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Biomedical subjects

D L Costill

Publications and source records attributed to D L Costill.

At least 55 records · Page 3Linked to original sources

Effect of L-carnitine supplementation on muscle and blood carnitine content and lactate accumulation during high-intensity sprint cycling.

This study examined the effects of 14 days of L-carnitine supplementation on muscle and blood carnitine fractions, and muscle and blood lactate concentrations, during high-intensity sprint cycling exercise. Eight subjects performed three experimental trials: control I (CON I, Day 0), control II (CON II, Day 14), and L-carnitine (L-CN, Day 28). Each trial consisted of a 4-min ride at 90% VO2max, followed by a rest period of 20 min, and then five repeated 1-min rides at 115% VO2max (2 min rest between each). Following CON II, all subjects began dietary supplementation of L-carnitine for a period of 14 days (4 g/day). Plasma total acid soluble and free carnitine concentrations were significantly higher (p < .05) at all time points following supplementation. L-carnitine supplementation had no significant effect on muscle carnitine content and thus could not alter lactate accumulation during exercise.

Acid-Base Equilibrium↗

Carnitine supplementation: effect on muscle carnitine and glycogen content during exercise.

This study investigated the effects of L-carnitine supplementation on muscle carnitine and glycogen content during submaximal exercise (EX). Triglycerides were evaluated by a fat feeding (90 g fat) and 3 h later subjects cycled for 60 min at 70% VO2max (CON). Muscle biopsies were obtained preexercise and after 30 and 60 min of EX. Blood samples were taken prior to and every 15 min of exercise. Subjects randomly completed two additional trials following 7 and 14 d of carnitine supplementation (6 g.d-1). During one of the two trials, subjects received 2000 units of heparin 15 min prior to EX to elevate FFA (CNhep); no heparin was administered during the other trial (CN). There were no differences in VO2, respiratory exchange ratio, heart rate, or g.min-1 of CHO and fat oxidized among the three trials. At rest serum total acid soluble (TASC) and free (FC) carnitine increased with supplementation (TASC; CON, 71.3 +/- 2.9; CN, 92.8 +/- 5.4; CNhep, 109.8 +/- 3.5 mumol.l-1) (FC; CON, 44.1 +/- 2.7; CN, 66.1 +/- 5.3; CNhep, 77.1 +/- 4.1 mumol.l-1). During EX, TASC remained stable, while FC decreased and short-chain acylcarnitine (SCAC) increased (P < 0.05). Muscle carnitine concentration at rest was unaffected by supplementation. During EX, muscle TASC did not change, FC decreased, and SCAC increased significantly in all three trials. Pre-EX and post-EX muscle glycogens were not different. Increased availability of serum carnitine does not result in an increase in muscle carnitine content nor does it alter lipid oxidation. It appears that there is an adequate amount of carnitine present within the mitochondria to support lipid oxidation.

Adult↗

Effect of passive and active recovery on the resynthesis of muscle glycogen.

The purpose of this investigation was to determine the effect of passive and active recovery on the resynthesis of muscle glycogen after high-intensity cycle ergometer exercise in untrained subjects. In a cross-over design, six college-aged males performed three, 1-min exercise bouts at approximately 130% VO2max with a 4-min rest period between each work bout. The exercise protocol for each trial was identical, while the recovery following exercise was either active (30 min at 40-50% VO2max, 30-min seated rest) or passive (60-min seated rest). Initial muscle glycogen values averaged 144.2 +/- 3.8 mmol.kg-1 w.w. for the active trial and 158.7 +/- 8.0 mmol.kg-1 w.w. for the passive trial. Corresponding immediate postexercise glycogen contents were 97.7 +/- 5.4 and 106.8 +/- 4.7 mmol.kg-1 w.w., respectively. These differences between treatments were not significant. However, mean muscle glycogen after 60 min of passive recovery increased 15.0 +/- 4.9 mmol.kg-1 w.w., whereas it decreased 6.3 +/- 3.7 mmol.kg-1 w.w. following the 60 min active recovery protocol (P < 0.05). Also, the decrease in blood lactate concentration during active recovery was greater than during passive recovery and significantly different at 10 and 30 min of the recovery period (P < 0.05). These data suggest that the use of passive recovery following intense exercise results in a greater amount of muscle glycogen resynthesis than active recovery over the same duration.

Adult↗

Time of day effects on sympathoadrenal and pressor reactivity to exercise in healthy men.

To investigate the influence of time of day on sympathoadrenal and pressor reactivity during exercise, eight trained men [age, mean (SD), 24 (0.5) years; maximal oxygen uptake (VO2max), 4.7 l.min-1] performed bouts of static (ST) and dynamic (DYN) exercise at 0600-0800 hours (AM) and at 1600-1800 hours (PM). The ST protocol utilized a two-leg isometric contraction at 30% maximum voluntary contraction until failure, and was monitored by a strain gauge interfaced from a leg extension apparatus to a computer. Heart rate (fc) and blood pressure (Pa) responses were recorded at rest, after 1 and 2 min of exercise, and at failure. Epinephrine (EPI) and norepinephrine (NE) levels were recorded before exercise, and after 2 min of exercise. The DYN exercise protocol involved stationary cycling for consecutive 6-min periods at 60% and 80% VO2max. fc, Pa, EPI, and NE were recorded before exercise and at each workload. No differences were observed in preexercise or exercise fc under any condition. Preexercise Pa did not differ under any condition. The Pa response to DYN was significantly higher at 80% VO2max during PM only. Pa was significantly higher in ST-PM at 1 min, 2 min, and failure. Elevations in both systolic and diastolic Pa contributed to this difference. Preexercise EPI-ST-AM was significantly elevated vs PM, but no other preexercise data were significantly different. Absolute exercise levels were significantly higher for EPI-ST-PM vs AM only, but the percentage change from baseline was significantly (P < 0.01) higher in ST-PM for EPI (+231% PM vs +32% AM) and NE (+352% PM vs +216% AM).(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Glands↗

Reduced training volume and intensity maintain aerobic capacity but not performance in distance runners.

It has recently been shown that a 70% reduction in training volume, while maintaining training intensity, results in the maintenance of VO2 max and 5 km running performance in distance runners. The purpose of this study was to examine the effects of a 4 wk reduction in training volume and intensity in distance runners. Ten well-conditioned males (VO2max = 63.4 +/- 1.3 ml.kg-1 x min-1) underwent 4 wks of base training (BT) at their accustomed training distance (71.8 +/- 3.6 km.wk-1) and intensity (76% of total distance > 70% VO2max). Training volume (-66%), frequency (-50%), and intensity (all running < 70% VO2max) were then decreased for a 4 wk reduced training period (RT). Treadmill VO2max was unchanged with RT (p > 0.05) as were resting plasma volume, estimated from haemoglobin and haematocrit levels, and resting heart rate (HR). Submaximal treadmill exercise VO2 (l.min-1), ventilation and HR were also unchanged, however, submaximal exercise RER and blood lactate accumulation following 4 mins at 95% VO2max (8.39 vs 9.89 mmol.l-1) were significantly elevated by RT (p < 0.05). Estimated percent body fat also increased (10.4% vs 11.8%) (p < 0.05). Five km race completion time significantly increased from 16.6 +/- 0.3 mins at week 4 of BT to 16.8 +/- 0.3 mins (12 seconds) at week 4 of RT. Nine of the 10 subjects were slower after RT. It is concluded that aerobic capacity was maintained in these runners, despite the combined reduction in training volume and intensity. However, it appears that training intensity during RT is important for the maintenance of 5 km running performance.

Adult↗

Carbohydrate ingestion during exercise: effects on muscle glycogen resynthesis after exercise.

To determine the effect of carbohydrate feeding on muscle glycogen resynthesis, 8 male cyclists pedaled for 2 hrs on a cycle ergometer at 70% of VO2max while consuming either a 10% carbohydrate solution (CHO) or a nonnutritive sweet placebo (No CHO). Muscle biopsies were obtained from the vastus lateralis prior to, immediately postexercise, and at 2, 4, and 24 hrs of recovery. Blood samples were taken before and at the end of exercise, and at specified times during recovery. During both trials food intake was withheld for the first 2 hrs of recovery, but at 2 hrs postexercise a 24% carbohydrate solution was ingested. The rate of muscle glycogen resynthesis during the first 2 hrs of recovery was similar for the CHO and No CHO trials. Following ingestion of the 24% carbohydrate supplement, the rates of muscle glycogen resynthesis increased similarly in both trials. These similar rates of resynthesis following ingestion of the carbohydrate supplement were obtained despite significantly greater serum glucose and insulin levels during the No CHO trial. The results indicate that the carbohydrate feedings taken during exercise had little effect on postexercise muscle glycogen resynthesis.

Adult↗

Carbohydrate feedings and exercise performance: effect of initial muscle glycogen concentration.

To determine whether the ergogenic benefits of carbohydrate (CHO) feedings are affected by preexercise muscle glycogen levels, eight cyclists performed four self-paced time trials on an isokinetic ergometer over a simulated distance of 70 km. Trials were performed under the following preexercise muscle glycogen and beverage conditions: 1) high glycogen (180.2 +/- 9.7 mmol/kg wet wt) with a CHO beverage (HG-CHO), 2) high glycogen (170.2 +/- 10.4 mmol/kg wet wt) with a non-CHO beverage (HG-NCHO), 3) low glycogen (99.8 +/- 6.0 mmol/kg wet wt) with a CHO beverage (LG-CHO), and 4) low glycogen (109.7 +/- 5.3 mmol/kg wet wt) with a non-CHO beverage (LG-NCHO). The CHO drink (ingested at the onset of exercise and every 10 km thereafter) provided 116 +/- 6 g CHO/trial and prevented the decline in serum glucose observed during both NCHO trials. Performance times ranged from 117.93 +/- 1.44 (HG-CHO) to 122.91 +/- 2.46 min (LG-NCHO). No intertrial differences (P > 0.05) were observed for O2 consumption (75% of maximal O2 consumption), power output (237 W), or self-selected pace (8.44 min/5 km) during the initial 71-79% of exercise. Over the final 14% of the time trial, power output and pace (231 W and 8.62 min/5 km) were similar for the HG-CHO, HG-NCHO, and LG-CHO conditions, but both variables were significantly lower during the LG-NCHO trial (198 W and 9.67 min/5 km, P < 0.05 vs. all other trials).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

Effect of fat emulsion infusion and fat feeding on muscle glycogen utilization during cycle exercise.

Elevated plasma fatty acids have been shown to spare muscle glycogen during exercise. However, on the basis of recent findings, the saturation of fatty acids may influence this response. The purpose of this study was to determine whether saturated or unsaturated fatty acids affected muscle glycogenolysis to varying degrees during cycle exercise. Five healthy men completed three 60-min cycle ergometer trials (EX) at approximately 70% maximal O2 uptake (VO2max). Triglyceride levels were elevated by a fat feeding (FF) composed of 90% saturated fatty acids (heavy whipping cream, 90 g) or by the infusion of Intralipid (IL; Clintec Nutrition; 45 ml/h of 20% IL, 9.0 g), which was 85% unsaturated. A control trial (CON) consisted of a light breakfast (43 g carbohydrate and 1 g fat). Heparin (2,000 U) was administered 15 min before EX in FF and IL trials, resulting in one- and threefold increases in free fatty acid (FFA) levels in IL and FF, respectively. Pre-EX muscle glycogen did not differ. The utilization of muscle glycogen during 60 min of EX was less (P < 0.05) during the FF (60.0 +/- 5.2 mmol/kg wet wt) and IL (58.6 +/- 6.2 mmol/kg wet wt) compared with CON (81.8 +/- 7.5 mmol/kg wet wt). There was no difference between FF and IL in the amount of glycogen utilized. Serum triglyceride levels were greater (P < 0.05) at preheparin in FF (1.58 +/- 0.37 mmol/l) and IL (0.98 +/- 0.13 mmol/l) compared with CON (0.47 +/- 0.14 mmol/l).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

Plasma lactate accumulation and distance running performance. 1979.

Laboratory and field assessments were made on eighteen male distance runners. Performance data were obtained for distances of 3.2, 9.7, 15, 19.3 km (n = 18) and the marathon (n = 13). Muscle fiber composition expressed as percent of slow twitch fibers (%ST), maximal oxygen consumption (VO2max), running economy (VO2 for a treadmill velocity of 268 m/min), and the VO2 and treadmill velocity corresponding to the onset of plasma lactate accumulation (OPLA) were determined for each subject. %ST (R > or equal to .47), VO2max (r > or equal to .83), running economy (r > or equal to .49), VO2 in ml/kg min corresponding to the OPLA (r > or equal to .91) and the treadmill velocity corresponding to OPLA (r > or equal to .91) were significantly (p < .05) related to performance at all distances. Multiple regression analysis showed that the treadmill velocity corresponding to the OPLA was most closely related to performance and the addition of other factors did not significantly raise the multiple R values suggesting that these other variables may interact with the purpose of keeping plasma lactates low during distance races. The slowest and fastest marathoners ran their marathons 7 and 3 m/min faster than their treadmill velocities corresponding to their OPLA which indicates that this relationship is independent of the competitive level of the runner. Runners appear to set a race pace which allows the utilization of the largest possible VO2 which just avoids the exponential rise in plasma lactate.

Anaerobic Threshold↗

Dry-land resistance training for competitive swimming.

To determine the value of dry-land resistance training on front crawl swimming performance, two groups of 12 intercollegiate male swimmers were equated based upon preswimming performance, swim power values, and stroke specialties. Throughout the 14 wk of their competitive swimming season, both swim training group (SWIM, N = 12) and combined swim and resistance training group (COMBO, N = 12) swam together 6 d a week. In addition, the COMBO engaged in a 8-wk resistance training program 3 d a week. The resistance training was intended to simulate the muscle and swimming actions employed during front crawl swimming. Both COMBO and SWIM had significant (P < 0.05) but similar power gains as measured on the biokinetic swim bench and during a tethered swim over the 14-wk period. No change in distance per stroke was observed throughout the course of this investigation. No significant differences were found between the groups in any of the swim power and swimming performance tests. In this investigation, dry-land resistance training did not improve swimming performance despite the fact that the COMBO was able to increase the resistance used during strength training by 25-35%. The lack of a positive transfer between dry-land strength gains and swimming propulsive force may be due to the specificity of training.

Adult↗

Glycogen resynthesis in skeletal muscle following resistive exercise.

The purpose of this investigation was to determine the influence of post-exercise carbohydrate (CHO) intake on the rate of muscle glycogen resynthesis after high intensity weight resistance exercise in subjects not currently weight training. In a cross-over design, eight male subjects performed sets (mean = 8.8) of six single leg knee extensions at 70% of one repetition max until 50% of full knee extension was no longer possible. Total force application was equated between trials using a strain gauge interfaced to a computer. The subjects exercised in the fasted state. Post-exercise feedings were administered at 0 and 1 h consisting of either a 23% CHO solution (1.5 g.kg-1) or an equal volume of water (H2O). Total force production, preexercise muscle glycogen content, and degree of depletion (-40.6 and -44.3 mmol.kg-1 wet weight) were not significantly different between H2O and CHO trials. As anticipated during the initial 2-h recovery, the CHO trial had a significantly greater rate of muscle glycogen resynthesis as compared with the H2O trial. The muscle glycogen content was restored to 91% and 75% of preexercise levels when water and CHO were provided after 6 h, respectively.

Adult↗

Effect of increased training volume on nutrient intake of male collegiate swimmers.

To assess the effect of a period of increasing training on dietary quantity and quality, a men's collegiate swim team (n = 24) was divided into two groups of equal skill at the start of a 25-week season of training and competition. After a 4-week conditioning period, the "Long" group underwent a 6-week period during which they swam up to 44,000 m.wk-1, while the "Short" group maintained their swimming at 22,000 m.wk-1. For the remainder of the season, the two groups swam together, performing the same volume and intensity of training. Two-day food intake records were obtained during the early season, during the period of increased training, and during the late season. Swimmers' diets during the early season averaged 15.3 MJ, with 55% from carbohydrate (500 g), and exceeded RDAs for all nutrients assessed. During the increased training period, energy and carbohydrate intakes of the Long group increased significantly (p less than 0.05) to 17.7 MJ and 600 g respectively, but the percentage of energy derived from carbohydrate, protein and fat was stable. Intakes of the Short group did not change over the season. Energy intake did not fully compensate for expenditure, as both groups maintained weight but lost subcutaneous fat. An increase in training volume appears to result in an increased consumption of the athletes' usual diets.

Adult↗

Reliability of the serial sampling technique for determination of gastric emptying.

The purpose of this study was to determine if gastric emptying data obtained in one trial (using the intubation and aspiration method) is representative of that obtained in subsequent trials or on repeated days. Nine healthy adults consumed a volume of water (5.5 ml/kg body weight) which contained a nonabsorbable marker. Following a fifteen-minute rest period, the stomach contents were aspirated using a 50 ml syringe. This procedure was repeated three additional times on the same day with a fifteen minute interval separating each trial. On two other days the identical procedures were performed. A significant daily variation was found for residue volume, gastric secretion, and percent of original drink emptied. However, no significant difference between trials within a day was found for the residue volume, gastric secretion, and percent of original drink emptied. Generalizability coefficients, which are "reliability-like" coefficients, were also calculated. These coefficients indicate that a combination of at least 2 days with at least 2 trials/day should be used in order to obtain reliable gastric emptying data.

Adult↗

Fluid replacement after dehydration: influence of beverage carbonation and carbohydrate content.

This investigation evaluated the effects of beverage carbonation and carbohydrate (CHO) content on fluid replacement following exercise/thermal dehydration. On four occasions separated by at least 7 days, eight healthy men cycled at 50% of VO2max in a hot environmental chamber (40 degrees C, 40% relative humidity) until a weight loss of 4.12 +/- 0.22% was attained. In the subsequent four hours, subjects ingested one of four solutions at 15-min intervals. The total volume ingested equalled that lost during dehydration. The solutions were administered in randomized order and varied in their carbonation and carbohydrate (CHO) content: 1. CK: carbonated 10% glucose-fructose solution, 2. NCK: non-carbonated 10% glucose-fructose solution, 3. CNK: carbonated non-caloric solution, and 4. NCNK: non-carbonated non-caloric solution. Plasma volume changes, total plasma protein concentration, plasma osmolality, and the plasma glucose concentration were determined at rest before and after dehydration, and at 30, 90, 150, and 240 min of recovery. Plasma volume changes and the plasma protein concentration were not different (p greater than 0.05) between treatments. Values for the plasma glucose concentration and the change in plasma osmolality were significantly elevated when CHO beverages were ingested when compared with non-CHO beverage ingestion. Five-min cycling bouts were performed at 70% of VO2max before and after dehydration and at 60, 120, 180, and 240 min of rehydration. The respiratory exchange ratio was elevated in both of the CHO treatments when compared with both of the non-CHO treatments at 60, 120, 180 and 240 min of rehydration.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

Day to day variation in time trial cycling performance.

In an attempt to assess the reproducibility of laboratory cycling performance, eight well-trained (VO2max = 4.6 +/- 0.2 l.min-1) male cyclists completed 12 trials involving 4 successive performance rides at each of three total work outputs (approximately 1600, 200, and 14 kilojoules, respectively). These trials, designated as long, medium, and short trials (LT, MT, ST), represented exercise bouts of 105.12 +/- 0.41, 12.03 +/- 0.17 and 0.55 +/- 0.11 minutes, respectively. The trials, conducted on a computerized cycle ergometer in an isokinetic mode, were separated by a minimum of 72 hrs. All trials for each subject were completed at the same time of day. In all trials, subjects were allowed to select the pace in order to complete the ride in the shortest possible time. The mean coefficient of variation (CV) for performance time in each trial was: LT = +/- 1.01%, MT = +/- 0.95%, and ST = +/- 2.43%, respectively. The CV for performance time in ST was significantly greater than the CV in either LT or MT. In LT, performance time was significantly faster, and the mean % VO2max was significantly higher in trial 4 versus trials 1-3. There was no order effect in the MT or ST rides. The CV for mean VO2 (l.min-1), mean % VO2max, and RER during the LT rides were +/- 3.02%, +/- 3.64%, and +/- 3.53%, respectively. These data suggest that trained cyclists have the ability to reproduce endurance performance with a CV of approximately 1.0% in a time-trial protocol.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

Psychological effects during reduced training volume and intensity in distance runners.

Improved mood state has ben linked with reduced training (RT). However, RT has been measured only as a reduction in training volume, either maintaining or not considering the intensity of training employed. To investigate the effects of a 4-week reduction in both training volume and intensity on running performance and mood state, 10 well-trained adult male runners trained for 4 weeks at baseline training distance and pace (BT), followed by 4 weeks training reduced in volume by 66%, with intensity diminished so that all workouts were below 70% VO2max. Subjects completed the Profile of Mood States (POMS) before BT (PREBT), before RT (PRERT), and after RT (POSRT). They ran 5 km time trials PRERT and POSRT. Comparisons were made for the positive mood state of Vigor with an average of the values for the 5 negative mood states (NM) of the POMS. Eight of 10 changes from PRERT to POSRT were toward more negative mood. Nine of 10 runners required more time for the 5 km run POSRT than PRERT. Overall, 7 of 10 runners exhibited both an increase in 5 km time and a change toward more negative mood state (p < .004). However, the magnitudes of these changes were unrelated. These results suggest that mood state and running performance may be linked. Moreover, because mood state did not improve, this study suggests that studies dealing with the topic of reduced training should be specific with regard to the influence of both training intensity and volume.

Adult↗

The effects of a carbonated carbohydrate drink on gastric emptying, gastrointestinal distress, and exercise performance.

To determine the effect of a carbonated carbohydrate (CHO) drink on gastric function and exercise performance, eight male cyclists completed four 120-min bouts of cycling. Each bout consisted of a 105-min ride at 70% VO2max followed by a 15-min self-paced performance ride. During each trial, one of four test solutions was ingested: carbonated CHO (C-10%), noncarbonated CHO (NC-10%), carbonated non-CHO (C), and noncarbonated non-CHO (NC). Following the performance ride, the subjects had their stomach contents removed by aspiration. There were no significant differences in gastric emptying (GE) except for Trial C-10%, which averaged 13.3% less than NC. However, there was no difference in the perception of gastrointestinal comfort between this trial and any other. Average power output during the performance ride was not significantly different between carbonated and noncarbonated trials, or between CHO-fed and no-CHO trials; however, the subjects worked at a greater intensity when fed CHO. Finally, acid base status did not change when a carbonated drink was ingested. This indicates that adding carbonation to a sport drink does not significantly alter gastric function, the perception of GI comfort, or exercise performance.

Adult↗

Time course of glycogen accumulation after eccentric exercise.

This study examined the time course of glycogen accumulation in skeletal muscle depleted by concentric work and subsequently subjected to eccentric exercise. Eight men exercised to exhaustion on a cycle ergometer [70% of maximal O2 consumption (VO2max)] and were placed on a carbohydrate-restricted diet. Approximately 12 h later they exercised one leg to subjective failure by repeated eccentric action of the knee extensors against a resistance equal to 120% of their one-repetition maximum concentric knee extension force (ECC leg). The contralateral leg was not exercised and served as a control (CON leg). During the 72-h recovery period, subjects consumed 7 g carbohydrate.kg body wt-1.day-1. Moderate soreness was experienced in the ECC leg 24-72 h after eccentric exercise. Muscle biopsies from the vastus lateralis of the ECC and CON legs revealed similar glycogen levels immediately after eccentric exercise (40.2 +/- 5.2 and 47.6 +/- 6.4 mmol/kg wet wt, respectively; P greater than 0.05). There was no difference in the glycogen content of ECC and CON legs after 6 h of recovery (77.7 +/- 7.9 and 85.1 +/- 4.9 mmol/kg wet wt, respectively; P greater than 0.05), but 18 h later, the ECC leg contained 15% less glycogen than the CON leg (90.2 +/- 8.2 vs. 105.8 +/- 8.9 mmol/kg wet wt; P less than 0.05). After 72 h of recovery, this difference had increased to 24% (115.8 +/- 8.0 vs. 153.0 +/- 12.2 mmol/kg wet wt; P less than 0.05). These data confirm that glycogen accumulation is impaired in eccentrically exercised muscle.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗