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PubMed1983

[Hygienic aspects of youth work brigades].

A comprehensive inquiry study was carried out on living conditions, labour and regime in youth brigades. Furthermore, a complex hygienic-physiological assessment was made of the work of the students gone on agricultural brigades on the base of studies on the changes in the cardiovascular system, energy expenditure, nervous-muscular and thermoregulatory apparatuses, as well as on the functional activity of sympathico-adrenal system. The work, done by the students-members of the brigades, is qualified as moderately heavy, and as heavy only in some labour operations. Regardless of the relatively heavy and intensive work, the students are not overtired, because the duration of the working time is shortened on account of the rests, made at their desire. Recommendations are presented for the improvement both of the conditions in brigade camps and organization of labour regime.

Adaptation, Physiological↗
PubMed1995

Morphological and biochemical effects of strenuous exercise on immature long bones.

To determine the effects of intense exercise on the growth of long bones in immature animals, young male white leghorn chickens were run five days per week starting at four weeks of age on motor-driven treadmills. Work intensity was determined on the basis of maximal oxygen consumption (VO2 max) with the exercise intensity maintained at 70-80 percent VO2 max. Young animals ran continuously for 30 minutes, older animals 45 to 60 minutes each day. Runners and controls (10 animals per group) were sacrificed at 8, 12, 14 and 20 weeks of age. The lengths of the femurs and tibiotarsus were significantly stunted at 8-, 12- and 14 weeks in the runners but had nearly recovered at 20 weeks of age. Both bones also demonstrated significantly decreased total cross-sectional areas in 8-, 12- and 14 week-old runners as well as decreased cortical cross-sectional areas. The tibiotarsus also remained significantly smaller in the 20-week-old runners, but the femur had recovered in terms of radial growth. Intermolecular pyridinoline collagen crosslinks were identical in amount in the two groups with the femur collagen significantly less cross-linked than the tibiotarsus. The delayed growth of the exercised avian young bone is consistent with data obtained from children and young mammalian models. The osteogenic response to exercise that produces an increased bone mass in adult tissue appears either suppressed or overcome in young avian bone indicating that it may be erroneous to assume that data obtained from adult tissue are also applicable to young growing bone.

Animals↗
PubMed1991

A new approach to rowing ergometry: establishing exercise intensity relative to maximum force output.

The present experiment evaluated a new approach to establish exercise intensity during hydraulic rowing ergometry. In contrast to the traditional approach where exercise intensity is augmented by systematically increasing workload, the new procedure increments the intensity of exercise while maintaining a constant percentage of maximum force output. Ten college females exercised on a hydraulic rower that allowed for control of rowing speed and resistance. The new method to establish work intensity was to row at a cadence of 30 c.min-1 at a force output equal to 50% of maximum rowing force at each setting determined dynamically prior to testing. Two protocols were used for the maximum tests on the hydraulic rower. Row 1 was a 17-min, six-stage, incremental continuous row test performed at increasingly difficult settings from easy (setting 1; 603 N) to difficult (setting 6; 893 N). Row 2 was identical to row 1 until 15 min when resistance was reduced to setting 2 (658 N) for "allout" effort during the last 2 min. During this time, cadence declined from 30 c.min-1 to 19.4 c.min-1 at dial setting 6 and increased to 35.4 c.min-1 at dial setting 2. Both rowing protocols were compared to maximal physiological responses during treadmill running (TM). Compared to TM, both rowing protocols elicited significantly lower maximum oxygen uptake (VO2max; P less than 0.05; row 1 = delta 29.0% and row 2 = delta 12.9%) and maximum heart rate (HRmax; P less than 0.05; row 1 = delta 12.9% and row 2 = delta 6.7%). Maximum ventilation (VEmax) during row 1 was also lower by 30.4% than TM (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Energy Metabolism↗
PubMed1993

The influence of high-intensity exercise training on the Wlim-Tlim relationship.

When exercise to exhaustion is performed using at least two different intensities, work to fatigue (Wlim) can be expressed as a linear function of time to fatigue (Tlim). Whereas the slope of this function is related to endurance ability, the y-intercept is associated with the potential to perform high intensity interval exercise. The purpose of the present investigation was to determine the influence of 8-wk intermittent high-intensity exercise training on the y-intercept derived from the Wlim-Tlim relationship. Eight healthy, untrained male students (19.1 +/- 0.6 yr) completed five 60-s bouts of maximal exercise on the cycle ergometer, three times a week, for 8 wk. Seven controls avoided regular activity for the same period. Prior to and immediately following the training period, the Wlim-Tlim relationship, VO2max, and total work completed in five 60-s exercise bouts on the cycle ergometer were determined. Correlational analysis established relationships between the y-intercept and total work accomplished in the interval test pre- (r = 0.90; P < 0.01; N = 15) and post-training (r = 0.92; P < 0.01; N = 15), confirming that the y-intercept is related to the ability to perform exercise of this nature. Moreover, the "anaerobic" energy yield, calculated from total work and oxygen consumed during the interval exercise, was also related to the y-intercept (r = 0.78; P < 0.01). Interval training significantly increased both the y-intercept (P = 0.0015) and total work accomplished in the interval test (P = 0.001), while the slope of the Wlim-Tlim relationship (critical power) remained unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗
PubMed2001

[Risk of health disorders among women working with precision sterile technologies].

Results of hygienic, clinical, epidemiologic research helped to identify occupational risk factors for female workers engaged into microelectronic devices construction. The studies revealed occupational diseases and reproductive disorders in the females. The higher occupational risk was set for workers subjected to combined effects of complex low intensity factors, intensive work under exposure to chemical hazards.

Adult↗
PubMed2006

Changes in neuromuscular function due to intermittently increased workload during repetitive work in cold conditions.

OBJECTIVES: This study attempted to determine whether repetitive work in the cold affects the number of electromyographic (EMG) gaps and whether cold-induced deterioration in neuromuscular function can be restored by altering work intensity. METHODS: During 2 hours of simulated sausage packing, the occurrence of EMG gaps was studied in eight upper-extremity muscles at 19 degrees C and 4 degrees C. The additional effect of continuous, light repetitive work [wrist flexion-extension 10% of the maximal voluntary contraction (MVC), Cwork] and intermittently increased workload (10% or 30% MVC) (Iwork) on forearm muscle EMG gaps, the median frequency of the EMG spectrum, EMG activity, and muscle fatigue (as indicated by changes in the MVC of wrist flexion) at 4 degrees C was studied. RESULTS: During work simulation, the mean skin temperature decreased from 33.3 (SD 0.1) degrees C to 30.6 (SD 0.2) degrees C (P<0.05), and the number of EMG gaps diminished in seven muscles by 1.4-68.2% (P<0.05). During Iwork there were 44% and 37% more EMG gaps in the forearm flexors and extensors, respectively, and the median frequency shifted to higher frequencies (P<0.05) as compared with the situation in Cwork. The average EMG activity of the forearm flexors was 13% lower (P<0.05) during Iwork than during Cwork. Wrist flexion MVC decreased 18% and 15% in Cwork and Iwork, respectively. CONCLUSIONS: The cold-induced decrease in the number of EMG gaps and increased muscle strain and fatigue can be, at least partially, restored by intermittently increasing the workload (ie, breaking the monotonous work cycle).

Adult↗
PubMed1998

Adrenal medulla and exercise training.

The adrenaline release from the adrenal medulla increases during exercise, but at a given absolute work intensity the magnitude of this response is less pronounced in endurance trained vs sedentary individuals most likely due to a lower sympathetic stimulation of the adrenal medulla. However, when trained and untrained subjects are compared at identical relative work loads as well as in response to numerous non-exercise stimuli. endurance trained athletes have a higher epinephrine secretion capacity compared to sedentary individuals. This indicates a development of a so-called "sports adrenal medulla" as a result of a long term adaptation of an endocrine gland to physical training. Such an adaptation is parallel to adaptations taking place in other tissues like skeletal muscle and the heart. and can be advantageous in relation to both exercise performance in the competing athlete and cause a biological rejuvenation in relation to aging.

Adrenal Medulla↗
PubMed1986

Effect of anaerobiosis on the kinetics of O2 uptake during exercise.

The anaerobic threshold is an O2-related threshold of metabolic acidemia of which the chief metabolic acid is lactic acid. As such, it is a crucial parameter of aerobic function. For power outputs that are below the anaerobic threshold, the dynamics of O2 uptake (VO2) is well characterized as a linear first-order exponential process. The system time constant for leg exercise in humans has been shown to be congruent to 25-35 s with a "delay" of 15-20 s. Steady states are therefore normally achieved within 3 min at this work intensity. Above the anaerobic threshold a second, slower component of VO2 becomes evident that delays the steady state (if attainable). Consequently, the difference in VO2 between the third and the sixth minute of exercise is zero if the work rate is subthreshold and becomes progressively greater, the higher the increment above this parameter; this also correlates highly with the increment of arterial blood lactate, [L-]. This slow phase of the VO2 kinetics results in "excess" VO2, in that the VO2 rises to values above those attained by fitter subjects. This excess VO2 correlates highly with the increased [L-] (and possibly other factors), although its magnitude increases even more rapidly at work rates for which the increase in [L-] exceeds 4-5 meq/liter.

Anaerobiosis↗
PubMed1994

The Baltimore Therapeutic Equipment work simulator: biomechanical and physiological norms for three attachments in healthy men.

OBJECTIVES: The Baltimore Therapeutic Equipment (BTE) work simulator is routinely used by occupational therapists in functional capacity evaluation. Currently, there is a lack of normative data for various attachments on this instrument. The purposes of this study were to (a) establish norms for the biomechanical and physiological responses during three tasks on the BTE work simulator, namely, wheel-turn, push-pull, and overhead-reach; (b) compare these responses during the three tasks, and (c) examine the interrelationships of these responses during the tasks. METHOD: Twenty healthy men completed five testing sessions: (a) task familiarization on the BTE work simulator to identify the work intensity, which was perceived as hard on the Borg scale; (b) an incremental arm ergometer exercise test to determine their peak oxygen uptake (pVO2) and peak heart rate (pHR); and (c) one of the three tasks on the BTE work simulator for 4 min in each of the next three sessions. RESULTS: Analysis of variance indicated that torque, work, and power during the overhead-reach were significantly higher (p = .000) compared with the wheel-turn and push-pull tasks. However, no significant differences (p > .05) were observed among the tasks for the VO2 and HR, which were approximately 50% and 70% of pVO2 and pHR respectively. Although there was a significant relationship (p < .05) among tasks for the torque, work, and power, the common variance ranged only between 38% and 67%. The relative pVO2 was significantly related to work (p = .028) and power (p = .027) only during the push-pull task but not the wheel-turn and overhead-reach tasks. CONCLUSIONS: These results suggest that occupational therapists should include as many tasks as possible when designing functional capacity evaluation test batteries, and that there is no consistent relationship between cardiorespiratory fitness and performance of various tasks on the BTE work simulator.

Adolescent↗
PubMed2000

[20 years without smallpox].

It is 20 years since the 33rd World Health Assembly (WHA) declared that "worldwide eradication of smallpox" was achieved. This was the outcome of many years intensive work of the World Health Organization (WHO) and its member countries. In 1958 the WHA adopted the recommendation that WHO should initiate the eradication of smallpox on a worldwide scale. In 1967 the eradication activities in hitherto endemic countries became more intense. Smallpox affected 31 countries and 15 countries recorded from occasional cases. Every year more than 10 million people contracted the disease and two million of them died. A ten-year limit for the eradication was set. Gradually smallpox were eradicated in South America, then in Asia and last in Africa where the last case of endemic smallpox was recorded in 1977 in Somalia. WHO ensured international collaboration, close coordination of activities and mobilization of financial, personal and material resources. It ensured also that tested methods were fully applied in the affected countries regardless of their political, religious and cultural differences. In the eradication activities participated hundreds of thousands of local and 700 health professionals from abroad, incl. 20 Czechoslovak epidemiologists. The worldwide costs of eradication amounted to some 300 million dollars, i.e. some 23 million per year. The most important contribution of the eradication of smallpox was in addition to the termination of human suffering, worldwide financial savings estimated to 1-2 billion US dollars per year. These saved personal and financial resources could be used for other important health projects. The eradication of variola was defined as eradication of clinical forms of smallpox not as the final eradication of the variola virus. The importance of laboratories keeping the variola virus increased steeply at the time when clinical cases of smallpox were eradicated. From the beginning of the eighties WHO made an effort to reduce their number to a minimum. Since 1984 strains of variola are officially kept only in two centres collaborating with WHO. The Organization suggested destruction of the kept viruses in 1987, i.e. ten years after the eradication of smallpox. Unfortunately some political and scientific circles did not agree with this intention. Even recommendations to destroy the virus in 1993 and again in 1999 were not accepted. In the nineties fear of bio-terrorism and secret modernization of biological weapons influenced some member countries to change their opinion on the intended destruction of the virus. Despite this in May 1999 the WHA adopted a resolution that the final destruction of all variola strains is the objective of all member countries of WHO and recommended to postpone the destruction of the virus to the year 2002. The reason for postponement is current research of new antiviral preparations and better vaccines. There is again hope that all that will be left of the variola virus will be magnetic signals on computer diskettes.

Bioterrorism↗
PubMed1977

[Evaluation of tolerance of prolonged physical work as a function of the degree of endurance. I. Useflness of various tests determining physical endurance and the physiological cost of long-term physical exertion].

The physical capacity was determined in 23 men (aged from 19 to 27) using the following set of tests: Astrand and Ryhming's test, PWC170, PWC130, LPI, Crampton's test. The 70 min effort on the bicycle ergometer was considered as the model of prolonged work and the following parameters were accepted as standards of physiological cost of work; oxygen consumption, mechanical efficiency, heart rate during the work, stroke volume and cardiac output as well as the sum of systoles during recovery. The results of the correlation analysis point out that, at a given work intensity. the heart rate depends on results of PWC170 test and the systoles sum during recovery on the results of Crampton's tests. The capacity determined with used tests had no effect on the remaining indices of the cost of physical work.

Adult↗
PubMed2002

Aerobic exercise attenuates an exaggerated exercise blood pressure response in normotensive young adult African-American men.

An exaggerated exercise blood pressure response (EEBPR) may be associated with an increased risk of hypertension. We hypothesized that aerobic exercise training can decrease EEBPR and the risk for hypertension by decreasing arterial resistance. We studied the effects of aerobic training on the submaximal exercise blood pressure (BP) of eight normotensive young adult African-American men with an EEBPR. Subjects were trained on a stationary bicycle at an intensity of 70% peak oxygen uptake (VO2peak), for 30 min, three times per week, for 8 weeks. BP, heart rate, cardiac output (CO), stroke volume (SV) and total peripheral vascular resistance (TPR) were measured at rest and during submaximal exercise at a work intensity of 50% VO2peak. Significance of the training effects were evaluated by comparing the pre- and post-training measures (t-test, p < 0.05). A 15% post-training increase in VO2peak (34.6 +/- 1.4 to 40 +/- 1.4 ml/kg/min) and a 9.5 ml post-training increase in mean resting stroke volume were found. A 16.2 mmHg decrement in mean systolic BP, an 11.5 mmHg decrement in mean diastolic BP, a 120 dyne/s/cm5 decrement in TPR and a 1.2 l/min increase in CO were detected during the post-training submaximal exercise tests. These results suggest that reductions in TPR may attenuate the EEBPR of normotensive African-American males following an 8-week training regimen of stationary bicycling at 70% VO2peak. Aerobic exercise training may, therefore, reduce the risk of hypertension in normotensive African-American males by the mechanism of a reduction in TPR. Because of the limited number of subjects, the results of this study should be interpreted cautiously pending confirmation by a larger controlled trial.

Adolescent↗
PubMed1979

Physiologic responses of juvenile-onset diabetic boys to muscular work.

The cardiorespiratory and metabolic responses of juvenile-onset diabetic (Dia) and nondiabetic (Con) boys to light, moderate, and maximal treadmill work were investigated. No significant differences were observed between the Dia and Con subjects in cardiorespiratory responses to maximal and submaximal work. The mean values for the Dia boys during maximal treadmill work for ventilatory volume, oxygen uptake, heart rate, and lactic acid were 91.5 L/min, 54.9 ml/kg . min, rate, and lactic acid were 91.5 L/nin, 54.9 ml/kg . min, 198 beats/min, and 7.0 mM/L, respectively. In the Dia boys, maximal-, light-, and moderate-intensity work produced significant plasma glucose decreases (P less than 0.05) of 1.64, 3.23, and 7.2 mM/L, respectively. In the Con boys, the submaximal work bouts were performed without significant change in plasma glucose levels, but glucose levels after maximal work were elevated 1.58 mM/L. Light and moderate work in both groups produced no changes in plasma triglycerides, free fatty acids, or lactic acid. However, for the Dia boys, maximal work was associated with a significant increase of 0.36 mM/L in triglycerides.

Adolescent↗
PubMed1983

Total cholesterol and HDL-cholesterol changes during acute, moderate-intensity exercise in men and women.

Chronic endurance exercise training has been associated with decreased levels of total cholesterol and increased HDL-cholesterol. To our knowledge rapid changes in cholesterol and HDL-cholesterol during acute exercise have not been described under controlled conditions. We studied 28 subjects (14 males and 14 females) during bicycle exercise for 40 min at a work intensity of 55% of their maximal oxygen consumption. Total and HDL-cholesterol levels were measured (and LDL-cholesterol calculated) at rest, 10, 20, 30, and 40 min of exercise, and 15 min postexercise. There was a significant (p less than 0.001) increase in HDL-cholesterol levels at 10 min of exercise (58.8 +/- 13.9 mg/dl, mean +/- SD) above rest (53.1 +/- 13.4 mg/dl) for all subjects. This increase persisted (p less than 0.001) at all time points throughout the exercise session, but declined by 15 min postexercise. There was a small, insignificant decline in LDL-cholesterol. It is concluded that apparent favorable changes in lipoprotein patterns occur acutely, and are sustained during short-term, moderate intensity exercise. Analyses of these changes appears necessary if the biochemical mechanisms which underlie these metabolic alterations are to be elucidated.

Adolescent↗
PubMedDate not supplied

Importance of dynamics of sweating in men during exercise.

Influence of dynamics of sweating on rectal temperature increase was tested in 3 groups of men performing cycle exercise with intensity of 65, 90 and 120 W, respectively, in 22 degrees C chamber temperature and 30% of relative air humidity. During exercise at 65 and 90 W the subjects wore suits while exercising with intensity of 120 W they wore only shorts. The dynamics of sweating was described by delay in onset of sweating and time constant of the reaction. Wearing caused significant increase in skin humidity and decreased evaporative rate of sweating. Sweat rate during steady state was related to the metabolic rate in naked (r = 0.89, p less than 0.002) as well as in wearing subjects (r = 0.93, p less than 0.01). Delay in onset of sweating was, in average, 5 min with a time constant of 7 min. Both factors showed a tendency to be shorter with increasing work intensity. Mean increase in rectal temperature was proportional to the intensity of exercise although the individual delta Tre correlated well with the dynamics of sweating in naked (r = 0.83, p less than 0.01) and wearing subjects (r = 0.84, p less than 0.01). Since delta Tre was smaller in subjects with shorter inertia time of sweating in response to beginning of exercise at the same intensity it is concluded that the dynamics of sweating can play an important role in limiting body temperature increase in working men.

Adolescent↗
PubMed1995

The impact of activity level on sweat accumulation and thermal comfort using different underwear.

The purpose of this study was to investigate the significance of work level and sweat production for the total amount accumulated and the location of the sweat in a three-layer ensemble as a function of material and textile construction. Furthermore, it was also an aim to investigate how this influenced thermoregulatory responses and thermal comfort during work and during a rest period. Long-legged/long-sleeved underwear manufactured from two different 100% fibre-type materials, polypropylene and wool, was tested as part of a three-layer clothing system. The underwear manufactured from 100% polypropylene was tested in two different knit constructions, a 1-by-1 rib knit and a fishnet structure, and the woollen underwear in a 1-by-1 rib knit construction. The test was performed on eight male subjects (Ta = 10 degrees C, RH = 85%, Va < 0.1 m/s), and comprised a twice-repeated bout of 40-min cycle exercise followed by 20 min rest. Each subject conducted two tests with the work level approximating 30% VO2 max and 40% VO2 max, respectively. Skin temperatures, rectal temperature, weight loss and humidity near the skin were recorded during the test. Total changes in body and clothing weight were measured separately. Furthermore, subjective ratings on thermal comfort and on sensation of temperature and humidity were collected. The results demonstrated that high heat and sweat production during work periods, leading to increased sweat accumulation, will give higher thermal discomfort ratings for rest periods as well as for work periods compared to intermittent work with lower work intensities. Distribution of accumulated sweat in the clothing ensemble after heavy sweating is dependent on the fibre type in the underwear. Further, it can be concluded that underwear construction clearly has an influence on the evaporation rate in a three-layer ensemble during work at a high activity level.

Adult↗
PubMed2003

Effects of shortening velocity and of oxygen consumption on efficiency of contraction in dog gastrocnemius.

Previous observations have shown that, in isolated perfused dog gastrocnemii in situ, stimulated to aerobic rhythmic isotonic tetanic contractions (at about 40% of maximal isometric force), only about 20% of the overall metabolic power (proportional to the rate of O2 consumption, VO2) was converted into mechanical power (W). Here we report that, in the same preparation, the maximal velocity during the shortening phase of each tetanus (v, mm s(-1)) increased with the rate of energy dissipation, as given by the difference between VO2 and W (W kg(-1)). The relationship between these variables was described by: v=2.85(VO2-W)(1.24) (R2=0.85; n=17). A mathematical analysis of this equation shows that the overall mechanical efficiency (eta=WVO2(-1)) decreased with increasing v (at constant VO2), whereas it increased with increasing VO2 (at constant v). The net effect of this state of affairs was that the decrease of eta over the entire range of work intensities was relatively minor (from 0.22 to 0.15), in spite of a large increase of v, (from 40 to 120 mm s(-1)), thanks to the concomitant increase of VO2 (from 10 to 25 W kg(-1)). So, under these experimental conditions, the energetics of work performance seems to be governed by two conflicting needs. The need for a sufficiently high shortening speed (and hence power output), itself requiring a sufficiently large energy dissipation rate, which, however, brings about a fall in eta. This is counteracted by the increased VO2, which in turn leads to an increased efficiency at the expense of a fall in shortening speed.

Algorithms↗
PubMed2002

Soccer specific aerobic endurance training.

BACKGROUND: In professional soccer, a significant amount of training time is used to improve players' aerobic capacity. However, it is not known whether soccer specific training fulfils the criterion of effective endurance training to improve maximal oxygen uptake, namely an exercise intensity of 90-95% of maximal heart rate in periods of three to eight minutes. OBJECTIVE: To determine whether ball dribbling and small group play are appropriate activities for interval training, and whether heart rate in soccer specific training is a valid measure of actual work intensity. METHODS: Six well trained first division soccer players took part in the study. To test whether soccer specific training was effective interval training, players ran in a specially designed dribbling track, as well as participating in small group play (five a side). Laboratory tests were carried out to establish the relation between heart rate and oxygen uptake while running on a treadmill. Corresponding measurements were made on the soccer field using a portable system for measuring oxygen uptake. RESULTS: Exercise intensity during small group play was 91.3% of maximal heart rate or 84.5% of maximal oxygen uptake. Corresponding values using a dribbling track were 93.5% and 91.7%. No higher heart rate was observed during soccer training. CONCLUSIONS: Soccer specific exercise using ball dribbling or small group play may be performed as aerobic interval training. Heart rate monitoring during soccer specific exercise is a valid indicator of actual exercise intensity.

Adult↗