Weekend warriors who exercise too hard on a hot summer day may seem like the most likely candidates for exertional rhabdomyolysis (ER), a condition in which muscle fibers break down and release intracellular elements into the bloodstream, causing dark urine, muscle swelling, pain, and weakness. But according to a recent study, college football players are also at risk for ER, which can result in renal failure and other complications.
Researchers examined a cluster of ER cases that occurred in 2011 in 13 members of the University of Iowa (UI) football team.
The cases occurred when players returned to training after a short holiday break. The initial training sessions were strenuous and included a long set of back squats—deep knee bends with weights—that require eccentric muscle contraction of the large quadriceps muscle group.
“Coaches should be aware that, if athletes are coming back to camp or school and need to get back into shape, the training sessions should proceed gradually,” said Ned Amendola, MD, director of the UI Sports Medicine Center and team physician for the UI football team, as well as one of the study’s authors.
Dr. Amendola and his fellow researchers conducted the study to determine risk factors for ER in college-level football players. They encourage coaches, athletic trainers, and members of the medical team to communicate with one another about variations in athletes’ ability to perform and tolerate strenuous eccentric exercise.
The UI football team played in a bowl game in late December 2010, followed by a 3-week break from training. The team then took part in offseason workouts on Jan. 20, 21, and 24. Players performed sled pushes as well as weight lifting activities, including completing 100 back squats at 50 percent of their 1-repetition maximums.
After completing the workout on Jan. 24, four players reported symptoms of ER, prompting the medical staff to instruct all players with similar symptoms to report to them. In total, 13 players were admitted to the hospital for treatment of ER.
The hospitalized athletes received intravenous normal saline titrated to produce 200 mL/h to 300 mL/h urine output, causing the athletes’ serum creatine kinase (CK) levels to trend down. After receiving treatment for 24 hours, 8 of 10 players had normal serum creatine values.
“The players were discharged after 4 to 6 days of hospitalization, after their myoglobinuria resolved, and their CK values were approximately 10,000 U/L,” explained Dr. Amendola, adding that no players required hemodialysis and that no cases of compartment syndrome developed.
Conditioning levels important
An investigative team appointed by the university’s president used information from interviews with the players as well as from a literature review to create a questionnaire that players completed anonymously. In addition, data were obtained from the head strength and conditioning coach about athlete demographics, the amount of weight each athlete lifted, the time (in minutes and seconds) needed, and the number of repetitions per set each player required to perform the 100 back squats.
In all, 78 of 84 players (92.9 percent) returned surveys, including the 13 hospitalized athletes. Statistical analysis showed that the risk of ER developing increased as the time and number of sets needed to complete 100 back squats increased. Affected players were significantly more likely to report going into muscle failure (P = 0.006), feel they could not complete the workout (P = 0.02), and perform extra squats (P = 0.02) than unaffected players.
In addition, athletes who played skilled or semiskilled positions had an increased risk of ER as the percent of body weight lifted increased (Odds Ratio [corresponding to a 10 percent increase], 1.77; 95 percent CI, 1.06–0.96; P = 0.0284). Odds of ER developing decreased 30 percent per each protein shake the athletes consumed prior to the workout.
Dr. Amendola was not surprised to find a correlation between ER and back squats, given that other studies of ER clusters have linked the condition with eccentric large muscle contraction, such as is required by this exercise.
“Workouts that suddenly increase in volume or intensity and place an emphasis on eccentric muscle contraction have a particularly high risk of leading to ER,” he noted.
The conditioning coach, athletic trainers, and the medical team should clearly communicate with one another regarding the appropriate level of exertion required of athletes in workouts. In addition, athletes should be well-hydrated and well-nourished.
“Interestingly, we found that protein shakes consumed during the day of the workout, or the day before the workout, seemed to protect the muscle from getting injured,” said Dr. Amendola.
“I think surgeons need to be careful about over-diagnosing athletes with compartment syndrome when they present with stiffness and swelling of the thigh,” he added. “When a patient is hospitalized and receives intravenous saline, orthopaedists should monitor the muscle compartments and give the hydration a chance to work, rather than assuming a fascial release is needed.”
In conclusion, said Dr. Amendola, “ER in elite athletes may be somewhat of an obscure topic, but when it occurs, it can be devastating.”
He added, however, that ER can be prevented with “appropriate understanding of the pathophysiology, appreciation of the tolerable volume of large eccentric muscle contraction, and athletic pre-conditioning prior to vigorous exercise.”
Dr. Amendola’s co-authors for “A Cluster of Exertional Rhabdomyolysis Affecting a Division I Football Team” include M. Kyle Smoot, MD; Elizabeth Cramer, MD; Christopher Doyle, MEd; Kevin C. Kregel, PhD; Hsiu-yin Chiang, MS, PhD; Joseph E. Cavanaugh, PhD; and Loreen A. Herwaldt, MD.
Disclosure information: Dr. Amendola—Arthrex, Inc.; Arthrosurface; MTP Solutions; Moximed; Clinical Journal of Sports Medicine; Foot & Ankle International; AAOS; American Board of Orthopaedic Surgery. All other authors—no information.
Jennie McKee is a staff writer for AAOS Now. She can be reached at email@example.com
- ER can affect college football players as well as nonathletes.
- Symptoms can include dark urine, severe muscle pain and swelling, and weakness; complications such as renal failure can occur.
- Exercise that involves eccentric large muscle contraction may cause ER, especially after several weeks of rest.
- To help avoid ER, athletes should be adequately hydrated and nourished, and coaches, athletic trainers, and the medical team staff must communicate about how athletes’ conditioning levels may affect their ability to perform exercises involving eccentric muscle contraction.
- AAOS Now audio podcast – Frank B. Kelly, MD, interviews Dr. Amendola about the study:
- Study abstract