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Biomedical subjects

G de Groot

Publications and source records attributed to G de Groot.

At least 55 records · Page 3Linked to original sources
PubMed1988

Supramaximal test results of male and female speed skaters with particular reference to methodological problems.

Six male and six female elite speed skaters were tested during two bicycle ergometer tests: a 30 s sprint test and a 2.5 min supra maximal test. During the 2.5 min test oxygen consumption was measured every 30 s. The males showed 30-31% higher mean power output values both during the sprint test (1103 versus 769 Watt) and during the 2.5 min test (570 versus 390 Watt). Maximal oxygen consumption was 31% higher for the males than for the females (5.10 versus 3.50 1.min-1). However, when expressed per kilogram lean body weight (LBM), power output and oxygen consumption was equal for both sexes. Differences between present and previous results are most likely due to methodological problems with the estimation of load during the supra maximal test. Subjects appear to experience difficulties in distributing their power output over the 2.5 min if they are tested for the first time. For experienced skaters and cyclists, fixed levels of 19 W.kgLBM-1 as initial load setting for the sprint test and 8 W.kg LBM-1 for the 2.5 min test are recommended.

Adipose Tissue↗
PubMed1988

Active drag related to velocity in male and female swimmers.

Propulsive arm forces of 32 male and 9 female swimmers were measured during front crawl swimming using arms only, in a velocity range between 1.0 m s-1 and 1.8 m s-1. At constant velocity, the measured mean propulsive force Fp equals the mean active drag force (Fd). It was found that Fd is related to the swimming velocity v raised to the power 2.12 +/- 0.20 (males) or 2.28 +/- 0.35 (females). Although many subjects showed rather constant values of Fd/v2, 12 subjects gave significantly (p less than 0.01) stronger or weaker quadratic relationships. Differences in drag force and coefficient of drag between males and females (drag: 28.9 +/- 5.1 N, 20.4 +/- 1.9 N, drag coefficient: 0.64 +/- 0.09, 0.54 +/- 0.07 respectively) are especially apparent at the lowest swimming velocity (1 m s-1), which become less at higher swimming velocities. Possible explanations for the deviation of the power of the velocity from the ideal quadratic dependency are discussed.

Acceleration↗
PubMed1988

A geometrical model of speed skating the curves.

The centripetal force in speed skating the curves has to be delivered by the push off force which also does the external work to maintain the speed. Based on the geometry of the speed skating oval and the sideward push off characteristics in speed skating, a mathematical model of the power output in skating the curves was deduced. The power required to follow the curve is dependent on the mean speed in the curve, the work per stroke and the radius of the speed skating oval. Measurements (by means of film and video analysis) during the 5000 m races at the European Championships for ladies (n = 16) yielded on the one hand power from the geometrical model and on the other hand power losses due to air- and ice- friction. The difference between power delivered and power lost is used by the skaters to increase their speed. The difference between predicted power and measured power used to increase the kinetic energy of c.g. was only 3% thereby providing strong support for the validity of the model. The analysis suggested that skaters who want to accelerate in the curves should increase their work per stroke. The model can be a useful tool to provide insight into this form of human locomotion and its optimization under competitive conditions.

Acceleration↗
PubMed1988

The concentration of morphine in serum of rats made dependent using a drug-admixed food method.

The present study reports on the induction of physical dependence in rats using morphine-admixed food and addresses the question of the resulting concentration of morphine in serum. The stability of morphine in food is good, since no decrease in concentration could be observed. The concentration of morphine in serum during the experiment was measured using a radioimmunoassay technique. A correlation was found between the food intake during a 7-hour period and the concentration of morphine in the serum at the end of that period, both for a 1 g/kg and a 2 g/kg batch of morphine-admixed food. The concentration of morphine in serum was also found to be dose-related during a period of 6-23 days when the rats were fed for a prolonged period. After long-term administration of 1 g/kg morphine in food a steady-state level of about 0.5 mg/l serum was obtained. Similarly with 2 g/kg morphine in food a steady-state level of 0.8-1.1 mg/l serum was reached. After withdrawal of morphine the serum concentration of morphine dropped to 0.1 mg/l within 24 hours and to below the detection limit within 48 hours. During the withdrawal period sharp drops were noted in body weight (20%) and food intake (50%) after one day.

Animal Feed↗
PubMed1988

Changes in locomotor-activity patterns as a measure of spontaneous morphine withdrawal: no effect of clonidine.

The anti-withdrawal action of clonidine was studied in a model of spontaneous morphine withdrawal in rats. After withdrawal the behaviour of the animals was registered continuously for several days. In the initial phase of induction of dependence the locomotor activity was enhanced during daytime. Partial tolerance to this increase developed in the course of 3 weeks. In morphine withdrawn animals the activity decreased strongly at night, and this effect was maximal on the second night after removal of morphine. After four nights the nightly activity was restored. Treatment with clonidine (100 micrograms/kg s.c. twice daily) changed neither the observed decrease in nightly locomotor activity nor other withdrawal symptoms such as a decrease in food intake and loss of body weight. In non-dependent animals clonidine induced a biphasic effect in locomotor activity, i.e. a decrease in the first few hours of the night and an increase in the second part of the night. The latter can be interpreted as a rebound phenomenon occurring after only three injections. It was concluded that clonidine was not effective as an anti-withdrawal compound in a model for spontaneous morphine abstinence. The low incidence of symptoms relating to a hyperactive sympathetic system during spontaneous withdrawal may be an explanation for the absence of an effect of clonidine.

Animals↗
PubMed1988

High-performance liquid chromatographic determination of doxorubicin in tissues after solid phase extraction.

A method is described for the determination of doxorubicin in tissues. The drug was selectively extracted from the biological matrix by solid phase extraction using 1-ml octadecyl silane extraction columns. Prior to extraction, tissue samples were digested by an enzymic digestion procedure. Daunorubicin was used as an internal standard. Quantitation was by high-performance liquid chromatography (HPLC) using ion-pair chromatography on a reversed-phase column. Detection was by fluorescence. Recovery of doxorubicin from tissue was 81.7 +/- 2.1% mean +/-SD. Doxorubicin concentrations as low as 0.01 mg kg(-1) could be determined. A typical value of the relative standard error of measurement was 3.7% at 2.1 mg kg(-1).

Journal Article↗
PubMed1988

Propelling efficiency of front-crawl swimming.

In this study the propelling efficiency (ep) of front-crawl swimming, by use of the arms only, was calculated in four subjects. This is the ratio of the power used to overcome drag (Pd) to the total mechanical power (Po) produced including power wasted in changing the kinetic energy of masses of water (Pk). By the use of an extended version of the system to measure active drag (MAD system), Pd was measured directly. Simultaneous measurement of O2 uptake (VO2) enabled the establishment of the relationship between the rate of the energy expenditure (PVO2) and Po (since when swimming on the MAD system Po = Pd). These individual relationships describing the mechanical efficiency (8-12%) were then used to estimate Po in free swimming from measurements of VO2. Because Pd was directly measured at each velocity studied by use of the MAD system, ep could be calculated according to the equation ep = Pd/(Pd + Pk) = Pd/Po. For the four top class swimmers studied, ep was found to range from 46 to 77%. Total efficiency, defined as the product of mechanical and propelling efficiency, ranged from 5 to 8%.

Adult↗
PubMed1988

Manual wheelchair propulsion: effects of power output on physiology and technique.

Eight wheelchair sportsmen conducted eight wheelchair exercise tests on a treadmill. Two workload strategies were followed: strategy 1--increments in speed at a constant slope and strategy 2--increments in slope at constant velocity. Thus, data on cardio-respiratory and propulsion technique parameters were obtained on two identical series of 16 speed and slope combinations. Between each two identical speed and slope combinations of strategies 1 and 2, a different workload history is apparent. A four-factor analysis of variance with repeated measures on the factors "strategy" (workload history), "speed," and "slope" was applied (P less than 0.05). No "strategy" effect was seen in the cardio-respiratory parameters (gross mechanical efficiency, ventilation, oxygen consumption, and heart rate), work/cycle, and cycle time. Thus, within the experimental set-up, workload history did not affect the parameters studied and 3-min workload periods appeared sufficiently long for experienced wheelchair users to adapt to the requirements of a given speed and slope combination. Significant effects were found on "speed," "slope," and their interaction in all parameters tested. Moreover, a comparison of two equal levels of power output, but different speed and slope, led to a significantly higher efficiency, cycle time, and work per cycle for the "low speed and high slope" combination. Push time and recovery time appeared highly dependent on speed and slope, respectively. The findings indicate that propulsion technique and cardio-respiratory parameters should not merely be studied in relation to power output, but also with respect to its constituents, speed, and slope/resistance.

Adult↗
PubMed1987

Physiological and biomechanical comparison of roller skating and speed skating on ice.

Eight well trained marathon skaters performed all-out exercise tests during speed skating on ice and roller skating. To compare these skating activities in relation to the concept of training specificity, relevant physiological (VO2, VE, RER and heart rate) and biomechanical variables (derived from film and video analysis) were measured. There were no significant differences between oxygen uptake (50.5 +/- 8.0 and 53.3 +/- 6.7 ml.min-1.kg-1), ventilation (102.4 +/- 11.2 and 116.0 +/- 11.1 1.min-1) or heart rate (174 +/- 12.2 and 176 +/- 14.5 min-1) between speed and roller skating. In roller skating a higher RER (1.16 +/- 0.1 cf. 1.05 +/- 0.1) was found. Power, work per stroke and stroke frequency were equal. Due to a higher coefficient of friction the maximal roller skating speed was lower. The effectiveness of push-off and parameters concerning the skating techniques showed no differences. In roller skating a 7.5% higher angle of the upper leg in the gliding phase occurred. It is speculated that the blood flow through the extensor muscles might be higher in roller skating. It is concluded that roller skating can be considered as a specific training method which may be used by trained speed skaters in the summer period.

Adult↗
PubMed1987

Respiratory valve for oxygen uptake measurements during swimming.

A detailed description of a respiratory valve to measure oxygen uptake while swimming is given. The effect on body drag of the addition of this equipment was measured in four subjects swimming over a range of speeds (0.9-1.9 m s-1). The respiratory valve has a low airflow resistance (29 Pa at an airflow of 8 l X s-1) and a small deadspace (30 ml). Total body drag when swimming while wearing the respiratory equipment did not differ significantly from that when swimming without the equipment. It is concluded that this respiratory valve is ideal for making valid and reliable measurements of oxygen uptake during swimming.

Evaluation Studies as Topic↗
PubMed1987

An estimation of drag in front crawl swimming.

Propulsive arm forces of twelve elite male swimmers during a front crawl swimming-like activity were measured. The swimmers pushed off against grips which are attached to a 23 m tube at 0.8 m under the water surface. The tube was fixed to a force transducer. Since at constant speed, mean propulsive force equals mean drag force this method also provides the mean active drag on a moving swimmer. The mean propulsive force at a speed of v = 1.48 m s-1 appeared to be 53.2 +/- 5.8 N which is two to three times smaller than what is reported by other authors for active drag but which is in agreement with values reported for passive drag on a (towed) swimmer who is not moving. Discrepancies with indirect active drag measurements are discussed.

Adult↗
PubMed1987

Central origin of respiratory arrest in beta-blocker intoxication in rats.

Propranolol HCl (7.5 mg X kg-1), timolol maleate (7.0 mg X kg-1), and sotalol HCl (10 mg X kg-1) were administered intracerebroventricularly (icv) to spontaneously breathing (SB) rats. The respiratory rate declined until the rats all died from respiratory arrest. Artificial ventilation resulted in survival of the rats for a 3-hr observation period. Intravenous (iv) administration of the same doses of the three beta blockers to SB rats did not result in either respiratory depression or death. Except for a decrease in heart rate (HR) the hemodynamic and respiratory parameters remained almost constant during the 3-hr observation period after iv administration to SB rats. After icv administration to SB as well as to ventilated rats no significant differences could be observed in the initial decrease in HR in comparison with iv administration. In SB rats at the end of the experiments a further decrease in HR was observed which might be ascribed to hypoxia since it did not occur in ventilated rats. After icv administration of each drug to the ventilated rats, mean arterial blood pressure showed a significantly greater decrease at the end of the 3-hr observation period than after iv administration. Plasma concentrations of the three drugs were determined just before death after icv administration in SB rats. In the other two groups they were measured at mean survival time and at the end of the experimental period. The plasma concentrations showed that the route of administration rather than the concentration of the beta blocker in plasma determines the occurrence of respiratory arrest. It was concluded that an overdose of propranolol, timolol, or sotalol can cause a centrally mediated respiratory arrest. Furthermore, a central mechanism appears to be implicated in the decrease in blood pressure.

Animals↗
PubMed1987

Moments of force, power, and muscle coordination in speed-skating.

Two well-trained speed-skaters were subjected to a biomechanical analysis incorporating push-off forces, cinematographic data, and link segment modeling. To gain knowledge on the backgrounds on technique and performance in speed-skating, the muscle coordination was studied by EMG and muscle contraction velocities. In speed-skating during the push-off, the body center of gravity (cg) is accelerated with respect to the point of application of the push-off force, with a forward gliding skate. The velocity of cg is a result of rotation of segments. Due to the absence of plantar flexion of the foot, the knee extension range is limited. The short and explosive push-off can be considered as a catapult-like action. The knee extensor muscles vastus medialis and rectus femoris are prestretched in the gliding phase by the antagonistic action of gastrocnemius and biceps femoris. In this phase the skater rotates his cg from the lateral to the medial side of the skate to reach an optimal push-off angle. The power output in the push-off phase is mainly generated by the monoarticular extensor muscles gluteus maximus and vastus medialis.

Ankle Joint↗
PubMed1987

Applied physiology of speed skating.

Speed skating exercise can be better understood by taking account of physiological and biomechanical considerations. Comparison with other sports shows the unique and peculiar way of skating propulsion. The relatively long lasting isometric muscle contractions during the gliding phase, alternated with high power output push-offs, place unusual demands on the (local) energy delivering systems. The short and explosive push-off needs a specific pattern of motor unit recruitment. Some mixture of slow twitch (to sustain skating posture) and fast twitch fibres (to effect push off) in the hip and knee extensors seems necessary for optimal skating performance.

Biomechanical Phenomena↗
PubMed1987

Comparison of physiology and biomechanics of speed skating with cycling and with skateboard exercise.

Eight well-trained speed skaters performed three all-out tests during ice speed skating, board skating and cycling. Compared to speed skating, cycling produced significantly higher values of oxygen consumption (57.2 +/- 4.9 vs. 53.9 +/- 4.2 ml/(kg X min], ventilation (111.3 +/- 10.2 vs. 98.8 +/- 7.3 l/min) and respiratory exchange ratio (1.18 +/- 0.13 vs. 1.03 +/- 0.05). This seems to suggest a different demand on the aerobic metabolism during cycling compared to speed skating. Board skating resulted in a significantly higher value of the ventilation (110.0 +/- 8.6 l/min) only. Kinematic analysis showed that during both skating activities the time series of the hip and knee angles, angular velocities and angular accelerations were similar. High peak values, especially of the knee angular acceleration, occur in the short push-off phase. During cycling completely different curves were found. The possible significance of these differences for movement co-ordination and motor unit involvement is discussed. The results show that board skating is a more specific training exercise for speed skating than cycling, at least when training for skating performances lasting 8-10 minutes at most.

Adult↗
PubMed1987

Specific characteristics of speed skating: implications for summer training.

Fourteen well-trained speed skaters performed all-out exercise tests during ice speed skating, low walking (walking-like movement in skating position), and dry skating (side to side deep sitting push-offs). These dry land training activities, widely used by speed skaters during the summer period, are compared to speed skating in relation to the concept of training specificity. Relevant physiological and biomechanical variables (derived from film and video analysis) were measured. The maximal oxygen uptake achieved in low walking (60.0 +/- 5.8 ml.kg-1.min-1) was not significantly different to that achieved during speed skating (62.1 +/- 6.9), but the maximal level attained in dry skating (48.4 +/- 5.5) was significantly less than both of these. The biomechanical differences measured are substantial. The forward directed push-off, the more dynamic movement pattern in hip and knee joints, and the use of plantar flexors during low walking are essentially different from speed skating. In dry skating, a more convulsive movement pattern due to the fixed push-off position compared to speed skating was found. The consequences of the typical skating position on the physiological responses is discussed. It is concluded that neither low walking nor dry skating can be considered as specific training activities for speed skaters.

Adult↗