Worldwide, many people face mental health problems and their effects. Research on this topic has hence become relevant. Their mechanisms and how they affect the human body, however, are currently insufficiently investigated and understood. As anyone can experience periods of negative thoughts, rumination, stress or anxiety, it is a topic of interest to all. There are many connections between these mental health problems and human behaviour. Since physical activity is considered a form of human behaviour, it is typically related to those mental health problems. This research aimed to learn even more about issues caused by mental health problems. This research aimed to investigate whether a correlation exists between physiological markers describing physical condition and the levels of depression, rumination, stress, and anxiety. Since most of the research done focused on specific groups, such as athletes, which makes the results inapplicable to the entire population, the participants of the study were healthy people without a history of mental health problems. For this study, 77 participants completed the questionnaires, followed by a cycle test on the ergometer. The questionnaires were used to examine the stress, rumination, depression and anxiety levels of the participants, whilst their fitness level was tested by means of the cycle test on the ergometer where the participants had to perform at their peak level. After cleaning the data, the correlation study could be performed followed by a regression. The correlation study showed that there was only one correlation between the questionnaires and the different physiological markers. This correlation was between the physical value of the participants describing the transition of acidification in muscles and their anxiety level. On the side, the correlation between the physical values themselves was also identified. The linear regression showed that factors other than the level of depression, rumination, stress and anxiety were likely to influence the physical markers. This result was unexpected considering that a few studies in the past showed that there is an association between mental health problems and physical activity. Of course, the conclusion of this study cannot rule out the fact that in another setting these variables can play a role. It is key to emphasise that this research is a cross-sectional study, meaning that the results cannot show causal relationships. To fully comprehend the long-term impacts of physical activity and mental health, a longitudinal study will be required in the future. It could therefore be envisaged to further refine the correlation study in the future and perform it again on that basis, to find a positive connection between performance and mental health. As a result, it will be possible for people to improve their performances even further or even detect mental health problems in an early phase which will benefit the health system in various ways. The significance of this research lies in the fact that people without a history of mental health problems must cope with such problems in different circumstances, for example, while being at work. Studies that investigated this issue in an average population are limited. Indeed, most studies focused on specific groups. Therefore, extrapolating the findings to the entire population without further research is wrong. People without a history of mental health problems use exercise to cope with the negative impacts of stress, rumination, depression and anxiety. This study hence searched for a correlation between the different human states and their physiological markers. Even though, as mentioned above, only one correlation has been found, this research has been helpful because the more awareness there is regarding this issue, the more effectively this issue can be addressed in the future. So, in another setting or with the limitations of this research in mind, more correlations and, more importantly, more solutions for this problem can potentially be found in the future.