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1.
Abstract

Twelve subjects were used to determine the effect of isotonic and isometric exercises on heart rate using a military press in a sitting position. The isotonic exercise was performed for 45 sec. with one half of maximum resistance, and the isometric exercises were performed for 45 sec, with one half, two thirds, and maximum resistance. The results indicated that isometric exercise performed for 45 sec. with one half of maximum resistance could stimulate heart rate to the same extent that isotonic exercise could, using the same intensity and duration. The results also showed that increasing the load in isometric contraction resulted in a proportional increase in heart rate and that increasing the load to maximum isometric contraction resulted in a near twofold increase in heart rate.  相似文献   

2.
Abstract

This study investigated the acute effects of different sizes of paddles on the force-time curve during tethered swimming and swimming velocity in front-crawl stroke. Fourteen male swimmers (20.0 ± 3.7 years; 100-m best time: 53.70 ± 0.87 s) performed two 10-s maximal efforts in tethered swimming to obtain peak force, average force, impulse, rate of force development, stroke duration and time to peak force. Swimming velocity, stroke rate and stroke length were obtained from two 25-m maximal swims. Both tests were repeated in five conditions: free swimming, wearing small (280 cm 2 ), medium (352 cm 2 ), large (462 cm 2 ) and extra-large (552 cm 2 ) hand paddles. Compared to free swimming, paddles provided significant increases of peak force (medium: 11.5%, large: 16.7%, extra-large: 21.7%), impulse (medium: 15.2%, large: 22.4%, extra-large: 30.9%), average force (medium: 5.1%, large: 7.5%), rate of force development (extra-large: 11.3%), stroke duration (medium: 9.3%, large: 11.8%, extra-large: 18.5%), time to peak force (medium: 11.1%, large: 15.9%, extra-large: 22.1%), swimming velocity (medium: 2.2%, large: 3.2%, extra-large: 3.7%) and stroke length (medium: 9.0%, large: 9.0%, extra-large: 14.8%), while stroke rate decreased (medium: –6.2%, large: –5.5%, extra-large: –9.5%). It is concluded that medium, large and extra-large paddles influence the force-time curve and change swimming velocity, suggesting these sizes may be useful for force development in water.  相似文献   

3.
This study examined age-group corresponding relationships of the controlled force exertion based on sinusoidal and quasi-random waveforms in 175 right-handed male adults aged 20 to 86 years. The subjects were divided into 3 groups based on age-level: 53 young (mean age 24.6, SD?=?3.3 years), 71 middle aged (mean age 44.3, SD?=?8.7 years), and 51 elderly (mean age 69.3, SD?=?6.4 years). The participants matched their submaximal grip strength by the dominant hand to changing demand values displayed as either a sinusoidal or a quasi-random waveform appearing on the display of a personal computer. The quasi-random waveform was changed in π with amplitude and in π/2 with frequency (peak and mean frequency were 0.1 Hz in both waveforms). The participants performed the controlled force exertion test three times with a 1-min interval (one trial was 40 sec) after one practice trial using the dominant hand. The measurement order was randomly assigned. The total of the differences between the demand value and grip exertion value for 25 sec were used as an evaluation parameter. The coefficient of variance was almost the same range in all age groups in both waveforms (CVSW ?=?30.8–35.6, CVRW ?=?26.3–37.7), but the elderly group showed the highest value in the quasi-random waveform. Significant correlations were found among the sinusoidal and quasi-random waveforms in the young, middle-aged, and elderly groups, but significant differences were not found in the correlations among each age group. The controlled force exertion evaluation based on the sinusoidal and quasi-random waveform displays has a moderate relationship, and this relationship does not show age-level differences.  相似文献   

4.
Abstract

Rapid, goal-directed elbow flexion movements were examined under interacting conditions of inertial loading and resistance to movement initiation. The resistance ceased when movement began, resulting in quick release movements. Inertial load slowed the movement and lengthened the agonist and antagonist electromyographic (EMG) burst durations. The quick release resulted in larger accelerations but only minimal changes in peak velocity. Most aspects of the triphasic EMG pattern were little affected by the quick release, but the build up of agonist EMG and the corresponding rate of static force development differed markedly between load and quick release conditions. These and other data suggest that the specific pattern of agonist muscle activation is set according to neuromuscular constraints of the antagonist muscle and the expectation of movement dynamics.  相似文献   

5.
Abstract

The effect of actively warming the forearm musculature on dynamic grip endurance was investigated by comparing the performance of the left and right hands, with or without warming-up, on a spring-loaded grip ergometer. There were 21 male subjects, aged 19 to 23. Warming-up consisted of 9 min. of four hand and wrist exercises conducted in 30-sec. bouts, at a rate of one repetition per sec., with 15-sec. intervals between bouts. This warm-up was shown to lead to temperature increases of between 1.6 C and 2.6 C in the flexor digitorum sublimis muscles of five subjects. Warming-up had no effect on grip endurance.  相似文献   

6.
Abstract

A recording spring-loaded hand ergograph with fast moving paper was utilized to obtain a record of the entire hand contraction sequence. The subjects (N=40) were given a series of six contractions, each beginning at a different initial tension: 0, 10, 15, 20, 25, and 30 kilograms. The contractions were separated by one minute and the order was systematically rotated to minimize either learning or fatigue. The development of force was found to progress exponentially according to a three-component mathematical equation. The control group (zero pre-tension) achieved a greater maximal force (F=4.5) than all others, and was the only one with a clear advantage in speed and tension. The rate of change constants were comparable, but the early initial (negative) component disappeared at the 20 kilogram condition and beyond. The factor of rate seemed to be independent of tension level.  相似文献   

7.
Abstract

In this study, we wished to investigate the factors that determine the direction of the spin axis of a pitched baseball. Nineteen male baseball pitchers were recruited to pitch fastballs. The pitching motion was recorded with a three-dimensional motion analysis system (1000 Hz), and the orientations of the hand segment in a global coordinate system were calculated using Euler rotation angles. Reflective markers were attached to the ball, and the direction of the spin axis was calculated on the basis of their positional changes. The spin axis directions were significantly correlated with the orientations of the hand just before ball release. The ball is released from the fingertip and rotates on a plane that is formed by the palm and fingers; the spin axis of the ball is parallel to this plane. The lift force of the pitched baseball is largest when the angular and translational velocity vectors are mutually perpendicular. Furthermore, to increase the lift forces for the fastballs, the palm must face home plate.  相似文献   

8.
This study aimed to examine the age and sex differences in controlled force exertion measured by the bar chart display in 207 males (age 42.1 ± 19.8 years) and 249 females (age 41.7 ± 19.1 years) aged 15 to 86 years. The subjects matched their submaximal grip strength to changing demand values, which appeared as a moving bar chart on the display of a personal computer. The subjects performed the controlled force exertion test using the dominant hand three times with 1-min intervals (one trial was 40 sec) after one practice trial. A total of the differences between the demand value and the grip exertion value for 25 sec was used as the evaluation parameter. The errors in controlled force exertion showed a right-skewed distribution in both sexes but showed a normal distribution after logarithmic transformation (males, W = .06; females, W = .74; p > .05). In addition, the errors in controlled force exertion tended to increase constantly with age in both sexes. Significant linear regressions were identified (r 2 males = .88, r 2 females = .81), but there was no significant difference in the increase rate of both sexes. The results of the analysis of variance and multiple comparisons showed insignificant sex differences among means, except for those in individuals older than 70 years; significant differences between means in the older than 40-year-old age group and the 20-year-old age group were found in both sexes. Individual differences were almost the same in both sexes (CVmales = 20.0～34.8, CVfemales = 17.7～36.2). Errors in controlled force exertion showed a nonsignificant sex difference and increased gradually with age in both sexes but increased remarkably with age after 40 years of age.  相似文献   

9.
Abstract

A study was made on the effects of a 10-sec. isometric exercise, which involved much of the large musculature, upon the heart-rate, blood pressure, and net oxygen cost. Six subjects exercised in a semireclining, fixed position against a Medart spring dynamometer. Each subject pulled to 60 percent of his previously determined maximum effort. Heart rate showed a slight increase during exercise followed by a sharp rise in the few seconds following exercise. This was followed by a drop almost to the resting level within 20 to 30 sec. following exercise. Systolic pressure rose following exercise and was highest in the period immediately following exercise, then dropped slowly to resting levels within 2 1/2 min. Oxygen consumption varied widely both between subjects and between experiments in the same subject.  相似文献   

10.
Abstract

This study investigated the effects of three types of recovery procedure on (a) circulatory recovery from a standardized bicycle ergometer exercise, (b) performance in a second standardized bicycle ergometer exercise, and (c) circulatory recovery from the second exercise. The recovery procedures were complete rest, light activity, and cold showers. Each of 10 male subjects underwent each recovery procedure on separate days. Analysis of variance for a randomized complete blocks design was used in the analysis of the data. Results indicated that cold showers decreased recovery heart rate after the first standardized exercise from 115 to 96 beats/minute and after the second exercise from 164 to 152 beats/ minute when compared with the other two conditions. Speed of performance in the second exercise was improved from 40.4 and 40.3 sec. in the case of rest and light activity to 38.9 sec. for cold showers. These improvements were all statistically significant at the .05 level. Three physiological explanations, not necessarily independent, are advanced: (a) local vasoconstriction of the skin vessels and vasodilatation of the muscle vessels causing a greater proportion of total blood flow to the working muscles, (b) establishment of a greater thermal gradient between the core and shell of the body allowing heat movement to the surface of the body by conduction between tissues rather than by skin blood flow, and (c) a decrease in sweat rate, thereby suppressing release of bradykinin, a vasodilator substance.  相似文献   

11.
Abstract

The purpose of the present study was to determine velocity discrimination characteristics of subjects in a difference threshold paradigm. After recruitment, 180 male and female subjects were randomly assigned to 1 of 6 groups differentiated by the length of the stimulus runway and the subjects' orientation to the stimulus. Stimulus velocities were presented on a modified Bassin Anticipation Timer with presentation rate controlled by a programmed timer. The criterion velocities were 134.11, 268.22 and 402.33, cm/sec with variable velocities ranging 44.7 cm/sec above and below the criterion in 8.94 cm/sec increments. The method of constant stimuli was used with 198 trial pairs presented (constant 7 second stimulus presentation interval). The results indicated that the discrimination of horizontal linear velocity follows a prothetic continuum. That is, the just noticeable difference increased in proportion to the increase in the criterion velocity. In addition, the subjects' orientation to the stimulus and the viewing distance (length of runway) seemed to play little or no role in the discrimination process.  相似文献   

12.
Abstract

A completely general three-dimensional dynamic model is presented for the motion of basketball shots that may contact the rim, the backboard, the bridge between the rim and board, and possibly the board and the bridge simultaneously. Non-linear ordinary differential equations with six degrees of freedom describe the ball angular velocity and ball centre position. The model includes radial ball compliance and damping and contains five sub-models: purely gravitational flight, and ball – rim, ball – bridge, ball – board, and ball – bridge – board contact. Each contact sub-model has both slipping and non-slipping motions. Switching between the sub-models depends on the reaction force at, and velocity of, the contact point. Although the model can be used to study shots from any point on the court, we here use it to study the sets of free throw release angle, velocity, angular velocity, and lateral deviation angle that result in success (capture), as well as underhand free throws and those using an under-inflated ball. Free throw shots with larger backspin, lower inflation pressures, and underhand release conditions are shown to result in larger capture percentages.  相似文献   

13.
Abstract

Five highly skilled canoe racers performed three trials each at race pace using a conventional straight canoe paddle and a modified paddle with the blade angled 15 degrees forward from the shaft. The use of the straight paddle resulted in a mean velocity of 290 cm/sec whereas the angled paddle resulted in a significantly faster mean velocity of 306 cm/sec (p<.05). There were no differences in the temporal sequences of the boat velocities. There were no significant differences in the time the paddles were in the air between strokes. It was also determined that the angled paddle had less absolute movement in the water than the straight paddle during the period of greatest boat acceleration. No significant differences were found in paddling technique through absolute measurement and temporal sequence of horizontal displacement of either hand relative to its corresponding shoulder, either shoulder relative to the spine, or the spine relative to the boat.  相似文献   

14.
Abstract

The effect of the number of reinforcements on the memory trace for a kinesthetically monitored force reproduction task was studied. Sixty college women were divided by a balanced order into three groups of 20 each. One group had one reinforcement, one had five reinforcements, and the third had nine reinforcements. The reproduction attempt was either immediate or after a 30-sec. delay. Analysis of variance for constant error indicated that multiple reinforcements improved the accuracy of performance for immediate reproduction but that the improvement was not retained over a retention interval of 30 sec. The tendency to overshoot the standard occurred for both the immediate and delayed reproduction conditions.  相似文献   

15.
Abstract

When the response movements are as short and simple as possible, the time lag between stimulus and response for one movement is shortened by introducing the stimulus for a second movement during the latent period for the first (usually about .22 sec). Under these conditions the latent period of the second movement is increased about 25 percent. This does not seem to be caused by true psychological refractoriness, since ability to accept the second stimulus and respond to it is still present. A control experiment furnishes evidence that it is probably a foreperiod-expectancy phenomenon. The length of the response latency of a simple single movement is increased about 40 percent if conditions are altered so that a second stimulus requiring a second movement is expected some time within a half-second after the first stimulus. All of these results are consistent with the recent memory drum theory of neuromotor response.  相似文献   

16.
Abstract

The aim of this study was to investigate counter-movement jump performance and its reliability in children and adolescents with respect to age, sex and activity level. We tested 1835 children and adolescents aged between 4 and 17 years. All participants performed three counter-movement jumps on a force platform with arms akimbo. The participants were divided into six age groups and subdivided by sex within each group, to analyse age and sex effects. Subsequently, jumping performance of active and sedentary participants was compared. Jump height was calculated and the highest jump out of three was used for the calculations of peak force and peak rate of force development. Variability of all parameters was quantified using the coefficient of variation over all jumps. Jump height increased significantly with increasing age while peak rate of force development decreased. Peak force was similar for all age groups. Jump height was significantly higher in male participants and peak force and peak rate of force development was significantly lower in male participants. Variability of jump height and peak force decreased significantly with increasing age leading to reliable data above the age of 10 years. Peak rate of force development showed a high variability and, therefore, should be interpreted with caution. This could be useful information for coaches as they need to know from which age onwards the counter-movement jump is applicable in performance diagnostics and which parameters are sensible for interpretation. Finally, the present study provides data to be used as normative references.  相似文献   

17.
Abstract

The aims of this study were to examine training characteristics, body composition, muscular strength, and endurance in sport climbers, and to demonstrate the relationship among these components by means of structural equation modelling. Altogether, 205 sport climbers (136 males, 69 females), with a performance RP (red point) of grade 4 to 11 on the Union Internationale des Association d'Alpinisme (UIAA) scale, took part in the study. The proposed structural model, with latent variable hand–arm strength and endurance (developed from reference values for simple tests), indicated by three manifest variables (grip strength, bent-arm hang, and finger hang) and three exogenous variables (body fat, volume of climbing, and climbing experience), explained 97% of the variance in climbing performance. The relationship between body fat and climbing experience/volume with climbing performance was not direct, but was better explained using the mediator hand–arm strength and endurance. We conclude that these simple tests, together with percent body fat, volume of climbing, and climbing experience, can satisfactorily predict climbing performance.  相似文献   

18.
Abstract

The aim of this study was to characterize forearm muscle fatigue identified by the decrease in electromyogram median frequency and/or fingertip force during intermittent exercise. Nine elite climbers (international competitive level, USA 5.14a on sight) and ten non-climbers were instructed to maintain a fingertip force of 80% of their maximal voluntary contraction force on a dynamometer mimicking a rock climbing grip during a 5 s effort/5 s rest cycle for 36 repetitions (i.e. 6 min of exercise). Elite climbers lasted twice as long as non-climbers (climbers: 3 min; non-climbers: 1 min 30 s) before the force could no longer be maintained (i.e. the failure point). After this moment, fingertip force decreased and stabilized until the end of the exercise around 50% maximum voluntary contraction force in non-climbers and 63% in elite climbers. Electromyogram median frequency showed a greater decrease in non-climbers than in elite climbers before the failure point. No change in median frequency was observed after the failure point in elite climbers or in non-climbers. These results confirm that elite climbers are better adapted than non-climbers for performing the intermittent fingertip effort before the failure point. After this point, the better fingertip force of elite climbers suggests different forearm muscle properties, while the electromyography results do not provide any indication about the fatigue process.  相似文献   

19.
Abstract

To determine the energy cost of low impact aerobic dance while varying arm movement height and the use of hand weights, 10 adults volunteered to participate in four choreographed trials. All trials consisted of identical leg movements. Arm movements, however, were performed above shoulder level both with and without 0.9-kg hand weights and below shoulder level both with and without 0.9-kg hand weights. Open circuit spirometry was employed throughout the 10-min videotape guided trials, and heart rate was measured by telemetry. Neither the use of hand weights nor the change in arm position height significantly altered the energy cost of low impact aerobic dance. However, heart rate responses were significantly different. Caution should be observed by aerobics instructors and participants as to the use of heart rate as an indicator of intensity for low impact aerobic dance.  相似文献   

20.
Abstract

In an effort to investigate the force-time characteristics during the acceleration phase of the sprint start, eight male sprinters were used as subjects. Runs up to 3 m were analyzed from film, and force-time parameters were measured on a force platform. In a starting stance the reaction time of the group was .118 ± .016 s and the force production lasted .342 ± .022 s. The maximal resultant force at the moment of maximal horizontal force was 19.3 ± 2.2 N x kg1, and the direction of the force was 32 ± 7°. In the very last instant before leaving the blocks the velocity of the center of gravity was 3.46 ± .32 m x s?1. In the first contact after leaving the blocks there was a braking phase (.022 ± .005 s in duration) during which the average horizontal force was ?153 ± 67 N. The braking phase was observed despite the body center of gravity being horizontally ahead by .13 ± . 05 m with respect to the first contact point. The percentage of deceleration in running velocity during that phase was 4.8 ± 2.9%. In the propulsion phase the average horizontal force was great (526 ± 75 N), and it was produced for a relatively long time (.171 ± .035 s). Significant correlation coefficients were observed between force production and running velocity. These results suggest that braking/propulsion phases occur immediately after the block phase and that muscle strength strongly affects running velocity in the sprint start.  相似文献   

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