Abstract
Introduction
Static muscle imbalance which leads to poor posture patterns can be the effect of reflexory muscle inhibition. Such disorders are often the result of stereotypical movements repeated for many years in everyday life and, first and foremost, of static activities of low intensity performed over a long period of time, including office work in front of a computer screen [1].
Therapy on a treatment table is an exceptionally important, be it preliminary stage of treating myofascial pain and postural disorders. However, long-term effects and effective methods of primary and secondary prevention of such disorders are to be found in appropriately selected and programmed physical exercises. Such exercises are regarded as a powerful working tool and they should be introduced into the therapeutic process as early as possible [2, 3].
Nordic Walking (NW) is an alternative physical activity, the essence of which is marching and doing exercises with the use of adapted race-ski poles. Due to the form of NW training, which engages the entire muscular system evenly, the potential of this form of exercise for rehabilitation is increasingly often recognized. Despite this fact, however, there are still relatively few scientific reports on the possibility of using NW for the primary and secondary prevention of pain. One of the few existing reports confirms the possibility of using this form of exercise for the treatment of lower back pain [4], another points to the positive effects of NW training in the treatment of fibromyalgia [5]. However, it still has not been established which upper-body muscles are engaged during a NW march and to what extent. It has only been indirectly shown that the muscles of the upper body are more engaged during NW training [6, 7] than during regular marching.
Objectives: An assessment of the effects of a 12-week Nordic Walking training program on the perceived pain threshold (PPT) and the flexibility of selected upper-body muscle groups in postmenopausal female office workers.
Materials and methods
Participants in the trial: 44 office, administrative and academic workers from 4 higher education institutions in Poznań, who met the inclusion and exclusion criteria and replied to the advertisement regarding the study (Table 1).
We tried to assess influence of NW training, on perceived pain threshold (PPT) upper body muscles, in postmenopausal women accordingly to earlier studies [8, 9]. We recruited posmenopausal women because of prevalence of neck pain has reported to be far higher in women than in men. Moreover, PPT values in soft tissues have been found to be significantly lower in women, compared to men, and simultaneously its value decreases with age [11–13].
Volunteers for the study participated in a detailed survey. They answered questions concerning the nature of their work, their diseases, experienced pain, drugs taken, painful areas of the body, and the intensity of pain in those areas. After a preliminary selection, the participants were randomly divided into two groups: the treatment or NW group and the control group, using unmarked envelopes. Five participants dropped out of the study because of they could not continue training or they took up additional forms of physical activity (Fig. 1)
Intervention
NW group underwent a 12-week Nordic Walking training routine, 3 times a week for 1 hour. The NW training was held outdoors, with at least two Nordic Walking instructors controlling the marching technique and regulating the pace. Every training session was preceded by a 10-minute warm-up and ended with a 5-minute cool-down phase. Every participant of the study was equipped with a portable myocardial contraction recorder. The intensity of the march was no higher than 70% and no lower than 40% of the heart rate reserve (HRR) [14, 15]. The HHR zone was set relatively low because the study included women with various levels of exercise capacity, and the intention of the study was to provide aerobic exercise to relive musculoskeletal symptoms, not to improve capacity.
Participants in the control group were explicitly told not to change their movement routines and habits for the period of 12 weeks.
Outcomes
In both groups the pressure pain threshold and the back scratch flexibility test was measured twice in every participant, before the beginning of the training program and 1–2 days after the last NW training session.
Perceived pain threshold tests
Physical therapists with at least 5 years of experience in working with trigger points measured the perceived pain threshold (PPT), that is, the minimum force applied which induces the feeling of pain (and not just of pressing on the muscle) with a possible referral. An electronic pressure algometer (Digital Force Gauges, Wagner Force Onetrademark - FDIX) was used for the test. The results were expressed in terms of the pressure force [kg/cm2]. In the study participants were asked to immediately report any discomfort suggesting the occurrence of pain, and not the sensation of pressure itself, in line with the guidelines set out in similar scientific studies [16–18].
The tested muscles were trapezius pars descendens., middle trapezius, infraspinatus, and pectoralis major, the disorders of which translate directly into poor upper body posture and which hypothetically are most overloaded during sedentary work.The brachioradialis muscle and the triceps brachii muscle were tested in order to indirectly assess their engagement during Nordic Walking.
The measurements were taken in accordance with the following procedure: the therapists did not know which group a given person belonged to. First, latent trigger points were determined manually, in accordance with the commonly accepted standards for the occurrence of such points and the methodological guidelines for such procedures [19, 20]. The trigger point sites chosen for the indicated muscles are presented in Table 2.
Immediately upon finding a latent trigger point – the feeling of pain (and not just of pressing on the muscle) with a possible referral – the manual stimulation of such a point was discontinued. After the lapse of one minute, the PPT measurements were taken using Digital Force Gauges. This test was performed twice (attempt and the proper measurement), 10 seconds apart, and the second result was chosen for the calculations.
Back Scratch Test [BS]
Before and after the training period, a test evaluating the flexibility of the upper body, being a standard component of the set of functional tests for sportsmen, adults and seniors, was performed in each group. BS measures how close the hands can be brought together behind the back. It is associated with lifestyle activities such as getting dressed, reaching for objects and putting on a car seat belt [21].
Statistical methods
The distribution of continuous data was assessed with the Shapiro–Wilk test. As data were not normally distributed, the comparisons between the two study groups were assessed with the Mann–Whitney test, and for paired variables, the Wilcoxon test was used. The P-value of 0.05 was considered significant.
Results
Participants in each group were similar in terms of the basic descriptive characteristics (Table 3).
Table 4 shows that when it comes to the decrease in the perceived tenderness (manifesting itself in the increase of the PPT values), a statistically significant improvement was only achieved in the following muscles: trapezius pars descendens, middle trapezius., infraspinatus and latissimus dorsi in the treatment group. No statistically significant improvement of the selected parameter was recorded in: pectoralis major, triceps, and brachioradialis in the treatment group, while in the control group no such improvement was recorded in any muscle group. No significant differences in PPT were observed between the baseline and end trials in the control group. PPT values were significantly lower in the Nordic Walking group at baseline in infraspinatus, brachioradialis and middle trapezius muscles.
A statistically significant improvement was recorded in the Back Scratch Test for the NW group compared to the control group (P = 0,02) (Table 5).
Discussion
This paper is the first attempt at indirect evaluation of the impact of aerobic NW exercise on the tension of upper-body muscles in office workers. It shows that selected muscles of this region may respond well to regular physical exercises of that kind, while tenderness may be reduced, as manifested in the increased PPT values. Additionally, this fact is corroborated by a functional test, measuring the flexibility of the upper body which showed statistically significant improvement only in the NW group.
It is proven that among office workers there is a strong association between perceived neck and shoulder pain intensity and muscle tenderness, and this tenderness is more common among women than men [22]. The previous studies argue that physical activity programmes in the workplace or even exercise reminder software applications may help reduce the perceived pain level among office workers [23, 24]. There is also strong evidence of the role of aerobic exercise in reducing muscle sensitivity to pressure [25, 26]. So far, the only effect of such exercise as stationary cycling [27–29] or marching on a treadmill [30] have been evaluated. The said tests wereperformed on patients with fibromyalgia [27], low back pain [28, 29] or musculoskeletal pain of unknown origin [30]. It has been pointed out that aerobic exercise may reduce the sensitivity of muscles to pressure within the lower body half in patients with low back pain and recommended that the exercise should be continued for over 30 minutes [29]. It was also mentioned that exercise of greater intensity (∼75% VO2 max) were more effective [31]. Note that the studies referred to herein evaluated the effect of more intense exercise (50–70 VO2max) of shorter duration (20–30 minutes) than the exercise analysed in our study (40–70% peak VO2, 60 minutes). Our study also focused on the effect of long-term exercise on PPT in the muscles and not solely on the immediate effect of aerobic exercise.
Many studies focus solely on the trapezius muscle as the potential cause of neck pain in office workers. It has been proven, for instance, that there is a strong correlation between neck pain and blood supply in the upper trapezius during prolonged sitting [32, 33]. Waling et al. showed that regular exercise reduces pain in trapezius muscles but did not recommend any specific form of physical activity [8]. In their study, Ylinen et al. demonstrated a statistically significantly higher pressure in pain threshold values in specific training groups (neck muscle endurance training, neck muscle strength training) in all muscle sites compared to the baseline, while no significant change occurred in the controls [9]. For our study, we selected several muscle groups hypothetically most involved in Nordic walking with direct access to these muscles. As it has been shown that regular aerobic exercises can improve blood supply of muscles [34, 35], we assumed that improvement in PPT after Nordic Walking training is probably connected with better microcirculation of blood in those muscles. This, however, requires further research. Regarding the treatment of pain, only the effectiveness of NW in physiotherapy of low back pain has been evaluated so far [4, 36]. Previous studies have shown an improvement of the upper-body fitness in elderly persons. In the study by Takshima et al. [37], a 44% improvement in the Back Scratch Test was shown and it was the greatest improvement achieved, compared to other forms of training. These results corroborate with our results. The documented improvement in the Back Scratch Test is probably related to the fact that the NW marching technique requires a dynamic work of the upper limbs and maintaining a greater joint mobility than a regular march. Finally, it worth be noted that although NW is regarded a potentially useful intervention in reducing musculoskeletal complaints in frequent computer users [38] the studies to date have never evaluated directly the effect of NW training on pain complaints in the neck and shoulder region.
The present study has several limitations which prevent drawing explicit conclusions concerning the effects of Nordic Walking on the tension of the upper body muscles. One limitation is the fact that the study subjects only experienced mild pain in their everyday lives, i.e. only the persons running a potential risk of developing such disorders and not suffering from the actual pain were examined. The PPT test is based on the subjective impressions of the patients. In future, it could be replaced e.g. by myotonometer measurements. Moreover, too few objective functional tests were used while the study was conducted on a selected group of workers from several institutions in the same city. Therefore, the results of the study should be treated as an introduction to further multidirectional studies which should enable a comprehensive evaluation of the possible effects of NW training on reducing neck and shoulder pain.
Conclusion
A 12-week Nordic Walking training routine improves shoulder mobility and reduces tenderness in such muscles as: trapezius pars desc. et mid. trapezius, infraspinatus and latissimus dorsi in female office workers. Therefore, NW seems to be a well-chosen physical activity for improvement of functional fitness of the upper body half and this form of exercise has a high potential of reducing sensitivity to pressure (increased PPT) in the muscles of that region, since it evenly and moderately engages the whole muscular system, including neck and shoulder muscles.
Conflict of interest
The authors have no conflict to report.