For decades, scientists have known that gradually lifting weights makes you physically stronger. But according to new research, the training initially change the brain before changing muscles
In a fascinating study published Monday in the Neuroscience Journal, Scientists analyzed these neural adaptations in an unconventional way: They taught the monkeys how to train hard and examined how activity transforms the brain and body.
The experiment revealed that weight lifting strengthens the nervous system through a motor tract called the reticulospinal tract, weeks before any muscle is added.
“Strength is not just about muscle mass,” says co-author Isabel Glover, a researcher at Newcastle University. Reverse. “When you start lifting weights, you get stronger because the neural input to your muscles increases. Only a few weeks later the muscles start to grow.”
The study was carried out on macaque monkeys. Their brain systems, when it comes to movement, are similar to people. The results should be “highly translatable” for humans, says co-author Stuart Baker, also a researcher at Newcastle University. Reverse.
“People see the benefits early on in terms of getting stronger, because changes in the nervous system mean they can activate their existing muscles more efficiently,” says Baker. “But they don’t see changes in muscle mass. That takes longer and appears to occur after changes in the brain and spinal cord.”
If people don’t immediately notice the stronger limbs after they start lifting weights, they must realize that something else is going on: powerful neural changes in the brain that can lead to long-term physiological benefits.
These results aren’t just relevant to bodybuilders looking for a new better personal brand, Glover says.
“If we understand the neural mechanisms of force, then we can begin to think about how to help people who experience a loss of strength, such as after a stroke.”
The researchers trained two macaque monkeys pulling a heavy handle with one arm rewarding animals with food. Over the course of three months, the researchers increased the resistance of a weighted loop week by week. The monkeys completed daily strength training sessions that included 50 weighted pulls (moving the handle at least four centimeters).
The training was “quite difficult,” says Baker. “We started by teaching the monkeys to pull the lever without weights. Then we slowly increased the weights, persuading them all the time to try the next level.”
“Sometimes it was a challenge to keep them motivated,” adds Glover. “Think about how many people left the gym. But after a few months, they reached their goal of 50 reps at 6.5 kilograms.”
These monkeys weighed only 6 to 6.5 kilograms (14.3 pounds), making it comparable to a human doing 50 one-arm pullups – an impressive display of strength, Glover adds.
On a daily basis, the team also stimulated the monkeys’ motor cortex and two motor pathways: the corticospinal tract (CST) and the reticulospinal tract (RST). They then measured the resulting electrical activity in his arm muscles.
The primary pathway, CST, carries information related to movement from the cerebellum to the spinal cord. This helps animals and humans move their limbs and trunk such as walking or reaching. Meanwhile, the old evolutionary pathway, RST, which is considered less dominant, influences posture and muscle tone.
Throughout the training regimen, the team found significant increases in the strength of the old evolutionary pathway (RST) and no change in the main pathway (CST).
“Therefore, although the primary path is typically associated with our more sophisticated or complex movements, the ancient evolutionary path appears to be the driving force behind the force,” says Glover.
After three months of strength training, RST stimulation elicited an increased response on the side of the spinal cord connected to the trained arm. In general, the RST results became more powerful during weight training.
An essential link between the brain and the body. Baker explains that while people new to weightlifting are known to initially get stronger due to increased connections in the nervous system, not by growing larger muscles, why this happened was unclear.
This study shows that the RST pathway may be responsible.
“The results show that strength training first increases the strength of the connections from the reticulospinal tract to the spinal cord, allowing the muscles to activate more strongly,” says Baker. “This occurs from the beginning, only later do the muscles grow, which further increases maximum strength.”
This indirect pathway is also involved in recovery from stroke. This implies that “improving the function of a hand-weakened stroke may be using the same mechanisms as strength training in a healthy young bodybuilder,” Baker explains.
“It is interesting that a young and healthy bodybuilder who exercises is causing the same changes in his nervous system to strengthen as occurs in a stroke survivor who is regaining use of his limb,” he continues. “It could be that resistance training [weight lifting] it provides a fairly direct route to stimulate these changes in the reticulospinal tract. “
If so, these results suggest that lifting weights might be a useful approach when helping recovering stroke patients, Baker explains.
The study, the first to study RST’s response to strength training in non-human primates, requires more attention on RST and its link to strength. Understanding the complex factors that lead someone to become stronger could inform new exercise techniques and new treatments for neurological damage in the future.
Summary: Following a resistance training program, there are neural and muscular contributions to gaining strength. Here, we measure changes in major central motor pathways during strength training in two female macaque monkeys. Animals were trained to pull a handle with one arm; Weights could be added to increase the load. Each day, the motor evoked potentials in the muscles of the upper extremities were first measured after stimulation of the primary motor cortex (M1), the corticospinal tract (CST) and the reticulospinal tract (RST). The monkeys then completed 50 trials with progressively increased weights over 8-9 weeks (final weight ~ 6 kg, close to the animal’s body weight). Muscle responses to M1 and RST stimulation increased during strength training; there were no increases in CST responses. The changes persisted for a two-week washout period without weights. After another three months of strength training, an experiment under anesthesia mapped potential responses to CST and RST stimulation in the cervical spinal cord enlargement. We distinguish early axonal volley and posterior spinal synaptic field potentials, and use the slope of the relationship between these at different stimulus intensities as a measure of spinal input-output gain. Spinal gain was increased on the trained side compared to the untrained side of the medulla within the medial zone and motor nuclei for RST stimulation, but not CST. We conclude that neural adaptations to strength training involve adaptations in the RST as well as the intracortical circuits within M1. On the contrary, there appears to be little contribution from the CST.
