Biomedical subjects

Steven T Devor

Publications and source records attributed to Steven T Devor.

13 recordsLinked to original sources

PubMed2006

Ingestion of starch-rich meals after exercise increases glucose kinetics but fails to enhance muscle glycogen replenishment in horses.

Fatiguing exercise substantially decreases muscle glycogen concentration in horses, impairing athletic performance in subsequent exercise bouts. Our objective was to determine the effect of ingestion of starch-rich meals after exercise on whole body glucose kinetics and muscle glycogen replenishment. In a randomized, cross-over study seven horses with exercise-induced muscle glycogen depletion were either not fed for 8 h, fed half of the daily energy requirements ( approximately 15 Mcal DE) as hay, or fed an isocaloric amount of corn 15 min and 4 h after exercise. Starch-rich meals fed after exercise, when compared to feed withholding, resulted in mild to moderate hyperglycemia (5.7+/-0.3 vs. 4.7+/-0.3 mM, P<0.01) and hyperinsulinemia (79.9+/-9.3 vs. 39.0+/-1.9 pM, P<0.001), 3-fold greater whole body glucose kinetics (15.5+/-1.4 vs. 5.3+/-0.4 micromol kg(-1)min(-1), P<0.05), but these only minimally enhanced muscle glycogen replenishment (171+/-19 vs. 170+/-56 and 260+/-45 vs. 294+/-29 mmol/kg dry weight immediately and 24 h after exercise, P>0.05). It is concluded that after substantial exercise-induced muscle glycogen depletion, feeding status only minimally affects net muscle glycogen concentrations after exercise, despite marked differences in soluble carbohydrate ingestion and availability of glucose to skeletal muscle.

Animals↗

PubMed2006

A comparison of military circumference equations to skinfold-based equations to estimate body composition.

UNLABELLED: Circumference-based military equations (CBEs) were compared with a skinfold-based equation (SBE) to estimate body fat. OBJECTIVE: We determined the correlation between CBEs and SBE, evaluated the efficacy of CBE methods, and examined the difference in methods to identify noncompliant personnel. Circumference and skinfold measurements were taken in sequential order for 1,191 male civil service employees (37.9 +/- 7.9 years). RESULTS: Percent body fat was estimated for SBE (18.4 +/- 6.1) and three different CBEs: Marine Corps (19.6 +/- 5.8), Navy/Air Force (20.4 +/- 5.8), and Army (20.6 +/- 5.2). A moderate correlation coefficient existed between SBE and CBEs (r = 0.76-0.79). A greater body fat percentage was estimated in noncompliant personnel with circumference methods. CONCLUSIONS: Data moderately correlate CBEs and SBE. However, CBEs predict higher estimates, resulting in a greater number of personnel classified as noncompliant.

Adolescent↗

PubMed2005

Nonthermal ultrasound and exercise in skeletal muscle regeneration.

OBJECTIVE: To determine whether continuous nonthermal therapeutic ultrasound (US) and low-intensity exercise (Ex) influence skeletal muscle regeneration after a standardized contusion injury in an animal model. DESIGN: Randomized controlled trial with blinded comparisons in a 2 x 2 factorial (US by Ex) design. SETTING: Animal care facility and exercise physiology biochemistry laboratory. ANIMALS: Twenty male Wistar rats (age, 8 mo) received a reproducible bilateral contusion injury to the gastrocnemius muscles. Ten gastrocnemius muscles from 5 noninjured, nontreated rats provided baseline control data. INTERVENTIONS: US (continuous duty cycle, 3 MHz; intensity, 0.1 W/cm2 ; transducer, 1cm2 ; duration, 5 min/d; duty cycle, 100%) and exercise (20 min/d of low-intensity treadmill walking at 14 m/min). Gastrocnemius muscles from injured rats received exercise treatment alone (Ex + NoUS), exercise and US treatment (Ex + US), US treatment alone (NoEx + US), and no treatment (NoEx + NoUS). MAIN OUTCOME MEASURES: Ninety-six-hour postinjury muscle mass, contractile protein concentration, fiber cross-sectional area, number of nuclei per fiber, and myonuclear density. RESULTS: Myonuclei per fiber were statistically greater in injured than in noninjured gastrocnemius muscle (P < .05). There were no statistical differences (P > .01) among the 4 injured treatment groups for any of the outcome measures chosen as biomarkers of skeletal muscle regeneration. CONCLUSIONS: There is no evidence that the specific continuous US and Ex protocols investigated enhanced skeletal muscle regeneration after contusion injury.

Animals↗

PubMed2005

Age-related changes in metabolic properties of equine skeletal muscle associated with muscle plasticity.

The purpose of the present study was to determine the age-related changes in myosin heavy chain (MHC) composition and muscle oxidative and glycolytic capacity in 18 horses ranging in age from two to 30 years. Muscle samples were collected by excisional biopsy of the semimebranosus muscle. MHC expression and the key enzymatic activities were measured. There was no significant correlation between horse age and the proportions of type-IIA and type-IIX MHC isoforms. The percentage of type-I MHC isoforms decreased with advancing age. Muscle citrate synthase activity decreased, whereas lactate dehydrogenase activity increased with increasing age. Muscle 3-OH acyl CoA dehydrogenase activity did not change with ageing. The results suggest that, similar to humans, the oxidative capacity of equine skeletal muscle decreases with age. The age-related changes in muscle metabolic properties appear to be consistent with an age-related transition in MHC isoforms of equine skeletal muscle that shifts toward more glycolytic isoforms with age.

3-Hydroxyacyl CoA Dehydrogenases↗

PubMed2004

Soy versus whey protein bars: effects on exercise training impact on lean body mass and antioxidant status.

BACKGROUND: Although soy protein may have many health benefits derived from its associated antioxidants, many male exercisers avoid soy protein. This is due partly to a popular, but untested notion that in males, soy is inferior to whey in promoting muscle weight gain. This study provided a direct comparison between a soy product and a whey product. METHODS: Lean body mass gain was examined in males from a university weight training class given daily servings of micronutrient-fortified protein bars containing soy or whey protein (33 g protein/day, 9 weeks, n = 9 for each protein treatment group). Training used workouts with fairly low repetition numbers per set. A control group from the class (N = 9) did the training, but did not consume either type protein bar. RESULTS: Both the soy and whey treatment groups showed a gain in lean body mass, but the training-only group did not. The whey and training only groups, but not the soy group, showed a potentially deleterious post-training effect on two antioxidant-related related parameters. CONCLUSIONS: Soy and whey protein bar products both promoted exercise training-induced lean body mass gain, but the soy had the added benefit of preserving two aspects of antioxidant function.

Journal Article↗

PubMed2004

Exercise training increases oxidative capacity and attenuates exercise-induced ultrastructural damage in skeletal muscle of aged horses.

Exercise training improves functional capacity in aged individuals. Whether such training reduces the severity of exercise-induced muscle damage is unknown. The purpose of the present study was to determine the effect of 10 wk of treadmill exercise training on skeletal muscle oxidative capacity and exercise-induced ultrastructural damage in six aged female Quarter horses (>23 yr of age). The magnitude of ultrastructural muscle damage induced by an incremental exercise test before and after training was determined by electron microscopic examination of samples of triceps, semimembranosus, and masseter (control) muscles. Maximal aerobic capacity increased 22% after 10 wk of exercise training. The percentage of type IIa myosin heavy chain increased in semimembranosus muscle, whereas the percentage of type IIx myosin heavy chain decreased in triceps muscle. After training, triceps muscle showed significant increases in activities of both citrate synthase and 3-hydroxyacyl-CoA-dehydrogenase. Attenuation of exercise-induced ultrastructural muscle damage occurred in the semimembranosus muscle at both the same absolute and the same relative workloads after the 10-wk conditioning period. We conclude that aged horses adapt readily to intense aerobic exercise training with improvements in endurance, whole body aerobic capacity, and muscle oxidative capacity, and heightened resistance to exercise-induced ultrastructural muscle cell damage. However, adaptations may be muscle-group specific.

Adaptation, Physiological↗

PubMed2004

The effects of land vs. aquatic plyometrics on power, torque, velocity, and muscle soreness in women.

The purpose of this study was to compare changes in performance indicators (power, torque, and velocity) and muscle soreness between plyometric training on land and in water. Thirty-two college age women were randomly assigned to 8 weeks of an identical plyometric training program on land or in an aquatic setting. Performance indicators were assessed pretraining, midtraining, and posttraining. Muscle soreness (ordinal scale) and pain sensitivity (palpation) were assessed after a training bout (0, 48, and 96 hours) during the first week of training and when training intensity was increased (weeks 3 and 6). Performance indictors increased for both groups (pretraining < midtraining < posttraining, p < or = 0.001). Muscle soreness was significantly greater in the land compared to the aquatic plyometric training group at baseline and each time training intensity was increased, p = 0.01. Aquatic plyometrics provided the same performance enhancement benefits as land plyometrics with significantly less muscle soreness.

Exercise↗

PubMed2004

Mg2+-creatine chelate and a low-dose creatine supplementation regimen improve exercise performance.

We tested the hypotheses that, compared with a placebo group or creatine (Cr) group, a Mg(2+)-Cr chelate group would demonstrate improvements in the 1 repetition maximum (1RM) on the bench press and be able to perform more work at 70% of the 1RM for the bench press. Thirty-one weight-trained men were randomly assigned in a double-blind manner to a placebo group (multidextran), a Cr group (2.5 g of Cr daily), or a Mg(2+)-Cr group (2.5 g of Cr daily). Baseline data were collected for the bench press 1RM and maximal work completed during a fatigue set at 70% of the 1RM. Following 10 days of Cr supplementation, follow-up tests were completed for the dependent variables. Groups were similar when the change in 1RM was evaluated either absolutely or relatively. Both the Cr and the Mg(2+)-Cr groups had significantly larger increases in work, both absolutely and relatively, when compared with the placebo group. Partial support for the hypothesis suggests that low doses of Cr are effective at increasing fiber Cr content, and consequently, performance. Further, the Cr and Mg(2+)-Cr groups were similar in both performance tests, suggesting that the proposed mechanism of entry is no better than the conventional method when 2.5 g of Cr is administered and performance is measured as work. This study raises the possibility that a low dose of Cr may be an effective means of enhancing performance after short-term ingestion.

Adolescent↗

PubMed2003

Maximal lactate steady state declines during the aging process.

Increased participation of aged individuals in athletics warrants basic research focused on delineating age-related changes in performance variables. On the basis of potential age-related declines in aerobic enzyme activities and a shift in the expression of myosin heavy chain (MHC) isoforms, we hypothesized that maximal lactate steady-state (MLSS) exercise intensity would be altered as a function of age. Three age groups [young athletes (YA), 25.9 +/- 1.0 yr, middle-age athletes (MA), 43.2 +/- 1.0 yr, and older athletes (OA), 64.6 +/- 2.7 yr] of male, competitive cyclists and triathletes matched for training intensity and duration were studied. Subjects performed a maximal O2 consumption (V(o2 max)) test followed by a series of 30-min exercise trials to determine MLSS. A muscle biopsy of the vastus lateralis was procured on a separate visit. There were differences (P < 0.05) in V(o2 max) among all age groups (YA = 67.7 +/- 1.2 ml x kg-1x min-1, MA = 56.0 +/- 2.6 ml x kg-1x min-1, OA = 47.0 +/- 2.6 ml x kg-1 x min-1). When expressed as a percentage of V(o2 max), there was also an age-related decrease (P < 0.05) in the relative MLSS exercise intensity (YA = 80.8 +/- 0.9%, MA = 76.1 +/- 1.4%, OA = 69.9 +/- 1.5%). There were no significant age-related changes in citrate synthase activity or MHC isoform profile. The hypothesis is supported as there is an age-related decline in MLSS exercise intensity in athletes matched for training intensity and duration. Although type I MHC isoform, combined with age, is helpful in predicting (r = 0.76, P < 0.05) relative MLSS intensity, it does not explain the age-related decline in MLSS.

Adult↗

PubMed2003

Swim performance following creatine supplementation in Division III athletes.

Creatine (Cr) supplementation has yielded inconsistent results when applied to competitive swimming. To further define the role of Cr, we tested the hypothesis that a Cr supplementation group of Division III swimmers would demonstrate enhanced performance when compared with placebo. In order to test this hypothesis, 8 male and 7 female collegiate Division III swimmers were assigned in a random, double-blind manner into either a Cr supplementation group (0.3 g Cr.kg(-1) body mass) or a placebo group. Loading was maintained for 5 days followed by a 9-day period where Cr-supplemented subjects consumed 2.25 g Cr regardless of body weight. A 50- and 100-yd sprint was performed prior to and following the supplementation regimens. The Cr supplementation group decreased their finish times in both the 50- and 100-yd sprints. Support of the hypothesis suggests that Cr supplementation for swimming events is effective for singular effort sprints of 50 and 100 yd in Division III athletes.

Adolescent↗

PubMed2003

Identical 3-MHz ultrasound treatments with different devices produce different intramuscular temperatures.

STUDY DESIGN: A counterbalanced, repeated-measures design with ultrasound device (Omnisound 3000C, Dynatron 950, Excel Ultra III) as the independent variable. The 2 dependent variables were intramuscular (IM) temperature at 6 minutes and at the end of a 10-minute treatment. OBJECTIVE: To compare IM temperatures produced by identical 3-MHz ultrasound treatments between 3 different ultrasound devices. BACKGROUND: Most recent studies prescribing intensity and duration parameters for thermal ultrasound treatments have been performed using an Omnisound device, but have not been verified in other common ultrasound devices. METHODS AND MEASURES: Six uninjured volunteers (mean age +/- SD, 22 +/- 3.4 y; mean height +/- SD, 171.9 +/- 11.0 cm; mean mass +/- SD, 66.1 +/- 11.1 kg) gave informed consent and served as subjects. Separate ultrasound treatments using identical parameters (3 MHz, 1.5 W/cm2, 10 minutes, treatment area equal to twice transducer surface area) were administered at 24 or 48 hours intervals using a different ultrasound device for each treatment. Left medial calf IM temperature was recorded every 20 seconds using implantable thermocouples at a depth of 1.6 cm below the treatment surface. Data were analyzed using MANOVA with Sidak adjusted multiple comparisons post hoc. RESULTS: Tissue heating using the Omnisound device was greater than with either the Dynatron or the Excel. The results of treatments using Dynatron or Excel devices did not differ. The Omnisound was the only device to consistently produce IM temperatures above the 40 degrees C therapeutic threshold and did so in less than 6 minutes. The other devices did not reach this threshold within the 10-minute treatment session. Subjects routinely reported heating sensations approaching discomfort when the IM temperature reached the 40 degrees C therapeutic threshold. CONCLUSIONS: Because there are differences in thermal effects between ultrasound devices, our results suggest that recently published parameters for ultrasound intensity and duration parameters will not produce equally therapeutic effects for all ultrasound devices.

Adult↗

PubMed2002

Glycemic index of a meal fed before exercise alters substrate use and glucose flux in exercising horses.

In a randomized, balanced, crossover study each of six fit, adult horses ran on a treadmill at 50% of maximal rate of oxygen consumption for 60 min after being denied access to food for 18 h and then 1) fed corn (51.4 kJ/kg digestible energy), or 2) fed an isocaloric amount of alfalfa 2-3 h before exercise, or 3) not fed before exercise. Feeding corn, compared with fasting, resulted in higher plasma glucose and serum insulin and lower serum nonesterified fatty acid concentrations before exercise (P < 0.05) and in lower plasma glucose, serum glycerol, and serum nonesterified fatty acid concentrations and higher skeletal muscle utilization of blood-borne glucose during exercise (P < 0.05). Feeding corn, compared with feeding alfalfa, resulted in higher carbohydrate oxidation and lower lipid oxidation during exercise (P < 0.05). Feeding a soluble carbohydrate-rich meal (corn) to horses before exercise results in increased muscle utilization of blood-borne glucose and carbohydrate oxidation and in decreased lipid oxidation compared with a meal of insoluble carbohydrate (alfalfa) or not feeding. Carbohydrate feedings did not produce a sparing of muscle glycogen compared with fasting.

Animal Feed↗

PubMed2002

Influence of racial origin and skeletal muscle properties on disease prevalence and physical performance.

Skeletal muscle properties are related to disease (e.g. obesity) and physical performance. For example, a predominance of type I muscle fibres is associated with better performance in endurance sports and a lower risk of obesity. Disease and physical performance also differ among certain racial groups. African Americans are more likely than Caucasians to develop obesity, diabetes mellitus and hypertension. Empirical studies indicate that aerobic capacity is lower in African Americans than Caucasians. Because genetics is a partial determinant of skeletal muscle properties, it is reasonable to assume that skeletal muscle properties vary as a function of race. As such, genetically determined and race-specific skeletal muscle properties may partially explain racial disparities in disease and physical performance. However, additional research is needed in this area to enable the development of more definitive conclusions.

Black People↗