Why are some people out of breath after a short jog, while others seem to glide along effortlessly? Training, fitness level, and muscle strength naturally play a role. Researchers have found that the brain also has a strong influence, especially on how strenuous physical activity is perceived.

Sport challenges not only the body, but also the way the brain interprets exertion. Scientists have found that vibrating the tendons before cycling allows people to exert themselves more without feeling like they are working harder. Their muscles and hearts worked longer, but their perception of exertion remained unchanged. This discrepancy between the brain and the body could one day help make exercise less intimidating, especially for people who find it difficult to stay active.

What Influence Does Chronobiology Have on Sports and Performance?

Chronobiology deals with the body’s internal clocks, especially the circadian rhythm (approximately 24-hour rhythm). These rhythms influence, among other things:

• the activity of certain brain regions,
• the processing of sensory stimuli (e.g., muscle tension),
• heart rate, muscle strength and metabolism,
• motivation, fatigue, and perception of pain and exertion

Both the perception of exertion and the performance capacity of the brain and body are controlled by internal biological rhythms that are dependent on time. Chronobiology shows that this processing functions differently depending on the time of day. For example, in the late afternoon, the brain often perceives physical exertion as less strenuous than in the early morning, even though the objective performance is the same. Chronobiological findings could explain when such effects (such as reduced perception of exertion through vibration) are particularly strong or weak and how to time training so that it feels subjectively easier. Chronobiological rhythms control how the brain and nervous system interpret bodily signals such as muscle tension, fatigue, and exertion. Tendon vibration alters precisely this central processing and decouples subjective perception of exertion from actual physical performance. Chronobiology thus provides the framework for understanding when and under what internal time conditions such effects are particularly effective. It thus links the neural control of effort with the biological timing of the body.

Why Effort Feels Different from Person to Person

Effort refers to the energy we expend on activities such as running, cycling, or weightlifting. While this energy expenditure can be measured physically, the perception of effort is not purely mechanical. It is also influenced by perception, which can vary greatly from person to person. This perception plays an important role in whether people stick with exercise. If a workout is perceived as too strenuous, people are more likely to quit or avoid it altogether. If the same activity is perceived as feasible, it is more enjoyable and easier to continue over a longer period of time.

This raises an interesting question. What if the feeling of exertion itself could be reduced so that people could overcome the feeling that exercise is simply too strenuous? Benjamin Pageaux, professor in the Department of Kinesiology and Movement Sciences at the Université de Montréal, is exploring this idea together with three researchers from the Université Savoie Mont Blanc in France as part of an international research project.

How Vibration Can Change the Brain’s Signals

In a recent study, the research team investigated whether vibrating certain tendons can reduce the perceived effort of cycling. They used a portable vibration device designed to stimulate tendons before exercise. Volunteers participated in laboratory tests on a stationary bike. Each participant completed two conditions: one session after tendon vibration and another without prior vibration. For the vibration condition, the device was attached to the Achilles tendons and hamstrings and activated for 10 minutes before cycling began. Participants then cycled for three minutes at a pace they perceived as moderate or intense, adjusting their effort to the target level. The results were impressive. After tendon vibration, participants generated more power and had higher heart rates than in the sessions without vibration. Although their bodies were working harder, their perceived exertion did not increase.

Researchers are now trying to understand how tendon vibration changes the brain’s interpretation of effort. While the exact biological mechanisms are still being investigated, Pageaux has proposed several possible explanations. “Depending on the amplitude and frequency of the vibration, we can either stimulate or inhibit the neurons in the spinal cord,” he explained. “In addition, prolonged vibration alters the reactivity of the neuromuscular spindles and changes the signal sent to the brain.” By altering the information that reaches the brain from the muscles, vibration appears to change the perception of movement and effort. As a result, exercise may feel easier, even though the muscles are exerting more force.

Motivating People to Exercise More

Although the results are promising, the research is still in its early stages. Tests to date have been limited to short cycling exercises under controlled conditions. “It hasn’t been tested in a marathon, only in a short, three-minute cycling exercise,” Pageaux pointed out. “Nevertheless, this is the first time it has been shown to work in this type of training.” Next, the team plans to study brain activity during exercise more closely. They want to use tools such as electroencephalography and magnetic resonance imaging to find out how tendon vibrations affect neural activity while people are exerting themselves physically.

The researchers are also investigating the reverse process. They want to better understand how pain and fatigue increase the feeling of exertion and make physical activities seem more difficult. Ultimately, the goal is to develop strategies that reduce perceived exertion and motivate more people to become physically active, especially those who currently lead a sedentary lifestyle. “By better understanding how the brain evaluates the relationship between effort and perceived reward during exercise, we hope to promote more regular physical activity,” Pageaux said. “And we all know how important it is for our health and well-being to stay active!”

More regular physical activity can be encouraged by specifically targeting the mechanisms in the brain that link effort and reward. When exercise is evaluated by the brain as less strenuous or more rewarding, the motivation to repeat it increases. Insights into how the brain perceives effort make it possible, for example, to:

• Developing forms of exercise that feel subjectively easier, even though they are effective.
• Using supportive stimuli (e.g., rhythm, vibration, music) that reduce the perception of effort.
• Plan training times to coincide with periods of higher motivation in the daily rhythm.
• Create early positive training experiences that activate the reward system and avoid negative associations.

As a result, exercise is no longer primarily remembered as a burden, but more as a positive, achievable experience. This increases the likelihood that people will integrate physical activity into their everyday lives in the long term.