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

Methods of examining immune function include a charting of susceptibility to infections, differential blood counts or lymphocyte counts, and measures of cell proliferation and immunoglobulin synthesis in response to external mitogens. The reported acute response to exercise is transient and quite variable, depending upon the type of exercise, the immunological methodology used, the intensity of effort relative to the fitness of the individual, and the timing of observation. A leucocytosis, a granulocytosis, a small lymphocytosis, and a decrease in the proportion of T to B cells reflect mainly changes of blood volume, demargination, and migration of cells. Lymphocyte subsets show a decreased helper/suppressor cell ratio and an increase of natural killer cells. Because of the lymphocytosis, mitogens induce an increased overall cell proliferation, but proliferation for a given number of cells is decreased. Prolonged exercise leads to a decrease of serum and salivary immunoglobulin levels. Soluble factors such as interleukin-1 and interferon are increased by a bout of exercise. Cross-sectional comparisons and training experiments suggest that under resting conditions well-conditioned individuals show some lymphocytosis, increased natural killer cell activity, higher levels of interleukin-1, and possibly an enhanced reaction to mitogens. Moderate training does not greatly change exercise responses at a given fraction of maximal effort. Excessive training suppresses immune function, but the changes are small, variable, and thus difficult to relate to overtraining. Moreover, because of their transient nature, they have only a limited influence upon the risks of infection or cancer.

This paper examines from a sociological and an ethical standpoint the problem of steroids in sport and competition. After a sociological analysis of some key ideological, social, political, and economic issues related to drugs in sport, we address the question of whether ethically we wish these developments to continue along the same path. A final analysis of the nature of the "authentic practice" makes the distinction between the practice itself with its intrinsic search for excellence and the organizations that sustain the practice but are essentially and necessarily concerned with extrinsic rewards from winning--money, power, status. Priorities have to be reexamined in light of certain fundamental ethical principles.

In order to study the movement pattern of soccer players, 14 top-level players were filmed during several competitive matches. In addition, the relationship between the observed activity during match play and blood lactate values was examined. The mean distance covered during competitive matches was 10.80 km, and the average individual difference between matches was 0.92 km, with no difference in regard to high intensity activities. Midfielders covered a 10% longer (p less than 0.05) distance (11.4 km) than defenders and forwards, with no difference concerning high intensity running. There was a significant correlation (r = 0.61, p less than 0.05) between the amount of high intensity running during the match and lactate concentration in the blood. The results suggest that high intensity running can be used for making comparisons in soccer and that the interpretation of blood lactate in soccer is limited to giving an indication of the type of activity that has been carried out a few minutes before sampling.

This study describes teaching and learning processes during a series of soccer training sessions. The predetermined course content formed the initial practicum for volunteer coaches who were in the first stage of their training. In general, the players demonstrated patterns of motor behaviour favourable to their motor learning. The coaches adopted most of the effective behaviors that had been recommended during the theoretical portion of their preparation. These observations tend to indicate the usefulness of having volunteer coaches participate in a practicum as part of their preparation, in order to improve the effectiveness of their subsequent instruction. Such instruction is likely to be even more effective if the practicum is based on training sessions of predetermined content.

The effects of 50 depth-vertical jumps (DJ) on counter-movement vertical jump (CMJ), squat jump (SJ), and DJ, isometric knee extension force (MVC), and patellar tendon response were examined in 12 men. There was no reduction in the height of the 50 DJs, but the contact time lengthened by 16%. Height of CMJ and DJ did not change after the 50 DJs, but the activity duration of the leg muscles averaged 13.2% longer. Conversely, height of SJ declined by 11.3%. MVC decreased by 20.1%. No changes occurred in reflex latency and peak-to-peak duration of the compound muscle action potential (AP), but reflex time, AP duration, and AP amplitude increased by 6.4, 6.1, and 23.3%. Thus, subjects compensated for the loss of voluntary force by lengthening the activity duration of the prime movers, potentiating muscle fiber action potentials, and/or enhancing muscle spindle sensitivity.