Your muscles get used to tough workouts over time, so they hurt less and recover faster the more you do them.
Evidence from Studies
Supporting (2)
Community contributions welcome
The study shows that doing a tough arm exercise once helps protect muscles from damage and soreness the next time, which supports the idea that the body adapts after the first workout.
MR measurements of muscle damage and adaptation after eccentric exercise
The study found that when people did the same hard muscle exercise twice, their arms were less sore and showed less damage the second time, which supports the idea that muscles adapt after being stressed once.
Contradicting (1)
Community contributions welcome
The study looks at chewing muscles and finds they get more damaged, not less, when injured again—unlike other muscles in the body. This goes against the idea that muscles always get more resilient after being stressed twice.
Gold Standard Evidence Needed
According to GRADE and EBM methodology, here is what ideal scientific evidence would look like to definitively prove or disprove this specific claim, ordered from strongest to weakest evidence.