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Biomedical subjects

L E Armstrong

Publications and source records attributed to L E Armstrong.

71 records · Page 4Linked to original sources
PubMed1988

Responses of plasma human atrial natriuretic factor to high intensity submaximal exercise in the heat.

No data exists regarding responses of human atrial natriuretic factor (ANF) to exercise in the heat. The purpose of this study was to examine the responses of plasma ANF to high intensity submaximal (71% +/- 0.9 VO2max) exercise in the heat over an eight day acclimation period. Fourteen healthy males volunteered to participate in the study. Subjects performed intermittent exercises on a treadmill (0% grade) during 50 min of each 100 min trial in an environmental chamber maintained at 41.2 +/- 0.5 degrees C, 39.0 +/- 1.7% relative humidity. Blood was obtained from an antecubital vein after standing 20 min in the heat prior to exercise, and immediately after exercise. Measures were compared on days 1, 4 and 8. ANF did not change pre- to post-exercise nor did it change over the eight day heat acclimation period despite other heat acclimation adaptations. Conversely, plasma aldosterone (ALDO), renin activity (PRA) and cortisol (COR) all increased (p less than 0.05) pre- to post-exercise on each day but again no changes were observed over the eight day period. These data support that ANF may not increase when ALDO and PRA increases are observed.

Acclimatization↗
PubMed1988

Heat intolerance, heat exhaustion monitored: a case report.

A 32-year-old male (Mr. A.), monitored during an 8-d heat acclimation (HA) investigation, unexpectedly exhibited heat intolerance and heat exhaustion. Thirteen other males completed HA without indications of either heat intolerance or heat exhaustion. Because Mr. A. responded normally to HA on days 1-4, the intervention of an unknown host factor on days 5-8 was suggested. Mr. A.'s heat exhaustion episode (day 8) was apparently forewarned by loss of body weight and increased delta HR, delta Tsk (days 5-8) and delta Tre (days 7-8) during daily 90-min trials. His symptoms indicated classical salt depletion heat exhaustion, but the calculated salt deficit (less than 0.1 g NaCl.kg-1 body weight) was mild. Post-heat exhaustion serum enzyme levels were either normal (ALT, AST) or acutely elevated (CPK). Blood beta-endorphin and cortisol levels were six times and two times greater than control values, respectively. This case report is unique because clinical/physiological measurements and blood analyses were performed before, during, and after heat intolerance and heat exhaustion.

Acclimatization↗
PubMed1987

Evaluation of a temperate environment test to predict heat tolerance.

A temperate environment heat tolerance test (HTT) was formerly reported (Shvartz et al. 1977b) to distinguish heat acclimatized humans from former heat stroke patients. The purpose of this investigation was to evaluate the ability of HTT to measure acute individual changes in the HR and Tre responses of normal subjects, induced by classical heat acclimation procedures, thereby assessing the utility and sensitivity of HTT as a heat tolerance screening procedure. On day 1, 14 healthy males performed HTT (23.2 +/- 0.5 degrees C db, 14.9 +/- 0.5 degrees C wb) by bench stepping (30 cm high, 27 steps x min-1) for 15 min at 67 +/- 3% VO2max. On days 2-9, all subjects underwent heat acclimation (41.2 +/- 0.3 degrees C db, 28.4 +/- 0.3 degrees C wb) via treadmill exercise. Heat acclimation trials (identical on days 2 and 9) resulted in significant decreases in HR (170 +/- 3 vs 144 +/- 5 beats x min-1), Tre (39.21 +/- 0.09 vs 38.56 +/- 0.17 degrees C), and ratings of perceived exertion; plasma volume expanded 5.2 +/- 1.7%. On day 10, subjects repeated HTT; day 1 vs day 10 HR were statistically similar (143 +/- 6 vs 137 +/- 6 beats x min-1, p greater than 0.05) but Tre decreased significantly (37.7 +/- 0.1 vs 37.5 +/- 0.1 degrees C, p less than 0.05). Group mean HTT composite score (day 1 vs day 10) was unchanged (63 +/- 5 vs 72 +/- 6, p greater than 0.05), and individual composite scores indicated that HTT did not accurately measure HR and Tre trends at 41.2 +/- degrees C in 6 out of 14 subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Acclimatization↗
PubMed1987

Heat acclimatization during summer running in the northeastern United States.

Five highly trained distance runners (DR) were observed during controlled 90-min thermoregulation trials in spring (T1) and late summer (T2) to document the nature of heat acclimatization in the northeastern United States. These trials simulated environmental (30.3 +/- 0.1 degrees C dry bulb, 34.9 +/- 0.5% relative humidity, 4.47 m X s-1 wind speed) and exercise (treadmill running at 80, 120, 160, and 200 m X min-1) stresses encountered by DR during summer training in the northeastern United States. Between T1 and T2, DR trained outdoors for 14.5 +/- 0.4 wk, but consequently exhibited few physiological adaptations classically associated with heat acclimatization. Statistical comparison of T1 and T2 indicated no significant differences in mean heart rate, rectal temperature, sweat Na+ and K+, plasma Na+ and K+, or change in plasma volume during exercise. Mean weighted skin temperature was unchanged except at 50 min of exercise, and sweat rate was also unchanged except during the initial 30 min segment: 73 +/- 6 vs 93 +/- 8 ml X m-2 X h-1. Significant decreases (P less than 0.05) in submaximal VO2 were observed: T1 vs T2 values were 13.97 +/- 0.27 vs 10.19 +/- 1.19, 31.38 +/- 1.15 vs 27.91 +/- 1.45, and 44.97 +/- 0.85 vs 41.24 +/- 0.97 ml X kg-1 X min-1, at treadmill speeds of 80, 120, and 200 m X min-1, respectively. We conclude that DR did not require 14.5 wk of summer training to maintain safe rectal temperatures (less than or equal to 38.4 degrees C) during T1, which simulated the hottest days of summer in the northeastern United States.

Acclimatization↗
PubMed1987

Changes in body water and electrolytes during heat acclimation: effects of dietary sodium.

In an effort to describe the influence of both high (HNA) and low (LNA) dietary sodium (399 vs. 98 mEq Na+ X d-1) on body fluids during heat acclimation (HA), nine untrained males underwent 8 d of HA twice (90 min treadmill walking, 5.6 km X h-1, 6% grade) in an environmental chamber (40.1 degrees C, 23.5% RH). Mean wholebody Na+ balance calculations indicated that HNA resulted in an increase of Na+ of $916 mEq per 8 days per subject, whereas LNA resulted in a relative Na+ deficiency of -230 mEq per 8 days per subject. Subjects exhibited typical HA adaptations of decreased heart rate (HR), decreased rectal temperature (Tre) during exercise, and an increase in resting plasma volume (PV) during both diets. Significant HNA vs. LNA differences (p less than 0.05) were observed in HR (days 3-5), Tre (days 3-6), PV (day 4), plasma osmolality (day 4), plasma Na+ (day 4), urine Na+ (days 2-8), and sweat Na+ (days 4 and 8). The between-diet differences in HR, Tre and PV were not detectable by the end of each dietary-exercise regimen. Needle biopsy samples (20-50 mg, lateral aspect of the gastrocnemius) indicated that muscle Na+ and muscle water were similar on all days, except day 9 when intracellular fluid expansion during LNA was noted. Change in body weight was not strongly correlated with delta PV (R2 = 0.47, 0.10) and neither osmotic forces nor plasma protein movements explained all PV shifts adequately.(ABSTRACT TRUNCATED AT 250 WORDS)

Acclimatization↗
PubMed1985

Effects of dietary sodium on body and muscle potassium content during heat acclimation.

It has been suggested that renal conversion of sodium (Na+) during training in hot environments results in potassium (K+) deficiencies. This investigation examined the influence of two levels of dietary Na+ intake (399 vs 98 mmol X d-1) on intramuscular, urinary, sweat, and whole body K+ homeostasis. Nine unacclimated, untrained males underwent heat acclimation during two 8 day dietary-exercise regimens (40.1 +/- 0.1 degrees C, 23.5 +/- 0.4% RH). Both diets resulted in depressed urinary K+ excretion. Sweat K+ and muscle K+ concentrations were not altered by diets or acclimation. The whole body stores of Na+ increased 31.1% (+916.8 mmol) during the high Na+ diet and decreased 7.8% (-230.4 mmol) during the low Na+ diet; whole body stores of K+ increased 4.1% (+137.6 mmol) during the high Na+ diet and increased 3.4% (+113.6 mmol) during the low Na+ diet. This dietary-acclimation protocol did not result in whole-body or intramuscular K+ deficits and offers no evidence to support previous claims that dietary sodium levels affect K+ balance.

Acclimatization↗
PubMed1985

Influence of diuretic-induced dehydration on competitive running performance.

A diuretic drug (40 mg of furosemide) was utilized to study the effects of dehydration (D) on competitive running performance, without prior thermal or exercise stress. Eight men competed in randomized races of 1,500, 5,000, and 10,000 m, while normally hydrated (H) and with mean plasma volume reductions of 9.9, 12.3, and 9.9%, respectively. As a result of the reduced body water (change in body weight = -1.9, -1.6, and -2.1%), mean outdoor performance times on a running track increased 0.16 min, 1.31 min (P less than 0.05), and 2.62 min (P less than 0.05) in the 1,500-m, 5,000-m, and 10,000-m trials. Running performance decrements due to dehydration were more strongly correlated with changes in body weight (r = -0.79, -0.65, and -0.40) than with urine volume or plasma volume differences. In addition, subjects were studied during submaximal and maximal treadmill exercise while H and D (mean change in plasma volume = -7.1%). Neither submaximal nor maximal oxygen uptake was significantly altered (P greater than 0.05) as a consequence of D. Mean treadmill run time to volitional exhaustion was reduced by 41.4 s (P less than 0.05) during the D treadmill trial. Therefore, it appears that competitive performance in trials of long duration (5,000 and 10,000 m) was affected to a greater extent by D than the shorter 1,500-m event, even though submaximal and maximal oxygen uptake was not altered.

Adult↗
PubMed1985

Voluntary dehydration and electrolyte losses during prolonged exercise in the heat.

The effects of water temperature (6 degrees, 22 degrees, 46 degrees C) and chlorination on voluntary dehydration (D), sweat electrolyte losses (SEL), and total body electrolyte losses (BEL) were studied in 12 healthy males during 6 h of intermittent treadmill exercise (1.34 m X s-1, 5% grade) in a climatic chamber (40.6 degrees C DB, 25.5 degrees C WB). Body weight (BW), rectal temperature (Tre), mean weighted skin temperature (Tsk), heart rate (HR), plasma osmolality (PO), sweat rate (SR), sweat sodium (Na+), chloride (Cl-), potassium (K+), and magnesium (MG++), urine volume, Na+, and K+ were measured. No differences were found between chlorinated and non-chlorinated treatments except SEL of Mg++. Subjects (Ss) who drank 46 degrees C (-2.1% BW) consumed approximately 50% less water (p less than 0.001), and had D which was 1.050 kg larger (p less than 0.001) than subjects who consumed 6 degrees C (-0.5 %BW). There were no significant between-group PO differences, but Tre and Tsk differed between 46 degrees and 6 degrees C (p less than 0.01), and the HR of 22 degrees and 46 degrees C were both different from 6 degrees C (p less than 0.05). SR of all groups were essentially equal, although differences in total sweat Na+ (p less than 0.02) and Cl- (p less than 0.04) losses were observed between 46 degrees and 6 degrees C. SEL of sweat K+ and Mg++ were not affected by the experimental design. Based on 24 h projections of BEL, it was concluded that K+ depletion is more likely than Na+ depletion because food is often supplemented with sodium chloride.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1984

Effect of a 42.2-km footrace and subsequent rest or exercise on muscular strength and work capacity.

This study 1) quantitates the effect of a 42.2-km footrace (marathon) on leg extensor strength (maximal peak torque, MPT) and work capacity (WC, measured during a leg extensor fatigue test), and 2) describes the effect of either a rest or exercise regimen for 1 wk after the marathon on the recovery of MPT and WC. Ten trained male runners performed personal records in a marathon and were then randomly assigned to either a rest or exercise-recovery group. The rest group did not train, whereas the exercise group ran 20-45 min/day at their selected intensity of exercise [50-60% maximal O2 consumption (Vo2max)] during the recovery week. MPT was measured at 1.1, 3.2, and 5.3 rad X s-1. The total work generated during a 50-contraction active extension-passive flexion fatigue test conducted at 3.2 rad X s-1 was defined as WC. Reports of perceived soreness of the quadriceps were obtained before each strength-testing session. These measurements were obtained before the marathon and 15-20 min and 1, 3, 5, and 7 days postmarathon. A significant reduction in MPT and WC resulted and continued 1 day postmarathon. MPT of both groups improved through day 5 postmarathon at 1.1 and 3.2 rad X s-1. MPT of the rest group improved through day 7 postmarathon but remained less than premarathon MPT. Recovery of MPT was impaired in the exercise group through days 5-7 postmarathon after 40-45 min exercise at 60% Vo2max. WC was recovered 3 days postmarathon in the rest group but was still impaired 7 days postmarathon in the exercise group.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1984

Oxygen tension in antecubital blood of trained and untrained males after maximal leg exercise.

This study compared oxygen tension (pO2) and percent oxygen saturation (SO2) in antecubital venous blood of six untrained (UT) and six endurance trained (ET) males during and following a graded leg exercise test to exhaustion on a cycle ergometer. Mean (+/- SE) resting values for pO2 were 29.3 (+/- 2.3) and 30.3 (+/- 2.0) mmHg, and SO2 were 51.8 (+/- 5.2) and 54.9 (+/- 4.6)% for the ET and UT men, respectively. At exhaustion pO2 decreased to 23.0 (+/- 4.5) and 23.3 (+/- 4.7) mmHg, while SO2 decreased to 29.6 (+/- 9.7) and 31.3 (+/- 9.7)% for the ET and UT subjects, respectively. There were no significant differences between the two groups in either pO2 or SO2 at rest or during exercise. However, there were marked increases in pO2 and SO2 during the 5 min recovery period for both groups. The ET cyclists demonstrated significantly higher pO2 and SO2 levels than the UT group at each min of recovery; e.g., at 4 min postexercise pO2 was 72 and 49 mmHg for the ET and UT men, respectively (p less than 0.05). The general rise in pO2 and SO2 for both groups was attributed to an increased arterialization of the antecubital venous blood while postexercise hyperventilation may have also elevated pO2 values. The higher values for the ET subjects during recovery were explained by a lower peripheral sympathetic tone and a presumably greater cardiac output at exhaustion for the ET group than the UT group, which may have allowed a relatively greater distribution of arterialized blood to the periphery.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1983

Using isokinetic dynamometry to test ambulatory patients with multiple sclerosis.

This study was designed to 1) determine whether isokinetic dynamometry is appropriate and safe for ambulatory patients with multiple sclerosis and 2) describe the idiosyncrasies the patients with multiple sclerosis exhibited during testing. Ten patients with multiple sclerosis and 20 healthy subjects were matched for age, sex, and weight. The isokinetic peak torque and endurance measurements of knee extensor and knee flexor muscles were recorded at selected angular velocities ranging from 0 to 275 degrees/sec and extensor:flexor muscle strength ratios were calculated. Statistical analysis (t tests) revealed that both the extensor and flexor muscle peak torque values for patients with multiple sclerosis were significantly lower than those for healthy subjects at all angular velocities (p less than .005 to p less than .001), and yet were similar in shape and slope. Mean extensor:flexor ratios for healthy subjects and for patients with multiple sclerosis were not significantly different at 70, 190, and 230 degrees/sec. Individual chart recordings identified any contractile difficulties or increased contraction time. Isokinetic testing is judged to be a safe and reliable form of objective neuromuscular testing for ambulatory patients with multiple sclerosis.

Adult↗
PubMed1983

Effect of a 42.2-km footrace and subsequent rest or exercise on muscle glycogen and enzymes.

The purpose of this study was to determine the effect of running a marathon and subsequent rest or exercise during a 7-day recovery period on muscle glycogen, glycogen synthase, hexokinase, and the activity of hexose monophosphate pathway enzymes. Ten well-trained runners were randomly assigned to either a postmarathon rest or exercise group. The rest group (n = 5) performed no physical activity, whereas the exercise group ran at their highest tolerable volitional intensity for 20-45 min during the recovery period. Muscle biopsies were obtained from the gastrocnemius before and after the marathon and 1, 3, 5, and 7 days after the marathon. Muscle glycogen was supercompensated before the marathon (196 mmol glucosyl units kg wet tissue wt-1, mmol X kg-1) and was reduced to 25 mmol X kg-1 after the marathon. Seven days later it was 141 and 109 mmol X kg-1 in the rest and exercise groups, respectively. Measurement of glycogen synthase activity ratio indicated an active enzyme only immediately postmarathon, whereas measurement of glycogen synthase fractional velocity and relative velocity indicated an active enzyme immediately postmarathon and 1 day postmarathon. Hexokinase activity was significantly elevated immediately after the marathon and remained elevated through 5 days postmarathon. The activities of the hexose monophosphate pathway enzymes declined steadily during the experimental period and were significantly reduced 5 and 7 days postmarathon. Low-intensity exercise during the recovery week did not significantly differentiate the exercise group from the rest group.

Adult↗
PubMedDate not supplied

Cortisol and testosterone concentrations in wheelchair athletes during submaximal wheelchair ergometry.

It is yet unknown how upper body exercise combined with high ambient temperatures affects plasma testosterone and cortisol concentrations and furthermore, how these hormones respond to exercise in people suffering spinal cord injuries. The purpose of this study was to characterize plasma testosterone and cortisol responses to upper body exercise in wheelchair athletes (WA) compared to able-bodied individuals (AB) at two ambient temperatures. Four WA [mean age 36 (SEM 13) years, mean body mass 66.9 (SEM 11.8) kg, injury level T7-T11], matched with five AB [mean age 33.4 (SEM 8.9) years, mean body mass 72.5 (SEM 13.1) kg] exercised (cross-over design) for 20 min on a wheelchair ergometer (0.03 kg resistance.kg-1 body mass) at 25 degrees C and 32 degrees C. Blood samples were obtained before (PRE), at min 10 (MID), and min 20 (END) of exercise. No differences were found between results obtained at 25 degrees C and 32 degrees C for any physiological variable studied and therefore these data were combined. Pre-exercise testosterone concentration was lower (P < 0.05) in WA [18.3 (SEM 0.9) nmol.l-1] compared to AB [21.9 (SEM 3.6) nmol.l-1], and increased PRE to END only in WA. Cortisol concentrations were similar between groups before and during exercise, despite higher rectal temperatures in WA compared to AB, at MID [37.21 (SEM 0.14) and 37.02 (SEM 0.08) degrees C, respectively] and END [37.36 (SEM 0.16) and 37.19 (SEM 0.10) degrees C, respectively]. Plasma norepinephrine responses were similar between groups. In conclusion, there were no differences in plasma cortisol concentrations, which may have been due to the low relative exercise intensities employed. The greater exercise response in WA for plasma testosterone should be confirmed on a larger population. It could have been the result of the lower plasma testosterone concentrations at rest in our group.

Adult↗
PubMedDate not supplied

Plasma opioid peptide responses during heat acclimation in humans.

Plasma beta-endorphin, Met-enkephalin and Peptide F immunoreactivity (ir) were measured at rest and following exercise on three days (days 1, 4, 8) of an eight day heat acclimation regime. Fourteen male subjects demonstrated physiological heat acclimation adaptations. Our data demonstrated a differential response of peripheral plasma levels of endogenous opioid peptides (EOP) to exercise in the heat. In addition, EOP did not follow the same time-course of other physiological adaptations as no differences (day 1 vs. 4 vs. 8) in resting or exercise levels were observed over the eight day heat acclimation regime. Significant increases in beta-endorphin ir (pre- to post-exercise) appear to reflect concomitant exercise-heat related changes. The increased peripheral levels of beta-endorphin were correlated to plasma levels of cortisol. Heat and exercise stress may result in a reduction of Met-enkephalin ir observed in peripheral plasma and might be due to degradation or a decrease in processing from the larger precursors. The differential responses of EOP suggest the possibility of separate physiological roles for these peptides during exercise in the heat but peripheral plasma levels of EOP do not appear to reflect acute heat acclimation changes.

Acclimatization↗