If you train regularly (running, cycling, lifting, anything that asks your body to recover well between sessions), you've probably noticed that the workout itself is the easy part. The hard part is what happens in the eighteen hours that follow. That's where mitochondria, NAD+, and consistency actually matter.
Training is breakdown. Recovery is the work
A hard session damages tissue, depletes substrates, and accumulates metabolic byproducts. None of that is a problem on its own: adaptation happens precisely because the body is forced to rebuild from a slightly more challenged baseline. But the rebuilding requires energy, and it requires the cellular machinery to be in good working order.
The mitochondria are the central player. They produce ATP, the energy currency, through a chain of reactions that depend on NAD+ at multiple steps. When NAD+ is comfortable, mitochondrial output stays comfortable. When it isn't, recovery slows, and over time, that shows up as flatter sessions, longer soreness, and a vague sense that the same training load isn't producing the same results.
What changes as we age
Two things drift in the wrong direction over the decades. First, mitochondrial number and efficiency in skeletal muscle tend to decline. Second, NAD+ levels in muscle tissue go down. Both have been documented across multiple studies: Massudi and colleagues found roughly a 50% reduction in NAD+ between younger and older adults in skin tissue, and similar trends have been measured in muscle.
You can fight back against the first part with consistent training. Endurance work, in particular, is one of the most reliable interventions for mitochondrial biogenesis. The second part (the NAD+ decline) is harder to influence through training alone, which is why the research interest in precursor molecules has grown.
Where NMN comes in
The Igarashi 2022 study published in NPJ Aging looked at older adults taking 250mg of NMN daily for twelve weeks. They measured a meaningful increase in blood NAD+ metabolites and improvements in muscle function on standard tests. It's a small study, and its participants were not well-trained athletes, so we shouldn't over-extrapolate. But the direction is interesting.
The case for NMN in an endurance context isn't "this will improve your VO2 max". That's not what the research has shown. The case is narrower: NMN supports NAD+ levels which decline with age, and NAD+ is involved in the mitochondrial energy production that recovery depends on. For people training seriously into their forties and beyond, that mechanism is worth paying attention to. For what the human trials found on tiredness and physical performance, see our page on NMN for energy.
What recovery actually looks like
Sleep is the foundation. Nothing else you do for recovery comes close to its impact, and there's no supplement on earth that compensates for under-sleeping by an hour a night for weeks on end. After sleep comes protein intake, hydration, deload weeks, and the discipline to take rest days seriously. NMN, if you take it, sits below all of that in priority.
Practical notes if you train and want to try it
Take it in the morning with breakfast, the same time most studies have used. Don't take it on an empty stomach, especially before a long session. Give it at least four to six weeks before forming a view, since the cellular changes the research measured took weeks to show up. And keep training: the supplement supports the system, but the system only adapts if you keep showing up to load it.
