Six weeks of high-dose ubiquinol (the reduced, more bioavailable form of CoQ10) made the energy-producing machinery inside human muscle measurably more efficient by cutting wasteful “leak” respiration, but this internal upgrade produced no improvement in exercise capacity, oxygen uptake, or economy.
Coenzyme Q10 has been marketed as an energy and endurance booster for decades, yet the evidence has been stubbornly underwhelming. A new placebo-controlled trial from Loughborough University helps explain why the story is more complicated than the supplement aisle suggests: the molecule can demonstrably tune up your mitochondria without making you any faster.
The researchers gave 54 healthy, recreationally active young men either 300 mg per day of ubiquinol or an identical placebo for six weeks. Ubiquinol is the reduced form of CoQ10, and it absorbs into the bloodstream far better than the older oxidised “ubiquinone” form used in most earlier studies. That bioavailability difference matters, because the central limitation of CoQ10 supplements has always been getting enough of the molecule into tissue to do anything.
The supplement worked at the level it was supposed to. Blood CoQ10 climbed roughly sevenfold in the ubiquinol group while staying flat on placebo. More importantly, in muscle biopsies the team found that a specific form of mitochondrial wastage, known as leak respiration, dropped sharply. In plain terms, the mitochondria were burning less fuel for no useful output, and a larger share of their activity went toward actual energy production. This is what physiologists call improved coupling efficiency, and it is genuinely interesting because tighter coupling is associated with lower production of reactive oxygen species, the reactive byproducts implicated in cellular ageing and tissue damage.
Here is the twist. None of that translated into the things athletes and biohackers actually care about. Time to exhaustion during a hard cycling test did not improve more than placebo. Peak oxygen uptake did not budge. Exercise economy was unchanged. The body became a slightly more efficient engine on paper, but the dynamometer registered nothing.
The disconnect is not new. Several prior studies have similarly decoupled mitochondrial efficiency gains from real-world performance, a reminder that whole-body endurance is limited by far more than mitochondrial coupling alone, including oxygen delivery, fibre recruitment, and fatigue at the muscle. For a young, already healthy population, the mitochondrial machinery may simply not be the bottleneck.
The findings sit awkwardly for the supplement industry but cleanly for the science: ubiquinol does something real inside the cell. Whether that “something” matters for health or ageing, rather than performance, is the question this study cannot answer.
Actionable Insights
For a healthy, active adult chasing performance, this trial offers a clear negative result: 300 mg per day of ubiquinol for six weeks produced no measurable benefit to endurance (time to exhaustion), peak aerobic capacity, or exercise economy. The supplement x time interaction for time-to-exhaustion was null (P = 0.79; partial eta squared less than 0.01). Both groups improved modestly over time, but that is a learning or familiarisation effect, not a drug effect.
What ubiquinol did do is biochemically real but functionally silent here. Within the supplemented group, mitochondrial leak respiration (complex I leak, mass-specific) fell about 39 percent (7.1 to 4.3 pmol O2 per second per mg), and the inverse respiratory control ratio fell about 40 percent (0.073 to 0.044). Effect sizes were large (Hedges g around 0.85 to 0.88 for within-group changes). Blood CoQ10 rose roughly sevenfold (Hedges g greater than 2.0).
Practical take-home: if your goal is a measurable performance or VO2 gain in an already-trained state, the expected effect size from this regimen is effectively zero, and your money is better spent on training stimulus, sleep, and iron or vitamin D status if deficient. The mitochondrial efficiency change may have theoretical relevance to redox biology and healthspan, but this study provides no health or ageing endpoint to act on. Treat any longevity claim as hypothesis, not evidence.
Source:
- Open Access Paper: Effect of six weeks ubiquinol supplementation on mitochondrial respiratory function and exercise capacity in healthy males
- Institution: Loughborough University (lead), with collaborating units at the University of Nottingham, University of Leicester, Coventry University, and King Abdulaziz University (Jeddah).
- Country: United Kingdom (primary).
-
Journal: European Journal of Applied Physiology (Springer).
Impact Evaluation: The European Journal of Applied Physiology has a 2024 Journal Impact Factor of approximately 2.7 (JCR, released June 2025; 5-year JIF 3.2) and a Scopus CiteScore of 5.1. It sits in Q1 of the Sport Sciences category (roughly 26 of 127 journals), therefore this is a Low-to-Medium impact journal**