Exercise is *NOT* Associated With Injury Risk in Overweight Individuals

 Image by Jespahjoy.

Just before moving to our new home here on Scienceblogs, I asked our readers for ideas on what types of content they would like to see here on Obesity Panacea.  One topic that came up several times was the issue of injuries.  I'm not sure why we haven't discussed injuries in the past (aside from the fact that it's not the focus of our research), but it was a great idea, and I've come across a study on the topic that I think will be of real interest. 

The study is titled "The influence of exercise and BMI on injuries and illnesses in overweight and obese individuals: a randomized control trial" and was performed by Carol Janney and John Jakicic at the University of Pittsburgh.  Participants in the study included overweight and obese individuals taking part in one of two  exercise studies - one focused weight loss and the other on weight maintenance.  The exercise component of the two studies were similar, with participants walking at a brisk pace 5 days/week (the major difference between the two studies is that one included caloric restriction to induce weight loss, while the other simply emphasized healthy eating patterns).  Every 6 months, participants reported any injuries or illnesses that impacted their ability to exercise.

During the 18-month interventions, 32% of all participants reported having an injury which impacted their exercise regime.  Not surprisingly, the most common injuries were in the lower body (suffered by 21% of participants) and the lower back (suffered by 10% of participants).  Of the lower body injuries, the most common issues were knee injuries, sprains, tendinitis, hip injuries, and "general muscle muscular injuries". What I find particularly interesting is that of those who experienced an injury, 59% said that it had nothing to do with their exercise participation.  In other words, these individuals felt that those injuries would have happened whether or not they were exercising.  In contrast, just 7% of injured individuals felt that their injuries were due entirely to their exercise program.  And most interesting of all?  The rate of injury did not differ between the experimental and control groups!  So individuals involved in the exercise programs were at no greater risk of injury than their sedentary peers.  What's more, injuries lasted for a significantly greater duration in control participants, in comparison to individuals in the exercise groups. Training volume appeared to have little to no impact on injury risk, while BMI had a strong influence on the risk of injury or illness - the greater an individual's BMI, the greater their risk.  In fact, the risk of injury increased by roughly 8% for each 1-unit increase in BMI whether the individual was performing exercise or not.

What's the take-home message?

This study suggests that in overweight and obese individuals, exercise (in the form of walking) has little or no association with injury or illness.  In fact, it suggests that excess body weight poses a far greater injury-risk than exercise itself.  That is extremely important, as I have met many  individuals who do not exercise specifically because they are worried about injuring themselves, especially an injury to their lower body.  Now it should be noted that the exercise employed in this study was brisk walking - we're not talking about intense Biggest Loser style bootcamps. But brisk walking is exactly the type of exercise that it advocated for this population, so I think that the results are quite promising.  It also underscores the important impact that body weight can have on the musculoskeletal system (one of the only instances where BMI is as good as advertised!), and suggests that anyone working with overweight or obese individuals should pay especially close attention to injuries, especially in the lower body.

I should mention that the paper I've discussed today is free to anyone with an internet connection via the nice folks at Pubmed Central.  It's a very well written and readable study, so I'd strongly recommend you check it out for yourselves.

Injury prevention is an important topic, and one that I plan to revisit in the future.  Issues having to deal with flexibility and over-use injuries like shin splints and plantar fasciitis affect people of all shapes and sizes, and I'm looking forward to discussing them in detail. In the meantime, just remember that for obese individuals, being sedentary poses as much risk of injury as being physically active - one more reason to start moving!


ResearchBlogging.orgJanney, C., & Jakicic, J. (2010). The influence of exercise and BMI on injuries and illnesses in overweight and obese adults: a randomized control trial International Journal of Behavioral Nutrition and Physical Activity, 7 (1) DOI: 10.1186/1479-5868-7-1

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Good use of BMI:

BMI had a strong influence on the risk of injury or illness - the greater an individual's BMI, the greater their risk. In fact, the risk of injury increased by roughly 8% for each 1-unit increase in BMI whether the individual was performing exercise or not.

To a first approximation, BMI scales with PSI -- which is directly correlated with orthopedic injuries.

By D. C. Sessions (not verified) on 07 Apr 2010 #permalink

Interesting. I suspect that for me, the causation goes the other way. I'm heavier than I would be otherwise because I tend to get injured and have to spend long periods of time where I can't exercise much and then I can't get back into it. I gained my last big chunk of weight right after I injured my foot so badly I needed surgery, and I haven't been able to shed it again.

The original injuries tend to have more to do with my hypermobility and severe clumsiness. I find some sort of exercise that I actually enjoy doing, then I hurt myself and can't do it any more. It's very frustrating.

I think that one of the keys to this study is that the amount and type of exercise used in the testing was relatively low impact. From my own experience, and from watching others do the same, I would overcompensate and make poor activity decisions whenever I would make the choice to lose weight and begin an exercise program. Many individuals, with no professional guidance, begin exercise programs that are far too intense and long in duration. In these circumstances, I could see an increase in injuries in these individuals being likely, but that would be based more on poor exercise decisions rather than a correlation with BMI.

Now what we really want to know is if the same results hold for treadmill biking.

By Andreas Johansson (not verified) on 08 Apr 2010 #permalink

Chiral, I hurt myself a lot too on account of clutziness. Staircases are a special hazard. But in the last year or so I've also fallen at a roller derby practice, busted my bum sledding down an icy, paved hill, and reaching for the alarm clock. Also a broken collarbone from carrying my bike over my head to get out of a very crowded bike rack. Road rash is also a bigger problem for me than it seems to be for most 46-y-o women I know. And yes, my bmi is awfully high, and IMO the psi factor definitely exacerbates the plantar fasciitis and the knee and hip pain when I run. But the latter three predate the bmi rise by a lot, and so does the clutzitude. And the exercise induced asthma. What bums me out is the suggestion that my weight is the cause, or that losing weight would cure all of it. Including the clumsiness. My bike would be faster, my teeth whiter, and the waxy yellow buildup would disappear from my floors.

Another commendable, informative blog post.

BMI may be a misleading metric, particularly for muscle-dense, lean individuals. Fat/lean mass ratio is preferred to document progress towards a metabolically healthy, working muscle mass composition.

Many individuals do not adequately moderate progress through the initial phase of a vigorous exercise program. This is essential for muscle and nerve cell acclimation to daily microtear repairs, and cell growth in response to initiation of daily physical activity.

Sleep and nutrition are active partners to nightly exercise-related tissue repair, but there are other benefits in immune system and sleep phase re-regulation and brain spatial learning (balance, coordination) as key learning centers respond to distant muscle group active motor junction-loading cues.

The poster who reports clumsiness and frequent injury is a classic case of inadequate exercise acclimation, with joint hypermobility an potentially poor tissue repair performance (especially in joints) as a risk complication. Attention to strengthening nearby support major muscle groups is essential, along with careful attention to diet to minimize inflammation tendency.

Improving hand-eye coordination with careful practice of ball-and-racket court sports (hitting a ball against a practice wall with line) is an ideal exercise for slowly improving brain spatial learning, balance and bipedal coordination. End result may include reduced injury risk.

The Woo-Masters are big on use of digestive enzyme supplements to address assertions of dietary insufficiency, without realizing that their true utility lies in the fact that they are still-functional, ancient (pre-mammalian) nuclear receptor regulatory cues for tissue repair.

I'm not sure why we haven't discussed injuries in the past (aside from the fact that it's not the focus of our research), but it was a great idea, and I've come across a study on the topic that I think will be of real interest.