Soreness - Does it Matter? MSI vs. MSD Explained

As you train longer, something interesting often happens: you get stronger and more capable, yet you may feel more soreness, stiffness, or minor discomfort than when you first started. This is where understanding the difference between MSI and MSD matters.

MSI: Musculoskeletal Injury

MSI refers to true tissue injury or dysfunction; strains, tendinopathies, joint issues, or anything that meaningfully limits training or performance.

With well-structured training:

• Tissue capacity increases

• Load tolerance improves

• Movement quality improves

Result: your risk of real injury generally goes down over time.

MSD: Musculoskeletal Discomfort

MSD is the perception of soreness, tightness, stiffness, or low-grade discomfort. This is not an injury, it's a sensation.

And counterintuitively, MSD often increases as you become more trained.

Why Discomfort Goes Up

Muscle is not just a motor; it’s a sensory organ. As you build muscle and spend more time under load:

• Neural awareness improves

  
  

• Your body gets better at detecting stress and fatigue

  
  

• You perceive more detail from your tissues

A more trained system is a more sensitive system, not a more fragile one. Soreness is feedback, not a diagnosis.

Soreness and stiffness are information about recent loading, volume, or novelty. They do not automatically mean something is wrong or that you should stop training. We use these signals to adjust training, not to avoid it.

What Really Matters

At M2, we prioritize function over feelings.

If you’re:

• Moving well

  
  

• Progressing appropriately

  
  

• Recovering as expected

Then increased awareness or soreness matters very little. We care about trends, capacity, and performance over time, not isolated sensations.