Nordic Walking Promoted Weight Loss in Overweight and Obese People: A Systematic Review for Future Exercise Prescription

The aim of this systematic review was to analyze the effect of Nordic Walking (NW) on anthropometric parameters, body composition, cardiovascular parameters, aerobic capacity, blood sample, and glucose tolerance in overweight and obese subjects. The main keywords “Nordic Walking” or “Pole Walking”, associated with either “obese”, “obesity”, “overweight”, or “weight loss” were used on the online database MEDLINE, PubMed, SPORTDiscus and Scopus. Additionally, references of the studies included were screened to identify eligible articles. Applying the inclusion and exclusion criteria, ten manuscripts were considered as eligible for this review. The results of the studies were categorized in several domains with regard to “anthropometric parameters and body composition”, “cardiovascular parameters and aerobic capacity”, and “blood sample and glucose tolerance”. The results showed positive effects on the anthropometric parameters, body composition, cardiovascular parameters, blood sample, and glucose tolerance. The greatest improvements were observed in supervised and high weekly frequency of NW interventions. NW could be considered as an effective modality through which to involve the obese in physical activity. For weight loss, NW should be prescribed 4–5 times per week, at least 60 min per session, preferably combined with diet control.


Introduction
Physical inactivity is the primary cause of most chronic diseases and is responsible for accelerating biological aging becoming one of the risk factors for premature death worldwide [1]. Insufficient level of PA predispose people to an increased risk for developing chronic conditions, including diabetes, cardiovascular disease, and cancer [2]. Moreover, the abundance of energy-enriched food associated with a sedentary lifestyle has caused an increase in the number of overweight and obese people worldwide, including in developing countries [3]. The American College of Sport Medicine 2018

Inclusion and Exclusion Criteria
Only studies published in English on peer-reviewed journals were considered for the inclusion. To be included, articles had to meet the following inclusion criteria, according to PICO model [15]-(a) Body Mass Index (BMI) higher than 25; (b) supervised or not supervised NW intervention; (c) the presence or not of a control group; (d) evaluation of anthropometric parameters, body composition, cardiovascular parameters, aerobic capacity, blood sample, and glucose tolerance; and (e) randomized controlled trial (RCTs) and no-randomized controlled trial (noRCTs). Both males and females from all races and different states of health were included. All studies that did not evaluate the outcomes through pre-and post-intervention comparisons, with mixed activity intervention, as well as cross-sectional studies and case reports, were excluded. Published abstracts, dissertation materials, or conference presentations were not considered as eligible documents.

Study Quality Assessment
The quality of the studies was assessed by applying an adapted nine criteria checklist, provided by the Cochrane Collaboration Back Review Group [16]. As in the previous review [17,18], the checklist had to be marginally adapted to rate the strength of the evidence. Each study in the review was scored on the basis of the following nine criteria: (1) "Was the method of randomization adequate?"; (2) "Were the groups similar at baseline regarding the outcome measures?"; (3) "Were inclusion and exclusion criteria adequately specified?"; (4) "Was the drop-out rata described adequately?"; (5) "Were all randomized participants analyzed in the group to which they were allocated?"; (6) "Was compliance reported for all groups?"; (7) "Was intention-to-treat analysis performed?"; (8) "Was the timing of outcomes assessment similar in all groups?"; and (9) "Was a followed up performed?". When the paper provided a satisfactory description, a positive value was assigned (+). If the criterion descriptions was considered absent, unclear, or lacked the specified content, a negative value was assigned (−). A study was qualitatively estimated as high quality, if it showed a positive score on 5 out of 9 of the criteria; otherwise, it was considered a low-quality study.

Data Extraction and Synthesis
Two researchers independently examined all abstracts of the sourced studies. Several studies were analyzed in more details to be included in the review. Additional articles were sourced, reviewing the reference sections of the included studies. The individual searches were combined, compared, and reviewed for applicability, where a consensus was made regarding the study inclusion. In case of discrepancies, the review process was repeated and a third researcher was consulted. A K-Cohen's coefficient of 0.87 indicated a perfect agreement between researchers. Quality assessment was applied independently by the two researchers, using the modified Cochrane methodological quality criteria, and was discussed before the final quality scores assignation ( Table 1). The same researchers who screened the titles, abstracts, full texts, and references, also performed the quality assessment. Several domains were identified for categorization of the study results. In particular, studies were analyzed with regards to "anthropometric parameters and body composition", "cardiovascular parameters and aerobic capacity", and "blood sample and glucose tolerance".

Study Group Comparison Results
Venojärvi et al.

Discussion
This systematic review aimed to analyze the effects of NW programs on overweight and obese subjects. The current results showed positive effects on the anthropometric parameters, body composition, cardiovascular parameters, blood sample, and glucose tolerance. The involvement of the upper and lower limb for performing NW, increased the energy expenditure during the workout, compared to normal walking alone. Moreover, the use of poles reduced the lower limb muscular activation [29], potentially, encouraging individuals with lower exercise tolerance to perform physical activity.

Anthropometric Parameters and Body Composition
Weight control in overweight and obese people was strongly recommended to reduce the risk of developing chronic diseases such as metabolic syndrome and type 2 diabetes. For this reason, lifestyle change, including PA increase and dietary modification was an effective way to improve the overall health. Moreover, weight loss lower than 5% was considered to be not clinically meaningful [30]. According to the previous studies [31,32], a major reduction in body weight and BMI were found in the Derengowska et al. studies, due to the integration of NW and diet control. Moreover, these studies were characterized of a high frequency and duration (60 min 5/6 times per week), with an overall weekly PA of about 300-360 min per weeks [21,22]. A significant reduction in body weight and BMI (5.6% to 6.4%) could be considered as clinically meaningful, confirming the need for a combined PA and diet interventions, for weight loss in overweight and obese people.
From another point of view, even if BMI was found to be the main indicator that helps identify overweight and obese people, WC was a stronger predictor for the risk to develop diabetes than BMI. Indeed, WC was an indicator of body fat distribution, which could identify people with an increased risk for cardio-metabolic disease [33]. Fritz and colleagues analyzed the effect of the non-supervised NW program on the overweight and obese people with NGT, IGT, and T2DM. Despite the long protocol (16 weeks), a significant reduction in body weight and BMI was only recorded in the NGT and T2DM groups. On the contrary, WC was significantly reduced in all the three groups (NGT −4.9%; IGT −2.2%; and T2DM −1.2%). Unfortunately, body fat was not evaluated in this study [25]. Body fat mass were analyzed in three studies that recorded a significant reduction after 12 or 16 weeks of NW (−7.4% [26], −3.4% [28], and −2.2% [27]) despite the minimal weight loss (−2.4% [26], −1.8% [28], and −1.7% [27]). These results highlighted the importance of body composition evaluation, in addition to body weight. In fact, the reduction in total body fat, abdominal obesity or both, without significant weight loss (more than 5%) showed improvements in the cardio-metabolic risk factors, such as insulin sensitivity [34]. Moreover, a major reduction on BFM was recorded in the supervised protocol with intensity progression from 55% to 75% of HR rest [26].

Blood Sample and Glucose Tolerance
Lifestyle change was the primary recommendation for the management of hematic parameters. The lipid profile changes after NW intervention showed contrasting results. Most studies reported improvement in blood lipid profile, but only three investigation displayed a significant reduction of TC, TG, LDL [19,21,22], and only the Derengowska et al. studies found a significant improvement in HDL [21,22]. As described in other research, the integration of diet and PA was more effective on HDL modification [35], and Derengowska and colleagues protocol included both the intervention.
With regards to the metabolic profile, Fritz and colleagues analyzed the effect of 16 weeks of non-supervised NW programs on glucose tolerance and HbAc1 in obese, with or without glucose impairment, such as diabetes mellitus. In their study, participants were required to reach a target of 300 min of non-supervised NW every week. As expected, the results showed a significant reduction in OGTT-2h in obese with IGT and T2DM, while HbAc1 only in T2DM [25]. This protocol was one of the longest and the extensive duration of the NW program, also with the higher adherence (78-96%) and higher minutes of exercise per week, could have concurred to produce these positive results.
In conclusion, exercise frequency and the weekly minutes of non-supervised NW seemed to positively influence the improvement of metabolic control. Results also indicated that a supervised NW program with a shorter duration (6 weeks) could lead to significant improvements in both glucose blood profile and glucose tolerance in middle-aged men with IGT that performed 240 min of activity, with an intensity of 60-75% of HR max [23].

Cardiovascular Parameters and Aerobic Capacity
Aerobic exercise was largely recommended to reduce blood pressure in hypertensive patients. In a recent document, Lopes et al. reported significant reductions in blood pressure, after at least 4 weeks of aerobic exercise, with a different magnitude of improvement among hypertensive, pre-hypertensive, and normal subjects [36]. Despite the protocols of our review being longer than 4 weeks, only one study depicted a significant reduction in DBP [27]. Likewise, these results did not significantly change with a change in heterogeneity of the groups and the hypertensive conditions of the recruited individuals. Despite this, results were aligned with a previous investigation that reported a mean reduction of 3.4 for SBP and 2.4 mmHg of DBP, after aerobic exercise [37]. In fact, the average blood pressure reduction of the included studies reported a 3.4 mmHg reduction for SBP and 2.8 mmHg reduction for DBP. As expected, the aerobic capacity increased after NW intervention. Nevertheless, non-supervised protocol [24] and low weekly minutes of training (only 90 min) [28] reported no significant improvements after NW. On the contrary, it seemed that supervised NW, in which the intensity augmented progressively from 55% to 75% of HR max during the intervention and lasted about 150 to 300 min per week, induced significant improvements of aerobic capacity [19,23,26].

Limitations
This review presented several limitations. First, the included subjects were overweight and obese people, without internal distinction into groups. Second, despite the importance of body fat reduction in people with obesity, body composition was not evaluated in many studies. From this point of view, future investigations should evaluate weight and body composition changes, following a NW protocol, to detect significant clinical changes. Third, diet control was described in only one study, despite it being well-known that the integration of PA and diet is preferable for obesity management. Finally, training modality and intensity were not reported in all the studies and not all included studies specified the prior level of PA in participants, or a minimal level of PA as the inclusion or exclusion criteria for participation. As a consequence, it was difficult to identify a precise dose-response of NW to promote an improvement in each parameter discussed in this systematic review. Moreover, it was not possible to identify a clear and efficient intensity progression to optimize weight loss and improve physical capacity, due to a general lack of information from the analyzed studies.

Conclusions
The results of this systematic review showed that NW programs could be considered as an effective modality to involve overweight and obese patients in physical activity. Additionally, NW was apparently able to modify different risk factors for cardiovascular diseases, even though the best improvement seemed was observed in a combination of exercise with diet control. To the best of our knowledge, clinicians could consider an NW program as a form of exercise in their prescription to increase PA in overweight and obese people. To promote weight loss, the minimum quantity of recommended NW is 4 times per week and for at least for 60 min per training session. This minimum quantity should preferably be coupled with diet control. Funding: This research received no external funding.

Conflicts of Interest:
The authors declare no conflict of interest.