Tuesday, May 10, 2011

The Link Between Bench Pressing and Glaucoma

Outline
I.  Introduction
II.  Bench Pressing Increases Intraocular Pressure
III. Decline Press Causes Further IOP Increase
IV. Conclusion
V.  Bibliography
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I.  Introduction
      Now, I’m sure many of us have heard this before while lifting…”Don’t hold your breath!  Breathe!  BREATHE!”  Well, it turns out that not only is breathing important for the quality of your training, it is also important for the health of your eyes.  Let’s start with a bit of background.

     Intraocular pressure (IOP) is the fluid pressure of a thick, watery substance between the lens and the cornea of the eye, known as the aqueous humor.  Its major function is to provide nutrients to tissues within the eye.  As new aqueous humor fluid is constantly produced, old fluid must be drained from the eye at a similar rate.  Small changes in the inflow or outflow of fluid (increased production or decreased outflow) can result in an increase in intraocular pressure, which plays a major role in the development of glaucoma by damaging the optic nerve, potentially leading to blindness.  Normal IOP ranges from 10 – 20 mm Hg.  IOP above 21 mm Hg is considered to be above normal.  Corneal thickness can also affect these measurements.
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II.  Bench Pressing Increases Intraocular Pressure

     So what in the world does this have to do with weight lifting??  Well, studies have shown that bench pressing can causes increases in IOP.  A study by Vieira et al., (2006) assessed the changes in IOP following 4 repetitions of bench press at a weight of 80% of 1 maximum repetition.  Subjects were instructed to exhale when pressing the weight and inhale when lowering the weight.  During the exercise, IOP increased in 62% of these subjects by an average of 2.2 mm Hg (up to 21 mm Hg; small, but still statistically significant change). 

     Interestingly, a second group of subjects was instructed to hold their breath during their last repetition.  During the exercise, IOP increased in 90% of these subjects by an average of 4.3 mm Hg (up to 23 mm Hg; more statistically significant change).  This is after holding their breath for only ONE REPETITION!  IOP measurements in both groups declined back to normal 1 minute after the 4 repetitions.
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III.  Decline Press Causes Further IOP Increase

Position of the head during bench press also plays a role in IOP changes.  A study by Song et al. (2009) showed that IOP before performing 1 maximum repetition was significantly higher in patients in the decline position (18.20 mm Hg) than subjects in the incline position (14.38 mm Hg).  Interestingly, higher BMI also correlated with higher IOP before exercise.  During the 1 maximum repetition, maximum IOP was reached when lifting the weight down during a decline bench press (22.10 mm Hg).  Mean IOP values for all three positions are in the chart below.

Song et al., 2009
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IV.  Conclusion

     Now, think about how many repetitions you do where you may be holding your breath. Think about how often you may hold your breath while performing a decline bench press. Based on these studies, you may be inducing significant increases in your IOP during your chest day, potentially putting you at greater risk for glaucoma.  Even though the IOP changes seem to be temporary, the cumulative effect of increased IOP may still put you at risk.  While I haven’t found any studies similar to this when doing other common exercises, at the very least, I would guess that holding your breath during shoulder press, leg press, or many other exercises would cause an increase in IOP.  

So, in order to minimize increases in IOP, potential damage to your optic nerve, and risk for glaucoma, I recommend the following:

1.  Breathe! – Exhale during concentric contractions (ex. the lifting phase of a biceps curl, squat, bench press, etc.) and inhale during eccentric contractions (ex. The lowering phase of a biceps curl, squat, bench press, etc.)
2.  Rather than using a decline barbell bench, try to use decline bench press machines that allow you to sit upright.
3.  Stay consistent with your eye exams! – Your IOP is always measured in an eye exam.  It’s not just for getting new glasses or contacts.

Dr. O 
"I don't live to eat...I eat to live!"

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V.  Bibliography
 
1.    Song, H.Y., et al., The Effect of Positional Changes during Heavy Weight Lifting on Intraocular Pressure. J Korean Ophthalmol Soc, 2009. 50(12): p. 1831-1839.
2.    Vieira, G.M., et al., Intraocular Pressure Variation During Weight Lifting. Arch Ophthalmol, 2006. 124: p. 1251-1254.

Thursday, May 5, 2011

Check out my article, "The Health Benefits of Broccoli", in the April 2011 issue of the Southern Indiana Fitness Source!
April 2011 Issue - Click to Read!