Thermoregulation mechanisms in children are under development
Compared to adults, thermoregulation mechanisms in children are under development , so the resistance to thermal stress associated with physical activity could be lower than in adults. The efficiency of thermoregulation depends on the proper functioning of other systems, e.g. the respiratory, circulatory, endocrinal. It should also be noted that the ability to adapt to strenuous exercise is lower in children compared to adults, which is why the energy cost of physical work performed by the child is higher.
Thermography as an important diagnostic tool
The use of thermography as a diagnostic tool for the analysis of thermal patterns in the superficial body layers after physical activity enables to asses indirectly the thermoregulatory mechanisms and its differences between children of 7, 9 and 12 years of age. Certain tendencies in the temperature distribution patterns could be observed in thermal images. The highest values were observed around the shoulder belt and in the trunk, whereas the lower extremities showed the lowest temperature. Such thermal distribution was also observed in other studies, e.g. by Dębiec-Bąk et al. in football players . The reason for that is the vasculature system and the presence of inner organs. Our research showed a reduction in average temperature values in all subjects, immediately after physical exercises. The highest drop could be observed in the group of 12-year-olds. It may indicate the highest level of development of the body cooling processes in the group of the oldest subjects. Effective sweating mechanisms facilitate the removal of excess heat from the body during exercise. Inbar et al.  compared thermoregulatory processes due to physical effort in three age groups: boys, young men and older men. The analysis of the results showed that the highest level of sweat secretion, which consequently cools down the body during exercise, is observed in young men. The oldest subjects were characterized by low efficiency of the sweating process, whereas the youngest boys had the lowest sweating levels.
Particularities of thermoregulation in children
The thermoregulation center gains the full independence between the age of 1 and 2 years. This capacity is lost again around the sixth decade of life, which results in similar, somehow impaired, thermoregulatory effectiveness of children and the elderly. Inoue et al.  in their research investigated how the ability to lose excess heat changes depending on age. Their results exhibited that children have low capacity to sweat in comparison with adults. Elimination of excess heat occurs by vasodilation of the skin vasculature. However, a high surface area to weight ratio can expose a child to excessive heat absorption in a hot climate. They also observed that due to the processes of involution, thermoregulatory abilities are again reduced in the elderly. Leites et al.  conducted an analysis of thermoregulatory processes in men and 10-year-old boys taking into account the body mass in both groups. The subjects performed 80 minutes of physical exercises in the form of cycling in four twenty-minutes units. The lower production of sweat and heat energy per unit of body surface area in boys, were observed. In addition, it was noted that men produced more mechanical energy of muscle work compared to younger subjects. Similar results were obtained by Shibasaki et al. , who compared the thermoregulatory response of the body in boys (10-11 years of age) and young men (21-25 years) performing moderate-intensity exercise. The differences between the groups concerned the amount of sweat secretion, which were higher in older subjects. These observations mentioned above and confirmed in our study, indicate the existence of a relationship between the degree of body cooling after exercises and age.
Thermoregulation is efficient adapting human body to physical exercises
An efficient thermoregulation mechanism enables the adaptation of the human body to physical exercises . It is also vital to avoid the negative impact of heat on health and productivity, e.g. during physical work . Cholewka et al.  examined by means of thermography the correlation between recorded thermal parameters during endurance effort and the generated power. Strong correlation between these parameters was recorded. This proves the usefulness of thermography as a method for analyzing energy expenditure and also for designing the tests performed during the training cycle.
In the research presented by Duffield et al. , it was shown that people undertaking regular physical activity have better efficiency of maintaining thermal balance. Their defense mechanisms operate more efficiently than in non-training people. Regular physical activity affects thermoregulatory processes. This research and our examination may be a hint for parents, demonstrating that a systematic and well-chosen form of training can have a positive impact on the development of their child’s thermoregulatory processes.
Interpretation of temperature patterns after exercise and recovery time
In our research, after the recovery time (Measurement 3), temperature values in children aged 7 and 9 were close to initial ones. However, the group of 12-year-olds was the only one which, after recovery time, did not reach the parameters recorded before exercises. This may be due to the fact that the oldest subjects showed the largest decreases in body temperature after general fitness training. The increase of the body surface temperature after the recovery time has also been demonstrated in studies by Chudecka and Lubkowska  using thermal recording. Having analyzed the temperature values in a group of volleyball players after a 90-minutes workout and a 10-minutes recovery time, they observed a drop of temperature immediately after physical exercise, while an increase in surface body temperatures followed the recovery time. These researchers conducted an analogous research in a group of handball players. The analysis of surface body temperature after a 10-minutes recovery time showed an increase in the temperature of the examined areas in all participants. In another study, Chudecka and Lubkowska  noted that a return to the initial temperature after a recovery time is more effective in people with a higher value of maximum oxygen uptake. The human body during physical activity has a higher body temperature, due to the increased metabolism of the individual systems. In physiological response to such stimulus as training, cooling mechanisms protecting against hyperthermia are activated, mainly due to increased sweating and vasodilation. Efficient thermoregulation processes are also responsible for returning to pre-exercise temperature. The ability to maintain the thermal balance during daily physical activities and exercises is crucial for the proper functioning of the body . The performed in our group analysis revealed that after physical exercises, a statistically significant decrease in temperature was noted in all age groups, in all areas of the body. The largest temperature reduction was observed in 12-year-olds, while the smallest temperature drop was recorded in the youngest subjects (7-year-olds). After a given recovery time, the temperature did not return to the initial values only in the group of 12-year-olds. The observed significant differences in the body surface temperature between the group of 7-year-olds and 12-year-olds indicate the need to differentiate the level of exercise intensity depending on the age.
When planning training load and physical activity in school curricula, one should take into account individual reactions of thermoregulatory mechanisms in children, as well as the criterion of children's age. Trainers and teachers of sports activities in schools should be acquainted of the thermoregulatory efficiency of the child's body what may constitute the basis for prevention against injuries and strain of the locomotory system in school children.
Concluding remarks and expert recommendations in the framework of 3P medicine
Thermoregulation is highly individual and predictive for potentially cascading pathologies.
Well-controlled thermoregulation is crucial for physical and mental human health. A relatively narrow body temperature range of 36.5–37 °C is rigorously kept allowing for timely enzymatic reactions by the optimal kinetic window and, therefore, an effective performance of all physiological processes. To this end, feeling cold is a normal response towards changing external temperatures, in order to win back the thermal comfort by physical activity and energy supply based on well-concerted regulation mechanisms. At low temperatures, an adaptive vasoconstriction and an increase in blood pressure and heart rates synergistically result in heat production and conservation for maintaining the optimal body temperature . Maintaining thermal comfort is energetically costly  and demands well-organised mitochondrial functionality. Mitochondriopaties causing dysfunction of the mitochondrial respiratory chain are characteristic for several pathologic conditions such as cancerous Warburg transformation and neurodegenerative disabilities, among others [48, 49, 50].
For example, abnormal thermoregulation has been demonstrated for breast cancer patients, who are frequently deficient in achieving thermal comfort . They feel excessively hot or cold, when disease-free attenders are well comfortable with ambient temperature conditions . To this end, pro-inflammatory cytokines (IL-1, IL-6, TNF-α) regulating the immune reactions  are frequently overexpressed by cancer patients  affecting thermoregulation by activating the cyclooxygenase 2 and production of prostaglandins .
Another example: detectable brain temperature disturbances and brain-systemic temperature decoupling are involved in the stroke pathology . Consequently, an altered brain thermoregulation may serve as a neuroimaging biomarker in CNS injury.
In conclusion, altered and deficient thermoregulation is considered an important diagnostic indicator which can be of great clinical utility for specialised screening programmes and individualised prediction of pathologies (individualised patient profiling) . Contextually, altered thermoregulation patterns are instrumental for specific phenotypes useful for detection of sub-optimal health conditions that can be exemplified by the Flammer syndrome phenotype and associated cascading pathologies [51, 57, 58].
Body exercise-based disease prevention is effective when adapted individually: multi-parametric guidance for prescribing exercises is needed
As stated above, physiologic versus abnormal thermoregulation is functionally linked with regular physical activities and optimal energy supply. These individual components are well-concerted together via systemic effects being therefore highly indicative for individual healthcare status and prediction of associated pathologies. In this context, individually adapted physical activities are crucial for the targeted disease prevention as stated in both EPMA Position Paper 2021  and ajoint position paper of the Suboptimal Health Study Consortium and European Association for Predictive, Preventive and Personalised Medicine. EPMA J. 2021 . To this end, topic dedicated research groups emphasise an importance of diversified physical activities in early childhood. Thus, most recently performed studies indicate that diversified physical activity at age six is important for developing optimal physical activities in general and, in particular, motor competence in adolescence. The authors do stress the point that not only the amount and intensity but specifically an increased diversity of children's daily physical activities is decisive for optimal behavioural patterns and health promotion later on in life .
Noteworthy, socioeconomic status was demonstrated to be inversely associated with outcomes related to the intensity and quality of youth physical and sports activity. To this end, a cross-sectional survey with 1038 students in 5-12th grades in USA (King County and Washington including 50% girls, 58% non-White, and 32% from homes where languages other than English are spoken) was conducted. Responders described their physical activity and sports experiences and demographic factors such as family affluence categorized as low, medium, and high . For children from low-affluence families, lower intensity of physical activity and rates of ever playing sports were reported. The barriers to sports these children described as “don't feel welcome on teams” and “too expensive”, among others. The disparity results in three times higher odds of meeting physical activity recommendations as well as three times higher odds of ever participating in sports reported for middle school children from high-affluence families compared to peers from low-affluence families. Consequently, socio-economical particularities have to be taken into consideration for coaching individually adapted physical activities to reach satisfactory health promoting benefits.
American College of Sports Medicine position stand stated that although general recommendations for physical exercises have been elaborated, the exercise program should be modified according to an individual's habitual physical activity, physical function, health status, exercise responses, and stated goals . Further, behaviourally based exercise interventions, the use of behaviour change strategies, supervision by an experienced fitness instructor, and exercise that is pleasant and enjoyable can improve adoption and adherence to prescribed exercise programs.
Body temperature measurements are instrumental for personalised couching towards regular physical activities in school children as demonstrated in this article.