The Effect of Travel, Minutes Played, Game Density and Sleep on Performance & Injury Likelihood

Last week, I was asked to make an appearance on ESPN’s Outside the Lines to give my thoughts on the NBA’s travel schedule and season length on quality of play and player injuries. In a nutshell, I stated that I thought the NBA season is too long, too many minutes are played, and the density of games and amount of travel leads to a lower quality of play and a greater risk of injury. My points weren’t a matter of opinion but backed by both anecdotal and research findings from not only basketball but other sports as well. As is the case in most of these types of opportunities, I wasn’t given the chance to share much beyond surface information. As one might expect when you hear someone suggest that multi-millionaires playing games for a living need more rest, there were more than a few fans who took to twitter and other outlets to argue that these ‘prima donnas’ should toughen up. Here’s a portion of the ESPN showing followed by a sample of some of the more unsympathetic tweets.

kennypowersNow I can definitely relate to these sentiments. If someone paid me the 20+ million dollars per year that some of these guys are paid I’d be more than willing to play every minute of every game during an 82 game season. Even if you’re an unsympathetic fan, I’m guessing you still want to see the best product on the floor. If that’ the case, you’d have to be willfully ignorant to ignore the impact that travel and game schedules have on performance.  If we’re truly interested in putting the best product on the floor then we have to look at these issues. And if I’m the owner of a team that’s paying players these exorbitant amounts, I would certainly be doing everything I can to protect my investments. To put it in to perspective, many of these guys are worth more than a jet plane. If I owned a jet plane I’m sure as hell not going to be flying it in inclement weather in a poorly maintained state because I’d be worried about the financial loss if something should happen. When you look at it like that and understand that the conditions that players are currently asked to play under likely wouldn’t meet OSHA standards for job safety you start to realize that despite the ridiculous sums these guys are being paid that it would be better for everyone (owners, fans, and players) if we approached the way the schedules, travel and rest are handled more intelligently. Any sport will bring with it some level of fatigue. That fatigue should subside though given sufficient rest and recovery. Similarly, if fatigue persists performance will drop off and the likelihood for injuries will increase.

As a coach, there’s only so much you can control. Two of the biggest predictors of injury – age and prior injury, are almost completely out of our control. And obviously no individual coach is going to change a league’s schedule or the time that games are played. But knowing how the different variables can impact performance and increase the likelihood for injury can help a coach formulate a plan to modify the things they can control to best prepare their players for success. Here’s a couple things to consider (this post is LOADED with hyperlinks so if you don’t see an obvious reference enumeration scroll over the text for the source):

  • In-game fatigue effects performance. Sure mental toughness is great but you can only fight physiology so long. No amount of willpower, Navy Seal training or sports drink is going to allow a player who is playing at full tilt to avoid fatigue. 
    No amount of willpower, Navy Seal training or sports drink will prevent a hard driving player from becoming fatigued
    The best you can do is delay it. This relationship has been well documented in several sports. The acute effects of fatigue in sport are clear when you look at what happens following flurried activity in games. Match analysis of soccer shows that 5 minutes of flurried activity is often followed by 5 minutes of significantly slower tempo even amongst the fittest of players. From a slightly broader perspective, we can see that in-game fatigue even occurs following half time breaks. A nice study on the effect of fatigue in rugby indicated that running performance is impaired in the last 10 minutes of play when compared to the first. Additionally, there’s also a decrement over the entire 2nd-half played. Similar findings have been made for soccer and other sports.
  • injuryIn-game fatigue correlates with injuries. You’d think this one would be a no-brainer but there are still some that are living in the stone ages. We’ve already seen that performance metrics tend to drop throughout the game as a result of fatigue and match analysis of several sports reveals that these metrics tend to show the sharpest decline towards the end of each half. So it should come as no surprise that one study on amateur soccer players found that 80% of all injuries occur within 15 minutes of the end of each of a match. Similar findings have also been found at the professional level (1, 2). Which leads us to the next point….
  • In-game fatigue is independent of competitive standard or playing position. This one is striking to many people because some incorrectly assume that because you’re a professional you must be fit enough to resist fatigue. On the flip side, you’ll hear people talk about players not playing at a high enough level to really truly exhaust themselves. The reality is that athletes will generally play at a level that matches or exceeds their level of fitness regardless of whether they are fit or unfit. Research indicates that the amount of high-intensity running performed in a game is reduced by roughly the same amount independent of competitive standard and playing position.
  • brain-fatigueFatigue isn’t just physical. Many chalk up fatigue as being something that exists purely at the energy system or even musculoskeletal level. This overly simplistic understanding is what leads people to think you can just ‘man up’ or fight your way through fatigue to maintain a high physical output. Really, physical fatigue is only part of the equation. In the body, everything is intertwined. That includes the brain. While mental fatigue is a little less tangible than its more physical peers (no one’s ever had a cramp in their brain) it is no less real. Because of the role of the central nervous system on things like decision making, focus of attention and reaction time, impaired cognitive abilities can lead to not only fatigue (which leads to impaired performance as we’ve seen above) but also increased likelihood for injury. For instance, a clear link has been established between this brain fatigue and knee injuries (1, 2).
  • Perception of fatigue IS fatigue. This is an important adjunct to the previous point. The research of Tim Noakes has painted a crystal clear picture that when it comes to fatigue, perception is reality. If an athlete is fatigued the root is a sensory manifestation of the neural regulatory mechanisms rather than a physiological issue. This provides great validation for establishing a relationship with the athletes and using things like wellness surveys to determine their current state.
  • chelsea-winsMatch outcome effects fatigue and psychological wellbeing. While many coaches may have noticed the effects of match outcome on recovery, it’s only recently been verified with research. Basically, a players sense of psychological wellbeing and perception of fatigue (remember perception is reality!) are more compromised following losses when compared to wins. In other words, if two opposing players of the same fitness level produced the same on-field physical outputs (meters run, number of sprints, etc), the player on the losing team would likely report a higher level of fatigue. This phenomenon linking outcome and perception of fatigue has been observed in a variety of sports and settings (1, 2, 3, 4).
  • Schedule Density is positively correlated with injuries Schedule density has been linked with greater injuries and decreased quality of play. One study on soccer players found that the closer together games are played without adequate rest, the greater the likelihood for injury. Interestingly, this relationship DOES NOT seem to occur for younger athletes. Likewise, there is data out of the very trustworthy MIT Sloan conference that suggests that back-to-back games and game density do not predict injuries.
  • Minutes Played in a game are positively correlated with injuries. Injury rates rise proportional to the number of minutes played. Sometimes this one can be convoluted and obscured by the fact that many injuries occur in the first couple minutes are on the court or pitch. This is misleading though because all players who see game action MUST go through the early minutes of playing time before reaching longer durations of play. This same rationale is used to misrepresent the fact that more car accidents occur closer to home. Of course they do! You have to leave home before you can go anywhere else. Once we take this fact in to account though, the evidence clearly indicates that injury likelihoods go up exponentially with minutes played. This has been observed in soccer (1, 2), rugby and basketball.
    ACL Injury Frequency by Minutes Played
    ACL Injury Frequency by Minutes Played (source: http://www.basketballprospectus.com/article.php?articleid=2261)
  • Increased individual workload increases the likelihood of injury. You’ll never get injured sitting on the couch. Similarly, if you’re sprinting, jumping and cutting at maximum intensity the probability for injury goes up. A study from the MIT Sloan conference indicated that variables like field goals attempted, average running speed, and distance covered are predictive of injury.
  • Games played is positively correlated with injuries. Based on what’s been shown above it should come as no surprise that the total number of games played in a season also increases the likelihood for injury.…particularly where players are consistently playing more minutes.
  • sleep-mainSleep quantity has been strongly linked with impaired performance. Unless you’ve been under a rock for the last 10 years of research on sleep, you know that it plays an important role in everything from sarcasm detection, memory consolidation, and motor skill acquisition. Insufficient sleep causes a detriment in cognitive and psychomotor skills that has been noted in such far reaching fields as medical practicestudent academic performance, and driving. This may be because sleep loss may “affect the capacity for performance and access to energetic resources.” Research indicates that while some maximal physical efforts and gross motor performances can be maintained while sleep deprived, sport-specific performance is often compromised. This could be due to autonomic nervous system imbalance which might actually simulate symptoms of overtraining. Furthermore, even moderate sleep deprivation has been clinically linked with negative mood disturbances and impaired reaction times. 
  • Sleep quantity has an inverse relationship with injury likelihood. In a recent study which gained significant attention, investigators found that the likelihood for injury is 1.7x higher for athletes who slept less than 8 hours per night when compared to those who have slept more than 8 hours per night. 
    Getting less than 8 hours of sleep increases likelihood for injury 170%
    While this study focused on high school aged athletes it was the first in what is likely to be a growing body of literature supporting the role of sleep in injury prevention.
  • sleep-cycleSleep QUALITY may be as important as quantity. Based on the above point you might think that if you just make sure you’re in bed for 8 hours everything’s ok. Unfortunately, that would be incorrect though.  The quality of sleep that you have may be just as important as the quantity of sleep. Anecdotally, we’ve all experienced this. Anyone who’s woken up drowsy off of 9 hours of sleep one day but ready to rock the world the next day after just 6 hours of sleep knows this to be true. The relationship hasn’t been studied much in terms of athletic performance but clear links have been established in academic performance and work place alertness and performance. In the athlete monitoring systems I’ve designed or consulted on for collegiate, national and professional teams, I always recommend including a measure of sleep quality even if it has to be a subjective rating. Unfortunately for athletes (especially those playing late night games and crossing multiple time zones), there are many factors that can compromise sleep quality. The time that games are played (especially relative to a player’s ‘home’ time zone) can be VERY disruptive to sleep quality. As you may know, in a night’s sleep we go through alternating phases of non-rapid eye movement (NREM) and rapid eye movement (REM) sleep.  The final stages of non-REM sleep is considered the deeper and more restorative form of sleep. It tends to occur more during the front end of the a night’s sleep and the time our sleep cycles shift from being NREM dominant to more REM dominant is somewhat fixed. In individuals with a normal circadian rhythm (excepting Advanced and Delayed Sleep Phase Disorders aka “Early Birds” and “Night Owls”), the deepest and most restorative sleep will occur between 10 pm and 2 am of your ‘internal clock’ or home time zone. This means that even if two athletes sleep equivalent total hours in a night but one goes to bed at 10 pm and the other goes to bed at 2 am the one who went to bed earlier is likely to have had a more restful and restorative night’s sleep because they would have spent a greater portion of their night’s sleep in NREM.
    Going to sleep too late can compromise the restorative qualities of sleep even when total hours are sufficient
    This is bad news for athletes who might finish a game at 10pm. They’d be lucky if they could be in bed by 2 am after showering, changing, meeting with the media, traveling home or to the hotel and falling to sleep after the excitement of a game. This bad news would be compounded even more for athletes based in the East Coast playing a night game on the West Coast. It would mean that exact same scenario would put them getting to bed at 5am on their normal “internal clock” time! Conversely, a West Coast team playing at night in the East Coast would actually have it BETTER than they do at home (from a sleep standpoint). It’s no wonder that previous research has found that changing time zones as little as once a week has an impact on sporting performance and West Coast teams have a distinct advantage over East Coast teams whether they are home or away. These findings have been found in American football (1, 2), baseball and basketball. In a league like the NBA where teams may be in as many 4 time zones in week, this could be a recipe for disaster not only on quality of play but also injury likelihood.
  • Sleep is linked with career longevity. Given the previous 3 points it should come as no surprise that sleep has been linked with professional sport career longevity. Two separate studies (both available here) looking at the role of sleep on NFL and MLB career longevity found that those who experience more daytime sleepiness are more likely are to experience attrition and early wear and tear.
Enhancing sleep quantity and quality is the most beneficial & cost effective performance enhancer

So to wrap this up let’s summarize with a couple take home points. The first is that you can’t cheat physiology. If you play sport, you will get fatigued. When you are fatigued your physical output and sport performance will be impaired and you will have an increased likelihood for injury. Fatigue (and by extension performance decrement and injury likelihood) is more likely as playing exposure accumulates without sufficient rest (more minutes in a game, number of games played, greater schedule density, etc). This means that since we can’t very well reschedule games because of fatigue, we need to do whatever we can to manage fatigue by monitoring daily readiness and controlling the variables which we do have power over (intensity and duration of practice, nutritional interventions, recovery modalities, etc). Finally, recognize that educating athletes on sleep hygiene and monitoring their sleep quality and quantity may be the most beneficial and cost effective means of enhancing performance, reducing injuries and increasing career longevity.

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Mike Young

Director of Performance at Athletic Lab
Mike is the Head Fitness Coach for the North Carolina Courage and North Carolina FC. He is also the owner and Director of Performance at Athletic Lab sports performance training center. He previously served as the fitness coach for the Vancouver Whitecaps and Carolina Railhawks. He has a PhD in Biomechanics, an MS in Coaching Science, and a BSS in Exercise Physiology and has coached Olympic and professional athletes in Skeleton, Track & Field, MLS and NASL Soccer, PGA Golf, NFL Football, MLB Baseball and Olympic Weightlifting. He has lectured around the world and authored 2 books and dozens of research and coaching articles.