The force–time profile of elite front crawl swimmers

Abstract

In this study, we used recently developed technology to determine the force–time profile of elite swimmers, which enabled coaches to make informed decisions on technique modifications. Eight elite male swimmers with a FINA (Federation Internationale de Natation) rank of 900+ completed five passive (streamline tow) and five net force (arms and leg swimming) trials. Three 50-Hz cameras were used to video each trial and were synchronized to the kinetic data output from a force-platform, upon which a motorized towing device was mounted. Passive and net force trials were completed at the participant's maximal front crawl swimming velocity. For the constant tow velocity, the net force profile was presented as a force–time graph, and the limitation of a constant velocity assumption was acknowledged. This allowed minimum and maximum net forces and arm symmetry to be identified. At a mean velocity of 1.92 ± 0.06 m · s^?1, the mean passive drag for the swimmers was 80.3 ± 4.0 N, and the mean net force was 262.4 ± 33.4 N. The mean location in the stroke cycle for minimum and maximum net force production was at 45% (insweep phase) and 75% (upsweep phase) of the stroke, respectively. This force–time profile also identified any stroke asymmetry.     

The 1985 C. H. McCloy Research Lecture Practical Problems in Exercise Physiology Research

Abstract

This paper examines the contribution of exercise physiology research to improvements in sports performance. By using illustrations from studies on competitive swimmers, attempts have been made to show the need to develop tests that evaluate the factors essential for success in sports. Such testing should be used to describe the strengths and weaknesses of the athlete, and to offer the athlete and coach valid information to gauge the benefits of training. Aside from the value of monitoring the adaptations to sports training, the primary role of physiological research in sports should be to solve problems that will ultimately aid athletes to achieve their full potential. This paper will conclude with examples of problem solving research and its contribution to performance.     

Estimation of the energy loss at the blades in rowing: Common assumptions revisited

Abstract

In rowing, power is inevitably lost as kinetic energy is imparted to the water during push-off with the blades. Power loss is estimated from reconstructed blade kinetics and kinematics. Traditionally, it is assumed that the oar is completely rigid and that force acts strictly perpendicular to the blade. The aim of the present study was to evaluate how reconstructed blade kinematics, kinetics, and average power loss are affected by these assumptions. A calibration experiment with instrumented oars and oarlocks was performed to establish relations between measured signals and oar deformation and blade force. Next, an on-water experiment was performed with a single female world-class rower rowing at constant racing pace in an instrumented scull. Blade kinematics, kinetics, and power loss under different assumptions (rigid versus deformable oars; absence or presence of a blade force component parallel to the oar) were reconstructed. Estimated power losses at the blades are 18% higher when parallel blade force is incorporated. Incorporating oar deformation affects reconstructed blade kinematics and instantaneous power loss, but has no effect on estimation of power losses at the blades. Assumptions on oar deformation and blade force direction have implications for the reconstructed blade kinetics and kinematics. Neglecting parallel blade forces leads to a substantial underestimation of power losses at the blades.     

Time Needed to Change the Isometric Force Production of a Response

Abstract

This study investigated the time needed to change a motor program that specified the elbow flexor muscles to gradually increase the isometric force production from 15% to 75% of one's maximum voluntary contraction (MVC). A double-stimulation paradigm was used with the restriction that subjects (N = 12) be at 15% of their MVC before the presentation of the first stimulus. Subjects reacted to the first stimulus (randomly presented) by gradually increasing their isometric force from 15% to 75% of their MVC and then reacted to the second stimulus by altering the force production in one of four ways: (a) increasing the force to the 75% level rapidly instead of gradually, (b) discontinuing the increase and maintaining the level of force attained, (c) discontinuing all force production, or (d) reversing the direction of force so that it is produced by the elbow extensors. The data revealed that more time was needed to increase the force rapidly than to perform any of the other three conditions.     

Measurement of active drag during crawl arm stroke swimming

In order to measure active drag during front crawl swimming a system has been designed, built and tested. A tube (23 m long) with grips is fixed under the water surface and the swimmer crawls on this. At one end of the tube, a force transducer is attached to the wall of the swimming pool. It measures the momentary effective propulsive forces of the hands. During the measurements the subjects’ legs are fixed together and supported by a buoy. After filtering and digitizing the electrical force signal, the mean propulsive force over one lane at constant speeds (ranging from about 1 to 2 m s^‐1) was calculated. The regression equation of the force on the speed turned out to be almost quadratic. At a mean speed of 1.55 m s^‐1 the mean force was 66.3 N. The accuracy of this force measured on one subject at different days was 4.1 N. The observed force, which is equal to the mean drag force, fits remarkably well with passive drag force values as well as with values calculated for propulsive forces during actual swimming reported in the literature. The use of the system does not interfere to any large extent with normal front crawl swimming; this conclusion is based on results of observations of film by skilled swim coaches. It was concluded that the system provides a good method of studying active drag and its relation to anthropometric variables and swimming technique.     

Maximal isometric force and muscle cross‐sectional area of the forearm in fencers

The maximal isometric force (MIF) of a muscle is directly related to its cross‐sectional area (CSA). Strength training produces an increase in muscular force while muscular hypertrophy becomes appreciable at a later time; in asymmetric sports, training causes significant increases in force and muscular mass of the dominant limb of the athlete. The aim of this study was to analyse the differences in muscular force and trophism between the dominant and non‐dominant forearms in fencers and in controls.

The data of 17 male distance runners (age 21.4±2.4 years, body mass 74.0±5.0 kg, height 180 ± 6 cm) were compared with those of 58 male fencers (age 23.0 ± 6.7 years, body mass 71.9±9.3 kg, height 178 ± 7 cm) drawn from the ranking lists of the National Fencing Committee. They trained for a mean of 11.4±6.0 (range 2–36) years, commencing at 10.7 ± 4.5 years of age.

Cross‐sectional area (muscle plus bone) was estimated in the dominant and non‐dominant forearm using a simplified anthropometric method. Maximal isometric force was determined using a mechanical handgrip dynamometer. The differences in CSA and isometric force between the two limbs and between fencers and controls were tested using paired and unpaired Student's i‐tests, respectively. Significant differences in CSA and maximal force were observed between the dominant and non‐dominant forearm in fencers (both P<0.001) and in controls (P<0.005 and P<0.001, respectively). The fencers showed a greater CSA (P<0.001) and force (P< 0.001) in the dominant forearm compared with the control group. Furthermore, the differences between the dominant and non‐dominant limb of the fencers were significantly greater than the differences between the dominant and non‐dominant limb of the controls (P<0.001 for CSA and P<0.05 for force). No significant differences in stress ratio (force/CSA) were obtained in either group.

The results of this study suggest that asymmetric sports training at submaximal intensities produces significant asymmetries in force and CSA which are independent of technical level and years of training. Despite this, the force/CSA ratio is constant and independent of training.     

On the Swing Mechanics of a Matched Set of Golf Clubs

Abstract

Some golf equipment manufacturers produce matched sets of golf clubs using an empirical method based on first moments of mass as well as shaft stiffness, whereas others claim to match sets on the basis of moment of inertia and dynamic considerations of shaft stiffness. This paper considers the significance of the mass distribution feature of club matching with regard to the parameters relating to physical exertion by the golfer. It is shown that dynamic considerations require a mass variation through the set almost identical to the variation prescribed by static swing weighting, and that conventionally static balanced golf clubs differ in mass by less than five percent from that suggested using a dynamic balance. It is also shown that the maximum driving force is relatively the same for a specific golfer using a variety of golf clubs but that the driving forces of the professionals were higher than those recorded for the amateurs.     

中西绘画语言的相关性研究

绘画就是学会去观察并给予形状、位置、方向以及所有其他视觉关系同样的关注程度,而不是去辨认实物并把它转换成文字。绘画需要用视觉思考,而不是用语言文字思考。中国画是中华民族文化智慧的结晶,近现代以来,无论是对西画人物造型中比例、透视等的吸纳,还是中西方理论的交融,对中国画造型艺术的研究与改良从未间断过。在西学渐进的今天,借鉴西方造型艺术的科学性同时,保持中国传统文化的特色,建立自己的造型艺术体系对中国画造型及发展具有重要意义。中西方绘画的造型语言表达方式虽不相同,但对造型规律的某些认识及目的却有着共性,无论中西方绘画造型的差异如何,通过对造型中运用的艺术技巧及表现手段相关性比较,对绘画造型的理论研究与实践都具有深远的影响。     

浅议钢琴教学中学生音乐表现力的培养

钢琴演奏不仅只是准备的弹出的音符,也同时是一门有血有肉的艺术表演。但是许多学生在钢琴的演奏过程中显得乏味枯燥,没有体现出音乐的表现力,感染不了听众。因此可知,音乐的表现力在钢琴演奏中的重要性,本文就学生的钢琴音乐表现力方面提出培养的方法。