by Bree Iskandar
By now, a great deal of us have likely given up on that new year’s resolution to get in shape (for those who are staying strong, I applaud you!) One study suggests that sticking with something for more than two months makes it much more likely to become a habit. We may have had strong determination at the year’s start, but once that stiff, all-over-body soreness set in, it literally became harder to get our butts back to the gym. So why is muscle soreness so debilitating, what causes it, and what does it mean?
When you exercise, you may notice your muscles getting tired over time—the first repetition in a set of pushups, for instance, feels a lot easier than the tenth. While lactic acid buildup is commonly blamed for muscle fatigue, it is actually innocent. Instead, a major cause is the inability of our brain to properly communicate with our muscles during exercise.
Our muscle cells contain and are surrounded by various kinds of charged ion particles (also called electrolytes), including sodium, potassium, and calcium. When instructed by the brain to contract, muscle cells open pores on their cell membranes. This allows electrolytes to flow between inside and outside the cell, inherently causing a change in the charge of the muscle cell relative to its environment. As a result, an electrical signal called an action potential travels throughout the cell telling it to contract. Muscle fibers then use an energy-providing molecule called adenosine triphosphate (ATP) to enable contraction. But as we exercise, the ATP we have in our body gets used up and the electrolytes needed to send contraction signals get depleted. So even if the brain tells muscles to contract, they may be physically incapable of doing so.
That explains why our muscles get tired as we work out, but what about the muscle soreness we feel a couple days after working out? This delayed onset muscle soreness, or DOMS for short, is caused by microscopic tears in our muscle fibers which happen during certain types of exercise movements. One of these movements, called an eccentric contraction, is the lengthening and contracting of a muscle at the same time. Imagine, for example, a bicep curl: you use your bicep muscle to curl a dumbbell up, then slowly bring it down while maintaining muscle tension. Your bicep muscle lengthens as you lower the dumbbell, but, since you’re lowering a heavy weight as well, it is still under constant tension. This simultaneous lengthening and contracting puts a lot of strain on your muscles, causing microscopic tearing. Tears trigger an inflammatory response from our bodies, which in turn activate specific sensory neurons called nociceptors. Nociceptors then send electrical signals to our brain which we ultimately interpret as pain.
I’m sure we’ve all wondered before if muscle soreness is an indicator of muscle growth, or if soreness means you’re getting stronger. The unsatisfying yet typical scientific answer is that it depends. Our bodies send blood and nutrients to the site of our microscopic muscle tears to repair them. If this occurs consistently over time, the nutrients used to repair our tears will eventually result in increased muscle mass. Larger muscles have a higher capacity to endure more tension for longer, making us stronger. However, the correlation between muscle soreness and strength ends when you try to equate the extent of muscle soreness with extent of increased strength. There is no significant evidence suggesting that one killer workout that leaves you immobile the next day will make you stronger than a workout that causes only mild or moderate soreness. Instead, the most important factor in building muscle mass is consistency over time.
The good news is that the body adapts to these stressors, causing the severity of muscle soreness to fade as we stick with our workouts. And it can be pretty rewarding when we find that one weight isn’t challenging us like it used to. We forget about the pain, sweat and dedication it took to get to this point—just in time to reach for a heavier dumbbell and start the process all over again.
