Biomedical subjects
Publications and source records attributed to D T Kirkendall.
Physical fitness is improved by manipulating the mode, frequency, intensity, and duration of exercise and its rate of progression. Well-documented guidelines can assist the primary care physician in outlining training programs for their healthy patients who wish to begin an exercise program to maintain or improve their physical fitness.
Improvement in cardiovascular fitness is related to the mode, frequency, duration, intensity, and rate of progression of exercise. These data suggest that dance as an activity for promoting fitness will improve aerobic and physical working capacity. The commercial classes studied were of short duration and relied on elevated intensity for improvement, whereas the classes for professional dancers were low in intensity and relied on frequency and duration for improvements. Other area studied were body composition and strength.
The traditional requirement for dancers to be lean coupled with the fact that dance is a nonendurance form of exercise makes it necessary for dancers, particularly females, to follow diets of relatively low caloric content. Food faddism and irrational use of nutritional supplements are common among dancers, who have little information about nutrition. Further investigation of the general medical and nutritional problems of dancers is needed, and the information from these studies should be incorporated into the curriculum of serious dancers.
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In this investigation, we determined the patterns of valgus laxity and acquired valgus laxity of the ulnar collateral ligament in the elbows of collegiate athletes involved in overhead and nonoverhead sports. Acquired valgus laxity of the elbow is defined as the differential amount of stress valgus opening between the dominant and nondominant elbows. Forty-eight asymptomatic male athletes involved in sports that require overhead arm movements (baseball, tennis, and swimming) and 88 asymptomatic male athletes involved in nonoverhead sports (track, lacrosse, fencing, and wrestling) underwent fluoroscan examination of both their elbows with (13 daN) and without (0 N) valgus stress. There were no statistically significant differences in the amount of valgus stress opening or in acquired valgus laxity between the two groups. In fact, 25% (34 of 136) of the athletes showed an acquired valgus laxity of more than 0.5 mm, and 51.5% (70 of 136) had an acquired valgus laxity that was actually negative. There was also no correlation between the number of years played and acquired valgus laxity. Our results show that acquired valgus laxity does not exist in asymptomatic athletes involved in overhead sports, and there is no threshold value of measurement indicative of acquired valgus laxity.
A unique aspect of soccer is the use of the head for directing the ball. The potential for resultant head injuries has been the focus of discussions worldwide. Prior work has attributed neuropsychologic deficits to the cumulative effects of heading, without evaluating concussion rates in soccer players. We prospectively studied the seven men's and eight women's varsity soccer teams in the Atlantic Coast Conference during two seasons to document concussion incidence. The 29 concussions diagnosed over the 2 years in 26 athletes, 17 (59%) concussions in men and 12 (41%) in women, resulted from contact with an opponent's head (8, 28%), elbow (4, 14%), knee (1, 3%), or foot (1, 3%); the ball (7, 24%); the ground (3, 10%); concrete sidelines (1, 3%); goalpost (1, 3%); or a combination of objects (3, 10%). Twenty concussions (69%) occurred in games; none resulted from intentional heading of the ball. The basic incidence was 0.96 concussions per team per season. The overall incidence was 0.6 per 1000 athlete-exposures for men, and 0.4 per 1000 athlete-exposures for women. By concussion grade, there were 21 (72%) grade 1, 8 (28%) grade 2, and no grade 3 concussions. These findings suggest that concussions are more common in soccer than anticipated and that acute head injuries may have potential for long-term neuropsychologic changes.
A unique feature of soccer is the purposeful use of the head for controlling, passing, and shooting a soccer ball. Some concern has been expressed in the literature on the cumulative effects of heading on soccer players. Certain neurophysiologic and neuropsychologic changes have been reported in current or retired players, with heading being blamed. A major factor that could influence some of the findings is a player's history of concussive episodes, which are known to influence brain function. These episodes can occur during aspects of the game other than heading. We interviewed all male and female soccer players (N = 137, average age = 20.5 years) who competed at the U.S. Olympic Sports Festival in 1993. The mechanisms of injuries, frequency, and sequelae were determined. There were 74 concussions in 39 male players (grade I = 50) and 28 concussions in 23 female players (grade I = 19). For the men, 48 of the 74 episodes were from collisions with another player. For the women, 20 of 28 were from such collisions. Headaches, being "dazed," and dizziness were the most common symptoms reported. Based on concussion history, the odds are 50% that a man, and 22% that a woman, will sustain a concussion within a 10-year period. The data indicate that concussions from player-to-player contact are a frequent hazard in soccer. Head injuries incurred this way may be more of an influence for published findings of physiologic and psychologic deficiencies than routine heading of the soccer ball.
Aging results in a gradual loss of muscle function, and there are predictable age-related alterations in skeletal muscle function. The typical adult will lose muscle mass with age; the loss varies according to sex and the level of muscle activity. At the cellular level, muscles loose both cross-sectional area and fiber numbers, with type II muscle fibers being the most affected by aging. Some denervation of fibers may occur. The combination of these factors leads to an increased percentage of type 1 fibers in older adults. Metabolically, the glycolytic enzymes seem to be little affected by aging, but the aerobic enzymes appear to decline with age. Aged skeletal muscle produces less force and there is a general "slowing" of the mechanical characteristics of muscle. However, neither reduced muscle demand nor the subsequent loss of function is inevitable with aging. These losses can be minimized or even reversed with training. Endurance training can improve the aerobic capacity of muscle, and resistance training can improve central nervous system recruitment of muscle and increase muscle mass. Therefore, physical activity throughout life is encouraged to prevent much of the age-related impact on skeletal muscle.