Research Reviews

Research Review: Can blueberries beat muscle soreness?

by Jennifer Koslo

Exercise-induced muscle damage (EIMD) after a tough workout causes muscle soreness and inflammation. Luckily, phytochemicals (plant chemicals) might protect us from this. Blueberries, in particular, can speed muscle recovery when eaten before and after strenuous exercise. And that’s in addition to their well-known antioxidant properties that help protect against chronic disease.

You try to keep things fresh so you mix up your workouts, try a new activity, or increase your intensity. You feel pretty good initially. Then you wake up the next morning and unnggghhh.

Welcome to the world of exercise-induced muscle damage (EIMD) or delayed-onset muscle soreness (DOMS). Whatever you call it, it sucks.

Exercise-induced muscle damage (EIMD)

Symptoms of EIMD or DOMS usually occur 12 to 48 hours after the workout and result from damage to the muscle tissue. We don’t yet know exactly what causes EIMD, but our best guess is that overloading muscle disrupts the muscle cell membranes along with their contractile proteins and sacroplasmic reticula.

Once this early damage is done, the body’s repair crew kicks in. Fluid and immune system cells move to the affected muscles to remove the cellular “debris”. This fluid is what causes the stiffness, swelling, and pain you experience.

It’s all in the name of a good cause: All of this has to occur before the muscle can start rebuilding. It’s the repair process that makes us stronger or fitter, not the workout itself. This is why good recovery is so important.

For more on exercise-induced muscle damage, see the Research Review “A New Supplement for Soreness?

Sore muscles usually result from exercise that involves eccentric muscle actions, where the muscle lengthens while simultaneously trying to contract. When you use muscles that you haven’t used in a while or participate in team sports that involve jumping and changing direction at rapid speeds, you’re doing activities that involve eccentric muscle contractions. (Think about how your quads feel after you’ve hiked down a mountain.)

To help reduce the pain and speed recovery, you may have:

  • swallowed a non-steroidal anti-inflammatory (aka NSAIDs, such as ibuprofen)
  • drunk lots of water
  • applied ice
  • downed a few antioxidant supplements like vitamin C or E
  • waddled around moaning, looking for sympathy

But did you ever consider loading up on blueberries?

Antioxidants and phytochemicals

Naturally, we all want a treatment for EIMD. Researchers have investigated many options, including dietary antioxidant supplements like vitamins C and E. Unfortunately, although antioxidants in general do help reduce free radical damage, there’s little evidence that supplementing antioxidants in pill form actually works (and supplementation with single-dose antioxidants may in fact be harmful). Other options, such as NSAIDs, also have unwanted side effects.

So what does help reduce EIMD — safely?

Food.

You may have seen or heard about drinking tart cherry juice for recovery post-exercise. Evidence suggests that cherries do in fact speed recovery time by reducing inflammation and loss of muscle strength (1). And it turns out that drinking cherry juice can also reduce pain associated with distance running (2).

While the virtues of cherries seem clear, in the study reviewed here, blueberries were chosen as the “test” berry because they contain the broadest range of phytochemical compounds and are especially high in anthocyanins, the compound that gives the fruit it characteristic blue color.

Because of this, blueberries have what is called a high antioxidant capacity —  otherwise known as “ORAC,” or oxygen radical absorption capacity. In other words, they can squash and neutralize free radicals formed as a result of exercise, environmental pollutants, etc.

Interestingly, blueberries are actually low in vitamins C and E, so their ability to reduce EIMD has been attributed to the anthocyanins, independent of their antioxidant capacity.

For more on phytochemicals check out “The Power of the Phytochemical”.

Phytochemicals work synergistically, which means that their combined effect is greater than the sum of their individual effects. Synergy is what you get when you eat whole, nutrient-rich foods rather than supplements or processed food. And it’s the source of blueberries’ superpowers.

Research question

This week’s research review question: Will eating blueberries change markers of exercise-induced muscle damage (EIMD) and inflammation after strenuous weight bearing lower body exercise?

McLeay, Yanita,  Barnes, Matthew J., Mundel, Toby, Hurst, Suzanne, M., Hurst, Roger, D., Stannard, Stephen, R. Effect of New Zealand blueberry consumption on recovery from eccentric exercise-induced muscle damage. J Int Soc Sports Nutr.2012, 9: 19 (7 May 2012).

Methods

Ten recreationally fit women aged 22 + 1 years took part in the study, which used a random crossover design: Subjects drank either a blueberry smoothie or a placebo smoothie at two intervals before, and at three intervals after, 300 repetitions of eccentric contractions of the quadriceps (thigh muscles).

Dietary intervention

Trial 1:

The subjects went to the laboratory three times: morning, midday, and evening. They were fed breakfast plus a blueberry smoothie, then at midday lunch plus a blueberry smoothie. In the evening they warmed up and did 300 (yes I said 300) eccentric contractions of the quadriceps, after which they were fed a dinner of curry and rice (yum) plus a third blueberry smoothie.

Then they came back to the lab the next two mornings and drank a blueberry smoothie each time.

On the final day they went to the lab for testing but no more smoothies (dang).

Each blueberry smoothie had 1 ½ cups of blueberries. That’s a total of 2.2 pounds of blueberries over the course of 3 days.

Trial 2:

The trials were separated by a month and used the same protocol, except that the blueberry smoothie was replaced by a similar tasting fruit smoothie, with 25 grams of dextrose plus a banana and some apple juice.

On the day of the study the participants had 3 of these smoothies, and then one on each of the two following mornings.

Smoothie vs. smoothie

Here’s the nutrient breakdown of each smoothie. As you can see, the blueberry smoothie contains many more phytochemicals than antioxidants.

Placebo Blueberry smoothie
Antioxidant capacity (ORAC: oxygen radical absorption capacity) 5298 5417
Total phenolics – (i.e. phytochemical content of the drinks) 29 168

Figure 1 blueberries vs placebo 1024x693 Research Review: Can blueberries beat muscle soreness?

Exercise intervention

In this study, eccentric contractions were used as the test exercise. With eccentric contractions, as mentioned, the muscle lengthens against force.

For example:

  • the lowering part of a biceps curl
  • step-downs from a bench with one leg at a time or,
  • as in this study, eccentric contractions of the quadriceps muscle (resisting the downward pull) with one leg.

Eccentric contractions produce more force than concentric contractions, which means they result in bigger gains in strength but also more exercise-induced muscle damage (EIMD).

The study protocol used a machine called an isokinetic dynamometer, which is used to monitor muscle performance or force, and looks like a fancy quadriceps extension machine connected to a computer. Participants are strapped in to stabilize and isolate the muscle being tested.

Once strapped in, this study’s participants completed 3 sets of 100 eccentric repetitions of the quadriceps muscle. They had 5 minutes of rest between sets and were allowed water. (How kind of the researchers!).

Measures

The researchers took one subjective measure and several laboratory measures from blood work to see what effect the blueberry intervention had on markers of exercise-induced muscle damage:

  • Perceived muscle soreness: The subjects rated their perceived muscle soreness on a scale of 0 to 10 (0 = no soreness, 10 = very, very painful) on three mornings following the exercise testing.
  • Creatine kinase: A marker of muscle damage.
  • Protein carbonyls: Biomarkers of damage caused by radical oxygen species. This measure is used by scientists to see if there is inflammation.
  • Radical oxygen species (ROS)-generating potential: A measure of oxidative stress.
  • Interleukin (IL)-6: An inflammatory cytokine (cell signaling chemical); another marker of muscle damage.
  • Antioxidant capacity: This measurement shows whether the dietary intervention resulted in a improved ability to reduce free radicals.

Results

The researchers wanted to find out if the phytochemicals in blueberries could help decrease the effects of exercise-induced muscle damage. What they learned was that there were some slight but significant differences in the 60 hour recovery window between the two trials.

Perceived muscle soreness and performance

Overall there were significant differences in ratings of muscle soreness between trials at 12, 36 and 60 hours post exercise.

Dang – so both groups felt about the same amount of soreness.

But in terms of performance, the participants in the experimental trial did slightly better on follow up muscle testing. This sounds promising – the blueberries may have helped speed recovery of the tested muscles in the experimental group.

Markers of inflammation and oxidative stress

In both trials, the exercises resulted in about the same level of inflammation and oxidative damage. However, in the blueberry trial these markers decreased slightly faster, which coincided with a gradual increase in antioxidant capacity over the 60 hour recovery window.

Conclusion

Drinking a blueberry smoothie at two intervals before and three intervals after eccentric muscle damage provided a slight but significant acceleration in recovery as measured by muscle performance and markers of EIMD. This appears to be a result of the phenolic compounds, aka the phytochemical content of the blueberries, independent of their antioxidant capacity.

However, several variables could affect the results.

  • First of all, the quantity of blueberries ingested to get this effect is a lot (2.2 pounds over 3 days). I don’t know about you, but I think I would end up like Violet in Willy Wonka and the Chocolate Factory. You know – the one who swelled up and turned into a huge blueberry? So more research needs to be done to better determine dose and timing.
  • Another important consideration is the variety of blueberry. The blueberries used in the study hailed from New Zealand, and represent just one of over 20 varieties of the fruit. Previous research on cherries suggests that levels of phytochemicals vary between cherry varietals, so the same might be true for blueberries.
  • It would also be interesting to test activity type — to look at a variety of other exercises such as running, cycling, and team sports to see if there is a performance effect for aerobic activities.
  • Finally, the researchers didn’t use any milk or milk products in the test smoothie; it was all fruit.  They did this for two reasons: to isolate the compounds being tested, and because they feared that milk products might decrease the effects of the phytochemicals. In applying this research to recovery routines for athletes, the absence of milk from the smoothie could be relevant. Many athletes make their recovery smoothie with a milk-based protein like whey, so more research is needed to determine how or whether milk interacts with blueberries’ phytochemicals.

Bottom line

Eating for long-term health and exercise recovery is all about synergy. Fruits and vegetables have so many components that can’t be duplicated in pill form. Choose real food over supplements.

In terms of athletic performance, smart nutrition may improve recovery and improve performance. Try replacing the banana in your smoothie with a cup or so of blueberries, and include other colourful fruits and vegetables in your diet as well.

More research is needed to find out the type of blueberry that is best (if there is one), the quantity that needs to be eaten, the timing, and the form – juice alone or with protein. One thing’s certain, though: phytochemicals are nutritional powerhouses and should be an integral part of everyone’s diet.

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Photo credit: Chris Nixon

References

Click here to view the information sources referenced in this article.

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