See if this sounds familiar: You went to the gym yesterday. Today, your muscles feel sore. You might think that means your workout was an effective one, and that growth is sure to follow. On the flip side, workouts that don’t leave you stiff and sore produce little in the way of results. If you’ve stopped feeling sore, you might think it's a sign that you need to switch things up if you want to get your muscles growing again.
While most people think that sore muscles after a workout are a sign that you’ve stimulated growth, and that more soreness equals faster results, it's not necessarily true. In fact, there’s very little evidence to show that muscle soreness is a reliable indicator of muscle damage, or that being sore means faster muscle growth, or that a lack of soreness means that your workout wasn’t effective. More about that in a moment, however.
First, let's discuss what causes delayed-onset muscle soreness—or DOMS, for short. To be blunt, scientists aren’t sure exactly why people get sore after a workout. But their best guess is that a tough workout, or even just a single exercise that you haven’t done before, typically leads to a bout of inflammation, which is the way your body handles an injury.
As part of the repair and recovery process, your body ramps up the production of cells that make certain nerve endings in your body more sensitive. When you move, these nerves send signals to the brain, which then creates the perception of soreness. These nerve fibers are located mainly in the connective tissue found between muscle fibers, as well as the junction between the muscle and tendon. In other words, the source of post-exercise muscle soreness appears to be the connective tissue that helps to bind muscle fibers together, rather than the actual muscle fibers themselves.
What’s more, an increase in muscle soreness doesn’t necessarily reflect an increase in muscle damage. Conversely, a decrease in soreness is not always indicative of less muscle damage, either. Muscle soreness can show up without any apparent damage to the muscle or signs of inflammation.
In one study, for instance, a team of Danish scientists got a group of young men to exercise one leg on an isokinetic dynamometer—essentially, a souped-up leg extension machine. The other leg had a couple of electrodes slapped on it, which delivered an electrical impulse to the muscle, causing it to contract.
Muscle soreness was assessed in both legs 24 hours later, and again after four and eight days. The researchers also extracted a slice of muscle tissue from each leg, and looked at it under an electron microscope in order to see how much damage was done. The result? Muscle soreness hit a peak 24 hours after exercise, and was still significantly higher four days after the workout. There was no significant difference in soreness between the two protocols. That is, subjects were just as sore in the days following electrically stimulated contractions as they were after voluntary exercise. The amount of muscle damage, however, was considerably higher from the extension machine.
Other studies report much the same thing, with only moderate levels of soreness associated with a high degree of damage. In short, you can’t rely on muscle soreness to gauge the extent to which a particular workout has damaged your muscles. So, can you still train if your muscles are sore?
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According to conventional wisdom, training a muscle that still feels sore will only delay the recovery process and put the brakes on muscle growth. But that doesn’t seem to be the case, either. That is, training a muscle when it still feels sore doesn’t appear to create any further damage or slow the recovery process.
In one study, scientists recruited a group of student athletes and split them into two groups. Both groups completed 30 negative reps of dumbbell curls, which is a highly effective way to create both muscle damage and soreness. The first group rested, but the second group came back to the lab three days later—when their muscles still felt sore—to do the whole thing again. Both groups were tested every day for nine days after the first workout.
You’d think that the second bout of training would interfere with recovery from the first, or at least make muscle damage worse. But this wasn’t the case. The researchers found no significant difference between the groups in terms of muscle soreness or markers of muscle damage. Some people also experience a far greater degree of soreness than others, even when they do the same workout. In fact, there seems to be a population of “high responders” to resistance exercise. Research shows
that these people lose more strength after a workout, take longer to recover, as well as experience a greater degree of muscle soreness.
There are also differences in the ability of various exercises to create soreness. Certain movements, particularly those involving high levels of muscle activation at long rather than short muscle lengths, are more likely to leave you feeling sore.
Let’s take the bench press as an example. At the bottom of the movement, with the bar just above your chest, the pecs are lengthened while simultaneously experiencing high levels of tension.
It’s a different story with an exercise like the dumbbell lateral raise. At the bottom of the movement, with the dumbbells in front of you, there isn’t much tension on the delts. Muscle activation increases as you raise both arms out to the side and the delts shorten. This “length-dependent component” is one of the reasons why the bench press (high levels of muscle activation at a long muscle length) leaves your chest feeling sore the next day, while the lateral raise (high levels of muscle activation at a short muscle length) doesn’t do the same thing for your delts.
When researchers have put high- and low-soreness training programs to the test, they've found that both deliver similar gains in muscle mass. In one trial, Brazilian scientists compared training a muscle once a week with a full-body workout performed five times a week, Monday through Friday. Subjects in the group that hit each muscle group once a week reported a much higher level of post-exercise muscle soreness. There was no significant difference in strength or size gains, however, between the two groups. In other words, both the “low soreness” and “high soreness” training programs increased muscle mass and strength to a similar degree.
Muscle soreness is nothing more than a sign that you did something your body wasn’t used to, or performed an exercise that just so happens to trigger more soreness than others. Some people will experience DOMS to a greater extent than others, while some exercises will stimulate more soreness than others. While being sore and stiff might feel oddly satisfying, however, it’s not a reliable sign that growth has been stimulated. Likewise, the fact you’re not sore doesn’t mean your muscles aren’t growing.
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Christian Finn is a UK-based personal trainer and exercise scientist. He blogs frequently about fitness and weight loss at muscleevo.com.