Forces in human swimming consist of two components, a drag force and a lift force. The lift force is assumed to be beneficial because of the relative small energy loss to the water. This energy loss can be quantified by determining the propelling efficiency, ep (defined as the ratio of the useful power to the total power output). The first purpose of this study was to investigate whether high values of propelling efficiency can be explained by a relatively high contribution of lift and/or a favorable direction of the generated force in front crawl swimming. Propelling efficiency was estimated using two methods, one based on a physiological approach (epp) by measuring oxygen consumption and one based on a kinematic approach (epk) by calculating forces generated by hands and forearm and power components, from a three-dimensional analysis. The second purpose of this study was to compare epp and epk. The contribution of lift to the total force as well as the direction of the force cannot explain the values of epp. The values of epp and epk did not correlate significantly. In swimming propulsion some processes play a role which cannot be explained at this moment. One of these processes might be the generation of vortices.

Sport scientists have identified many factors as prerequisites for a good athletic performance in various sports. It is not clear whether these factors also influence the best performers in the homogeneous groups of top athletes selected for national teams. In this study, this issue is addressed with members of the Dutch National Junior Speed Skating Team. A total of 237 different technical, physiological, anthropometrical, and psychological parameters were collected, including many that correlated with performance in previous studies. High speed film analyses during the National Championships provided the technique parameters. A 30-s sprint test and a 150-s supramaximal test on a cycle ergometer underlie the physiological data, and questionnaires were used to measure personality traits and emotional feelings. Only trunk position and the direction of push-off (push-off angle phi) correlated consistently with skating performance in this group (r = 0.61-0.73 and r = -0.65 to -0.70, respectively). The small number of meaningful correlations means that sport scientists will have to develop more reliable methods, models, and theories to contribute significantly to knowledge useful to top athletes and their coaches.

To prevent the tip of the blade from scratching through the ice, the technique in speed skating requires that plantar flexion is largely suppressed during the gliding push off. This not only prevents the plantar flexors from contributing to external work but also causes the skater to lose contact with the ice long before the knee is fully extended. To prevent these disadvantages of the gliding technique, a new skate was developed that permits the shoe to rotate relative to the blade in a hinge between shoe and blade. In a case control study the progression between the 1993/1994 and 1994/1995 skating seasons of 11 male skaters from a regional junior selection who consented to switch to this new skate was compared with the progression of 72 skaters of this and all other regional and national male junior selections of The Netherlands. The experimental group appeared to improve their personal best times by 6.2 +/- 2.3%, which is a significantly (P < 0.001) larger progress than the 2.5 +/- 1.6% improvement of the control group. The new skate will therefore most likely add a new dimension to the art of speed skating.

To calculate the power output during actual cycling, the air friction force Fa and rolling resistance Fr have to be known. Instead of wind tunnel experiments or towing experiments at steady speed, in this study these friction forces were measured by coasting down experiments. Towing experiments at constant acceleration (increasing velocity) were also done for comparison. From the equation of motion, the velocity-time curve v(t) was obtained. Curve-fitting procedures on experimental data of the velocity v yielded values of the rolling resistance force Fr and of the air friction coefficient k = Fa/v2. For the coasting down experiments, the group mean values per body mass m (N = 7) were km = k/m = (2.15 +/- 0.32) x 10(-3)m-1 and ar = Fr/m = (3.76 +/- 0.18) x 10(-2)ms-2, close to other values from the literature. The curves in the phase plane (velocity vs acceleration) and the small residual sum of squares indicated the validity of the theory. The towing experiments were not congruent with the coasting down experiments. Higher values of the air friction were found, probably due to turbulence of the air.

Forces acting on the forearm and hand during swimming can be decomposed into drag forces and lift forces. In this study drag and lift forces were measured on two models of a human hand and forearm when towed in a towing tank. To compare the results of models with different size at different velocities force data were normalized to drag and lift coefficients (Cd and Cl). Influence of the orientation of the model with respect to the flow, velocity, size of the model and the relative contribution of the hand and forearm on Cd and Cl were studied. The orientation of the model with respect to the line of motion was varied by rotating the models around three axes, and quantified using the angle of pitch (AP: the angle between the hand plane and flow) and the sweep-back angle (SB: the orientation of the flow vector when projected on the hand plane). Cd was maximal when the plam of the hand is almost perpendicular to the flow (AP = 65°, SB = 342°). Cl shows maximal values at two different orientations: with the hand in a thumb-leading position, AP = 31°, SB = 358°, and with the hand in a little finger-leading position, AP = 48°, SB = 193°. The orientation of the hand was very critical in generating lift forces. By contrast, the influence of velocity and size of the model on the values of Cd and Cl was limited. The relative contribution of the hand and forearm on Cd and Cl was examined by varying the immersion depth of the model. In the experiments where only the hand was towed Cd was about the same as for the condition where hand and forearm together were towed. Cl reached the highest values in the experiments where only the hand was towed. The hands are the main contributors for the generation of lift force.

A longitudinal analysis of a group of speed skaters was done to identify the performance-determining factors for a successful speed skating career. This paper presents both the physiological and anthropometric results of this longitudinal study. Twenty-four athletes from the Dutch National Junior Speed Skating Team were followed from age 16-17 yr to age 20-21 yr. During the development from junior to senior speed skater, a number of anthropometric and physiological variables changed. There were no differences between successful and unsuccessful speed skaters from an anthropometric perspective; consequently, it was not possible to distinguish successful from unsuccessful athletes on anthropometric grounds. The longitudinal data showed that at a younger age the successful speed skaters had similar oxygen consumption, mechanical efficiency, and power output values compared with the unsuccessful speed skaters. Later in the study, successful speed skaters distinguished themselves by the ability to produce higher power output values. There were no anthropometric or physiological relationships found in this study on which performance at the age of 20-21 yr could be predicted with measurements at a junior age.

Cycling performance is affected by the interaction of a number of variables, including environment, mechanical, and human factors. Engineers have focused on the development of more efficient bicycles. Kinesiologists have examined cycling performance from a human perspective. This paper summarizes only certain aspects of human ergonomics of cycling, especially those which are important for the recent current research in our departments. Power is a key to performance of physical work. During locomotion an imaginary flow of energy takes place from the metabolism to the environment, with some efficiency. The 'useful' mechanical muscle power output might be used to perform movements and to do work against the environment. The external power is defined as the sum of joint powers, each calculated as the product of the joint (net) moment and angular velocity. This definition of external power is closely related to the mean external power as applied to exercise physiology: the sum of joint powers reflects all mechanical power which in principle can be used to fulfil a certain task. In this paper, the flow of energy for cycling is traced quantitatively as far as possible. Studies on the total lower limb can give insight into the contribution of individual muscles to external power. The muscle velocity (positive or negative) is obtained from the positions and orientations of body segments and a bar linkage model of the lower limb. The muscle activity can be measured by electromyography. In this way, positive and negative work regions in individual muscles are identified. Synergy between active agonistic/antagonistic muscle groups occurs in order to deliver external power. Maximum power is influenced by body position, geometry of the bicycle and pedalling rate. This has to be interpreted in terms of the length-tension and force-velocity-power relationships of the involved muscles. Flat road and uphill cycling at different saddle-tube angles is simulated on an ergometer. The measured pedal forces (magnitude and direction) are only dependent on the intersegmental orientation of saddle tube, crank position, upper and lower leg, and foot. The changed direction of the gravitational force with respect to the saddle-tube does not interfere with the co-ordinated force production pattern. During locomotory cycling at constant speed the external power is mainly used to overcome the aerodynamic friction force. This force and the rolling resistance are determined by coasting down experiments, yielding the external power.(ABSTRACT TRUNCATED AT 400 WORDS)

The purpose of this study was to describe the intermuscular coordination and power production for the constrained asymmetrical movement during skating the curves. Seven elite male speed skaters took part in the experiments. The speed skaters were simultaneously filmed from frontal and sagittal views. EMGs were obtained telemetrically and push-off force was registered with special skates. Inverse dynamic analysis yielded power production data, which differed for left and right leg. Marked differences were also found in intermuscular coordination of each leg. The activation patterns of the muscles were influenced by the asymmetrical nature and the typical body position during the speed skating movement. External power output was determined by three methods. The mean joint power output for left and right leg showed similar values as the external power output calculated from air and ice friction. These values were lower than the values predicted with a geometrical model for skating the curves.

In this study the gross efficiency of swimming was determined in a group of male (N = 6) and female (N = 4) competitive swimmers. The gross efficiency is defined as the ratio of the power output (W) to the power input (W). In a range of swimming velocities (0.95-1.6 m.s-1), the power input (rate of energy expenditure, 445-1137 W) was calculated from the oxygen uptake values (1.33-3.25 1 O2.min-1). The total power output (26-108 W) was directly measured during front crawl swimming using a system of underwater push-off pads instrumented with a force transducer (MAD-system). Using the MAD-system, the effect on total body drag due to the addition of the respiratory apparatus was evaluated to be negligible. The gross efficiency ranged from 5 to 9.5%. At equal swimming speed, the male competitive swimmers demonstrated a higher gross efficiency. However, this was due to the higher power output required by the male swimmers at a given speed. Gross efficiency was dependent on the absolute power output such that as power output increased so did the calculated gross efficiency. At the same power output, the values for the gross efficiency do not differ between the male and female competitive swimmers.

Mechanical characteristics of the sprint start in speed skating were measured during the 1988 Winter Olympic Games. From three-dimensional film analysis of the first 4 seconds of the male and female 500-m races, biomechanical variables were determined. The first strokes during the start appeared to be performed by a running-like technique. At a forward velocity of approximately 4 m/sec, the skaters are forced to change this technique to the typical gliding technique as used during speed skating at steady speed. In explaining the time differences on the first 100 meters of the 500-m speed skating race, the effectiveness of the push-off appears to be more important than the observed high power output levels.

The effect of a triathlon wet suit on drag was studied in 12 subjects (eight male, four female) swimming at different velocities (1.10, 1.25 and 1.50 m.s-1). The active drag force was directly measured during front crawl swimming using a system of underwater push off pads instrumented with a force transducer (M.A.D. system: 6). Measurements were made when swimming over the system with and without a wet suit. A 14% reduction in drag (from 48.7 to 41.8 Newtons) is found at a swimming velocity of 1.25 m.s-1, which is a typical swimming speed for triathlon distances. At 1.50 m.s-1 a reduction in drag of 12% was observed, which suggests that the wearing of such a suit might be beneficial in conventional swimming events. The reduction in drag can explain the higher swimming velocities observed in triathletes using a wet suit. The effect of the reduction is probably largely due to an increased buoyancy inducing less frontal resistance. However, since the effect of the suit on the lighter female swimmers was not different from the effect on the heavier male swimmers, a reduction in friction drag and drag coefficient may also be significant.

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.

The improvement of electromyographic (EMG) devices for the detection of electric potentials produced in voluntary complex movements and the evolution of methodological approaches to data acquisitio...

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.

Characteristics of stroke mechanics of elite and trained speed skaters were measured during the skating of curves. Film and video analysis from the 5000-meter races at the Dutch National Championships yielded biomechanical variables that were correlated to performance. There are fundamental differences in push-off mechanics between skating the straight parts and skating the curves. The left stroke shows a more powerful push-off in the curve, caused by a greater push off angle compared to the right leg. The high speed and power output of the better skaters is a result of a high amount of work per stroke, caused by a short and effective directed push-off. These results strongly support the previous finding that skaters of different performance levels can be distinguished by differences in amount of work per stroke and not by differences in stroke frequency.

The mechanics of speed skating, as many other endurance sports, can be described by an energy flow equation. With such an equation the influence of suit, local pressure, altitude, shielding, and body position on speed is predicted. Next to these model predictions, the peculiar properties of the skating technique are discussed and their practical implications for skating the straight parts and the curves are indicated.

In speed skating, performance is related to the product of the amount of work per stroke and the stroke frequency. Work per stroke is dependent on the component of the push-off force in the direction perpendicular to the gliding direction of the skate. The push-off force at different velocities was measured in three trained speed skaters. The results showed that the peak push-off force and mean force do not change at different velocities, and that the stroke time was decreased at higher velocities. It can be concluded that these speed skaters regulate their velocity not by changing the push-off force but by changing their stroke time. The shape of push-off–time curves is dependent on push-off technique and differs during straight lane and curve skating.

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.

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.