Understanding DOMS: Why You Feel Sore After a Workout

Imagine crushing a workout that pushes your limits—you feel strong, accomplished, and ready to tackle the day. The next morning, you wake up and think, Not too bad! I was expecting worse. But as the day wears on—or perhaps even the day after—your muscles suddenly remind you of every squat, lunge, and press. This experience is the hallmark of delayed onset muscle soreness, or DOMS, and it’s a rite of passage for fitness enthusiasts of all levels.

DOMS is one of the most talked-about sensations in fitness circles, often leaving people wondering if it’s a sign of progress or a problem to fix. Why does it happen? Why does it sometimes take two days to hit? And does it mean your workout was effective? Let’s explore the science, the myths, and practical tips to help you embrace—or at least better understand—this common post-workout phenomenon.

What Is DOMS?

Delayed onset muscle soreness (DOMS) refers to the muscle pain and stiffness you feel after intense or unaccustomed exercise. Unlike the burning sensation you may feel during a workout due to lactic acid buildup, DOMS sets in hours later, often peaking between 24 and 72 hours post-exercise. But what exactly causes this delayed soreness?

At its core, DOMS is the result of microscopic damage to your muscle fibers. Here’s how it works:

1. Eccentric Contractions Cause Stress:
   During certain movements, your muscles lengthen while under tension—this is called eccentric contraction. For example:

   • Lowering a weight during a bicep curl.

   • Descending into a squat.

   • Walking or running downhill.

   These movements place higher mechanical stress on the muscle fibers compared to concentric (shortening) contractions.

2. Microtears in the Muscle Fibers:
   The mechanical stress creates tiny tears in the muscle fibers and surrounding connective tissues. This damage is entirely normal and, in fact, necessary for muscle growth and adaptation.

3. Inflammation Kicks In:
   In response to the damage, your body activates its repair systems. Immune cells like macrophages flood the area, breaking down damaged tissue and clearing debris. This process also releases inflammatory chemicals such as cytokines and prostaglandins, which contribute to swelling and heightened sensitivity in the affected muscles.

4. Fluid Accumulation and Sensitization:
   The inflammation causes fluid to accumulate in the muscle tissue, increasing pressure and stretching the fibers. This mechanical stretch, combined with chemical signals, sensitizes the nerve endings in and around the muscle. This is why the pain and stiffness can intensify over time, peaking a day or two after exercise.

5. Repair and Strengthening:
   During the recovery phase, your body synthesizes new proteins to repair the damaged fibers, making them stronger and more resistant to future stress. This adaptation is a critical part of improving performance over time.

DOMS is a sign that your body is adapting to new demands, but the extent of soreness varies greatly depending on factors like the intensity of the workout, your fitness level, and your individual recovery processes. While DOMS can be uncomfortable, it’s a normal and temporary part of muscle recovery—and, for many, a badge of honor signaling hard work.

What Causes DOMS?

Why Eccentric Muscle Contractions Cause DOMS

The leading cause of DOMS is eccentric muscle contractions—when a muscle lengthens while under tension. These movements create unique mechanical and cellular stress compared to concentric contractions, where the muscle shortens. Eccentric contractions are integral to many everyday and exercise motions, such as:

• Lowering into a squat.

• Running downhill.

• Slowly lowering a dumbbell during a bicep curl.

Let’s break down what happens at the cellular level during these movements and how it leads to DOMS:

1. Mechanical Stress on Muscle Fibers
   During eccentric contractions, muscle fibers are forced to resist an external load while elongating. This generates high tension, especially in the sarcomeres, the basic contractile units of muscle tissue. Sarcomeres are made up of overlapping actin and myosin filaments, which slide past each other during muscle contraction.

   In eccentric movements, the alignment of these filaments becomes disrupted, causing small microtears in the sarcomeres. Additionally, some weaker sarcomeres may be stretched beyond their capacity, further exacerbating the damage.

2. Damage to Surrounding Structures
   The stress isn’t limited to the muscle fibers themselves. The connective tissues, including the endomysium, perimysium, and epimysium, which surround and support the muscle fibers, also sustain microscopic tears. This structural damage contributes to the overall sensation of soreness and stiffness.

3. Calcium Leakage and Disruption
   Eccentric stress can damage the sarcoplasmic reticulum (SR), the cellular structure responsible for storing and releasing calcium. This damage leads to the leakage of calcium ions into the surrounding tissues. Excess calcium interferes with normal cellular function and triggers the activation of enzymes such as calpains, which break down damaged proteins and exacerbate inflammation.

4. Inflammatory Response
   The body recognizes the microtears as injury and initiates an inflammatory response to repair the damage. Immune cells, including macrophages and neutrophils, are recruited to the damaged site. These cells release pro-inflammatory cytokines, such as interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α), which:

   • Break down damaged muscle fibers.

   • Stimulate the release of prostaglandins, which increase blood flow and contribute to swelling.

   • Sensitize nociceptors (pain receptors), amplifying the perception of soreness.

5. Fluid Accumulation and Pressure
   The inflammatory process increases the permeability of blood vessels around the damaged tissue, causing fluid to accumulate. This fluid exerts pressure on the muscle fibers and surrounding tissues, adding to the sensation of tightness and pain commonly associated with DOMS.

6. Muscle Repair and Adaptation
   Once the damaged fibers are cleared, the body begins the repair process. Satellite cells, which are specialized muscle stem cells, become activated in response to the damage. These cells fuse with the existing muscle fibers, donating their nuclei to help synthesize new actin and myosin filaments. Over time, this repair process strengthens the muscle, making it more resilient to future stress.

This entire cycle of stress, damage, inflammation, and repair is what makes eccentric contractions so effective for muscle growth and adaptation—but it’s also why they’re the primary driver of DOMS. While this process may leave you sore for a few days, it’s a sign that your body is working hard to recover and come back stronger.

Why Does DOMS Peak on the Second Day for Some?

If you’ve been training for a while, you might notice that you don’t always feel sore the day after a workout. Instead, the soreness peaks on the second day. This delay is a classic feature of delayed onset muscle soreness (DOMS) and is influenced by several factors, particularly if you’re an experienced trainee. Let’s break this down further:

The Timeline of Inflammation and Recovery

When you exercise intensely, your muscles sustain microscopic damage during eccentric contractions. The body’s response unfolds in distinct stages:

1. Immediate Post-Exercise (0–12 Hours):

   • Mechanical stress and microtears in muscle fibers occur during the workout.

   • The inflammatory response begins, but it’s in the early stages. Immune cells such as neutrophils start to gather at the site of damage, but they haven’t fully activated yet.

   • Pain or discomfort isn’t pronounced yet, as the inflammatory markers and tissue swelling are still minimal.

2. Next Day (12–24 Hours):

   • The immune response intensifies, and macrophages begin to clear out damaged tissue.

   • However, the peak inflammatory markers (e.g., cytokines like IL-6) and the associated chemical irritation of pain receptors haven’t occurred yet.

   • You might feel a bit of stiffness or tightness, but full-blown soreness usually hasn’t set in.

3. Second Day (24–48+ Hours):

   • Peak inflammation occurs during this window. Cytokines, prostaglandins, and other inflammatory chemicals flood the area, increasing fluid accumulation and sensitizing nociceptors (pain receptors) in the muscle and surrounding tissues.

   • The breakdown of damaged tissue by macrophages reaches its highest activity, amplifying the soreness.

   • This delay is why soreness often feels worse on the second day rather than immediately after the workout.

Why This Happens More Often for Experienced Trainers

If you’ve been training consistently, your body is more adept at handling muscular stress. Here’s why this can delay soreness:

1. Conditioned Muscles Have Reduced Damage:

   • Experienced athletes have more structural integrity in their muscles. Regular training increases the density of connective tissues and improves the alignment of muscle fibers, making them more resistant to tearing.

   • The lower degree of damage means inflammation takes longer to build up, delaying the onset of soreness.

2. More Efficient Recovery Systems:

   • A well-trained body often prioritizes immediate repair processes, like stabilizing calcium ion levels and minimizing early disruptions in cellular function. This delays the inflammatory response to peak closer to the second day.

3. Greater Tolerance to Discomfort:

   • Regular training can desensitize pain pathways, meaning you’re less likely to notice mild soreness on the first day. By the second day, however, the buildup of inflammatory markers and swelling may overwhelm this tolerance, making soreness more noticeable.

4. Tighter Adaptation Windows:

   • Experienced lifters are typically working closer to their body’s adaptive ceiling. They need more intense or novel stimuli to create enough microtrauma to induce significant DOMS. This can result in a delayed response as the body adjusts to this higher level of demand.

What It Means If You’re Sore Two Days Later

• Your Recovery Process is Normal: The two-day delay in soreness indicates that your body is undergoing the natural inflammatory and repair cycle associated with DOMS.

• You May Be Pushing Harder: A second-day peak can mean you’ve introduced a new movement, increased volume or intensity, or incorporated more eccentric-focused exercises—pushing your muscles slightly out of their comfort zone.

• You’re Building Resilience: For seasoned trainers, this delayed soreness often represents a positive adaptation. It’s a sign that your muscles are strong enough to resist immediate damage but still benefit from recovery and repair for future gains.

In short, feeling sore two days after a workout rather than the next day is a common and completely normal occurrence, particularly for those with a solid training foundation. It highlights your body’s efficiency in managing stress and adapting to grow stronger, even if the process feels a bit delayed!

What Does It Mean If You Don’t Feel Sore?

Not feeling sore doesn’t mean your workout was ineffective. DOMS isn’t the sole indicator of a good workout. Instead, consider these factors:

• Adaptation: Regular training reduces DOMS over time as your muscles adapt to the exercises.

• Intensity vs. Volume: A lower-intensity workout or one focused on concentric movements might stimulate muscles without causing significant soreness.

• Recovery: Proper warm-ups, cool-downs, and recovery strategies can minimize DOMS.

How to Alleviate DOMS

While DOMS can’t be completely avoided, you can manage it with these strategies:

1. Active Recovery: Light movement, like walking or yoga, can increase blood flow and reduce stiffness.

2. Hydration and Nutrition: Staying hydrated and consuming sufficient protein aids muscle repair.

3. Cold or Contrast Therapy: Alternating between hot and cold treatments may reduce inflammation.

4. Gentle Stretching: While it doesn’t directly heal DOMS, stretching can improve range of motion and reduce discomfort.

5. Gradual Progression: Avoid jumping into high-intensity workouts without preparation.

A 2013 study published in the Journal of Strength and Conditioning Research found that eccentric-focused exercise leads to greater muscle soreness compared to concentric or isometric movements. The research highlighted that inflammation peaks 48 hours post-exercise for most individuals, explaining why soreness can be delayed.

Another study from Medicine & Science in Sports & Exercise (2017) noted that trained individuals often experience less intense DOMS than beginners because their muscles have adapted to the stress.

DOMS is a natural part of the training process and signifies your muscles are adapting and growing stronger. However, it’s not the sole marker of an effective workout. By understanding the science behind DOMS, you can better navigate your recovery process and train smarter. Whether you feel sore the next day or two days later, listen to your body, prioritize recovery, and remember that consistency is key to long-term progress.

https://jps.biomedcentral.com/articles/10.1186/s12576-023-00896-y

https://eric.ed.gov/?q=menstrual+AND+cycle&id=EJ967173

Hope that helps!

Happy Exercising,

Robyn