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Biomedical subjects

A C Snyder

Publications and source records attributed to A C Snyder.

34 records · Page 2Linked to original sources
PubMed1992

Effects of chronic intense exercise training on the leukocyte response to acute exercise.

Circulatory leukocytes vary significantly in response to acute bouts of exercise. However, little is known concerning the adaptability of this response to chronic intense exercise training. We investigated the circulating leukocytic response to acute exercise in trained athletes during a 28-day intense exercise training program. On day 0, 14, 28 and two days after cessation of the increased training, eight trained male athletes (VO2max greater than 60 ml.kg-1.min-1) were subjected to a 20-km bicycle ergometer time trial. Blood samples were drawn before (PRE, for resting baseline values) and five minutes after (POST, response to acute exercise) the time trial. Beginning on day 0, athletes were instructed to increase the duration of their training 50%. The intense exercise training, which lasted 28 days, was verified weekly. Acute bouts of exercise caused a significant increase (p less than 0.05) in circulating white blood cells, lymphocytes, polymorphonuclear neutrophils and monocytes. The baseline resting values and the magnitude of the response to the acute bouts of exercise in the above parameters were not different during the 28 days of chronic intense exercise training or 2 days after cessation of training as compared to the values observed on day 0. Similarly there was a significant increase (p less than 0.05) in cortisol levels in response to the acute bouts of exercise during the chronic intense exercise training, but the increases were not different from that observed under baseline conditions. These results lead to the conclusion that chronic intense exercise training does not alter the circulating leukocytic response to acute exercise.

Analysis of Variance↗
PubMed1992

A new approach for the determination of ventilatory and lactate thresholds.

In order to determine the ventilatory threshold (VT) and the lactate threshold (LT) in a reliable way, a new method is proposed and compared with conventional methods. The new method consists of calculating the point that yields the maximal distance from a curve representing ventilatory and metabolic variables as a function of oxygen uptake (VO2) to the line formed by the two end points of the curve (Dmax method). Male cyclists (n = 8) performed two incremental exercise tests a week apart. Ventilatory/metabolic variables were measured and blood was sampled for later lactate measurement during each workload and immediately after exercise. No statistical differences were observed in the threshold values (expressed as absolute oxygen uptake; VO2) determined by the Dmax method and the conventional linear regression method (according to O2 equivalent; EqO2) and venous blood at the onset of blood lactate (OBLA), while VT assessed with the conventional linear method (according to the slope of CO2 output; Vslope) yielded significantly lower threshold values. Similar results were obtained from the reproducibility test. Thus, the Dmax method appears to be an objective and reliable method for threshold determination, which can be applied to various ventilatory or metabolic variables yet yield similar results. The results also showed that breathing frequency can be used to determine VT.

Adolescent↗
PubMed1992

Physiological changes in male competitive cyclists after two weeks of intensified training.

To study the physiological response to heavy training, seven male competitive cyclists intensified their normal training program for two weeks (IIT) in order to achieve a state of short-term overtraining. The subjects underwent a graded cycle ergometer test to exhaustion, an outdoor 8.5 km time trial and a computerized test to study reaction time and visual perception, before, during and after the two weeks of intensified training and after two weeks of recovery. Furthermore subjects kept a daily log in the form of a questionnaire. After two weeks of IIT all subjects showed symptoms of overtraining: the general state of well being declined as indicated by the questionnaire while performances on time trial (mean +/- SEM: 830 +/- 14 sec-871 +/- 19 sec), contests and maximal power output (mean +/- SEM: 336 7 watt-310 +/- 5 watt) declined significantly. Maximal (mean +/- SEM 11.8 +/- 1.1 mmol.l-1-5.9 +/- 0.5 mmol.l-1) and submaximal lactate values were significantly lowered during ergometer test after the IIT, while the workload at the 4 mmol point increased significantly (mean +/- SEM 234 +/- 10 watt-267 +/- 13 watt). Sleeping heart rate increased significantly (mean +/- SEM 49.5 +/- 9.3 BPM-54.3 +/- 8.8 BPM). Maximal heart rate (mean +/- SEM 185 +/- 3 BPM-178 +/- 2 BPM, mean heart rate during the time trial (mean +/- SEM 178 +/- 2 BPM-169 +/- 2 BPM) and VO2max (mean +/- SEM 4801 +/- 121 ml.min-1-4409 +/- 101 ml.min-1) were all significantly lowered by the IIT.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Muscle glycogen loading with a liquid carbohydrate supplement.

This study compared two high carbohydrate (CHO) diets in 14 male runners for effects on muscle glycogen deposition, endurance, and sensations of gastrointestinal discomfort. Muscle glycogen was measured in the vastus lateralis at rest and run time to exhaustion at 75% VO2max was measured following 3-1/2 days on a 50% CHO diet. After 14 days the subjects consumed a 20% CHO diet and continued training to reduce glycogen. During the next 3-1/2 days, subjects ran less and consumed a 90% CHO diet emphasizing pasta and rice (Pasta, n = 7) or lesser amounts of pasta and rice supplemented by a maltodextrin beverage (Supplement, n = 7). Glycogen was again measured, followed by a second run to exhaustion. Compared to the 50% CHO diet, Pasta increased muscle glycogen by 27.1 +/- 12.2 mmoles/kg muscle (M +/- SE; P < 0.05) and run time by 15.7 +/- 5.9 min; Supplement increased glycogen by 43.2 +/- 13.5 mmoles/kg (P < 0.05) and run time by 29.0 +/- 7.4 min (P < 0.05). Total glycogen concentrations and run times were not significantly different for Pasta versus Supplement. Subjects reported less gastrointestinal discomfort and greater overall preference for Supplement than for Pasta. Thus, glycogen loading can be accomplished at least as effectively and more comfortably by substituting a maltodextrin drink for some of the pasta and rice in a glycogen loading diet.

Adult↗
PubMed1989

Influence of dietary iron source on measures of iron status among female runners.

The purpose of the present investigation was to determine whether female runners who consume a modified vegetarian diet are predisposed to iron deficiency. Two groups of female runners who were matched for age, weight, aerobic capacity, miles run per week, and number of pregnancies were obtained for this study. One group (N = 9) regularly consumed a modified vegetarian diet (MV, less than 100 g red meat.wk-1), while the other group (N = 9) consumed a diet which included red meat (RM). Serum ferritin values were significantly (P less than 0.05) lower for the MV group (X +/- SE, 7.4 +/- 1.4 ng.100 ml-1) than for the RM group (19.8 +/- 4.2 ng.100 ml-1). Total iron binding capacity (TIBC) of the serum was also significantly different between the two groups of subjects (MV, 366.5 +/- 12.2 micrograms.100 ml-1; RM, 327.2 +/- 9.6 micrograms.100 ml-1). While dietary iron intake was comparable for the two groups (MV, 14.7 +/- 2.0 mg.d-1; RM, 14.0 +/- 2.2 mg.d-1, the bioavailability of the dietary iron was significantly different (MV, 0.66 +/- 0.08 mg.d-1; RM, 0.91 +/- 0.10 mg.d-1). As the presence of heme iron (from meat, fish, and poultry) increases the bioavailability of dietary iron, the results of the present investigation suggest that vegetarian athletes have altered iron status due to the form in which their dietary iron is consumed.

Adult↗
PubMed1989

Nutritional, physiological, and menstrual status of distance runners.

Amenorrheic runners (AR; N = 8), regularly menstruating runners (RMR; N = 9), and regularly menstruating sedentary controls (RMSC; N = 7) were compared for plasma progesterone levels, plasma lipid levels, menstrual cycle characteristics, physical characteristics, and nutritional adequacy to determine whether exercise training was the major factor associated with menstrual cycle disturbances. Plasma progesterone levels were significantly lower in the AR group subjects than those found during either the follicular or luteal phases of the menstrual cycle for either the RMR or the RMSC subjects. The RMR subjects had a shorter luteal phase length relative to their cycle length than did the RMSC subjects. The AR subjects consumed significantly less fat, red meat, and total calories than did the RMR subjects, while the RMSC subjects consumed significantly less total calories than did the RMR subjects. Serum LDL-C was significantly higher in the AR subjects when compared to that of the RMR subjects, while serum HDL-C was significantly higher for both the AR and RMR subjects when compared to that obtained for the RMSC subjects. The nutritional inadequacy would appear to separate the AR from the RMR, and, thus, the exercise training performed by the athletes at the time of the present investigation alone does not appear to be the major factor associated with athletic amenorrhea.

Adult↗
PubMed1988

Normalization of the blood lactate profile in athletes.

The power output-blood lactate or velocity-blood lactate relationship, the lactate "profile", is a widely used method for the evaluation of athletes. Recent observations have suggested a shift in the blood lactate profile when athletes are fatigued, as at training camps. This study was designed to determine whether the blood lactate profile could be corrected for progressive muscle glycogen depletion by normalizing for the peak exercise blood lactate concentration. Ten well-trained subjects performed incremental cycle ergometer exercise followed by supramaximal exercise (Wingate test) following 3 days of usual and 3 days of heavier than usual training. Following heavier than usual training, blood lactate accumulation was reduced during submaximal exercise such that the power output associated with a lactate concentration of 4 mM was significantly increased (3.08 vs 3.51 W/kg). The maximal blood lactate concentration was also reduced (14.8 vs 12.7 mM) although average supramaximal power output was unchanged (9.03 vs 8.92 W/kg). When the submaximal blood lactate concentrations were normalized for the maximal blood lactate concentration, there were no significant differences in the power output associated with 20% (2.6 vs 2.7 W/kg), 25% (3.1 vs 3.2 W/kg), or 30% (3.3 vs 3.5 W/kg) of maximal lactate. The results suggest that normalization based on peak exercise blood lactate may be a useful strategy for circumventing one of the primary practical barriers to the use of the blood lactate profile in athletes.

Adult↗
PubMed1988

Evaluation of contact lenses by microbial enumeration and protein determination.

Contact lenses worn for varying periods of time (from 1 to 48 months) were subjected to microbiological examination by plate counts and protein determination. Seventy percent of the lenses displayed bacterial colony counts below 120 colony-forming units (CFU)/lens, 28 percent were in the range of 140 to 9060 CFU/lens, and one lens was contaminated with greater than 6 x 10(4) CFU/lens. Fungal contaminants were detected in three lens specimens in the range of 220 to 760 CFU/lens. Protein accumulation showed wide variation of up to 1.2 mg of protein per lens. Statistical analysis indicated highly significant associations (p less than 0.001) between the bacterial colony counts obtained with three different media. Some significant associations were found between the protein concentration and bacterial counts. The data did not indicate statistically significant relations between the above variables and either the water content or the length of wear of the contact lenses.

Adolescent↗
PubMed1987

Validity of optical pachometry measurements made with contact lenses in situ.

Traditionally changes in corneal thickness associated with contact lens wear have been measured with optical pachometers after the lenses are removed from the cornea. In studies of corneal response to the extended wearing of hydrogel and silicone elastomer contact lenses, optical pachometry measurements may be improved by uninterrupted lens wear during the measurements. Using four flexible lens types differing in design and thickness, a single observer made pachometric measurements both with and without the lenses in place on eight subjects. This study demonstrates that valid and reliable measures of corneal thickness may be made without removing flexible lenses from the eye.

Contact Lenses↗
PubMed1987

Effects of refrigeration on daily microbial bioburden of hydrogel lenses.

Microbial bioburden of contact lenses was evaluated in connection with lens care by refrigeration. Subjects wore new hydrogel contact lenses for approximately 8 hours. The microbial bioburden initially and after an overnight refrigeration of the lens was evaluated with the use of viable counts on three different media. No major changes in viable counts were observed resulting from this method of storage. Scanning electron microscopy indicated the presence of foreign material on both new and worn lenses, presumed to be debris from lens manufacture and mucoid deposits from daily wear. Microbial colonization was not apparent and single bacterial cells could not be discerned on the micrographs.

Bacteria↗
PubMed1985

Comparison of oxygen tension measurement methodologies: further studies.

The oxygen quantifying techniques of Hill and Rasson and Fatt have been compared by Roscoe and Wilson, who have also derived an "average" equivalent oxygen percentage (EOP) calibration equation. This study provides additional data which support their conclusions. Eight subjects wore three different hydrogel contact lens types of various center thicknesses and oxygen transmissibilities. Open-eyelid oxygen polarographic data were taken for each of these lenses worn by the subjects. The "average" EOP calibration equation was used to calculate the EOP values. The relation between center thickness and the ratio of the oxygen tension values derived by the two methods agrees relatively well with that found previously.

Adult↗
PubMed1984

Myofibrillar protein degradation after eccentric exercise.

Male rats were run downhill for 90 minutes (nonexhaustive). Following the exercise, muscle protein degradation was increased, as determined by urinary 3-methylhistidine. However, minimal changes were observed in the relative percentage of the minor myofibrillar proteins and in the protease calcium activated factor in the long head of the triceps brachii muscle (eccentrically exercised) following the exercise bout.

Animals↗
PubMed1984

Optical pachometry measurements: reliability and variability.

Polymethyl methacrylate (PMMA) lenses of known thickness were measured by one investigator with a pachometer. This experienced pachometrist held variation in thickness measurements to within 1% over time. The measurements were repeatable with a SD less than 1%. The data indicate that measured corneal thickness changes should be greater than 1 to 2% to be considered true changes in thickness.

Calibration↗
PubMed1983

Corneal thickness changes associated with daily and extended contact lens wear.

Human corneal thickness was measured during daily wear of hydrogel contact lenses and then during the initial 2 weeks extended wear of hyper-thin (0.035 mm), low water content (38.6%), hydrogel lenses (polymacon). Results show that subjects wearing standard thickness (0.12 mm) and ultra-thin (0.07 mm) hydrogel lenses of low water content for daily wear will exhibit a diurnal swelling of the cornea. Subjects wearing hyper-thin (0.035 mm) low minus power hydrogel contact lenses of low water content for extended wear will exhibit overnight (closed eye) swelling of the cornea followed by a deswelling throughout the day (open eye). The degree of swelling and deswelling can vary greatly among individual subjects.

Circadian Rhythm↗