The findings suggested that quercetin can help activate hard-to-reach muscle fibres, delivering strength improvements similar to those that come with high-intensity training — but reportedly without the risks.
Addressing a key challenge in ageing
As people age, they naturally lose muscle strength, particularly in the fast-twitch fibres used for quick, powerful movements. These fibres are controlled by motor units that require a stronger signal from the brain to activate. In older adults, these signals often weaken, making it harder to fully engage the muscles, even during exercise.
This decline is linked to falls, reduced mobility, and loss of independence. While resistance training can help, high-intensity workouts that activate these fibres aren’t always safe or realistic for seniors. Many can’t tolerate heavy resistance training due to joint pain, cardiovascular issues or low mobility.
Promising initial results
The double-blind, placebo-controlled study followed 26 adults aged 65 to 82 as they completed a structured leg training program that required them to perform leg resistance exercises three times per week for six weeks, using a machine to do isometric knee extensions.
The training intensity was set at 60% of each participant’s maximum voluntary force (MVF), which was measured before and after the program. Researchers used high-density electromyography (HDsEMG) to track how individual motor units responded during the training and over time.
Both groups followed the same diet and physical activity guidelines. Half received a daily 200mg dose of quercetin glycosides, a plant-based antioxidant, while the other half received a placebo. The group taking quercetin saw a 15% increase in muscle strength—significantly higher than the 5% gain seen in the placebo group.
The researchers found that quercetin helped the nervous system better recruit motor unit (bundles of muscle fibres and the nerves that control them) that are usually harder to activate in older people. This led to better strength improvements with the same training load.
By the end of the study, both groups had improved their muscle strength, but those taking quercetin saw significantly higher gains. Their firing rates — the rate at which nerves send signals to muscle fibres — increased particularly in motor units with higher activation thresholds, which are responsible for powerful, fast movements.
The researchers also noted that the gains came without a noticeable increase in muscle size, suggesting the improvements were driven by neural changes and not muscle growth.
Why quercetin makes a difference
While quercetin is found in foods like apples, onions and berries, diet alone would not provide the 200mg daily dose used in the study. The researchers also used a highly bioavailable version of quercetin, which the body is better able to absorb.
Quercetin works by blocking adenosine receptors in the brain that normally reduce nerve activity. When blocked, nerve cells release more neurotransmitters like dopamine and acetylcholine, which play a key role in muscle activation.
By increasing these signalling chemicals, quercetin helps the nervous system fire up motor units more effectively, which is especially important for older adults with naturally reduced motor unit activation.
A safer alternative to high-intensity training
In addition to the findings mentioned above, study also showed that muscle mass did not increase in either group. This is not unusual for a six-week program, and points to improved neuromuscular efficiency rather than hypertrophy. In other words, the brain and nerves became better at activating the muscles that were already there.
Importantly, the group who received quercetin supplementation reached similar strength gains to those seen in previous studies using high-intensity training — but without the associated safety concerns. This makes the quercetin-plus-training approach an attractive option for practitioners working with frail or mobility-limited older adults.
Future research and limitations
The researchers acknowledged that the study had a small sample size and a short intervention period. They also didn’t measure quercetin levels in the blood, or explore its long-term effects. Further studies could explore higher doses, longer training periods, and different exercise types, such as functional movements used in daily life.
They also noted that since men and women may respond differently to quercetin due to differences in muscle biology and nervous system behaviour, this area should be studied further.
They concluded the study by stating: “We investigated the effect of quercetin ingestion on motor units’ behaviour and muscle strength following six weeks of resistance training in older adults.
“Our findings indicate that quercetin ingestion enhances the improvements of muscle strength following resistance training involving adaptations of motor units with higher recruitment thresholds in older adults. The present study suggests that combining quercetin ingestion with resistance training is an effective strategy for improving muscle strength in older adults.”
Source: European Journal of Nutrition
“Quercetin ingestion alters motor unit behavior and enhances improvement in muscle strength following resistance training in older adults: a randomized, double-blind, controlled trial”
https://doi.org/10.1007/s00394-025-03634-9
Authors: Taichi Nishikawa, et al.
