Lifting heavy weights can enhance your physical strength better than low-load training, as it conditions the brain to send more signals to the muscles, scientists have found.

The study shows that physical strength might stem as much from exercising the nervous system as the muscles it controls.

Researchers studied how the brain and motor neurons – cells that send electrical signals to muscle – adapt to high versus low-load weight training.

Muscles contract when they receive electrical signals that originate in the brain's neuron-rich motor cortex.

Those signals descend from the cortex to the spinal tract, speeding through the spine while jumping to other motor neurons that then excite muscle fibres, researchers said.

The team found that the nervous system activates more of those motor neurons – or excites them more frequently – when subjected to high-load training.

This increased excitation could account for the greater strength gains despite comparable growth in muscle mass, researchers said.

“If you are trying to increase strength – whether you are a weekend warrior, a gym rat or an athlete – training with high loads is going to result in greater strength adaptations,” said Nathaniel Jenkins, assistant professor at the Oklahoma State University in the US.

Low-load training remains a viable option for those looking to simply build mass or avoid putting extreme stress on joints, a priority for older adults and people rehabbing from injury. However, when it comes to building strength – heavier is better, researchers said.

“I don't think anybody would argue that high-load training is more efficient. It's more time efficient. We are seeing greater strength adaptations. And now we are seeing greater neural adaptations,” Jenkins said.

Researchers randomly assigned 26 men to train for six weeks on a leg-extension machine loaded with either 80 or 30 per cent of the maximum weight they could lift.

Participants lifted three times per week until they could not complete another repetition.

They were able to replicate the findings of several previous studies, seeing similar growth in muscle between the two groups but a larger strength increase – roughly 10 pounds' worth – in the high-load group.

The study was published in the journal Frontiers in Physiology.