Showing papers in "Journal of Sports Sciences in 1987"

Biomechanical aspects of playing surfaces

Abstract: The purpose of this paper is to discuss some biomechanical aspects of playing surfaces with special focus on (a) surface induced injuries, (b) methodologies used to assess surfaces and (c) findings from various sports. The paper concentrates primarily on questions related to load on the athlete's body. Data from epidemiological studies suggest strongly that the surface is an important factor in the aetiology of injuries. Injury frequencies are reported to be significantly different for different surfaces in several sports. The methodologies used to assess surfaces with respect to load or performance include material tests and tests using experimental subjects. There is only little correlation between the results of these two approaches. Material tests used in many standardized test procedures are not validated which suggests that one should exercise restraint in the interpretation of these results. Point elastic surfaces are widely studied while area elastic surfaces have received little attentio...

Optimal duration of static stretching exercises for improvement of coxo‐femoral flexibility∗

Abstract: The purpose of this study was to determine the effect of different durations of static stretching exercises on coxo‐femoral (hip) flexibility. The experimental group, consisting of 20 sedentary women (20–30 years of age), participated in an exercise programme of static stretching exercises with emphasis on the hamstring muscles. The programme lasted for 10 weeks and consisted of two 50‐min sessions per week. A control group of 15 sedentary women did not participate in the programme. Hip flexibility was determined before, during and at the end of the programme by means of a goniometric measuring technique developed by us and described elsewhere. Three sub‐groups were formed, each following the same programme except that the duration of the static stretch differed (group 1,10 s; group 2, 20 s; group 3, 30 s). The ANOVA tests showed that for all groups ‐ the control group excepted ‐ the hip flexibility had improved significantly after 10 weeks (P <0.05). No significant differences in hip flexibility...

The skinfold: Myth and reality∗

Abstract: The interest in skinfolds, given the easy accessibility of the subcutaneous layer and its non‐invasive nature, has led to a proliferation of ‘skinfold’ applications and formulae. To obtain data to investigate body composition methods, particularly the use of skinfolds, two separate cadaver dissection studies were undertaken, allowing for the analysis of data from 32 cadavers with more than 2500 data per cadaver. In addition, 40 elderly ‘living’ subjects of the same age range were compared with the cadaver population and no significant macro‐morphological differences were found. The available data have clearly demonstrated that skinfold compressibility is by no means constant. Adipose tissue patterning by assessment of skinfold thickness using calipers and incision confirms significant sex differences but emphasizes the neglected importance of skin thickness. It appears that the best adipose tissue predictors are different from those used in general. Also the problem of estimating body fat content...

Bone dynamics: Stress, strain and fracture

Abstract: Bone is a dynamic tissue whose functional mass is controlled by the balance between the endocrine drive towards bone resorption and the mechanically‐engendered drive towards bone formation. Strain is the key intermediate variable between loading forces and bone remodelling. Animal studies have shown that static loading of bone has no osteogenic effect; bone loss occurs as if there were no loading at all. However, dynamic loading, that is, cyclic change in internal strain, is strongly osteogenic, with relatively few cycles required for maximum effect. However, if a sufficient number of cycles is applied, repetitive loading can cause stress fractures. This number decreases as internal strains increase. Thus strain redistribution within bone, as caused by muscle fatigue or improper sports equipment, is a significant cause of fracture.

A study of the forces exerted by an oarsman and the effect on boat speed.

Abstract: A model of the motion of a single‐scull rowing hull has been developed and verified against rowing performance data. The model was then used to explore the effect of changes in the cyclic rowing force on the boat speed. The calculations have shown that the shape of the rowing force curve and the proportion of recovery time in the total stroke can have an important effect on the boat speed. It has also been shown that a study of the fluid mechanics of the oar blade would be advantageous in determining whether a reduction in the power wasted can be obtained by changing the ratio of rowing force to normal force.

The effect of training on aerobic power characteristics of young cross-country skiers.

Abstract: The influences of growth, training and various training methods were investigated by analysing long‐term training effects in young cross‐country and biathlon skiers (n = 129). Some athletes (n = 49) were studied six times in three years and some at least once a year during a four year period (n = 48). During three summer training periods skiers emphasized either intensive training or distance training or continued to train normally. The results indicated that maximal oxygen uptake (VO2 max) and heart volume increased between 15 and 20 years of age and the most significant changes in heart volume were observed between 16 and 18 years of age. International level skiers were able to increase their VO2 max and heart volume even after 20 years of age. Anaerobic threshold (AT, ml kg‐1 min‐1) increased like VO2 max but when expressed as a percentage of VO2 max, the AT was similar in every age group over 16 years of age. Intensive training at the intensity of anaerobic threshold or higher was observed to...

Specific muscular development in under‐18 soccer players

Abstract: A comparison of the under‐18 (U‐18) and under‐16 (U‐16) squads of the Canadian national soccer team with a representative sample of Canadians (Canada Fitness Survey, 1983) showed a tendency for the development or selection of the older players in teams of stature (U‐18, 175.8 cm; U‐16, 171.1 cm; CFS, 170.9 cm) and lean body mass (U‐18, 63.4; U‐16, 57.9; CFS, 54.2 kg). The larger lean mass of the older players could not be explained simply by size. The U‐18s also showed greater isokinetic leg extension force (particularly for rapid movements) and explosive strength (vertical jump) relative to the younger players, although the knee extension force was less than in some classes of athlete. Part of the gain in mass seems due to local training of the hip and leg muscles and part to a more general muscular development. Contrary to some reports, the hip flexibility of the Canadian players (sit and reach test) was greater than for a national sample; this may be important in avoiding soft tissue injuries ...

Standard score assessment on physique and performance of Brazilian athletes in a six tiered competitive sports model

Abstract: The use of large cross‐sectional norms on Brazilian children and youths aged 7 to 18 years within a six level competition plan helps to assess development status and monitor change. Non‐athletic prototypes for comparative purposes are illustrated by the use of the lowest competitive level of 18 year olds to assess differences from internationally elite players. The purpose of this study was to establish the efficacy of this practice in male and female basketball and volleyball samples. Comparisons were made on 11 anthropometrie and performance variables using percent difference (%?) and z‐score values. The z‐scores were highest for height, weight, and jumping ability in both sports groups. The volleyball players were the more linear in physique and the better jumpers. Related to their prototypes the female basketball players had the highest estimated VO2 max(ml kg‐1 min‐1), and the best values of anaerobicpowermeasures.lt is concluded that differences in physique and performance at various levels...

Applied physiology of speed skating

Abstract: 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.

Skiing accidents in the past 15 years

Abstract: For the last 15 years a statistical analysis of distances skied and of alpine skiing accidents has been performed in the Davos‐Klosters skiing area, a ‘closed’ skiing area, where every skier has to return from the top to the bottom station. Distance skied is measured by vertical drop in 106 km determined by calculations from frequency surveys by lift‐operators. About 2.5 million km per season have been skied during the past years, a number remaining constant for the last 15 years. In the same time the requirement for rescue‐transports in this area has shown a decline of 46% to 288 transports per season due to a decrease of the number of injuries with initial immobilization. Therefore the so‐called transport‐quotient (one rescue‐transport per 104 km of vertical drop skied) has decreased from its initial value of 4 to 1 per 104 km. During the same time all winter sport injuries were analysed at the hospital of Davos. About 90% are injuries caused by alpine skiing resulting in a total of 17 246 alpi...

Physical structure of winter sports athletes

Abstract: A review of the results concerning the body size, growth, maturation, shape, composition, and strength of ice hockey players, cross‐country skiers, alpine skiers, ski jumpers and Nordic combined skiers is presented. The comparisons of the results in body height, weight, somatotypes, percent fat, LBM and hand grip from various authors are made. Also the differences between ice hockey players and skiers of all disciplines are shown. The review covers all the available results. It may be concluded that the elite athletes in each studied sport form a highly select group which has, from the biomechanical point of view, the best physical structure for their sport discipline.

Iron status in Winter Olympic sports

Abstract: Iron status was surveyed amongst 92 Winter Olympic sport athletes from Nordic and Alpine skiing, figure and speed skating and ice hockey. Haemoglobin and serum ferritin values were obtained by physicians as part of a monitoring programme, since iron deficiency would have an adverse effect on maximal performance. Four (7%) of 56 men were anaemic (Hb < 14.0 gdl‐1) and three (8%) of 36 women had haemoglobin values less than 12.0 gdl‐1. Nine men (16%) and 14 women (39%) had prelatent iron deficiency (serum ferritin < 30 ng ml‐1). Ice hockey had the lowest while Nordic skiing had the highest incidence of sub‐optimal iron status. A total of 50% of Nordic women skiers had prelatent iron deficiency and 7% were anaemic. An equal percentage of women speed skaters were low in serum ferritin as well. Only one of 20 male ice hockey players was low in serum ferritin. These results suggest there would be value in instituting screening procedures for iron status in Winter Olympic Sports.

Standardization indices of cardiac hypertrophy in weight lifters.

Abstract: In order to investigate further the use of standardization procedures to determine training effects on cardiac dimension and function, two groups of subjects were analysed noninvasively. A control group of sedentary men (n = 7) and an experimental group of weight lifters (n=12) volunteered for a standard M‐mode echocardiographic assessment. Indices of cardiac function as well as absolute left ventricular dimensions and left ventricular mass were similar between the groups. Standardizing for body surface area and body weight separated the groups. The weight lifters were shown to have a more muscular left ventricular posterior wall. The weight lifters also demonstrated a dilated left ventricle when indexing for body surface area. All other dimensional and volumetric indices were non‐significant. The present investigation underlines the need for matching control and experimental groups to biometric variables in order to avoid misinterpreting cardiac enlargement. There is evidence for a true relative...

Bioenergetics of ice hockey: Considerations for fatigue

Abstract: This paper addresses the potential role of fatigue as a factor contributing to the deterioration of high level performance in ice hockey. Particularly, attention is given to the general description of different types of fatigue and the mechanisms underlying each type. Data have been presented illustrating the nature and extent of different types of fatigue in ice hockey practices and games. A bioenergetic description of ice hockey is presented and implications drawn as to the role of metabolism in causing specific fatigue patterns observed in ice hockey. The paper concludes with an overview of the inter‐relationship between the characteristics of the performer, the environment and the game itself.

Anthropological status of international calibre speed skaters

Abstract: The purpose of the study was to determine the anthropological status of elite male and female speed skaters, who were members of the 1985–7 Canadian national teams. The data were compared to those for a control group of University students. The subjects were 8 males and 6 females between 19 and 27 years of age. Nine breadth, 14 girth, 16 length and 15 skinfold measurements were used to compute parameters of body build and the composition; corrected diameters, masses, volumes and fat‐free volumes of the upper arm, forearm, thigh and calf. The speed skaters were found to be similar in body height and mass (males: 178 ± 7.6 cm and 75.5 ± 5.5 kg, females: 165.8 ± 3.8 cm and 62.3 ± 5.8 kg) to the student controls, but they had relatively and absolutely shorter legs and longer trunks. The speed skaters had a lower amount of body fat and higher FFM than their respective student controls and significantly greater relative (P ≤ 0.01) and absolute (P ≤ 0.05) total muscle mass. Analysis of composition withi...

Influence of single‐leg training on muscle metabolism and endurance during exercise with the trained limb and the untrained limb

Abstract: We have previously shown that single‐leg training results in improved endurance for exercise with the untrained leg (UTL) as well as for exercise with the trained leg (TL). The purpose of this study was to see whether the improved endurance of the untrained leg could be explained on the basis of changes in muscle metabolism. Exercise time to exhaustion at 80% of maximum oxygen uptake (VO2 max) was determined for each leg separately, pre‐ and post‐training. Muscle metabolite concentrations were measured pre‐ and post‐training in biopsy samples obtained immediately before this endurance test and at the pre‐training point of exhaustion (END1). After six weeks of single‐leg training endurance time was increased for both the UTL and the TL (UTL 34.0+16.4 min vs 97.9±26.3 min, P<0.01; TL 28.3 + 10.1 min vs 169.0 + 32.6 min, P < 0.01). No changes in muscle metabolite concentrations were found in resting muscle. Training increased muscle ATP (P <0.05) and glycogen (P <0.01) concentrations and decreased m...

Aspects of traumatology in ice hockey.

Abstract: Ice hockey is the fastest team game played and is also considered to be one of the roughest of all sports, with a high injury incidence. Injuries and their causes were recorded by the questioning of players in the first league of the Federal Republic of Germany. Eighty‐eight out of a total of 207 first league players were included in this study. Head injuries were found to occur most frequently: however, lesions of the shoulders and of the upper and lower extremities had a more detrimental effect. The links between causes and mechanisms of the different kinds of injuries make it clear that a marked tightening of the rules and an improvement in protective clothing would serve to reduce the incidence of injuries in ice hockey.

Changes in serum haptoglobin as an acute response to a marathon road race.

Abstract: In order to assess the possible occurrence of acute haemolysis with prolonged exertion, serum haptoglobin levels were determined from venous blood samples collected from eight male runners immediately preceding (PreRH), immediately following (PRH1), and 6 h following (PRH2) completion of a marathon road race. The subjects’ mean age, percentage of body fat, and maximum oxygen uptake (VO2max) were 46 ± 9 years, 12.1 ± 3.4% and 54.9 ± 8.4 ml kg‐1 min‐1, respectively. The mean race finish time for the subjects was 3:35 ± O: 18 h:min. The PreRH, PRH1 and PRH2 averaged 129 ± 18, 97 ± 48 and 86 ± 35 mg dl‐1 respectively. Significant differences of –32.5 mg dl‐1 between PreRH versus PRH1 and –42.5 mg dl‐1 between PreRH versus PRH2 were found. The difference between PRH1 and PRH2 of –10.6 mg dl‐1 was not significant. No significant correlations were found between the decreases in serum haptoglobin and VO2max or race finish time. The data suggest the occurrence of an acute haemolysis with performance of th...

Frequency and aetiology of injury in cross-country skiing.

Abstract: A comparative analysis was carried out on 1263 injured downhill skiers and 85 cross‐country skiers with regard to risk of injury, diagnosis, localization and age distribution. While 48% of the injuries to crosscountry skiers involved the upper extremities, 77% of the injuries to downhill skiers involved lesions of the leg. Contusions accounted for 31.8% in the case of cross‐country skiers, while 37.8% of downhill skiers suffered distortions, 22.8% sustained torn ligaments and 22.2% suffered fractures. A total of 57% of downhill skiers are under the age of thirty, while 87% of cross‐country skiers are at least 30 years of age. Female cross‐country skiers tend to suffer more injuries. The chief causes are falls on downhill slopes, but also on the level usually on icy or well‐trodden courses. Another course is the ski getting caught. Good equipment, a good state of fitness and preparation, protection against hypothermia, appropriate choice of cross‐country courses and cross‐country skiing lessons ar...

Two critical psychological components of ski racing: Fun and feelings

Abstract: The concepts of having fun and being aware of feeling states are presented as two critical factors in ski racing. First, the positive motivational characteristics of ‘fun’ are outlined. It is suggested that fun is not only a concept for young athletes but elite ones as well. Preliminary data based on a questionnaire, completed by the United States Alpine Ski Team and approximately 150 ski coaches, are presented. Second, the discussion on feelings refers to the mental programming of tactile sensations and determining one's emotional arousal (feeling state) prior to, and during, competition. Practical suggestions are made with regard to the psychological states and their effects on ski racing.