The pumping function of the heart in athletic tourists during a PWC<Subscript>170</Subscript> exercise

Changes in the pumping function of the heart (cardiac output) were studied in athletic tourists and untrained subjects during a PWC₁₇₀ test. It was confirmed that regular training remarkably improves the pumping function of the heart. At rest and during the PWC₁₇₀ test, the athletes exhibited more pronounced changes in the cardiac output than their untrained counterparts.     

Blood Rheology, Sex Hormones, and Cortisol in Athletes

The interrelations of blood rheology, plasma proteins and lipids, and steroid hormones (total testosterone, estradiol, and cortisol) were studied in athletes (N = 14). Blood (BV), plasma (PV), and erythrocyte suspension (ESV) viscosities; fibrinogen; total cholesterol (Ch); low density lipoprotein (LDL) Ch; and plasminogen activity were lower in the athletes than in control subjects (N = 10). The specific peripheral vascular resistance (SPVR) to BV ratio and PWC₁₇₀ were lower in the athletes. All these parameters correlated with decreased estradiol. Discriminant analysis indicated PWC₁₇₀, estradiol, and ESV to be the main parameters discriminating the groups. Decreased estradiol seemed to be associated with an increased physical activity in the athletes, as evident from its correlation with PWC₁₇₀ and differences in the body composition (a correlation with the body mass index). No significant difference was found in total Ch and cortisol. However, in the combined sample, decreased testosterone was associated with decreased BV, which was explained by direct correlations of the hormone with hematocrit (Ht) and PV through relationships with Ch and triglycerides (TG). Increased cortisol correlated with the higher plasma fluidity in the athletes as a result of inverse correlations of the hormone with TG and the increased suspension stability of the blood. Training-induced changes in hormonal and metabolic parameters were assumed to play an important role in the regulation of blood fluidity in athletes.     

A Fitness Performance Test for School Children and its Correlation with Physical Working Capacity and Maximal Oxygen Uptake

The Canadian Association for Health, Physical Education and Recreation fitness test (CAHPER test) composed of six items was compared to two laboratory tests of endurance fitness, physical working capacity at a minute pulse rate of 170 (PWC₁₇₀) and maximum oxygen uptake (Vo₂ max.) in over 500 Winnipeg school children of both sexes aged 6 to 17 years. CAHPER test results were similar to the national average published by CAHPER in a test booklet. Correlation coefficients (r) of Vo₂ max. for boys with the CAHPER tests were: sit-ups .42, broad jump .69, shuttle run .50, arm hang .43, 50-yard dash .60, 300-yard run .65; for girls the r values were about half the values for the boys. Much of the correlation between CAHPER tests and Vo₂ max. or PWC₁₇₀ depended on the association of each test with body size. When multiple correlations were obtained including surface area as the first variable, the only significant factor correlating with the endurance tests was the arm hang; none of the other tests showed a significant correlation. “Physical fitness” is task-specific, so that a subject''s position in the scoring scale of a fitness test depends entirely upon the test. The CAHPER test for physical fitness shows little or no correlation with standard laboratory measures of endurance in average children.     

Postural stability during static strain before and after a submaximal aerobic bicycle test in athletes

Control of static balance was studied in wrestlers (n = 31) in the normal state and against the background of physical fatigue, i.e., before and after a bicycle PWC ₁₇₀ test, respectively. The static balance was evaluated using a Ritm force platform (Russia) during normal basic stance (BS) and static strain (half-squatting position (HS) with the eyes open). Before physical exercise, i.e., during BS, the differences in postural control of the center of pressure (CP) between athletes and control subjects (n = 40) were nonsignificant. In the HS position, both linear and angular sway velocities of CP (LSV and ASV, respectively) were significantly lower in wrestlers (p < 0.001), and these parameters were negatively correlated with the PWC ₁₇₀ index (r = −0.454 and r = −455, p < 0.001 for LSV and ASV, respectively), which suggests that up to 20% of the sway velocity variance during static strain is dependent on the working capacity of the subjects. After the PWC ₁₇₀ test, the sway velocities of CP increased in both groups during BS (p < 0.01) and HS (p < 0.001), which testifies to the important role of muscular fatigue in the decrease in postural stability in both groups. During BS, an increase in LSV and ASV was about the same in both groups; however, during HS, an increase in the sway velocities of CP after PWC ₁₇₀ was lower in wrestlers (the intergroup differences at p = 0.037 and p = 0.008 for LSV and ASV, respectively); this parameter was negatively correlated with the recovery of the heart rate (HR) after the bicycle test (r = −0.378, p < 0.001 and r = −0.265, p < 0.05 for LSV and ASV, respectively), which suggests that rapid recovery contributes to a certain extent (about 6.5–14.2%) to the postural stability during static strain of wrestlers against the background of their physical fatigue.     

The problem of optimization of the physical state of school students by means of physical education

The study of the influence of different training regimens on the individual components of the physical state of 7- to 17-year-old school students of different morphofunctional types was carried out. A complex of methods for determining the level of physical development, motor fitness, the muscular capacity for work, the state of the cardiovascular system, and child and adolescent morbidity was used. The study showed the absence of a universal index capable of characterizing the “physical state” on the whole, the measurement of which would make it possible to judge unambiguously the effectiveness of the training process. None of the motor regimens used ensured complete optimization of all the components of the physical state and a decrease in the students’ morbidity. In the course of the experiment, there were many cases in which a training regimen aimed at improving the autonomic regulation of the heart exerted little effect on the total morbidity, a considerable increase in aerobic capacity (as evidenced by the PWC ₁₇₀ test) was not accompanied by an increased level of overall fitness, etc. It was shown that, to optimize different aspects of the physical state of age-matched students with the same constitutional type, it is necessary to use motor activity regimens that differ in their physiological action.     

The morphological features and functional state of the adolescent organism under conditions of adaptation to the north

Features of physical development and constitution, functional parameters of the cardiorespiratory system (PWC₁₇₀ and maximal oxygen consumption), and sympathetic and parasympathetic influences on the regulation of blood circulation were studied in 12–16-year-old children of newcomers under conditions of adaptation to the Tyumen North. The percentage of adolescents with an excessive or a deficient body weight, growth lag, and delayed puberty was increased. The girls had a decreased efficiency. Age- and sex-related differences of the morphological and physiological parameters of subjects under study were found.     

Effects of β-alanine supplementation on the onset of neuromuscular fatigue and ventilatory threshold in women

Summary. This study examined the effects of 28 days of β-alanine supplementation on the physical working capacity at fatigue threshold (PWC_FT), ventilatory threshold (VT), maximal oxygen consumption ( O_2-MAX), and time-to-exhaustion (TTE) in women. Twenty-two women (age ± SD 27.4 ± 6.1 yrs) participated and were randomly assigned to either the β-alanine (CarnoSyn™) or Placebo (PL) group. Before (pre) and after (post) the supplementation period, participants performed a continuous, incremental cycle ergometry test to exhaustion to determine the PWC_FT, VT, O_2-MAX, and TTE. There was a 13.9, 12.6 and 2.5% increase (p < 0.05) in VT, PWC_FT, and TTE, respectively, for the β-alanine group, with no changes in the PL (p > 0.05). There were no changes for O_2-MAX (p > 0.05) in either group. Results of this study indicate that β-alanine supplementation delays the onset of neuromuscular fatigue (PWC_FT) and the ventilatory threshold (VT) at submaximal workloads, and increase in TTE during maximal cycle ergometry performance. However, β-alanine supplementation did not affect maximal aerobic power ( O_2-MAX). In conclusion, β-alanine supplementation appears to improve submaximal cycle ergometry performance and TTE in young women, perhaps as a result of an increased buffering capacity due to elevated muscle carnosine concentrations.     

Fatness and Physical Fitness of Girls 7 to 17 Years

A two-fold approach was used to investigate the association between fatness and fitness of girls 7 to 17 years of age: first, age-specific correlations between fatness and measures of health-related and motor fitness, and second, comparisons of fitness levels of girls classified as fat and lean. A representative sample of 6700 between 7 to 17 years was surveyed. Adiposity (fatness) was estimated as the sum of five skinfolds (biceps, triceps, subscapular, suprailiac, medial calf). Physical fitness included health-related items (step test, PWC₁₇₀ the sit and reach, sit-ups and leg lifts, flexed arm hang) and motor performance items (standing long jump, vertical jump, arm pull strength, flamingo stand, shuttle run, plate tapping). Age-specific partial correlations between fatness and each fitness item, controlling for stature and weight, were calculated. In addition, in each age group the fattest 5% (presumably the obese) and the leanest 5% were compared on each fitness test. After controlling for stature and weight, subcutaneous fatness accounts for variable percentages of the variance in each fitness item. Estimates for health-related fitness items are: cardiorespiratory endurance - step test (3% to 5%) and PWC₁₇₀ (0% to 16%), flexibility - sit and reach (3% to 8%), functional strength - flexed arm hang (6% to 17%) and abdominal strength - sit-ups/leg lifts (1% to 8%). Corresponding estimates for motor fitness items are more variable: speed of limb movement -plate tapping (0% to 3%), balance - flamingo stand (0% to 5%), speed and agility - shuttle run (2% to 12 %), static strength - arm pull (4% to 12%), explosive strength - standing long jump/vertical jump (11% to 18%). At the extremes, the fattest girls have generally poorer levels of health-related and motor fitness.     

Diurnal rhythms of plasma growth hormone,somatostatin, thyroid hormones,cortisol and glucose concentrations in rainbow trout,Oncorhynchus mykiss,during progressive food deprivation

Abstract

The diurnal patterns of changes in plasma cortisol, growth hormone (GH), somatostatin‐14 (SRIF), thyroid hormones (L‐thyroxine, T₄ and triiodo‐L‐thyronine, T₃) and glucose were investigated in rainbow trout, Oncorhynchus mykiss, both during single meal‐feeding and during a progressive fast of 13 weeks. All measured variables exhibited a diurnal pattern in fed rainbow trout, most of which appeared to be correlated with the time of feeding (30–60 min after the onset of light), while additional changes, associated with the scotophase were also found for cortisol. Although fasting had no affect on mean daily plasma cortisol or SRIF concentrations, there was a progressive increase in mean daily plasma GH concentrations and a progressive decrease in mean daily plasma thyroid hormone and glucose concentrations associated with fasting. However, for GH, significant changes were not evident until week 10 of the fast. In addition, fasting appeared to phase‐shift the diurnal patterns of plasma GH, cortisol and glucose concentrations; the consequence of such a shift is that conclusions as to the effects of fasting, if based on a single time of sampling, may be flawed.     

Long-term adaptation capacity of ponies: effect of season and feed restriction on blood and physiological parameters

Domesticated horses are increasingly kept under semi-natural housing conditions, whereas their adaptation capacity is not fully investigated. In all, 10 Shetland pony mares were held under semi-extensive conditions for 1 year. In winter animals were allocated into two feeding groups (60% and 100% of maintenance energy requirement, respectively). Triiodothyronine, thyroxine, non-esterified fatty acids (NEFA), total bilirubin, total protein, triglyceride, glucose, insulin and hair length were measured at monthly intervals, whereas BW, body condition score, cresty neck score and resting heart rate were recorded every 2 weeks. From summer to winter all Ponies showed a reduction in resting heart rate (P<0.001) and triiodothyronine (P<0.001) but an increase in NEFA (P<0.001), thyroxine (P<0.001) and triglyceride (P<0.001) concentrations. Feed restriction led to a reduced resting heart rate (P=0.009), increased NEFA (P<0.001) and total bilirubin (P=0.008) concentrations. Thyroid hormones did not differ between feeding groups (P>0.05). Refeeding of restrictively fed ponies resulted in a rapid increase in resting heart rate and BW and a return of blood parameters to reference values. Adequately supplied animals adapted without difficulty to varying environmental conditions, whereas feed restriction in ponies during winter resulted in reduced resting heart rates suggesting a reduced basal metabolic rate. The energy restriction was compensated by mobilizing body fat reserves which led to changes in blood parameters. Refeeding in feed restricted animals revealed a remarkably quick recovery of physiological and blood parameters to reference values. We therefore suggest that year round-outdoor housing can be a suitable housing system for robust horse breeds provided that an adequate food supply is available.     

Effect of primary hypohydration on physical work capacity

Physical work capacity (PWC₁₈₀) was assessed with different levels of hypohydration in 25 heat-acclimatized male volunteers in hot dry (45°C DB, 30% RH) and hot humid (39°C DB, 60% RH) conditions equated to a heat stress level of 34°C on the WBGT scale. Heat acclimatization was carried out by exposing the subjects for 8 consecutive days in a climatic chamber with moderate work for two 50 min work cycles and 10 min intervening rest pauses. Acclimatization resulted in significant decreases in heart rate (27 bpm), oral temperature (0.8°C), mean skin temperature (1.2°C) and a significant increase in sweating rate (120 g h^–1 m^–2). Day-to-day variations in body hypohydration levels during heat acclimatization were not significantly different, although water intake was found to increase significantly from day 3 onwards when the subjects were in ad lib water intake state. The heat acclimatized subjects were then hypohydrated to varying degrees, viz. 1%, 2% and 3% body weight deficit, with moderate work in heat in the climatic chamber and after successful recovery from the effects of thermal stress and exercise; their physical work capacity was assessed individually. Physical work capacity was found to decrease significantly with hypohydration as compared to controls. The decrease was of the order of 9%, 11% and 22% in the hot dry condition and 6%, 8% and 20% in the hot humid condition with hypohydration levels of 1%, 2% and 3% respectively. The decrease was more pronounced during 3% hypohydration level under both heat stress conditions. This decrease was in spite of significant increases in maximal ventilation. However, the PWC₁₈₀ under the two heat stress conditions, when compared, did not reveal any significant difference. It was concluded that the heat stress vehicle did not adversely affect the physical work capacity. On the other hand, the decreases in physical work capacity were found to be closely related to the primary hypohydration level in heat-acclimatized tropical subjects.Abbreviations WBGT wet bulb globe temperature - bam beats per minute - YSI Yellow Springs Instrument - EKG electrocardiogram     

Seasonal patterns of pore-water nutrients, benthic chlorophyll a and sedimentary AVS in a macrobenthos-rich tidal flat

Monthly field investigations were carried out at controlled low-tide in an estuarine intertidal sandflat of the Seto Inland Sea (Japan) between January 1995 and April 1996. We assessed the spatial and temporal distribution of pore-water nutrient [NH ₄ ⁺ -N, (NO ₃ ⁻ + NO ₂ ⁻ )-N, PO ₄ ³⁻ -P and Si(OH)₄-Si], chlorophyll a (chl a) and acid-volatile sulphide (AVS) concentrations in the uppermost 0–10 cm sediment horizon, and evaluated their relationships with macrobenthic assemblages. Monthly hydrological data, nutrient and chl a concentrations in low-tide creek water adjacent to the flat were used as a complementary environmental characterisation of the study area. All different pore-water nutrients showed a 10 to > 30-fold variability between different layers and periods. NH ₄ ⁺ -N, PO ₄ ³⁻ -P and Si(OH)₄-Si concentrations were lowest in winter, progressively increased throughout spring and summer, and were highest between September and October, with a major increase at intermediate (4–8 cm) layers. In contrast, (NO ₃ ⁻ + NO ₂ ⁻ )-N concentrations, correlated positively with chl a, peaked in winter and sharply decreased with depth in all different seasons and in most occasions. Depth-integrated NH ₄ ⁺ -N, PO ₄ ³⁻ -P and Si(OH)₄-Si pools were correlated positively with biogenic nutrient flux calculated from the nutrient excretion rates of dominant bivalves Ruditapes philippinarum and Musculista senhousia. These relationships indicated rapid removal pathways of P, Si and N (i.e., every 0.1, 0.24 and 0.34 day, respectively), implying highly dynamic sediments. Based on the mass balance P = F + I, biogenic production (P) vs. diffusive flux (F) estimates suggested a predominant contribution of animal bioirrigation (I) to the upward flux of nutrients. AVS concentrations, correlated negatively with both (NO ₃ ⁻ + NO ₂ ⁻ )-N and chl a, showed a progressive increase from late summer throughout winter, subsequent to that of NH ₄ ⁺ -N, PO ₄ ³⁻ -P and Si(OH)₄-Si. The results indicate that in our study area the spatial and temporal distribution of pore-water nutrients, chl a and AVS in sediments are strongly interlinked and suggest that the metabolic processes (e.g., excretion, bio-deposition) and behavioural activities (e.g., particle mixing, bioirrigation) of abundant macrobenthos play an important role in the year-round biogeochemical processes occurring on this flat.     

Occurrence and Implications of SEM-AVS for Surface Sediments from Baihua Lake,China

The concentrations of acid volatile sulfide (AVS) and simultaneous extracted metals (SEMs, including SEM_Cu, SEM_Cd, SEM_Pb, SEM_Zn, SEM_Ni, SEM_Hg, SEM_As and SEM_Cr) in 17 superficial sediment samples were determined to better understand their spatial distribution in Baihua Lake, Guizhou Province, in southwest China. The SEMs/AVS ratio was employed to assess the bioavailability of the eight cationic metals. The SEMs/AVS ratio was significantly lower than 1.0, indicating that AVS in the sediments was sufficient to shield the eight selected heavy metals; thus the eight heavy metals showed no significant bioavailability to the benthic organisms. In addition, a preliminary study on the crystal composition in the sediments from Baihua Lake before and after SEMs’ extraction by X-ray diffraction analysis partly confirmed the efficiency of the cold-acid purge-and-trap technique.     

Effect of intensive swimming training on lung volumes, airway resistances and on the maximal expiratory flow-volume relationship in prepubertal girls

The aim of the present study was to analyse the effect of 1 year of intensive swimming training on lung volumes, airway resistance and on the flow-volume relationship in prepubertal girls. Five girls [9.3 (0.5) years old] performing vigorous swimming training for 12 h a week were compared with a control group of 11 girls [9.3 (0.5) years old] who participated in various sport activities for 2 h per week. Static lung volumes, maximal expiratory flows (MEF) at 75, 50 and 25% of vital capacity, 1-s forced expiratory volume (FEV_1.0) and airway resistance (R _aw) were measured by means of conventional body plethysmograph techniques. Prior to the training period there were no significant differences between the two groups for any of the parameters studied. Moreover, for both groups, all parameters were within the normal range for children of the corresponding age. After 1 year of training, vital capacity (VC), total lung capacity (TLC) and functional residual capacity (FRC) were larger (P<0.05) in the girl swimmers than in the control group, while physical development in terms of height and weight was similar. FEV_1.0 (P<0.01), MEF₂₅, MEF₅₀ (P<0.05) and MEF₇₅ as well as the ratio MEF₅₀ / TLC (P<0.05) had increased in the girl swimmers but were unchanged in the control group. R _aw tended to be lower in the girl swimmers and higher in the control group. The results indicate that intensive swimming training prepuberty enhances static and dynamic lung volumes and improves the conductive properties of both the large and the small airways. As to the causative mechanism, it can be speculated that at prepuberty intensive swimming training promotes isotropic lung growth by harmonizing the development of the airways and of alveolar lung spaces. Accepted: 5 March 1997     

Bioavailability of zinc in the sediment to the estuarine amphipod <Emphasis Type="Italic">Grandidierella</Emphasis><Emphasis Type="Italic">japonica</Emphasis>

The utility of interstitial water concentrations of metals and simultaneously extracted metals/acid-volatile sulfide differences (SEM–AVS) in two seasons were investigated to explain the biological availability of zinc in sediments to benthic organisms exposed in the laboratory. The amphipod Grandidierella japonica was exposed, in 10-day acute toxicity tests, to clean sediment spiked with zinc to obtain nominal treatments ranging from 0.25 to 74.4 mol g^–1 dry weight with respect to the molar difference between SEM_Zn and AVS. When the molar difference between SEM_Zn and AVS (i.e., SEM–AVS) was <0 mol g^–1, the concentration of zinc in the sediment interstitial water was low and few adverse effects were observed for any of the biological endpoints measured. Conversely, when SEM_Zn–AVS exceeded 0 mol g^–1, the concentration of zinc in the interstitial water and amphipod mortality increased. These data compare favorably with observations made in short-term exposures and thus support the use of AVS as a normalization phase for predicting toxicity in metal-contaminated sediments in different season.     

Sulfate reduction in fine-grained sediments in the Eastern Scheldt,southwest Netherlands

Sulfate reduction and sulfide accumulation were examined in fine-grained sediments from rapidly accreting abandoned channels and mussel culture areas in the Eastern Scheldt, which covered 4 and 5% of the total surface area, respectively.Reduction rates were measured in batch experiments in which the SO₄ ^2– depletion was measured during anoxic incubation. The reduction rates in summer varied between 14–68 mmol SO₄ ^2– m^–2 day^–1 and were related to the sedimentation rate. In the most rapidly accreting channels, SO₄ ^2– was exhausted below 15–50 cm and methanogenesis became the terminal process of organic carbon oxidationOne-dimensional modelling of sulfate profiles in mussel banks indicated that the subsurface influx of SO₄ ^2– was almost of the same order as the diffusive flux at the sediment-seawater interface, during the initial stages of the mussel bank accretion. The energy dissipation of waves and tidal currents on the mussel bank surface increased the apparent sediment diffusivity up to 3-fold, especially in the winterThe results indicate that acid volatile sulfide (AVS) was the major, in-situ reduced, sulfur compound in the sediment. The sulfidation of easily extractable iron was nearly complete. Pyrite concentrations (40–80 M S cm^–3) were as high as the AVS concentrations, but there was apparently no in-situ transformation of AVS into pyrite. The detrital pyrite originated from eroding marine sediments elsewhere     

Effects of streptozotocin-diabetes and l-thyroxine treatment on TSH and GH,and circulating glucose and glycerol in thyroidectomized rats

• 1.1.The response to exogenous thyroxine in thyroidectomized rats made diabetic by treatment with streptozotocin was greatly impaired, as shown by their growth retardation and the lack of increase in plasma GH and pituitary GH and TSH concentrations.
• 2.2.Insulin administration partially compensated for these endocrine alterations in diabetic thyroidectomized rats. When these animals received enough exogenous thyroxine to normalize their plasma PBI and TSH levels, insulin administration did not decrease their augmented glucose and glycerol concentrations.
• 3.3.These findings show the permissive action between thyroid hormones and insulin although some effects of the former counteract those of insulin.

     

Cardiorespiratory power across adolescence in male soccer players

Despite the recognition of the beneficial role of cardiorespiratory power (CRP) for health and sport performance, the development of this physical fitness parameter in adolescent soccer players was not well studied. Aim of this cross-sectional study was to investigate the effect of age on CRP of adolescent soccer players, the influence of anthropometric characteristics and body composition on it, and to establish normative data. Male adolescent (N = 274; aged 12.07–20.98 y), classified in nine one-year age-groups, child (N = 12, aged 7.71–11.8 y) and adult players (N = 22; aged 21.12–31.59 y), all members of competitive soccer clubs, were examined for anthropometric characteristics and body composition and they performed Physical Working Capacity in heart rate 170 test (PWC₁₇₀) on cycle ergometer. Analysis of variance revealed significant difference between age groups with respect to PWC170 in absolute (F _10,.297 = 29.58, P < 0.001, η² = 0.5), relative to body mass (F _10,.297 = 5.28, P < 0.001, η² = 0.15) and relative to fat free mass values (F _10.297 = 4.98, P < 0.001, η²= 0.14). In addition, age was in positive association with these parameters (r = 0.6, P < 0.001, r = 0.24, P < 0.001 and r = 0.23, P < 0.001, correspondingly). The main finding of this study was that CRP increased during developmental period in soccer players, even when it was adjusted to body mass or FFM, which increased during development. This documentation of the development of CRP provided useful tool for coaches and fitness trainers in order to apply optimal exercise interventions for health and performance.     

Determination of cardiac output by the CO2 - rebreathing method in fifteen-year-old boys subjected to graduated loading.

The dynamics of cardiac output changes were studied in 23 15-year-old boys subjected to graduated loading up to maximum on an bicycle ergometer and relationships between cardiac output and other indexes of cardiorespiratory functions were determined. The correlation between cardiac output (Q in 1/min) and oxygen consumption (VO2 in 1/min) was Q = 6.84 + 5.64. VO2. CO2-rebreathing was found to be a suitable non-invasive method for determining cardiac output in loading tests in adolescents. Maximum cardiac output correlated with maximum oxygen consumption, maximum pulmonary ventilation, body weight, lean body mass and physical working capacity W 170 and did not correlate with systolic volume, the arteriovenous oxygen difference, the pulse rate and ballistocardiographic force. The absence of any statistically significant differences between the various functional indexes of the physical fitness of trained and untrained boys indicates that training was not very effective.     

A field investigation of the relationship between zinc and acid volatile sulfide concentrations in freshwater sediments

Understanding relationships between cationic metals such as cadmium, copper, nickel, lead and zinc, and amorphous iron sulfides, measured as acid volatile sulfide (AVS), is key to predicting metal bioavailability and toxicity insediments. The objective of the present study was to assess seasonal and spatial variations of AVS in freshwater sediments contaminated with zinc. Sediments were sampled from three streams with varying levels of zinc contamination at two different times, March and June of 1995, representing cold- and warm-weather situations. Interstitial (pore) water concentrations of zinc, and solid phase concentrations of AVS and zinc were measured in surficial and deep sediment horizons. Toxicity tests (10-d) with the amphipodHyalella azteca were conducted using intact cores. Sediment zinc concentrations from six sites within the primary test stream differed by about five-fold, and also varied seasonally. Acid volatile sulfide concentrations were generally lower than those of zinc, and pore water zinc concentrations typically were elevated. There was a positive correlation between solid-phase AVS and zinc concentrations, suggesting that the system was dominated by zinc, as opposed to iron sulfides. In contrast to expectations arising from some studies of seasonal variations of AVS in iron-dominated systems, AVS concentrations were smaller in June than in March. However, this was likely due to a major storm event and associated sediment scouring before the June sampling, rather than to seasonal processes related to variations in temperature and dissolved oxygen. Based upon an indirect analysis of depth variations in AVS, there was some indication that zinc sulfide might be less prone to oxidation than iron sulfide. There was a strong correlation between toxicity of the sediment samples toH. azteca and interstitial water concentrations of zinc; however, the possible contribution of other contaminants to sediment toxicity cannot be dismissed.