Canadian journal of sport sciences = Journal canadien des sciences du sport最新文献

Children have long been suspected of having a diminished capability of responding to endurance training with improvements of maximal oxygen uptake compared to adults. However, studies examining the trainability of children have been beset with methodologic flaws that have precluded firm conclusions about such adult/child differences. Most studies in children that have involved adequate intensity, type, and duration of training have demonstrated the same qualitative changes as would be expected from adult subjects. Some information suggests that children may need a greater exercise intensity than adults to trigger cardiovascular adaptations to training. Other data raise questions regarding differences in autonomic influences on the heart and myocardial function in children that could relate to age-dependent responses to training.

The accuracy of the Caltrac accelerometer was studied in 28 young (26.1 +/- 1.1 yrs) and 28 older (64.8 +/- 1.0 yrs; M +/- SEM) men and women to determine its usefulness as an activity monitor for young and older adults. Oxygen uptake was measured by indirect calorimetry while subjects walked on a motorized treadmill at six different speeds while wearing an accelerometer on the hip and on the upper back. The test-retest reliability of the Caltrac was r = .95 and r = .98 for young and older subjects, respectively. In the young group, activity counts correlated highly to net caloric expenditure (absolute minus estimated resting expenditure) (hip vs. kcal/kg: r = .89; back vs. kcal/kg: r = .88) when averaged across speeds, but the relationship was only moderate (back: r = .51; hip: r = .46) when the influence of speed was removed. In the older group the correlations were considerably weaker (back: r = .73; hip: r = .25), and essentially zero when the influence of speed was removed. These data indicate that the Caltrac is a highly reliable accelerometer that is useful for assessing qualitative differences in the level of physical activity among groups, but it lacks accuracy in quantifying energy expenditure in individuals, especially in older adults.

This study examined the relationship among three predictive tests of aerobic capacity when analyzed within and across gender. Sixty-three active college students (37 males, 26 females) performed the multistage 20-metre shuttle run (SR), the Canadian Aerobic Fitness Test (ST), and the 1.5-mile run (DR). Predicted VO2max (ml.kg-1 x min-1) scores were obtained for each subject. Significant correlations were found among the VO2max results on all possible pairings of tests analyzed as a group, and by gender (p < .001) except for the females' SR and ST pairing (p > .05). One-way analysis of variance was performed for each of the three subject pools with significant F values for the grouped (F = 5.8, p < .01) and male (F = 30.7, p < .01) samples. Tukey HSD post hoc comparison identified significant differences among the SR and ST, and ST and DR VO2 max scores for both samples. However, there were no significant differences between the cell means when females were analyzed separately.

Resistance training, under conditions of high intensity and volume loading, is effective in increasing strength in pre- and early pubertal children. The mechanisms underlying strength gain with resistance training in this population have not been established unequivocally. However, resistance training appears to have little if any effect on muscle size (hypertrophy), but it has resulted in neurological (percent motor unit activation and increased integrated EMG activity) changes and changes in intrinsic muscle function (twitch torque), which could account for part of the training-induced increases in voluntary strength. Changes in motor skill coordination (synchronization of muscle action) probably also contribute substantially to resistance-training-induced strength increases in children, particularly for multijoint, complex strength manoeuvres. Most, but not all, studies indicate that pre- and early pubertal children make similar relative strength gains compared to adolescents and adults, but usually demonstrate smaller absolute strength gains following training. Training-induced strength gains appear to decay during detraining, and maintenance training consisting of only one training session per week appears to be ineffective in preserving prior strength gains.

This study evaluated the effect of time of day on performance of high-intensity, constant-power cycle ergometry by both men and women. Subjects performed all-out cycle ergometer tests in the morning and in the afternoon in randomized order. For all tests, work rate was a constant 5.0 W.kg-1 (women, n = 6) or 6.0 W.kg-1 (men, n = 8). Total work performed was 9.6% greater in the afternoon (mean +/- SE, 348.8 +/- 40.6 J.kg-1) compared to the morning (318.2 +/- 39.5 J.kg-1). The greater amount of work in the afternoon was associated with a 5.1% higher aerobic power and a 5.6% larger anaerobic contribution. There was no interaction between gender and the effect of time of day on the aerobic or anaerobic contributions. These results provide evidence of a circadian rhythm in aerobic and anaerobic responses to high-intensity short-duration exercise, in women as well as in men.

During semistructured interviews, coaches and players have expressed their perception of violence in hockey through several game situations. The responses reveal that coaches disapprove and even sanction players receiving too many useless penalties, but occasionally congratulate them for a penalized action executed to save a goal. During matches, verbal intimidation is high and not always criticized, especially when it causes the opponent to lose concentration and take a penalty. Body checks have been identified as a main generator of frustration and lack of discipline among players. Data analysis suggests two interventions in training programmes for coaches: the development of teaching material on body checking and on individual counselling techniques to impart sportsmanship attitudes to young players.

This study investigated the criteria that coaches of university women's basketball teams used when calling a timeout. Thirty-five of Canada's university coaches of women's basketball responded to Likert scale questions rating the importance of six factors in calling a timeout. Differences due to sex, coaching experience, and team success indicated that some factors were perceived to influence timeout decisions more than others. Specifically, responses from female coaches, coaches with less than 5 years of experience, and coaches whose teams were ranked in the CIAU's top 10 within the last 3 years indicated that they used offensive game events more frequently than their counterparts did. Interactions were also found for Experience x Gender and Experience x Gender x Success in the way that offensive game events were perceived, and for gender and success for the factor attentional state of players.

The influence of exercise training on body composition changes in children is examined in terms of muscle, bone, and fat development. Because of the inexact body composition methodologies in general use and an over-reliance on the two-components system--fat and fat-free body--the extent of changes especially for muscle and bone with exercise training has not been well quantified. With the recent development of new methodologies these limitations may be overcome. The relationship of body composition to health related fitness is also explored with an emphasis on establishing fitness standards for body fatness and the need for research on the etiology of lower back pain and osteoporosis.

The positive influence of physical activity on chronic disease has been well established for the adult population. Much less is known about the relationship between physical inactivity and risk factors for coronary heart disease in children. It has not been clearly established how active children are, nor do we know the factors that determine physical activity patterns among youth. The purpose of this brief review is to describe different techniques used to assess physical activity that are consistent with the operational definition of physical activity. Descriptive information from the National Children and Youth Fitness Studies related to children's level of physical activity is provided which indicates that children are physically active. Nevertheless, it is suggested that the importance of regular physical activity should be emphasized to our youth to promote lifetime activity participation for long-term health and well-being.