A cluster of exertional rhabdomyolysis affecting a Division I football team

Journal Title (Medline/Pubmed accepted abbreviation):Clin. J. Sport Med.
Year: 2013
Volume: 23
Issue: 5
Page numbers: 365-372
Website: www.cjsportmed.com

Summary of background and research design:
Background: Exertional rhabdomyolysis (ER) is when muscle is worked too hard, causing excessive breakdown of muscle fibers and release of cellular components into the blood stream. Symptoms include: pain, swelling, and weakness of muscle as well as brownish urine that resembles tea or cola. Severe and/or untreated ER can cause kidney failure as well as other life-threatening complications.
    The prevalence of ER is not well characterized, but reports have been made in athletes ranging from untrained high school students to elite athletes and in swimming, football, lacrosse, military training, and other sports.
    This article stemmed from a case report from the University of Iowa football team in January 2011. On the first off-season workout after winter break, 78 athletes executed a workout including 100 back squats at 50% of their one-repetition maximum. Within 5 days, 13 (17%) players were hospitalized with ER. This article investigates what practices were associated with ER in attempts to provide training and nutritional recommendations for preventing ER.

Experimental Design: “outbreak” investigation

Subjects: Division I football players, age 19-21 y

Protocol: The investigative team did a thorough analysis of all clinical data, exercise logs, and supplement usage in order to identify the risk factors associated with ER. Ten of the 13 players to the hospital allowed authors to review their medical records.

Summary of research findings:
  • At the time of admission to the hospital, creatine kinase levels in the blood (marker of muscle damage) were 96,987-331,044 U/L where normal levels are less than 200 U/L. Serum creatinine levels (indicator of kidney function) were 1.0-3.4 mg/dL.
  • Random drug tests that were performed the same week as the ER incidents. Twenty-eight samples were collected, two of which were from athletes who later suffered from ER. All samples were negative for illegal drugs.
  • Age, height, weight, body mass index (BMI), race/ethnicity, field position, and the number of semesters in the football program were not factors that correlated with risk of ER.
  • The number of sets and the time it took to complete the 100 squats were recorded. As time increased and as the number of sets increased, so did the risk of ER (p = 0.005 and 0.006, respectively).
  • For athletes who played skilled positions (ex. defensive backs, wide receivers) and semi-skilled positions (ex. linebackers, fullbacks), but not linemen, the risk for ER increased as the percentage of body weight squatted increased (p = 0.03). This may be because athletes that played skilled and semiskilled positions have more Type IIx muscle fibers, which are associated with quick contractions. These glycolytic muscle fibers may have fatigued more quickly than linemen’s type I oxidative fibers, thereby predisposing them to muscle damage from squats.
  • A similar workout was performed by the same team in December 2007 (towards the end of the season). Fifteen players responded to a survey saying that they had completed the workout then but did not show symptoms of ER; two of these 15 players experienced ER in 2011. Twenty-three former players who had done the workout in 2007 reported that they did not experience dark colored urine after the workout.
  • Athletes who experienced ER were more likely to report that they went to muscle failure during the workout (p = 0.006) and that they did not think they could complete the workout (p = 0.02).
  • Performing extra squats during the workout also increased risk (p = 0.02).
  • As expected, those with ER were more likely to experience muscle swelling soon after the workout, use anti-inflammatory medication, and reduce subsequent activity.
  • Fluid, supplements, and medications during or after the workout were assessed including water, sports drinks, protein shakes or supplements, energy drinks, pre-workout supplements, caffeinated drinks, soda without caffeine, creatine, carnitine, and licorice.
    • None of the fluids or supplements appeared to affect risk of ER except protein.
    • Consumption protein shakes or supplements was negatively correlated with ER (p = 0.02). In other words, those that consumed a protein supplement were less likely to experience ER.
    • In fact, it was predicted that with every post-workout protein shake consumed, the odds of experiencing ER decreased 30%.
    • Those that experienced ER and those that did not reported similar levels of consumption for both water and sports drinks.
  • Those that did not experience ER were more likely to report that they trained hard over break and performed back squats during the last week of the break (statistics not performed).

Key practice applications: It is believed that the players were more vulnerable to ER because this workout occurred after a 3-week break when lifting volume was relatively low. Moreover, ER is typically associated with high volume, high intensity, eccentric contractions, and the 100 back squat workout was akin to this description.
    These data suggest that post-workout protein beverages may protect against muscle damage and the development of ER. However, it is recommended that workloads be planned appropriately; consumption of protein shakes will not fully protect against ER.
    Knowledge of ER and its symptoms are not widely known. It is important for coaches, athletes, parents, trainers, and other athletic staff educate others on the symptoms of ER (namely, muscle failure, dark-colored urine) and emphasize its danger. It is also important to ease back into workouts after time off in order to prevent severe muscle damage and ER.

Limitations: Based on other studies, it is believed that there were athletes on this team that had significantly high creatine kinase levels but did not exhibit symptoms severe enough to warrant hospitalization.
    It is possible that the players that experienced ER were ill immediately after the workout, causing them to not consume protein shakes. Because this was not a randomized, clinical trial, this study does not provide proof that protein shakes protected against ER.
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