Should I train when I am sore?
Usually yes: soreness is not damage you need to wait out, though a muscle that is still weak or painful to move deserves another day.
Most soreness comes from doing something new, or more of it than usual. Repeat the same session and it shrinks, which is why week three of a program hurts far less than week one even though you are lifting more.
Train the sore muscle again when it can produce force normally. If your warm-up sets feel heavier than usual, drop the load rather than skipping the session. Hold off only when a specific spot hurts sharply, when the pain is in a joint rather than a muscle, or when a muscle still cannot move through its full range.
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- Damas, F. et al. (2018). The development of skeletal muscle hypertrophy through resistance training: the role of muscle damage and muscle protein synthesis. Eur J Appl Physiol 118(3). Damage and soreness fade as you repeat a session, and they are not what drives growth.
- Schoenfeld, B.J. & Contreras, B. (2013). Is postexercise muscle soreness a valid indicator of muscular adaptations? Strength Cond J 35(5). Soreness tracks novelty and lowering work, not the quality of the session.