You're doing everything right and your muscles still ache. Here's the biological reason.

COMT is an enzyme that breaks down catecholamines, the neurotransmitters your brain uses to modulate pain. When COMT is working normally, it keeps these pain-modulating chemicals at the right level. Too slow a clearance, and pain signals amplify. Too fast, and your pain relief system doesn’t work well either.

The Val158Met variant is extremely common. Roughly 25% of people of European ancestry are homozygous slow, meaning both copies of their COMT gene are the slow version. When you carry the slow variant, your nervous system takes much longer to clear dopamine and norepinephrine, which amplifies pain signaling in the central nervous system and leaves you hypersensitive to soreness.

What this feels like: Your muscles stay sore longer than they should. A workout that causes mild soreness in fast COMT people can leave you uncomfortable for a week. You’re not weaker or less fit. Your pain modulation system is just turned up louder.

Your brain produces its own opioid-like molecules called endogenous opioids. These chemicals activate opioid receptors in your nervous system and dramatically reduce pain signaling. OPRM1 codes for the mu-opioid receptor. How sensitive your receptors are to these natural opioids directly determines your baseline pain tolerance.

The A118G variant (rs1799971) is carried by roughly 10-15% of people of European ancestry and about 40% of people of East Asian ancestry. The G allele reduces the receptor’s sensitivity to endogenous opioids. That means your brain is producing pain-relief molecules, but your receptors aren’t responding as strongly as they should, leaving you with reduced natural pain suppression capacity.

What this feels like: Even when you’re at rest, soreness feels more intense than it should. You have less baseline pain tolerance than your friends. A massage that helps others feels barely noticeable for you. Your nervous system simply doesn’t have access to as much natural pain relief.

Your nervous system produces endocannabinoids, particularly anandamide, which is sometimes called the “bliss molecule.” Anandamide binds to cannabinoid receptors throughout your nervous system and dramatically reduces pain signaling. FAAH is the enzyme that breaks down anandamide. If FAAH is very active, anandamide is cleared quickly and pain relief is short-lived. If FAAH is slow, anandamide persists longer and pain suppression is more durable.

The C385A variant, carried by roughly 20-30% of the population, has the A allele which reduces FAAH activity. People with the A allele have higher baseline anandamide levels, which means stronger and longer-lasting endogenous pain suppression even at rest. If you don’t have this variant, your endocannabinoid system is clearing pain-relief molecules faster than optimal.

What this feels like: Your soreness fades more slowly because your natural pain-relief system doesn’t keep pain-suppressing endocannabinoids active long enough. You might feel fine in the moment but sore an hour later. Recovery feels dragged out.

BDNF (brain-derived neurotrophic factor) is a protein that allows your nervous system to form new connections and adapt. In pain pathways, BDNF does something important but double-edged: it strengthens pain-signaling connections in your spinal cord and brain. If you have the BDNF Val66Met variant with the Met allele, your nervous system’s pain-learning system is more plastic, meaning it more easily “learns” that tissue is damaged and needs protection.

The Val66Met variant, carried by roughly 30% of people, has complex effects. The Met allele is associated with altered pain response and increased central sensitization, where your nervous system starts amplifying pain signals even from normal sensory input. This is especially true if you’ve had multiple bouts of muscle soreness or inflammation over time.

What this feels like: Your nervous system has learned to interpret muscle soreness as a bigger threat than it actually is. A small amount of normal exercise-induced soreness gets amplified into weeks of discomfort. The longer you’re sore, the more sensitized your nervous system becomes, creating a feedback loop.

GCH1 (GTP cyclohydrolase 1) is an enzyme that produces BH4 (tetrahydrobiopterin), a cofactor that nitric oxide synthase and other pain-modulating enzymes absolutely require to function. Without sufficient BH4, your nervous system cannot produce enough nitric oxide and other pain-suppressing signals. This is a less well-known gene but functionally critical for pain modulation.

Certain GCH1 variants, carried by roughly 15-20% of people, reduce BH4 synthesis, which means your nervous system has less of the raw material needed to produce pain-suppressing neurotransmitters like nitric oxide. This creates a functional pain-relief deficit at a biochemical level.

What this feels like: Your nervous system simply has less capacity to produce pain-suppressing signals. You might do everything right, sleep well, manage stress, and still feel sore because your baseline pain-suppression capacity is lower than it needs to be.

MTHFR codes for an enzyme that converts folate into its active form, methylfolate, which is required for methylation reactions throughout your body. One of those reactions is the production of the very neurotransmitters your pain-modulation system runs on: dopamine, serotonin, and others. If your MTHFR gene is impaired, your neurotransmitter production is compromised at the source.

The C677T variant, carried by roughly 40% of people of European ancestry, reduces enzyme efficiency by 40-70%. That means even if you eat enough folate, your cells cannot convert it efficiently enough to support optimal neurotransmitter production, leaving your nervous system chronically underfunded for pain modulation.

What this feels like: Your soreness is partly a neurotransmitter deficit. You feel it as a dull, persistent ache that doesn’t fully resolve. You might also notice brain fog, low mood, or fatigue alongside the soreness, because the same methylation problem affects your entire nervous system.