Why your muscles don't hurt as much the second time you lift

Original Title

Reduced muscle lengthening during eccentric contractions as a mechanism underpinning the repeated-bout effect.

Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms

Summary

When you first do a new exercise, your muscles stretch a lot and get damaged. The second time, they stretch less — so they don't get hurt as bad.

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Surprising Findings

Muscle lengthening increased over sets in the first bout but stayed flat in the second—despite identical mechanical output.

People assume muscles adapt by becoming stronger or more resilient. This shows they adapt by changing how they move—literally limiting their own stretch to avoid damage.

Practical Takeaways

If you’re new to lifting, do the same exercise twice—4 weeks apart. You’ll feel dramatically less sore and recover faster the second time, even if you push just as hard.

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