THE PHYSICIAN AND SPORTSMEDICINE - VOL 25 - NO. 9 - SEPTEMBER 97
A genetic link to boxing impairment?
Dementia pugilistica—a constellation of neurologic impairments that afflicts many longtime professional boxers—may have a genetic predisposition, according to preliminary research findings (1).
Neurologists Barry D. Jordan, MD, and Norman R. Relkin, MD, PhD, wondered why not all boxers suffer from cognitive deficits and other neurologic symptoms later in life. Jordan served as the ringside physician for fights featuring Sugar Ray Leonard, Evander Holyfield, Mike Tyson, George Foreman, and other boxers. "This made me suspect there might be some sort of genetic predisposition involved," says Jordan, adjunct associate professor of psychiatry at the Biobehavioral Research Center at the Charles R. Drew University of Medicine in Los Angeles. Relkin is director of the Memory Disorders Program and an associate professor in the Department of Neurology and Neuroscience at New York Hospital-Cornell University Medical College in New York City.
Jordan was also struck by the similarities between boxer's dementia and Alzheimer's disease, including neurofibrillary tangles and ß-amyloid plaque formations. When Alzheimer's disease investigators identified a certain gene that predisposed its carriers to late-onset familial and sporadic Alzheimer's disease, Jordan wondered if this same gene might influence the development of neurologic problems in susceptible prizefighters.
The gene in question is apolipoprotein APOE, which comes in three common alleles: APOE 2, APOE 3, and APOE 4. Alzheimer's researchers found that men and women who had at least one APOE 4 allele were significantly more likely than those without it to develop Alzheimer's disease at an earlier age. The APOE 3 allele, on the other hand, appeared to exert neutral effects, and the APOE 2 may actually afford its carriers some protection against Alzheimer's disease.
To see if this same correlation held with boxers, Jordan recruited 24 volunteer and 6 referred boxers aged 23 to 76. After determining their APOE genotype, Jordan, Relkin, and their colleagues analyzed each man on a 10-point chronic brain injury scale. Those who had abnormal scores were further classified as to whether their impairments were possibly or probably related to boxing. The investigators also determined each fighter's boxing exposure (number of bouts).
Of the 30 boxers studied, 11 showed no effects of chronic brain injury, 12 showed mild deficits, 4 were moderately impaired, and 3 were severely impaired. Perhaps not surprisingly, high-exposure fighters (12 bouts or more) were much more likely to be impaired than those who had fought fewer than 12 bouts. For the latter group, APOE genotype did not correlate with degree of impairment. In the high-exposure group, however, boxers having at least one APOE 4 allele showed significantly higher chronic brain injury scores than those lacking this allele. Moreover, all three men with severe impairment had at least one APOE 4 allele.
"There was also some suggestion that the APOE 2 may be protective," says Jordan, "but the sample size was too small to make this finding statistically significant."
The study raises significant ethical questions, not just for boxing but for other contact sports that involve repetitive head trauma. Even if further study proves the correlation, Jordan believes it would be hard to disqualify an athlete based on this gene alone. Instead, he says, the real value of APOE testing would be to better inform athletes who have the APOE 4 APOE gene about their increased risk and to alert physicians who care for them about the need for heightened vigilance.
Cross-training can lead to injuries
Cross-training breaks the monotony of practicing a primary sport, but it can also lead to injuries that interfere with participation in any sport. Sometimes cross-training pushes athletes to do too much, and the risks outweigh the expected benefits.
In the only known published study of documented cross-training injuries (1), 68 female collegiate swimmers were followed for 7 years. About the same number of injuries occurred during cross-training (55 or 44% of all injuries) as when swimming (56 or 45%), although the types of injuries differed. Swimming injuries mainly involved the shoulder (55% of all swimming injuries), whereas in cross-training injuries, the leg was the most common site (24% of all cross-training injuries). Running or sprinting accounted for 47% of the swimmer's cross-training injuries, and running stadium steps for 13%.
Swimmers were ideal to study because their primary sport depends mainly on upper body muscles not used in their cross-training activities, making it easier to identify the source of injury. Edward G. McFarland, MD, lead author of the study on swimmers, says clinical observations and anecdotal reports suggest that cross-training injuries to little-used bones and soft tissues occur in other sports, as well. Tennis players often strain their backs during weight lifting, for example, and football players commonly sprain their ankles playing basketball. McFarland is director of sports medicine and shoulder surgery at Johns Hopkins University School of Medicine in Baltimore.
"Cross-training can improve aspects of performance," says McFarland, "but it should not be done to a point that detracts from performance." For instance, building upper-body strength increases bat velocity in baseball. Yet the common cross-training routine of running stadium steps has never been shown to improve the performance of any athlete, but it does damage the knees.
Study coauthor Mike Wasik, ATC, says he cautiously recommends that athletes cross-train. Wasik is an athletic trainer for the football team at the University of Florida in Gainesville. He recommends swimming, cycling, softball, and golf as safer alternatives to cross-training sports that stress leg muscles. Strength training programs for cross-training should be designed by weight-lifting coaches who understand the special needs of particular sports. Swimmers do not need to lift as much weight as football players, Wasik says.
Coaches as well as athletes, say Wasik and McFarland, need to be educated that cross-training should be done in moderation with specific goals for improvement. The injuries sustained by the collegiate swimmers happened during supervised cross-training sessions designed by a well-intentioned coach who adopted training methods from football. When cross-training, "keep your goals lower than you would for your main sport, and don't try to be a champion in the sport you're using for cross-training," says McFarland.
More studies of cross-training are needed, McFarland says, to determine whether injuries are more common in some sports or athletes (professional, collegiate, or recreational), and how cross-training relates to overtraining.
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