Scientists from the University of Nebraska-Lincoln say new research shows that physical strength might come as much from exercising the nervous system as it does from training the muscles.

In a study, they asked some participants to lift lighter weights at higher repetitions, and others to complete fewer repetitions of heavier weights.

While muscle mass in both sets of participants built at the same rate, those who trained with the heavier weights became stronger.

The research team say this could be explained by the electrical signals sent by the brain's motor neurons, which differed depending on whether an individual was doing high or low-load weight training.

Assistant professor of exercise physiology Nathaniel Jenkins and his colleagues said their findings suggested that high-load weight training teaches the nervous system to transmit more electrical signals from the brain to the muscles being exercised, allowing those muscles to produce more force.

This, the team believes, would explain how the strength gains differed between participants despite their muscle mass remaining the same.

Dr Jenkins said: "If you're trying to increase strength - whether you're Joe Shmoe, a weekend warrior, a gym rat or an athlete - training with high loads is going to result in greater strength adaptations."

He said low-load training remained an important form of exercise for those who want to build muscle mass and avoid putting extreme stress on their joints, something which is often a priority for older adults and those recovering from injuries.

However, he said the new study provided even more evidence in support of the idea that when building strength, especially amid a busy schedule, heavier loads are better.

"I don't think anybody would argue (with the idea) that high-load training is more efficient," Dr Jenkins said.

"It's more time-efficient. We're seeing greater strength adaptations. And now we're seeing greater neural adaptations."

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