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Why Do Your Muscles Get Sore After Exercise? (It's Not Lactic Acid) · So That's Why

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Jen Oliver: Welcome to the So that's Why podcast where we unpack the
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science behind everyday questions.
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I'm Jen.
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Chris Smith: I'm Chris.
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Matt Edmundson: And I'm Matt.
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Jen Oliver: So today we're tackling something that virtually everyone
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who exercises has experienced.
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Why do we get sore muscles after exercising that familiar ache
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that settles in a day or two after a challenging workout?
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What's actually going on?
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Matt Edmundson: That special feeling where getting off the sofa
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becomes like a strategic operation.
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You all know what I mean?
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Where you genuinely consider whether the journey to the bathroom is really
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worth it because your legs have gone and put in a formal complaint.
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Jen Oliver: Exactly.
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And here's what's interesting.
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For decades, we've all been told it's lactic acid feel the burn.
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That's the lactic acid building up.
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But actually the science tells a completely different story.
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Chris Smith: It certainly does, and this lactic acid explanation
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has been comprehensively disproven.
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So lactic acid actually clears from your bloodstream within 30
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to 60 minutes after exercise.
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That timeline alone makes this theory impossible because muscle soreness
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typically doesn't begin until 12, even 24 hours post-exercise, sometimes longer.
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Matt Edmundson: And it's mad, isn't it?
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How widespread that lactic acid myth still is.
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You hear it?
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I hear it in the gym all the time.
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Jen Oliver: Yeah, and it's completely the wrong culprit.
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The real cause is microscopic damage to muscle fibers and the
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surrounding connective tissue.
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It's called delayed onset muscle soreness or doms for short, and it triggers an
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inflammatory response that peaks about 72 to 48 hours after you exercise.
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Chris Smith: That's right and that's why it's called the delayed onset
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because you feel fine immediately after your workout even the next day.
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I mean, I remember many times playing football on a Saturday, feeling fine on
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the Sunday or okay on the Sunday, but then walking like John Wayne by Monday morning.
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Matt Edmundson: Yeah, I get that.
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I get that.
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I mean, I've had workouts where I've walked out the
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gym feeling like a champion.
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Then sort of woke up the next day moving, like I'd aged
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literally 40 years overnight.
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Um, you're right though.
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Sometimes it's the day after, isn't it?
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That this sort of all kicks in.
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Jen Oliver: So if it's not lactic acid, what's actually
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happening at the cellular level?
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Chris Smith: So when you exercise, particularly during movements where
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your muscles lengthen under load, things like lowering weights or
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running downhill, you create tiny tears in individual muscle fibers.
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Now tears sound bad.
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Mm-hmm.
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But this is completely normal and nothing to worry about.
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Jen Oliver: And then the body launches are complex inflammatory cascades,
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and the damaged tissue releases chemical signals that trigger an
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immune response, bringing inflammatory cells and fluids to the affected area.
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Chris Smith: Yeah, exactly.
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And this inflammation causes swelling within the muscle tissue
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and activates your pain receptors.
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It's not damaging a harmful sense.
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It's your body's repair mechanism kicking into gear.
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Matt Edmundson: So the soreness then is actually a repair job in progress.
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Like my body's got builders in.
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And they're making just an awful lot of noise.
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Chris Smith: Yeah, it's a good way of, uh, thinking about it.
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So the inflammatory response, um, releases specific hormones called
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prostaglandins and leukotrienes that contribute to pain and swelling.
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And this whole process takes time to develop, which is why soreness
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peaks one to three days after exercise rather than straight away.
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Jen Oliver: And some researchers also propose that dos involves damage to the
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deep fascia, which is the connective tissue that wraps around your muscle.
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And that tissue's densely populated with pain sensitive nerve endings, which
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might explain why even gentle pressure on sore muscles can be so uncomfortable.
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Matt Edmundson: Oh, yes.
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Oh yes, I know exactly what you mean.
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And it's not just the muscles themselves, is it?
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The whole neighborhood seems to be affected by it.
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Yeah.
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Chris Smith: Yeah, very true.
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And research shows that even a 2% drop in performance can result from
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that process, and studies found that Dons can reduce strength.
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By 20% temporarily, which is significant if you're trying
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to maintain a training program.
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Jen Oliver: And the type of muscle contraction makes a huge difference too.
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So eccentric contractions where muscles actively lengthen under load
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are the most potent triggers, and that explains why running downhill causes
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more soreness than running uphill.
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Even though running uphill feels harder at the time.
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Matt Edmundson: Yeah.
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Why would you wanna run up anyway?
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Jen Oliver: You might not get a choice.
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Matt Edmundson: Why would you just wanna run?
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Um, but it does make sense, isn't it?
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I, I mean, I, after I've had gym sessions, I've had that you sort
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of finish thinking it was fine, especially when the lifts sort of felt.
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You know, controlled, but then two days later, I can barely get out of my chair
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and it's like, it's this slow lowering under load that catches you out, not the
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parts that feel toughest at the time.
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Chris Smith: That's exactly right.
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And it's because the force distribution across muscle fibers
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becomes uneven, and that creates disruption to the muscle fibers.
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Which means more repair work needed and therefore more soreness.
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Jen Oliver: And the variation between individuals is significant to research
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shows that after the same workout, some people experience severe soreness
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while others feel relatively fine.
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And there's a genetic component to how efficiently your body
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manages the inflammatory response.
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Matt Edmundson: So when I'm hobbling around then and my friend who did exactly
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the same workout, we've all got them, uh, is bouncing around like nothing happened.
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That's not me being weak.
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That's biology.
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Chris Smith: Yeah, precisely right.
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And um, studies on over a thousand athletes found enormous variation in
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sauna responses to identical exercise.
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So your individual inflammatory response, your muscle fiber
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composition, your training history.
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All of these things affect how sore you get.
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Jen Oliver: And age plays a role too because older adults may experience
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soreness differently 'cause their inflammatory response and
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recovery capacity change over time.
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But interestingly, fit individuals of any age typically return to
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normal faster, around 40 to 60% quicker than less conditioned people.
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Matt Edmundson: Okay, so fitness doesn't stop me getting sore.
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It just helps me bounce back faster, is what we're saying.
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Jen Oliver: Exactly right.
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Which brings us to one of the biggest myths in fitness.
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The idea that soreness means you've had an effective workout, and this
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needs ing because it's so widespread.
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Chris Smith: You're right, and it is completely false.
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So research conclusively demonstrates that doms, this delayed onset
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muscle soreness is neither necessary nor sufficient for muscle growth.
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You could build significant muscle without experiencing much soreness at all.
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Matt Edmundson: So does that mean the no pain, no gain thing is nonsense?
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Jen Oliver: Well, muscle growth occurs through mechanical tension and
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metabolic stress, not through damage.
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Some muscle groups like shoulders rarely experience significant
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soreness, yet they still grow perfectly when they're trained properly.
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Chris Smith: Yep, that's right.
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So the no pain, no gain thing does still count because your body
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adapts to exercise through something called the repeated bout effect.
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That means you'll experience progressively less soreness for the
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same workout, even as your strength and muscle mass continues to increase.
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So the pain has turned into gain in that sense.
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Matt Edmundson: So getting less sore over time is actually a sign.
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Your body is a. Adapting and improving.
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Right,
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Chris Smith: exactly.
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But back to that, no pain, no gain.
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Constantly chasing maximum soreness can actually be counterproductive.
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It increases injury risk, it creates excessive fatigue, and
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it might even slow your progress.
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Jen Oliver: So what about the common advice that you
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shouldn't exercise when you sore?
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There's a lot of conflicting information out there.
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Chris Smith: There is, and, and I'd say so for mild to moderate soreness,
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uh, light activity can actually help.
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It's called active recovery, and it works by increasing blood flow to
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damage tissues, delivering oxygen and nutrients while removing waste products.
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Matt Edmundson: So gentle movement then is better than lying on a sofa.
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Well, if it was me, I'd lie on the social feel sorry for myself.
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I know, I know.
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But So this gentle movement, this active recovery is, is better than that.
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Chris Smith: Yeah, the sofa does sound quite appealing though,
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to be fair, but no, yeah.
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In, in most cases, yes.
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So walking, light, cycling, uh, swimming, anything, lowden low intensity and
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research has found that active recovery at 30 to 60% of your maximum heart
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rate is more effective for com than complete rest for reducing soreness.
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Jen Oliver: And the key distinctions between productive training and harmful
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overexertion training through severe soreness that compromises your form.
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Or prevents proper movement.
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I mean, that's when you risk injury, but modified training, reduced
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intensity for all, where in different muscle groups can help you maintain
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consistency while recovering.
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Chris Smith: That's right.
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And if we looked at the other side of it, so red flags, these things would include.
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Such as a sharp pain rather than a dull, aching pain.
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Localized to a specific point.
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Visible swelling or bruising or soreness that persists beyond a week.
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They're symptoms that warrant caution and might need medical attention.
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Matt Edmundson: So what about things then like um, uh, ice baths, the super popular,
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my preference, massage, stretching.
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I like stretch.
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Is any of that working?
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Jen Oliver: So analysis of about 120 studies identified which treatments
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actually have evidence behind them.
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Active recovery ranks highly up there as does you'd be pleased to hear massage
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therapy, um, because that increases blood flow and that may stimulate endorphin
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release so you feel a bit better.
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Chris Smith: Yeah.
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And another one is cold water immersion, and that shows effectiveness too
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at around 10 to 15 degrees Celsius for a few minutes after exercise.
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And contrast therapy, which is alternating hot and cold, also demonstrates benefits,
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although both sound fairly horrific to me.
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I've gotta say that.
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Matt Edmundson: I love the sauna.
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Uh, what about stretching though?
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Um, that's not major list.
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Uh, so I want to know, because I've spent years doing hams
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streak stretches, uh, hams streak, hamstring stretches after leg day.
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Jen Oliver: Actually, this is where the research gets surprising.
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Multiple reviews found that stretching.
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Whether before, after, or both produces only minimal
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reductions in muscle soreness.
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Matt Edmundson: Wow.
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Jen Oliver: And we're talking effects that they're too small
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to be clinically meaningful.
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Matt Edmundson: So all that post-workout stretch stretching them wasn't, wasn't
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preventing or helping my soreness.
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Chris Smith: No, not significantly.
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And, uh, there was one systemic review that found stretch and reduced
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soreness by less than two millimeters on a 100 millimeter pain scale.
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So, as, as Jen said, effectively undetectable.
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But stretching does have other, other benefits.
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It improves your flexibility, your range of motion.
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But preventing this doms is not one of them.
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The time might be better invested in proper nutrition and sleep.
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Jen Oliver: Sleep is genuinely powerful for your recovery.
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During deep sleep, your body releases growth hormones, which stimulates the
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tissue repair and muscle regeneration.
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Sleep, also modulates the inflammatory response, releasing
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anti-inflammatory compounds that can help reduce that muscle pain.
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And you should really aim for seven to nine hours a night
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to optimize your recovery.
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Matt Edmundson: So what you're saying, Jen, is uh, don't stay up late scrolling
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through your phone because that's gonna make your muscle recovery.
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Well, much slower.
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Jen Oliver: Essentially, yes, sleep deprivation can increase pain sensitivity
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and impair the re whole repair process.
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Chris Smith: And, uh, protein intake matters too.
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So we need amino acids to repair damaged muscle fibers and amino acids are the
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building blocks of protein, which is why each meal should ideally contain
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20 to 40 grams of protein to optimally stimulate muscle growth and repair.
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Jen Oliver: And foods with anti-inflammatory properties can help too.
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Things like berries, food riches in Omega-3 nuts and olive oil.
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And of course, staying well hydrated is equally important as dehydration
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can intensify that muscle soreness.
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Matt Edmundson: So lo and behold, what you're saying is the fundamentals matter.
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More perhaps than the fancy recovery gadgets that are available
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Chris Smith: far more, although I know you love your gadgets.
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But, uh, yeah, adequate sleep, proper nutrition, gradual progression in your
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training and active recovery when needed.
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They're the things that will work much better than, um, these
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expensive pieces of equipment
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Jen Oliver: and gradual progressions.
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Probably the most effective prevention strategy slowly increase in exercise
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intensity, duration, or load.
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It gives you muscles time to adapt without overwhelming them.
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Chris Smith: That's it.
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And experts typically recommend increasing training volume
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by no more than 10% per week.
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So that allows for progressive adaptation without triggering
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this excessive soreness.
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Matt Edmundson: You know what?
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I think plenty of people, including myself, if I'm honest,
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have made the mistake of doing too much too soon after a break.
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Like you go on holiday, you come back, start exercising, thinking
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like you should just kick off, you know where you left off.
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Which you, I've always found a recipe for total soreness.
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Jen Oliver: Absolutely.
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But understanding why you get sore can help you be patient with the process
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rather than pushing through unnecessarily.
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Chris Smith: Yeah, and it's, it's worth remembering that some soreness
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is completely normal when you're challenging your body with new
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activities or increased intensity.
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It's not a sign of failure or weakness.
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Matt Edmundson: Okay.
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So why do we get so muscles after exercising?
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Chris Smith: It's because exercise, particularly intense movements where
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muscles lengthen under load, it create microscopic tears in muscles fibers.
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Your body responds with an inflammatory cascade that repairs the damage, and
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that process causes a characteristic dull aching sensation we call delayed
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onset muscle soreness or Doms.
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Jen Oliver: The soreness peaks one to three days after exercise.
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'cause the inflammatory response takes time to fully develop.
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And crucially, this isn't caused by lactic acid, which
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actually clears within an hour.
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It's a repair process that's completely normal.
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And healthy.
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Matt Edmundson: So the post-workout ache isn't punishment.
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I must remember this.
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It's my body's maintenance crew showing up for work.
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Bit inconvenient time-wise, but it's doing important stuff.
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Jen Oliver: Exactly.
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And so now you know that chasing maximum soreness isn't the goal.
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That light movement can help, and that the fundamentals of sleep, nutrition, they
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matter more than most recovery trends.
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So that's it for this week.
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Make sure that you hit that subscribe button.
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We're unpacking the science behind everyday questions each week.
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Tell us in the comments what you'd like us to explore next.
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Thanks for geeking out with us, but for now, that's it from me.
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Matt Edmundson: That's it from me.
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Chris Smith: And that's it from me.
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Jen Oliver: Bye for now.