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Biomedical subjects

A G Nelson

Publications and source records attributed to A G Nelson.

At least 37 records · Page 2Linked to original sources
PubMed1997

Creatine supplementation enhances intermittent work performance.

To determine the impact of creatine supplementation on high-intensity, intermittent work, 18 participants each performed 2 sets of 4 different work bouts to exhaustion. For 5 days prior to the first set of work bouts, all participants received a placebo (5 g of calcium chloride daily). For the second set of work bouts, 9 participants again received the placebo, while the other 9 received creatine supplementation (18.75 g creatine monohydrate daily for 5 days prior to and 2.25 g creatine daily during testing). The four work bouts in each set consisted of cycling to exhaustion at 150% peak oxygen uptake (VO2peak) either nonstop (A), intermittently for either 60-s work/120-s rest periods (B), 20-s work/40-s rest (C), or 10-s work/20-s rest (D). Creatine supplementation significantly increased (p < .01) the total work time of all bouts. Protocol D showed the greatest increase (> 100%); C increased 61.9%; B increased 61.0%; and A increased 23.5%. These results demonstrate that creatine supplementation significantly extends one's capacity to maintain a specific level of high-intensity, intermittent exercise.

Adult↗
PubMed1997

Does shivering thermogenesis enhance the individual's ability to maintain rectal temperature during immersion in cold water?

Shivering thermogenesis may enable individuals to maintain rectal temperature during acute cold exposure. This data analysis revisited this hypothesis and compared previously published data with unpublished data from our laboratory on those subjects that were terminated from cold water immersion early because of a reduction in rectal temperature (T(re)) - 35 degrees C. T(re), mean skin temperature (T(sk)), and oxygen uptake (VO2) were recorded at 5, 30, 60, and 90 min of immersion and were used to calculate 3delta readings for each exposure, that is, deltaT(30) minus T5, T60 minus T(30), and T(90) minus T(60). Single group t-tests were used to examine differences in deltaT(re), deltaT(sk), and deltaVO2 between the published data (PD) group and the individual subjects who were terminated early (TE) at each of three water temperatures (18 degrees C, 22 degrees C, 26 degrees C). For deltaVO2 the TE subjects were dichotomized by fatness (low percent fat, 8%-12%; or high percent fat, 18%-22%) to account for the VO2 differences between these groups (i.e., fatness) during cold water immersion. deltaT(re) was significantly (p < 0.05) decreased in TE subjects compared with PD subjects at all timepoints for 18 degrees C and 26 degrees C. At 22 degrees C, the TE subject exhibited a significantly greater (p < 0.05) decrease in deltaT(re) than the PD group at 90 min of immersion only. No significant (p > 0.05) differences in deltaT(sk) between the PD and TE groups were detected for any of the exposure temperatures over all time points. No difference (p > 0.05) between PD subjects and TE subjects for deltaVO2 was exhibited at any time point at any temperature. It appears that with respect to the TE group, elevations in VO2 were comparable to the PD group, but the TE group was unable to maintain T(re) during cold water immersion. In conclusion, from these data it appears that shivering thermogenesis does in part enhance the individual's ability to maintain T(re); however, as evidenced in the TE group, it also appears that the alterations in shivering thermogenesis for certain individuals may not be great enough to offset heat loss.

Adult↗
PubMed1997

Does capsaicin affect the thermal sensation of males during immersion in 18 degrees C and 22 degrees C?

Animals respond to acute local or systemic administration of capsaicin with strong nociceptive reactions. The present investigation examined the thermal sensation in males who were given capsaicin (CAP, 2 mg x kg(-1) body weight) vs a placebo (PL, a maltodextrin capsule) before immersion in cold water. Seven Caucasian males ages 20-28 years were immersed in 18 degrees C and 22 degrees C twice (PL vs CAP) for 120 minutes. The following were examined: metabolism (VO2; L x min(-1)), rectal temperature (Tre; degrees C), and thermal sensation (TS). For VO2 there were no significant differences between treatments (PL vs CAP) when the variables were pooled jointly over the two immersion temperatures (18 degrees C and 22 degrees C) and across time. However, for Tre there were significant differences detected across time (p = 0.01) when Tre was pooled jointly across two treatments and two immersion temperatures. Postanalysis of variance revealed specific significant differences between 5 minutes (mean +/- SE; 37.2 +/- 0.07) and 120 minutes (36.0 +/- 0.09). For TS, there was a trend (p = 0.0699) which demonstrated differences between immersion temperatures only when TS was pooled jointly over the two treatments and across time, whereby TS was lower in 18 degrees C (6.2 +/- 0.5) than in 22 degrees C (3.7 +/- 0.6). From these data it appears that although Tre differed across time and temperature, respectively, a CAP feeding did not affect differentially the TS and metabolic response of males during acute cold water immersion.

Adult↗
PubMed1996

Effects of caffeine ingestion on endurance racing in heat and humidity.

A hot and humid environment can be detrimental to race performance. Caffeine, on the other hand, has been shown to be an ergogenic aid for improving endurance performance. To examine the influence of caffeine ingestion on race performance during high heat stress, seven endurance trained competitive road racers aged between 23 and 51 years (five men, two women) performed three maximal effort 21-km road races outdoors in hot and humid conditions. The caffeine dose, randomly assigned in a double-blind fashion, consisted of either 0, 5, or 9 mg.kg-1 body mass. During each run, the subjects were allowed to drink water ad libitum at each 5-km point. Blood samples were obtained immediately before and after each run and analysed for changes in concentrations of Na+, K+, glucose, lactate, and hematocrit. Pre and postrun data were also collected for body mass and tympanic membrane temperature. Race times were not significantly different among the races or caffeine doses, with the average times within 1.1% of each other. In addition, none of the other variables measured varied significantly among the races or caffeine doses. In summary, caffeine intake did not affect race performance. Therefore it was concluded from our study that caffeine is not of ergogenic benefit in endurance races during high heat stress.

Adult↗
PubMed1996

Morderate diabetes alters myosin isoenzyme distribution in cardiac but not skeletal muscle of male rats.

Diabetes is known to alter the myosin phenotype of striated muscle, but the impact of the same diabetic state on different types of striated muscles remains unknown. Therefore, this study determined the myosin isoenzyme profile in the left ventricle, soleus, plantaris, and extensor digitorium longus (EDL) of young male rats made moderately diabetic with streptozotocin, (45 mg/kg, ip). Eight weeks after the single streptozotocin injection, tissues were collected and subsequently electrophoretically analyzed for native myosin isoenzyme distribution. Skeletal muscles were additionally analyzed for myosin heavy chain distribution. Neither the native myosin isoform nor the myosin heavy chain (MHC) distribution profiles of the skeletal muscles were altered by the diabetic state. In contrast, the high ATPase cardiac isoform, VI, was significantly replaced by the low ATPase isoform, V3 (p < 0.05). These results demonstrate that striated muscle responds to a moderate diabetic state in a limited and muscle specific fashion. Significantly, the change in the cardiac myosin isoform profile is comparable to that which occurs in a more severe diabetic state.

Adenosine Triphosphatases↗
PubMed1996

Effect of hyperbaric oxygenation on peripheral nerve regeneration in adult male rabbits.

Oxygen environments were used to study the regenerative effects of hyperbaric oxygen on crushed sciatic nerves in 30 adult male rabbits. Six different oxygen environments were used, and treatments were initiated 4 days post injury. Transmission electron microscopy and light microscopy were used to evaluate the regenerative morphology of crushed nerves. The morphology of crushed nerves after 7 wk of treatment with compressed oxygen at 202, 242, and 303 kPa resembled normal uncrushed nerves, with nerve fibers uniformly distributed throughout the section. The treatment groups receiving 202 kPa compressed air, 100% normobaric oxygen, or ambient air did not display morphologies similar to normal uncrushed nerve. The nerves in these animals were edematous and contained disarrayed nerve fibers. Myelination in the animals receiving 100% O2 at high pressures resembled undamaged nerves. Collagen and blood vessels were more evident in the lower pressure/oxygen tension treatments than in the animals receiving 100% O2 at higher pressures. The neurofilamentous material inside the crushed control axons was dense, whereas in the axons of animals treated with compressed O2 it was loosely packed. These differences in morphology suggest that treatments consisting of 100% O2 under pressure can accelerate a peripheral nerve's recovery from a crush injury.

Animals↗
PubMed1995

Cocaine alters myosin isoform expression in the rat soleus.

The purpose of this study was to determine whether chronic cocaine administration alters the expression of myosin isoforms in the rat soleus. Forty-five adult Sprague-Dawley rats were divided into three groups: chronic cocaine (n = 15), 12.5 mg/kg cocaine-HCl injected intraperitoneally twice daily for 14 days and one injection of cocaine (12.5 mg/kg ip) on day 15; acute cocaine (n = 15), saline injections twice daily for 14 days and one injection of cocaine (12.5 mg/kg ip) on day 15; and chronic saline (n = 15), saline injections twice daily for 14 days and one saline injection on day 15. Myosin isoform content of the soleus (native and heavy chains) was identified by electrophoresis. The solei samples from the chronic saline and acute cocaine animals contained slow myosin only. However, solei samples from the chronic cocaine group contained slow myosin and two to three other myosin isoforms and the associated heavy chains IIa and IIx. Therefore, chronic cocaine administration causes in the rat soleus a shift in myosin expression from slow isoforms to fast isoforms.

Animals↗
PubMed1995

Effect of body composition on metabolic responses to carbohydrate feeding in males during exposure to 8, 12, and 27 degrees C.

The effect of body composition on thermoregulation in response to a feeding regime was evaluated in eight male volunteers (21-27 years of age) during 120 min of exposure at 8, 12, and 27degrees C. Subjects were divided with respect to body fat [high fat (HF) = 19-28%, N = 4: low fat (LF) = 10-15%, N= 4] and randomly assigned the three air temperature conditions twice to examine the thermogenic effect of a sequential timed feeding regime of either a carbohydrate (CHO) or placebo (PL) beverage during exposure. Tissue insulation (I), rectal temperature (T(re)), mean skin temperature (T(sk)), metabolism (M), and respiratory exchange ratio (R) were examined. T(re), T(sk), M, and I revealed no significant differences between treatment (PL vs. CHO) at any temperature (8, 12, or 27 degrees C). However, pooled T)(sk) at 27 degrees C, and pooled I at 12 degrees C revealed significant (p < .05) differences between the LF and HF groups. In addition, at 8, 12, and 27 degrees C, pooled T(re), T(sk), and I decreased (p < .05) during the length of exposure, whereas pooled M increased (p < .05) at 8 and 12 degrees C. Pooled R increased during the length of exposure (p < .05) at 8 and 12 degrees C and differed (p < .05) between the LF and HF groups at 8 degrees C only. From these data, it appears that whereas substrate utilization differed between dietary treatment (8 degrees C) and across time (8 and 12 degrees C), there was a differential effect between LF and HF groups (T(sk) at 27 degrees C and I at 12 degrees C) that was not influenced by feeding regime.

Adult↗
PubMed1995

Influence of cold water immersion on heat debt and substrate utilization in males varying in body composition: a retrospective analysis.

The present article is a retrospective analysis of previously published data. This analysis examined the effect of immersion in 18, 22 and 26 degrees C cold water, on heat debt (kJ), substrate utilization [i.e., R (respiratory exchange ratio) calculated using indirect calorimetry], and aerobic metabolic rate (i.e., VO2 (oxygen consumption) 1 # min(-1)] in 24 male volunteers (20-35 years) given a preexposure meal (60.2 g carbohydrate, 12.0 g protein, and 2.8 g fat at 60 min prior to the experimental trial) and examined during 90 min of immersion to the first thoracic vertebrae. Body composition was determined via underwater densitometry. Subjects were divided with respect to high body fat (HF; 18-22%, n = 12) or low body fat (LF; 8-12%, n = 12) and randomly assigned to one of three water temperatures. Body heat debt and R did not differ between the LF or HF groups, between temperatures, or across time. Percent calories utilized indicated that for these experimental conditions the predominant substrate utilized between the LF and HF groups across time was derived from carbohydrate. In addition, VO2 was greater (p = .0004) in the LF than HF group, and the latter was greater (p = .0013) in the 18 degrees C group versus the 26 degrees C group and increased across time (p = .0001); that is, VO2 after 5 min of immersion was less than at 60 and 90 min, and values obtained after 30 min of immersion were less than those at 90 min of immersion. Based on these data, it appears that the LF group would expend more calories (308.9 vs. 199.9 kcal, respectively) and more likely derive these calories from a carbohydrate source than the HF group during 90 min of cold water immersion. It would appear beneficial to consider a feeding supplement for the low-fat individual if immersion was in a more thermal stressful environment or extended for a protracted period of time.

Adipose Tissue↗
PubMed1994

The thermogenic effect of a carbohydrate feeding during exposure to 8, 12 and 27 degrees C.

The increased metabolic heat production in humans exposed to cold stress results from an increased oxidation of both carbohydrate and fat to provide energy to sustain temperature homeostasis. Research suggests that dietary manipulations may enhance metabolic heat production, thereby delaying hypothermia. Therefore, the present investigation examined the thermogenic effect of a sequential timed feeding regime of either a carbohydrate (CHO) or a placebo beverage (PL) before and again midway through 120 min of exposure to 8, 12 and 27 degrees C in well-nourished men. The following were examined: tissue insulation (I), rectal temperature (Tre), mean skin temperature (Tsk), metabolism (M), time-weighted heat production and respiratory exchange ratio (R). Tre, delta Tre, Tsk, M, delta M, I and time-weighted heat production revealed no significant differences between treatment (PL vs CHO) at any temperature (8, 12 and 27 degrees C). However, Tre decreased (P < 0.05) as time increased at 8, 12 and 27 degrees C while M increased (P < 0.05) and I decreased (P < 0.05) at 8 and 12 degrees C. At 8 and 27 degrees C, R differed (P < 0.05) between the PL and CHO treatments. In addition, at 8 and 12 degrees C, R increased (P < 0.05) across time reflecting the feeding. From these data it appears that while substrate utilization differed between dietary treatment (8 and 27 degrees C) and across time, this feeding regime did not differentially affect M, Tre, Tsk and I during 120 min of exposure to 8, 12 and 27 degrees C.

Adult↗
PubMed1994

Contractile properties and myosin phenotype of single motor units from neonatal rats.

The unloaded shortening velocity (Vus), twitch time to peak force (TTP), and myosin heavy chain (MHC) composition of motor units from soleus muscles of neonatal rats (7-8 and 16-18 days) were compared. The Vus range was from 2.2 to 7.1 fiber lengths (fl).s-1 and was unchanged from 7-8 to 16-18 days. TTP shifted from 7-8 (range, 66-120) to 16-18 days (range, 41-95). MHC-specific antibody staining of motor units revealed a correlation between MHC and Vus of individual motor units. Slowest motor units contained type I MHC. Intermediate Vus motor units contained both embryonic, neonatal, and/or type IIa MHCs. Fastest motor units contained neonatal and/or type IIa MHCs. These findings demonstrate that an individual motor unit of a neonatal muscle contains a nonrandom distribution of fiber types. The range of myosins present within the motor units of the soleus translates into a range of possible Vus.

Animals↗
PubMed1994

A thermal perception scale for use during resting exposure to cold air.

The present investigation introduces a thermal perception scale (TS) for use during protracted resting cold exposure. The scale contains categories ranging consecutively from 0, i.e., Nothing at all, to 10, i.e., Very, very cold. Eight Caucasian men were randomly exposed to ambient air in a climatically controlled environmental chamber of 8 degrees, 12 degrees, and 27 degrees C for 120 min. on 3 separate occasions and monitored for rectal temperature (Tre), mean skin temperature (Tsk), ventilation (VE), and oxygen consumption (VO2). The terminal perceptual categories were anchored for 8 subjects and a standard set of instructions was presented prior to each trial. The anchor temperature was the room air in the anteroom which was 27 degrees C, representing 0, i.e., "Nothing at all," to extend the scale so that subsequent judgments on the scale were expressed in relation to this category. In addition, the subjects were also asked to imagine the coldest that they have ever experienced and this was designed to anchor "Very, very cold." The relations between scale scores and the thermoregulatory variables were examined with a simple linear regression and coefficients of correlation and determination for each subject. High coefficients of determination between Tsk, VO2, and VE indicated that, for individual subjects, the scores on the scale were related to VE, Tsk, and VO2. High reliability coefficients for TS were also reported. In addition, the ratings and VO2 relation tended to be similar between subjects. Therefore, this scale appears to be a valid and reliable tool for measuring the perception of cold when at rest in air.

Acclimatization↗
PubMed1994

Influence of delayed hyperbaric oxygenation on recovery from mechanically induced damage.

This study examined whether subjecting a crushed muscle to a delayed intermittent hyperbaric oxygenation protocol would facilitate healing, the marker for healing being a return toward 100% uncrushed muscle in selected mechanical, morphologic, and biochemical parameters. Thirty-six rabbits (4 groups of 9) had the right lateral head of their gastrocnemius muscle surgically crushed. After surgery, the rabbits were exposed daily for 90 min 5 days/wk to either 100% O2 at 243 kPa, 8.5% O2 and 91.5% N2 at 243 kPa, 100% O2 at 101 kPa, or 21% O2 at 101 kPa. Initial treatments were administered 16-18 h post-muscle crush. After 10 days of treatment, maximal twitch and tetanic tension of the crushed muscle and its contralateral counterpart were measured. The muscles were then removed and analyzed morphologically, and the activity of citrate synthase, phosphofructokinase, and glucose-6-phosphate dehydrogenase were measured. The treatment group means for any of the parameters measured were not significantly different from each other. The extent of muscle damage, however, was determined to be minor as the control group recovery threshold was approximately 80%. Thus, it seems that the treatment protocol used does not facilitate healing for this type of muscle crush injury.

Animals↗
PubMed1994

Hyperbaric oxygenation treatments and metabolic enzymes in the heart and diaphragm.

We previously found that intermittent hyperbaric oxygen exposure increases metabolic enzyme activity in soleus muscle. Since the metabolic enzyme activities of the heart and diaphragm of healthy animals are difficult to alter, we questioned whether intermittent hyperbaric oxygenation would provide a stimulus sufficient to increase metabolic enzyme activity. Therefore, we exposed 36 rabbits (4 groups of 9) twice daily for 90 min 5 days/wk to either 100% O2 at 243 kPa, 8.5% O2, and 91.5% N2 at 243 kPa, 100% O2 at 101 kPa, or 21% O2 at 101 kPa. After 4 wk of treatment, the activities of citrate synthase, succinate dehydrogenase, alpha-glycerophosphate dehydrogenase, phosphofructokinase, and glyceraldehyde-3-phosphate dehydrogenase were measured. In both the heart and the diaphragm, none of the treatments significantly altered the mean enzyme activities for any of the enzymes measured. Therefore, it seems that the hyperbaric oxygenation treatment protocols used do not induce an increase in metabolic enzyme activity in the heart and diaphragm in healthy animals.

Animals↗
PubMed1993

Effects of body morphology and mass on thermal responses to cold water: revisited.

Seven male volunteers were divided into two groups based on body morphology and mass. The large body mass (LM) group (n = 4) was 21.2 kg heavier and 0.32 m2.kg-1 smaller in surface area-to-mass ratio (P < 0.05) than the small body mass (SM) group (n = 3). Both groups were similar in total body fat and regional skinfold thicknesses. All subjects were immersed to the first thoracic vertebrae for 120 min in stirred water at 18 degrees C. Overall, tissue insulation was similar (P > 0.05) between the SM and LM groups across time. Perceptual ratings of thermal sensation increased (P < 0.05) across time. Therefore, as cold water immersion progressed, tissue insulation was similar and thermal sensation increased (P < 0.05) in males matched for subcutaneous fat and total fat but differing in body mass and morphology.

Analysis of Variance↗
PubMed1993

Does feeding regime affect physiologic and thermal responses during exposure to 8, 20, and 27 degrees C?

When the loss of body heat is accelerated by exposure to low environmental temperatures, additional substrates must be oxidized to provide energy to sustain temperature homeostasis. Therefore, the present investigation examined the relation between feeding regime [pre-experimental carbohydrate feeding (FED) vs a fast (FAST)], during 120 min of exposure to 8, 20, and 27 degrees C in well-nourished men. The following were examined: tissue insulation (I; degrees C.m2:W-1), rectal temperature (Tre; degrees C), and oxygen consumption (VO2; ml,kg-1.min-1). VO2, Tre, and I revealed no significant differences between treatments (FED vs FAST) at any temperature. At 27 degrees C, I was less (P < 0.05) than at 20 and 8 degrees C, and decreased (P < 0.05) as exposure time increased. At 8 degrees C, VO2 was higher (P < 0.5) than at 20 or 27 degrees C, and VO2 increased as time increased (P < 0.05). Tre decreased (P < 0.05) as time increased for all conditions. Respiratory exchange ration (R) differed (P < 0.05) between treatments (FED vs FAST), temperature (8 vs 20 degrees C), and across time. Values for R suggests that carbohydrate accounted for 56% and 33% of caloric utilization during the FED vs FAST conditions, respectively. At 8 vs 20 degrees C, R represented 54% vs 30% of carbohydrate utilization. Across time, R demonstrated that in both conditions (FED vs FAST) there was a decreased reliance on carbohydrate utilization for energy provision.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Skeletal muscle metabolic enzymes are altered by hyperbaric oxygenation treatments.

To test whether repeated HBO exposures would increase activity of skeletal muscle metabolic enzymes, 27 rabbits (3 groups) were exposed 90 min/day, 5 days/wk to either 100% O2 at 243 kPa (HBO), 100% O2 at 101 kPa (HIO), or 21% O2 at 101 kPa (CON). Four animals per group were killed after 2 wk treatment, and the remaining five per group were killed after 8 wk of treatment. Soleus, plantaris, and tibialis anterior muscles were removed, and the activities of adenylate kinase, alpha-glycerophosphate dehydrogenase, and citrate synthase were measured. After 8 wk there was no difference in enzyme activity between groups for either plantaris or tibialis anterior. In the soleus after 8 wk there was no difference between groups in adenylate kinase activity, but alpha-glycerophosphate dehydrogenase activity was 56% greater (P < 0.05) in HBO than in HIO and 50% greater than in CON, and citrate synthase activity in HBO was 24% greater (P < 0.05) than that in HIO and 36% greater than that in CON. Inasmuch as the soleus is a postural muscle, these results suggest that long-term HBO treatments can increase enzyme activity in an actively contracting muscle.

Adenylyl Cyclases↗