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Biomedical subjects

W J Evans

Publications and source records attributed to W J Evans.

At least 19 recordsLinked to original sources
PubMed1997

Nutrition, exercise, and healthy aging.

Advancing age is associated with a remarkable number of changes in body composition, including reduction in lean body mass and increase in body fat, which have been well documented. Decreased lean body mass occurs primarily as a result of losses in skeletal muscle mass. This age-related loss in muscle mass has been termed "sarcopenia". Loss in muscle mass accounts for the age-associated decreases in basal metabolic rate, muscle strength, and activity levels, which, in turn are the cause of the decreased energy requirements of the elderly. In sedentary persons, the main determinant of energy expenditure is fat-free mass, which declines by about 15% between the third and eighth decade of life. It also appears that declining energy needs are not matched by an appropriate decline in energy intake, with the ultimate result being increased body fat content. Increased body fatness and increased abdominal obesity are thought to be directly linked to the greatly increased incidence of non-insulin-dependent diabetes mellitus among the elderly. In this review we will discuss the extent to which regularly performed exercise can affect nutrition needs and functional capacity in the elderly. We will also discuss a variety of concerns when prescribing exercise in the elderly, such as planning for a wide variability in functional status, medical status, and training intensity and duration. Finally, we will attempt to provide some basic guidelines for beginning an exercise program for older men and women and establishing community-based programs.

Adult↗
PubMed1997

Olfactory event-related potentials to amyl acetate in congenital anosmia.

Olfactory function was evaluated by olfactory event-related potentials and standardized psychophysical measures including the Smell Identification Test and odor detection threshold tests for 3 chemosensory stimulants in 9 subjects with isolated congenital anosmia and 9 age- and gender-matched normosmic controls. There was a significant difference in Smell Identification Test scores (P < 0.001) and odor detection thresholds for phenylethyl alcohol (P < 0.001) and isoamyl acetate (P < 0.001) between the anosmic and normosmic subjects. Detection thresholds for chloracetyl phenone, a trigeminal stimulant, did not differ between the 2 groups. Olfactory evoked potentials were recorded in response to amyl acetate and air control stimuli presented at volume flow rate of 5 l/min, stimulus duration of 40 ms, and randomized interstimulus intervals of 6-30 s. In the control subjects, evoked potentials to amyl acetate were characterized by 4 reproducible components (P1, N1, P2, and N2). In the subjects with congenital anosmia, no reproducible evoked potential components were identified in response to amyl acetate. No reproducible evoked potential components were seen in response to the air control stimulus in either the anosmic or normosmic groups. These data suggest that olfactory evoked potentials provide a specific measure of olfactory function.

Adult↗
PubMed1997

Energy requirement for long-term body weight maintenance in older women.

The total dietary energy requirement of healthy, free-living older women was examined by determining the total energy intake (TEI) required for long-term body weight maintenance in nine women aged (mean +/- SD) 67 +/- 9 years (range, 56 to 78). For 14 weeks, each woman consumed defined amounts of foods and beverages prepared at a General Clinical Research Center (GCRC) to provide 0.8 g protein.kg-1.d-1 and a nonprotein energy ratio of 40% fat to 60% carbohydrate. Adjustments to TEI were made to keep body weight within +/-0.5 kg of each woman's starting body weight. All women were asked to maintain their habitual level of daily activity, and the energy cost of physical activity was estimated using the Yale Physical Activity Survey (YPAS). Resting energy expenditure (REE) was measured with each woman in the postabsorptive state just after awakening, using an indirect calorimeter at baseline and week 14. The energy requirement expressed as the ratio of TEI to REE was 1.82 +/- 0.15, a value 21% higher (P < .001) than the energy allowance of 1.5 x REE suggested for women beyond age 50 years in the 1989 Recommended Dietary Allowances (RDAs). Using the RDAs equation to predict REE from body weight (pREE), the ratio of TEI to pREE was 1.73 +/- 0.18 (P < .005, comparison with 1.50 x REE). Estimates of the energy expenditure for physical activity (EEPA) based on the energy intake-balance data and the YPAS data were similar (3.18 +/- 0.92 and 3.14 +/- 1.42 MJ/d, respectively) for the group of women, but were more variable on an individual basis. Results of this long-term energy balance study suggest that the RDAs underestimate the dietary energy requirement of older women.

Aged↗
PubMed1997

Aging and the acute phase response to exercise: implications for the role of systemic factors on skeletal muscle protein turnover.

Declines in exercise capacity throughout an individual's life span can affect function and can ultimately limit the ability to perform activities of daily living. Along with these changes in exercise capacity and function, studies have reported age-associated changes in several parameters of immune status including declines in cell-mediated and humoral immunity. Exercise has been shown repeatedly to activate host-specific defense mechanisms in a series of coordinated metabolic events similar to the acute phase response to infection. This review will focus on the role of the acute phase response on skeletal muscle remodeling after exercise. In particular, we will discuss the physiological role of exercise-induced neutrophilia and monocyte production of the cytokine interleukin-1 on skeletal muscle remodeling in young and older individuals. The implications of these responses in mediating the metabolic adaptations to exercise will be addressed.

Acute-Phase Reaction↗
PubMed1997

Chromium picolinate supplementation and resistive training by older men: effects on iron-status and hematologic indexes.

Chromium competes with iron for binding to transferrin, and high-dose chromium supplementation has been hypothesized to adversely affect iron status. This study examined the effects of chromium picolinate supplementation on hematologic indexes and selected indexes of iron status in 18 men aged 56-69 y who participated in an introductory resistive training program. The men were randomly assigned (double-blind design) to groups (n = 9) that consumed either 17.8 mumol Cr/d (924 micrograms Cr/d) as chromium picolinate or a low-chromium placebo for 12 wk while engaging in resistive training twice weekly (3 sets of 8-12 repetitions at 80% of one repetition maximum for 5 exercises). Hematocrit, hemoglobin, red blood cell (erythrocyte) count, mean corpuscular volume, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, red blood cell distribution width, platelet count, and mean platelet volume were within normal clinical ranges and were unchanged by either chromium picolinate supplementation or resistive training. Resistive training decreased total-iron-binding capacity from 38.4 +/- 9.3 to 27.3 +/- 5.6 mumol/L (P < 0.0001) and increased transferrin saturation from 35.7 +/- 16.3% to 45.4 +/- 16.9% (P = 0.050). Chromium picolinate supplementation did not influence these responses. Serum iron concentrations and serum ferritin concentrations were unchanged by either resistive training or chromium picolinate supplementation. These data suggest that high-dose chromium picolinate supplementation for 12 wk did not influence hematologic indexes or indexes of iron metabolism or status in older men. The decrease in total-iron-binding capacity and increase in transferrin saturation (%) with resistive training are largely opposite to changes associated with iron depletion and suggest a novel effect of resistive training on iron transport.

Aged↗
PubMed1997

The reproducibility of the Bruce protocol exercise test for the determination of aerobic capacity in older women.

The reproducibility of the Bruce exercise test protocol for the determination of maximal aerobic activity was evaluated in sedentary older women. Seventeen women between the ages of 51 and 68 yr performed five maximal graded exercise tests to volitional fatigue on a treadmill. VO2max (mL.kg-1.min-1) values averaged 27.5 +/- 1.1; 28.3 +/- 1.3; 28.4 +/- 1.3; 29.6 +/- 1.5; and 28.2 +/- 1.4 for trials 1-5, respectively, and were not significantly different. Criteria for a plateau in VO2 at the point of exhaustion were met in 21 out of 85 tests (25%). The mean coefficient of variation VO2max for the subjects for the 5 tests was 6.5% (range, 2.0-14%). Pearson's correlation coefficients for the study variables were significant, indicating good agreement between repeated tests (r2: between 0.70 to 0.89). Although there were no significant differences among the mean VO2max values in the 5 trials, 11 subjects had a 1.0 ml.kg-1.min-1 or greater increase in the VO2max from test 1 to test 2, and only 6 subjects had no change or a decrease in VO2max. The mean difference between T2 and T3 was lower (T1 vs T2: 0.8 mL.kg-1.min-1, T2 vs T3: 0.1 mL.kg-1.min-1) indicating slightly better agreement between the second and third set. Estimates of the between and within subject variance revealed a low within subject variance (4.2 (mL.kg-1.min-1)2) compared to the between subject variance (22.1 (mL.kg-1.min-1)2). This study demonstrates that a commonly used exercise testing protocol generates highly reproducible measurements of VO2max in women between 51 and 68 yr. The mean differences between tests and the high level of agreement between repeated tests suggests that a single measurement of VO2max can be performed to assess functional aerobic capacity in this population.

Aged↗
PubMed1997

Attentional mechanisms of saccadic eye movements in schizophrenia.

Saccadic latency of schizophrenics (N = 15) and normal controls (N = 11) was measured to the left and right visual fields with three fixation conditions that differentially affect saccade latency. Fixation was offset either 1) prior to the target (gap condition), 2) simultaneous with the target onset (control condition), or 3) after target onset (overlap condition). Saccade latencies are typically reduced in the gap condition, which is attributed to the fixation offset acting to facilitate attentional disengagement or as a preparatory warning signal. Repeated measures Analysis of Variance (ANOVA) revealed that whereas the saccadic latencies of schizophrenics and normal controls do not differ for right visual field targets, the schizophrenics' latencies were prolonged to left visual field targets. This difference was most pronounced in the overlap condition, where normal controls produced faster saccades to the left visual field targets, whereas schizophrenics showed the opposite asymmetry. Because the overlap condition provides no early warning of the upcoming target, the lateralized finding suggests a deficit in the right hemisphere mechanisms responsible for sustained attention.

Adolescent↗
PubMed1996

Analysis of body-composition techniques and models for detecting change in soft tissue with strength training.

The purpose of this study was to compare the ability of various body-composition assessment techniques to detect changes in soft tissue in older, weight-stable women (50-70 y of age) completing a 1-y randomized, controlled trial of progressive resistance training. The intervention group (n = 20) performed high-intensity strength-training 2 d/wk with five different exercises; the control group (n = 19) was untreated. Hydrostatic weighing, 24-h urinary creatinine, computed tomography of thigh sections, total body potassium, and tritium dilution techniques were used to measure increases in total fat-free mass (FFM) and the muscle and water components of FFM. A decrease in fat mass (by hydrostatic weighing) was seen in the strength-trained women compared with the control subjects (P - 0.01-0.0001). Anthropometry, bioelectric impedance, dual-energy X-ray absorptiometry, and total body nitrogen and carbon did not measure any significant change in soft tissue. The choice of a body-composition technique is important when designing a study expected to affect soft tissue, because not all techniques available are precise enough to detect small changes.

Absorptiometry, Photon↗
PubMed1996

Effects of age on energy expenditure and substrate oxidation during experimental overfeeding in healthy men.

Relatively little is known about the influence of age on energy regulation during energy imbalance. We compared the effects of overfeeding on changes in energy expenditure, substrate oxidation, and energy deposition between young men (age 23.7 +/- 1.1 [SEM] years) and older men (age 70.0 +/- 7.0) of normal body weight who were leading unrestricted lives. Changes in total energy expenditure, resting energy expenditure (REE), the thermic effect of feeding (TEF), respiratory quotient (RQ), and body energy content were determined in response to overeating by 4.09 +/- 0.07 Megajoule (MJ)/day for 21 days in 16 healthy subjects consuming a typical diet. After excluding data from one young subject with unusual results and adjusting for individual differences in excess energy intake, there was a tendency towards a smaller increase in REE in older men compared to the young men (p = .07) which was accounted for by their lower fat-free mass (p = .016). There was also a significantly smaller increase in resting energy expenditure averaged over fasting and fed states (i.e, REE + TEF) with overfeeding in older men than in young men (p < .01). Combined, these smaller increases in energy expenditure with overfeeding in the older subjects averaged an estimated 365 kilojoule (kJ)/day (8.9% of the excess energy intake) (p < .02). There were also significant effects of age on fasting RQ (p < .001) and the change in RQ with overfeeding (p < .001), but no significant increase in energy expenditure for physical activity and thermoregulation with overfeeding in either age-group. These results are consistent with the suggestion that older individuals experience both a reduction in the ability to increase energy expenditure, and an alteration in the pattern of substrate utilization, in response to overfeeding. These changes may promote cumulative increases in body energy during normal cycles of positive energy balance unless compensated for by adaptive variations in energy intake.

Adult↗
PubMed1996

Insulin stimulation of protein synthesis in rat skeletal muscle following resistance exercise is maintained with advancing age.

This study examined whether or not insulin elevates rates of protein synthesis in muscle following four days of resistance exercise in young (4-mo), middle-aged (12-mo), and old (32-mo) rats. Thirty-six male Fischer 344/BN F1 rats (n = 12 in each group) performed an operantly conditioned activity which required full extension of the hindlimbs with weights over the scapula (ACUTE; n = 6 for each age group) or with no additional weight (nonexercised; NONEX; n = 6 for each age group). Acutely exercised animals engaged in four distinct exercise sessions with each session separated by 48 h. Rates of protein synthesis were assessed in soleus, gastrocnemius (GAST), and extensor digitorum longus (EDL) muscles 16 h after the last exercise bout using a bilateral hindlimb perfusion to measure the incorporation of tritiated phenylalanine (F) into muscle protein. One limb of the bilateral hindlimb preparation received a medium that contained rat insulin at a physiological concentration (6.25 ng.ml-1), while the other limb did not. Rates of protein synthesis in soleus with insulin supplementation were significantly higher within all age groups following resistance exercise vs ACUTE without insulin and NONEX with or without insulin (p < .05). Rates of protein synthesis in soleus were not different within age groups for NONEX with or without insulin (p < .05), but rates of protein synthesis for young NONEX were significantly higher (p < .05) than middle-aged or old NONEX (204 +/- 9 vs 149 +/- 6 or 141 +/- 9 nmol F incorporated.g-1.h-1, respectively; means +/- SE). Rates of protein synthesis in GAST with insulin were also significantly higher within all age groups following resistance exercise than ACUTE without insulin or NONEX with or without insulin (p < .05). Unlike soleus, rates of protein synthesis in GAST were significantly higher for old NONEX vs young NONEX (68 +/- 6 vs 45 +/- 5 nmol F incorporated.g-1.h-1, respectively; P < .05), but not middle-aged NONEX (51 +/- 3 nmol F incorporated.g-1.h-1). Translational efficiency (rates of protein synthesis.unit of RNA-1.h-1) for GAST supplemented with insulin was significantly greater in ACUTE with insulin than ACUTE without insulin or NONEX with or without insulin (p < .05). There were no effect of age, insulin, or exercise on rates of protein synthesis in EDL (p > .05). These data suggest that following resistance exercise, insulin increased rates of protein synthesis in both soleus and GAST regardless of age, and it appeared that this insulin-mediated elevation may have occurred at the level of translation.

Aging↗
PubMed1996

A 20-yr longitudinal study of Olympic oarsmen.

Nine 1972 silver-medalist oarsmen were studied before the Olympic Games and 10 and 20 yr later. Peak power, metabolic responses, and heart rate were recorded during rowing ergometry; blood lactate was measured following exercise. The skinfold equation yielded percent body fat. The average change (multiple analysis of variance) among measurements from 1972 to 1992 was 37.5 +/- 3% (P < 0.01). Average changes between 1972 and 1982 and between 1982 and 1992 were similar, 17 and 18%, respectively (P < 0.01). The most significant change between 1972 and 1992 was decreased peak blood lactate (106%). Decreases in peak power, VE, and VO2 (ml.kg-1.min-1) were all similar, approximately 40%, and were significant. Body fat increased (from 12.3 to 15.6%), and absolute VO2 and relative VO2 (lean body mass) decreased 30% (P < 0.01). Only body weight, heart rate, and O2 pulse showed smaller changes, but these changes were still significant (P < 0.05). Relative peak VO2 decreased from 65.5 to 46.8 ml.kg-1.min-1 from 1972 to 1992 and at a rate of 10%.decade-1. The most significant changes between 1972 and 1982 were increases in percent body fat (from 12.3 to 16.3%) and decreases in VO2 values (P < 0.01). There was less change in body fat between 1982 and 1992, but lactate significantly decreased (P < 0.01), as did peak power and absolute and relative VO2 and VE. Although fitness levels in former elite oarsmen decreased each decade, these declines were somewhat arrested by regular aerobic training. Body fat increased and metabolic capacity decreased rapidly during the first decade, whereas anaerobic capacity decreased more significantly in the second decade. Anaerobic capacity diminished at a significantly greater rate than aerobic capacity, probably as a result of the aging process and emphasis on aerobic training in post-competitive years.

Adult↗
PubMed1996

Reversing sarcopenia: how weight training can build strength and vitality.

Sarcopenia, the loss of skeletal muscle mass with advancing age, results in lower basal metabolic rate, weakness, reduced activity levels, decreased bone density, and low calorie needs. The related increase in body fatness is linked to hypertension and abnormal glucose tolerance. Many consequences of sarcopenia are preventable or even reversible. Progressive resistance exercises can produce substantial increases in strength and muscle size, even in the oldest old. For many older patients, exercise represents the safest, least expensive means to lose body fat, decrease blood pressure, improving glucose tolerance, and maintain long-term independence.

Aged↗
PubMed1996

Protein requirements of elderly people.

Based on N balance calculated in accord with the recommendations of the 1985 Joint FAO/WHO/UNU Expert Consultation, a summary of conclusions from the six N balance studies in elderly people is presented in Table 3. The data, with one flawed exception, indicate that the safe level of protein intake for older adults may be higher than currently recommended. In the only study directly comparing elderly and young subjects (Cheng et al, 1978), no differences in protein requirement were found. However, the data suggest that the 0.8 g protein/kg/d would be inadequate for both groups. Additional direct comparisons between younger and older adults are desirable as a basis for any revised recommendations. In the only study directly comparing the protein requirements of both elderly men and women (Uauy et al, 1978), the variability was too great to allow adequate assessment of possible gender differences. More research is needed to determine whether gender-related differences occur.

Adult↗
PubMed1996

Strength and power training: physiological mechanisms of adaptation.

Adaptations in resistance training are focused on the development and maintenance of the neuromuscular unit needed for force production [97, 136]. The effects of training, when using this system, affect many other physiological systems of the body (e.g., the connective tissue, cardiovascular, and endocrine systems) [16, 18, 37, 77, 83]. Training programs are highly specific to the types of adaptation that occur. Activation of specific patterns of motor units in training dictate what tissue and how other physiological systems will be affected by the exercise training. The time course of the development of the neuromuscular system appears to be dominated in the early phase by neural factors with associated changes in the types of contractile proteins. In the later adaptation phase, muscle protein increases, and the contractile unit begins to contribute the most to the changes in performance capabilities. A host of other factors can affect the adaptations, such as functional capabilities of the individual, age, nutritional status, and behavioral factors (e.g., sleep and health habits). Optimal adaptation appears to be related to the use of specific resistance training programs to meet individual training objectives.

Adaptation, Physiological↗
PubMed1995

Olfactory event-related potentials in normal human subjects: effects of age and gender.

Behavioral and electrophysiological testing of olfactory function was performed in 33 normal human male and female subjects, 18-83 years of age. Acuity for odor identification and odor detection was verified by standard psychophysical tests. For evoked potential testing, a constant flow olfactometer provided odorant stimuli (amyl acetate) or air control stimuli that were presented to the right nostril by a nasal cannula at a flow rate of 5 l/min, duration of 40 msec and random interstimulus intervals of 6-30 sec. The behavioral tests revealed no significant difference between males and females, whereas increasing age was associated with a decline in performance on the odor identification test. No reproducible evoked potentials were recorded in response to the air control stimulus. Potentials to the odorant stimulus consisted of 4 components named P1, N1, P2 and N2. A significant correlation was found between P2 latency and odor identification test scores, suggesting a relationship between the generation of the P2 component and olfactory processing. P2 peak latency increased significantly with age at 2.5 msec/year. An age-related decline in N1-P2 interpeak amplitude was seen in male subjects. Topographic differences were seen in the P2 peak amplitude and the N1-P2 and P2-N2 interpeak amplitudes such that their amplitudes were greatest at Cz and Pz. On average, N1-P2 interpeak amplitudes were larger in the female subjects than in the male subjects, possibly revealing a hormonal influence on the olfactory event-related potential.

Adolescent↗
PubMed1995

Smooth pursuit eye movement differences between familial and non-familial schizophrenia.

Disrupted smooth pursuit eye tracking characterizes a greater proportion of individuals with schizophrenia than in the normal population. The finding of a similar increased incidence of eye tracking abnormality in first degree relatives of schizophrenics implicates this disorder as a potential biological marker for schizophrenia. To test the assumption that the eye tracking dysfunction of schizophrenics is genetically related, left and right smooth pursuit gain and phase shift were compared between 20 schizophrenics with a family history of schizophrenia or schizophrenia-related disorders, 18 schizophrenics without a family history, as well as for 18 normal controls. Subjects tracked pendular targets on an LED light bar moving at frequencies of 0.2 and 0.7 Hz. Horizontal eye movements were recorded using DC-electro-oculography. Results indicate that schizophrenics with a positive family history had significantly reduced right pursuit gain compared with controls, while right gain for negative family history schizophrenics did not differ from either group. Schizophrenic subjects also were administered neuropsychological tests. Linear regression by groups analyses reveal that neuropsychological measures significantly predicted right gain to slower targets (0.2 Hz) for the positive family history schizophrenics, but not for negative family history schizophrenics.

Adolescent↗