Starting to work out, coming back after a long break, or trying a new exercise frequently comes with an unpleasant side effect: muscle soreness. Sometimes it’s bad enough to completely derail the best of intensions and put you back on the sidelines. It can even lead to chronic pain and lingering injuries. So what causes post-workout pain [aka Delayed Onset Muscle Soreness (DOMS)] and what can you do about it? NOTE: this post is discussing the regular achy muscle stiffness and soreness that comes several hours to days after unaccustomed exercise. It is NOT talking about any sudden pain you may get during exercise – if this happens to you, you should stop whatever you are doing immediately and consult your physician.

Many of you have probably heard the persistent myth that lactic acid causes DOMS. This idea came about in 1922 when German physician Otto Meyerhof placed amputated frog legs into an air-tight jar and applied electric shocks until the muscles would no longer contract. When he later examined the leg muscle tissue, he found a high concentration of lactic acid. Meyerhof concluded that muscle contraction in the absence of oxygen (anaerobic exercise) used up the energy source stored in muscles (glycogen), produced lactic acid, and that the lactic acid was responsible for muscle fatigue (inability to further contract). Muscle fatigue must cause pain, therefore lactic acid was responsible for post-exercise muscle pain. 

Here’s the problem with Meyerhof’s research – although this model may work in dead tissue, it isn’t applicable to living muscle. Yes, stored muscle energy can be converted into lactic acid during anaerobic exercise and it can build up in muscles. This is the source of the burn you may feel when performing an exercise under more strain than usual (like increasing your bicep curls by 10 reps or your squats by 20 pounds). However, lactic acid is then used for energy in the body and is cleared out of muscle tissue within 60 minutes. Yet, DOMS usually starts 12 to 24 hours after exercise, so the pain can’t be fully explained by lactic acid build up.

A newer hypothesis is that DOMS is the result of microscopic trauma and inflammation in muscle tissue. Biopsies of muscle tissue show damage to the fibers and an increased concentration of pro-inflammatory molecules. Proteins that are supposed to be inside of the muscle cells leak out, indicating that the cells have been damaged. Inflammatory cells flood the area. All of these factors have led researchers to believe that trauma and inflammation cause muscle soreness. The issue with this idea is that non-steroidal anti-inflammatory drugs don’t reliably relieve DOMS. If muscle soreness was strictly due to inflammation, anti-inflammatory drugs should reduce or eliminate it. Furthermore, scientists have found that DOMS can be felt even when no muscle fiber damage is present. 

So how is the newest research explaining post-workout muscle soreness? Nerve damage in the muscle. Muscle contraction and relaxation is controlled by nerve endings that interface directly with muscle cells. Scientists are hypothesizing that compression and damage to these nerve endings in a specific part of the muscle (muscle spindle) is responsible for DOMS. The body releases nerve growth factors in order to repair and regenerate injured nerve endings. Scientists are able to reduce DOMS by treating sore muscles with anti-nerve growth factors. They concluded that although surrounding injury to the muscle tissue may contribute further to muscle soreness (e.g., inflammation), nerve compression and damage in muscles is the main causative factor. This may explain why anti-inflammatories like over-the-counter NSAIDS don’t reduce DOMS pain.

What can you do to prevent post-exercise muscle soreness if you don’t happen to have a bottle of anti-nerve growth factors handy? The worst of DOMS is caused by the eccentric part of an exercise – this is the part where your muscle is lengthening under tension. An example of this is when you are lowering a dumbbell after doing a bicep curl – your biceps are going from their shortest, most contracted length in the curl to stretching while still supporting the weight. (The curling up part of the motion is called the concentric contraction and your muscles are shortening while under tension.)

Therefore, you can prevent DOMS by spending as short of an amount of time in the eccentric part of the lift as possible. Make your eccentric and concentric parts of the lift equal – lift and lower the weight quickly. Doing isometric holds will help prevent DOMS, too. Isometric exercises are where your muscle contracts, but doesn’t shorten or lengthen, like doing wall sits for 30 seconds. Weak eccentric contractions help, too. For these, you would use lighter weights when trying a new exercise. 

Do you always want to avoid the eccentric part of an exercise – absolutely not! Research indicates that eccentric training appears to be more effective at increasing muscle mass than concentric training, although there is disagreement as to how significant the difference is. However if you’re new to exercise or DOMS is going to completely derail your exercise plan, it’s worth giving these methods a try. 

What’s the worst DOMS you ever experienced? What did you try and did it work? Leave a comment below about your DOMS history and what worked for you.