16 September 2025

Second Day Soreness - The Science Behind

 

The Science of DOMS (Delayed-Onset Muscle Soreness )

 

DOMS is a complex biological process that scientists are still working to fully understand, but the leading theory attributes it to microscopic tears in muscle fibers. When you lift weights, especially heavy or new-to-you weights, you cause tiny, localized damage to the contractile proteins within your muscle cells. This damage is a normal and necessary part of building strength and muscle mass.

The sensation of soreness doesn't appear immediately because it's not the direct result of the tearing itself. Instead, it's the result of your body's inflammatory response to that damage. This is a multi-step process:

  • Initial Damage: During your workout, the mechanical stress on your muscle fibers creates micro-tears.

  • Inflammation: In the hours following your workout, your body's immune system sends inflammatory cells (like neutrophils and macrophages) to the damaged area. These cells help to clean up cellular debris and initiate the repair process.

  • Repair and Swelling: As these cells work, they release chemicals that can sensitize nerve endings, leading to the sensation of pain. This process also causes a slight swelling in the muscle tissue. It's this inflammatory cascade that takes time to build, which is why the soreness is delayed.

  • Peak Soreness: The peak of this inflammatory response often occurs between 24 and 72 hours after the workout, which is why the soreness is often most intense on the second day.

 

Why Not Immediately After?

 

The pain you feel during your workout is a different sensation, often described as a burning or "pumped" feeling. This is due to the buildup of metabolic byproducts like lactate and hydrogen ions, as well as the swelling of the muscle from increased blood flow. This sensation subsides shortly after you stop exercising. DOMS, however, is a separate and distinct type of pain related to the body's repair process.

 

Why Does It Happen?

DOMS is most common when you do something your body isn't used to. This could be:

  • Starting a new exercise program.

  • Increasing the intensity or duration of your workouts.

  • Performing exercises with a lot of eccentric movements (like going downhill or lowering a heavy weight slowly).

    Over time, as your muscles adapt, they become more resilient to this kind of stress, and DOMS will become less frequent and less severe.
 
The Bottom Line: Is It a Good Thing?

 

While DOMS is a sign that your muscles have been challenged, it's not a perfect indicator of a good workout or necessary for muscle growth. You can still make excellent progress without feeling sore every time. The most important factor for building muscle is progressive overload—consistently challenging your muscles to do a little more over time, whether that's lifting a heavier weight, doing more reps, or increasing the intensity.