Despite the high popularity of Nordic walking training among seniors, there are still only a few studies on the assessment of its effect on blood parameters. Based on the available literature, it may be concluded that few researchers have addressed this topic. Therefore, an attempt was made to evaluate the effectiveness of a 12-week Nordic walking training programme on vitamin D levels and quality of life among older women. The obtained results allow to indicate that 12 weeks of Nordic walking may have caused changes regarding vitamin D levels D in the blood of the subjects and their quality of life. Below is a brief review of literature concerning the influence of various forms of physical activity on blood vitamin D levels and the assessment of quality of life in the elderly. The results of other authors' research were compared with the results obtained in this study.
Physical activity in the form of Nordic walking training has a positive effect on health, well-being and quality of life among seniors . Aerobic exercise contributes to a number of physiological changes which, as the body adapts to exercise, provide many benefits to the entire human body. Appropriate frequency and duration of training may allow to maintain favourable conditions regarding body functioning for a prolonged period of time. In addition, ‘dosed’ exercise for seniors, regardless of its form, contributes to slowing down the progress of involutional changes and, at the same time, promotes the process of successful aging, i.e. reaching old age with a low risk of developing various types of diseases while maintaining an appropriate level of physical and mental fitness [17,18]. In our study, we noted that Nordic walking training contributes to an increase concerning the level of vitamin D in the blood and improves quality of life among women aged 65-74.
In research carried out to date, the authors have proved the positive effect of Nordic walking training on the processes taking place in an aging body. Improvement in balance, functional fitness, muscle strength and aerobic endurance have been observed in the elderly population. It has also been confirmed that Nordic walking, thanks to the use of poles, allows to improve gait patterns in the elderly. Analysing the impact of using Nordic walking poles on temporal-spatial parameters of walking, i.e. walking speed, stride length, cadence and phases of double and single support, as well as posture-related characters of older people, it has been confirmed that this form of physical activity influences the extension of stride, increases walking speed and forces the body to maintain more vertical positioning. Additionally, the use of poles while walking reduces fears related to falling [19-27].
Knapik et al. (2011) studied 161 subjects above the age of 60 to assess the impact of Nordic walking training on self-evaluation of health. The study included people with at least 2 months of training experience at a frequency of at least 60 minutes a week, who were assigned to one group declaring the above-mentioned physical activity, and a second group, in which participants were physically active but did not have experience with Nordic walking training. The obtained results of the questionnaire showed a higher level of self-assessment with regard to mental and physical health (tested via the SF-36 questionnaire) in the group performing Nordic walking .
The influence of Nordic walking training on the assessment of quality of life was also investigated by Saulicz et al. (2015). In their research, 48 women at a perimenopausal age were qualified for the study. The subjects were randomly assigned to one of 2 groups. In the experimental group, a 4-week Nordic walking training unit was carried out, while in the control group, no intervention was applied. After only 10 training sessions, a significant increase in self-perceived health evaluation was noticed with regard both to physical as well as mental health components .
On the other hand, different results were obtained by Lipowski et al. (2019), who did not notice any improvement in self-reported level of health tested via the SF-36 questionnaire among individuals after being subjected to 12 weeks of Nordic walking training. The study group consisted of 52 elderly women who were assigned to a group with Nordic walking experience (minimum of 4 years), or a beginner group (no previous contact with Nordic walking training). After applying the intervention at a frequency of 3 times a week for 1 hour, no improvement in the quality of life results was achieved in any of the study groups. The authors state the reason for this to be the fact that the SF-36 questionnaire relates the quality of life to health, while the study participants were healthy individuals. The authors also suspect that in the case of such a population, extending the training period could have led to obtaining the expected results .
The results of our research confirm the reports and assumptions proposed by other authors. The 12-week Nordic walking training unit induced definite improvement in all aspects of the quality of life analysed using the SF-36 questionnaire.
The 12-week intervention in the form of regular Nordic walking training significantly influenced the level of vitamin D in the NW group by increasing its concentration (I: 25.38 ± 10.73 II: 29.52 ± 9.59). In group C, no statistically significant differences in vitamin D levels were noted before or after the trial. As is well-known, cutaneous synthesis of vitamin D depends on the level of sun exposure. Therefore, when assessing the test results, the time during which the intervention was carried out should be taken into account. The study was conducted in the period from April-June, i.e. the months with the best conditions for sunlight exposure in a temperate climate. This relationship would explain the results of research obtained by Pilch et al. (2017), which took place in the months of late autumn - from mid-October to early December, in a temperate climate, i.e. a period with relatively short and little intense sunlight. In the discussed studies, it was shown that the intervention in the form of 6-week regular Nordic walking training among postmenopausal women resulted in a significant decrease in vitamin D levels. Pilch et al. suggest that intensified energy expenditure during training could have had influence on the decrease in vitamin D levels, thus, as a consequence, an increased demand of muscle cells for vitamin D. Therefore, it may be assumed that in our study, a key role for the final vitamin D level in the NW group was played by the time of the year in which the intervention took place .
Touvier et al. (2015) showed that people representing high levels of physical activity also exhibited higher concentrations of vitamin D. The highest values of vitamin D were obtained by people declaring activity in open-air conditions, i.e. performing mountain climbing . Interestingly, there are also studies in which it is indicated that there are positive effects of physical activity carried out in closed rooms on the concentration of vitamin D. Wanner et al. (2015) examined 6,370 people to study the relationship between the level of physical activity and vitamin D - the results showed a directly proportional relationship (the greater the activity, the higher the vitamin D levels). What is of great importance, the comparison of results between people declaring indoor physical activity and those training outsider, showed no significant differences . The lack of variance in the concentration of vitamin D between people practicing outdoor sports and those training indoors was also demonstrated by Aydin et al. (2019) and Villacis et al. (2014), whose study groups comprised professional athletes. In both cases, however, the vast majority of athletes showed vitamin D deficiencies - the great frequency and intensity of training in professional athletes causes the need for vitamin D to increase significantly .
In light of the above facts and the results of our research, it may be concluded that physical activity of average intensity, carried out indoors (without direct exposure to sunlight) and outdoors (with sun exposure), is a factor that can positively affect the level of vitamin D. However, taking the results of research conducted by Sela et al. (2012) into account, which clearly show that older people have a better tolerance for physical activity undertaken outdoors, it may be concluded that Nordic walking is one of the best forms of activity supporting the prevention of vitamin D deficiency in the elderly .
The currently available literature lacks studies on the effects of Nordic walking training on vitamin D levels in the elderly. Alarming data on the problem of vitamin D deficiencies in the older population and awareness concerning the importance of its role in the human body, indicate the need for further research on effective and appropriate forms of combating these deficiencies. The results obtained in this study and a detailed review of the literature, allow us to conclude that regular Nordic walking training has a holistic effect on the quality of life among older people, positively affecting the concentration of vitamin D and all components of health-related self-assessment in women above the age of 65. Therefore, Nordic walking may be considered a greatly effective form activating seniors.
A limitation of the study was the lack of accurate assessment of the sun exposure index in the intervention and control groups. Additionally, during the study, the participants were not controlled in terms of changes in diet or lifestyle, which could have had influence on the results.