacy of an increase in protein, if muscle hypertrophy is the goal, a higher protein intake within the context of an athlete's overall dietary requirements may be beneficial. However, there are few convincing outcome data to indicate that the ingestion of a high amount of protein (2-3 g x kg(-1) BW x day(-1), where BW = body weight) is necessary. Current literature suggests that it may be too simplistic to rely on recommendations of a particular amount of protein per day. Acute studies suggest that for any given amount of protein, the metabolic response is dependent on other factors, including the timing of ingestion in relation to exercise and/or other nutrients, the composition of ingested amino acids and the type of protein.

Amino Acids↗

PubMed2004

Ingestion of casein and whey proteins result in muscle anabolism after resistance exercise.

PURPOSE: Determination of the anabolic response to exercise and nutrition is important for individuals who may benefit from increased muscle mass. Intake of free amino acids after resistance exercise stimulates net muscle protein synthesis. The response of muscle protein balance to intact protein ingestion after exercise has not been studied. This study was designed to examine the acute response of muscle protein balance to ingestion of two different intact proteins after resistance exercise. METHODS: Healthy volunteers were randomly assigned to one of three groups. Each group consumed one of three drinks: placebo (PL; N = 7), 20 g of casein (CS; N = 7), or whey proteins (WH; N = 9). Volunteers consumed the drink 1 h after the conclusion of a leg extension exercise bout. Leucine and phenylalanine concentrations were measured in femoral arteriovenous samples to determine balance across the leg. RESULTS: Arterial amino acid concentrations were elevated by protein ingestion, but the pattern of appearance was different for CS and WH. Net amino acid balance switched from negative to positive after ingestion of both proteins. Peak leucine net balance over time was greater for WH (347 +/- 50 nmol.min(-1).100 mL(-1) leg) than CS (133 +/- 45 nmol.min(-1).100 mL(-1) leg), but peak phenylalanine balance was similar for CS and WH. Ingestion of both CS and WH stimulated a significantly larger net phenylalanine uptake after resistance exercise, compared with the PL (PL -5 +/- 15 mg, CS 84 +/- 10 mg, WH 62 +/- 18 mg). Amino acid uptake relative to amount ingested was similar for both CS and WH (approximately 10-15%). CONCLUSIONS: Acute ingestion of both WH and CS after exercise resulted in similar increases in muscle protein net balance, resulting in net muscle protein synthesis despite different patterns of blood amino acid responses.

Administration, Oral↗

PubMed2003

Effect of carbohydrate intake on net muscle protein synthesis during recovery from resistance exercise.

The purpose of this study was to determine the effect of ingestion of 100 g of carbohydrates on net muscle protein balance (protein synthesis minus protein breakdown) after resistance exercise. Two groups of eight subjects performed a resistance exercise bout (10 sets of 8 repetitions of leg presses at 80% of 1-repetition maximum) before they rested in bed for 4 h. One group (CHO) received a drink consisting of 100 g of carbohydrates 1 h postexercise. The other group (Pla) received a noncaloric placebo drink. Leg amino acid metabolism was determined by infusion of 2H5- or 13C6-labeled phenylalanine, sampling from femoral artery and vein, and muscle biopsies from vastus lateralis. Drink intake did not affect arterial insulin concentration in Pla, whereas insulin increased several times after the drink in CHO (P < 0.05 vs. Pla). Arterial phenylalanine concentration fell slightly after the drink in CHO. Net muscle protein balance between synthesis and breakdown did not change in Pla, whereas it improved in CHO from -17 +/- 3 nmol.ml(-1).100 ml leg(-1) before drink to an average of -4 +/- 4 and 0 +/- 3 nmol.ml(-1).100 ml leg(-1) during the second and third hour after the drink, respectively (P < 0.05 vs. Pla during last hour). The improved net balance in CHO was due primarily to a progressive decrease in muscle protein breakdown. We conclude that ingestion of carbohydrates improved net leg protein balance after resistance exercise. However, the effect was minor and delayed compared with the previously reported effect of ingestion of amino acids.

Adult↗

PubMed2003

Independent and combined effects of amino acids and glucose after resistance exercise.

PURPOSE: This study was designed to assess the independent and combined effects of a dose of amino acids (approximately 6 g) and/or carbohydrate (approximately 35 g) consumed at 1 and 2 h after resistance exercise on muscle protein metabolism. METHODS: Following initiation of a primed constant infusion of H -phenylalanine and N-urea, volunteers performed leg resistance exercise and then ingested one of three drinks (amino acids (AA), carbohydrate (CHO), or AA and CHO (MIX)) at 1- and 2-h postexercise.(5) RESULTS: Total net uptake of phenylalanine across the leg over 3 h was greatest in response to MIX and least in CHO. The individual values for CHO, MIX, and AA were 53 +/- 6, 114 +/- 38, and 71 +/- 13 mg x leg x 3h. Stimulation of net uptake in MIX was due to increased muscle protein synthesis. CONCLUSIONS: These findings indicate that the combined effect on net muscle protein synthesis of carbohydrate and amino acids given together after resistance exercise is roughly equivalent to the sum of the independent effects of either given alone. The individual effects of carbohydrate and amino acids are likely dependent on the amount of each that is ingested. Further, prior intake of amino acids and carbohydrate does not diminish the metabolic response to a second comparable dose ingested 1h later.

Amino Acids↗

PubMed2002

Acute response of net muscle protein balance reflects 24-h balance after exercise and amino acid ingestion.

The purpose of this study was to determine if the acute anabolic muscle response to resistance exercise and essential amino acids (EAA) reflects the response over 24 h. Seven subjects participated in the following two 24-h studies: 1) resting (REST) and 2) rest plus resistance exercise and consumption of EAA (ES). Net balance (NB) across the leg was determined for four amino acids. [(13)C(6)]phenylalanine was infused to determine mixed muscle fractional synthetic rate (FSR). Twenty-four-hour FSR was significantly greater for ES than for REST (P = 0.003). Exchange of phenylalanine across the leg was -194 +/- 74 (SE) mg for ES and -371 +/- 88 mg for REST (P = 0.07) over 24 h and 229 +/- 42 mg (ES) and 28 +/- 15 mg (REST; P < 0.01) over 3 h corresponding to exercise and EAA consumption for ES. The difference in phenylalanine exchange between REST and ES was not different for measurements over 24 and 3 h. Increases in NB during ES were primarily the result of increases in protein synthesis. Results for other amino acids were similar. The acute anabolic response of muscle to EAA intake and exercise is additive to the response at rest and thus reflects the 24-h response.

Amino Acids↗

PubMed2002

Essential amino acids and muscle protein recovery from resistance exercise.

This study tests the hypothesis that a dose of 6 g of orally administered essential amino acids (EAAs) stimulates net muscle protein balance in healthy volunteers when consumed 1 and 2 h after resistance exercise. Subjects received a primed constant infusion of L-[(2)H(5)]phenylalanine and L-[1-(13)C]leucine. Samples from femoral artery and vein and biopsies from vastus lateralis were obtained. Arterial EAA concentrations increased severalfold after drinks. Net muscle protein balance (NB) increased proportionally more than arterial AA concentrations in response to drinks, and it returned rapidly to basal values when AA concentrations decreased. Area under the curve for net phenylalanine uptake above basal value was similar for the first hour after each drink (67 +/- 17 vs. 77 +/- 20 mg/leg, respectively). Because the NB response was double the response to two doses of a mixture of 3 g of EAA + 3 g of nonessential AA (NEAA) (14), we conclude that NEAA are not necessary for stimulation of NB and that there is a dose-dependent effect of EAA ingestion on muscle protein synthesis.

Adult↗