The effects of exercise and diet program in overweight people – Nordic walking versus walking

Introduction

In recent years, the prevalence of overweight and obese adults has dramatically increased in European countries.¹ Obesity can raise the risk of chronic diseases and early mortality² and lead to disabilities and a reduced quality of life.³ In this context, physical exercise plays a crucial role in preventing and counteracting obesity.^4,5 Given that people with excess weight are not inclined to an active lifestyle,⁶ it is of great importance to promote enjoyable and well-tolerated forms of physical exercise.

Walking is probably the safest form of physical activity,^7,8 and it can easily be adapted to people with pathological conditions while still providing substantial health benefits.⁹ In the last 20 years, Nordic walking (NW), ie, walking with the dynamic use of specific poles, has become an increasingly popular form of exercise. A correct NW technique recruits the muscles of the upper extremities,¹⁰ maintains a long stride at sustained gait speeds and elicits high exercise demands with low impact forces.¹¹ In NW, the movement of the arms raises the heart rate (HR), oxygen consumption (VO₂) and energy expenditure while keeping the rate of perceived exertion (RPE) lower than would occur while walking at the same speed.^10,12–15 These characteristics make NW a stimulating form of exercise for overweight or obese persons.^16,17

Although the acute physiological responses to NW and W are well documented,^12,13,18 the studies that investigated the health benefits of NW and W exercise included shorter training periods (ie, 4–12 weeks).^19–22 However, it would be of great importance to compare the effects of NW and W throughout longer training periods, particularly in sedentary and clinical populations.²³ After 12 weeks of training, previous studies^20,21 found positive effects of NW and W training on aerobic fitness variables, but the possible benefits on muscle strength are still not clear.^19,20,24 Moreover, it is also suggested that a deeper investigation, in terms of weight loss with a detailed body composition analysis (eg, obtained with dual-energy X-ray absorptiometry [DXA]) or the combination of a training period with a controlled diet, could better highlight some meaningful differences.²⁴

Therefore, the aim of this study was to investigate the effects of a prolonged (>12 weeks) period of supervised NW and W training, combined with a controlled diet, in overweight adults. We expected that NW could lead to greater benefits in cardiopulmonary and aerobic fitness variables, in upper and lower limbs’ muscle strength and in anthropometric and body composition indexes.

Materials and methods

Subjects

Thirty-eight participants were randomized into NW (6 men and 13 women) and W (5 men and 14 women) groups that took part in a 6-month training and diet program. To randomize the subjects in the two groups, a randomization list with variable width was created of size 4 or 6. This list was prepared using the STATA/SE 11 software (StataCorp, College Station, Texas, United States). With this software, two randomization lists were created to also stratifying by sex.

The inclusion criteria were sedentary male and female (post-menopausal), aged 50–80, body mass index (BMI) >27 kg/m² and no considerable weight loss (>5%) in the previous 2 months. The exclusion criteria included cardiovascular diseases and musculoskeletal pathologies. The flow chart of the study is shown in Figure 1.

Figure 1 Flow chart of the study. Abbreviations: NW, Nordic walking; W, Walking; D, Diet; PA, Physical activity.

The study included some data that are part of a larger study (ClinicalTrials.gov number, NCT03212391). The study was approved by the Human Ethics Committee of the University of Verona and was conducted in accordance with the Declaration of Helsinki. The subjects gave their written informed consent.

Training program

The NW and W groups trained three times per week for 24 weeks under the supervision of an instructed NW coach and an assistant graduate in Sports Sciences. Each participant wore an HR monitor (Polar FT1, Polar, Kempele, Finland) and a pedometer (Geonaute Onwalk 900, Decathlon Group, Villeneuve d'Ascq, France). Each participant received instructions on the correct use of these devices and standardized guidelines on the Cr-100 Borg scale²⁵ from the same investigator. During the first month, the NW participants learned the NW technique in accordance to the International NW Federation (INWA) guidelines, whereas the W group followed the instructions for improving the walking technique.

Each training session lasted between 60 and 90 mins and was divided into three phases: i) warm-up (5 mins), ii) central (40–60 mins) and iii) cool down (10 mins). In the central phase, the participants walked in a natural environment characterized by different pathways that could be covered in maximum of 90 mins. The exercise intensity was prescribed by using the heart rate reserve (HRR), ie, from 40–59% HRR to 60–84% HRR.²⁶ Each participant knew his own range of HRR (ie, moderate and vigorous) which they had to check frequently while walking. At the end of every session, the coaches registered the number of steps, the mean of HR and RPE achieved by each subject. To be included in the data analysis, each subject had to achieve at least 75% of the attendance during the 6 months of training sessions.

Dietary intake and hypoenergetic diet

A trained dietician performed a 7 days dietary recall interview, lasting approximately 40 mins, in order to assess the initial dietary habits of each subject enrolled in the study. A recall grid representing 7 days of the prior week and all possible food-encounter times was used. Portion sizes were estimated for foods and fluids by comparing with reference foods and fluids in a booklet of photographs. Daily intake of energy, protein, fat, carbohydrate and alcohol was then calculated based on the tables furnished by the Italian National Institute of Nutrition.²⁷

During the study, all the subjects underwent a weight-loss program designed to achieve a loss of 5–10% of the initial weight as previously reported.²⁸ The caloric restriction was 500 kcal below the resting energy expenditure, as evaluated by indirect calorimetry and multiplied by a physical activity level of 1.4. Each subject received a diet providing 62% carbohydrates, 24% fat, 14% protein, and 20 g fiber. The subjects underwent monthly clinical and nutritional follow-ups. Dietary adherence was checked by a 24-h recall every 4 weeks during an outpatient visit.

Anthropometry and body composition measurements

Waist circumference (WC) was measured at the midpoint between the highest point of the iliac crest and the lowest point of the costal margin in the mid-axillary line.²⁹ Total body and regional composition (lean and fat mass) was evaluated by means of DXA, using a total body scanner (QDR Explorer W, Hologic, MA, USA; fan-bean technology, software for Windows XP version 12.6.1). The android region was taken as the area between the ribs and the pelvis, with an upper demarcation that was 20% of the distance between the iliac crest and neck and a lower perimeter that coincided with the top of the pelvis.³⁰ All scanning and analyses were performed by the same operator to ensure consistency. The estimated precision of whole-body DXA measurements was 2.3% and 0.5% for fat and lean mass, respectively.

Aerobic capacity measurements

An incremental ramp test was performed on a cycloergometer (Excalibur Sport Device, Lode, Netherlands). The protocol consisted of a 1-min rest period, a 3-mins period of warm-up at 20 W and an increase in power output (PO) of 2 W every 12 s (ie, 10 W/min) for females and 3 W every 12 s (ie, 15 W/min) for males until volitional exhaustion. During the test, gas exchange and minute ventilation (V_e) were collected breath by breath using a metabolimeter (Quark PFT, Cosmed, Rome, Italy), HR was monitored through a connected computer, and PO and pedaling frequency were continuously collected by the cycloergometer. Before each test, the metabolimeter was calibrated following the manufacturer’s instructions. Two expert evaluators determined ventilatory thresholds³¹ by visual inspection. The first ventilatory threshold was identified at the first rapid increase in V_E followed by an increase in ventilatory equivalent in VO₂ (V_E/VO₂) and partial pressure of O₂ (PO₂) whereas ventilatory equivalent in VCO₂ (V_E/VCO₂) and partial pressure of CO₂ (PCO₂) remained stable. The second ventilatory threshold was identified with the breakpoint where PCO₂ began to fall, with an additional increase in V_E, V_E/VO₂, V_E/VCO₂ and PO₂. The POs at the first (PO_vt1) and second (PO_vt2) ventilatory thresholds were calculated.

On a different day, each subject performed the 6-min walking test (6MWT) in a course of 30-m (marked every 5 m with a tape on the floor) delimited by two training cones. Before starting the 6MWT, the experimenter asked to cover the maximal distance at a self-selected speed for 6 mins. During the test, each participant received verbal encouragement. At the end of the test, the investigator measured the distance covered by the participant.

Strength measurements

The forces during an isometric maximal voluntary contraction of the brachial biceps (MVC_BB) and the quadriceps femoris (MVC_QF) were measured through a strain gauge, collected with a sampling frequency of 200 Hz and recorded on a personal PC using LabChart7. For testing the MVC_BB, the subject was sitting on a chair with the dominant arm flexed at 90°. For testing the MVC_QF, the subject was sitting on the tested chair with a flexion angle of 90° of the dominant knees, with the ankle fixed by a strap in line with the strain gauge. Before the tests, the experimenter gave the instruction to execute a contraction “as hard as possible,”³² and during the tests, participants were encouraged to deliver the maximal force. After a standardized warm-up and a familiarization trial, the subjects performed six MVCs interspersed by 60 s of rest. Averaged peak force values of the best three over a total of six contractions provided the MVC_BB and the MVC_QF.

Arm curl (AC) and chair stand (CS) tests³³ were used to test muscular endurance. Participants were asked to perform in 30 s the maximal number of flexion–extension of the dominant elbow with a dumbbell (8 or 5 lbs for men and women, respectively) and the maximal number of stand-ups, starting on a seated position with both arms crossed on the chest.

Statistical analysis

A Student’s t-test was used to verify any baseline differences between the groups and differences in the training sessions. A two-way (group × time) repeated measures ANOVA was conducted. In the case of a time × group interaction, a between-group (ie, NW vs W) ANOVA was also used to assess for changes across time within each group. In the case of statistically significant differences, a pairwise comparison between groups was carried out, adjusting the significance level with Bonferroni correction. To further investigate changes over time in the NW and W groups separately, a within-group one-way repeated measure ANOVA was run. The assumption of normality and sphericity was ascertained before using parametric tests. SPSS software (IBM SPSS Statistics Version 22, Chicago, IL, USA) was used for the statistical analysis. A level of significance was accepted at P<0.05.

Results

No significant differences between the groups were found for diet (Table S1) and for the parameters at baseline (Tables 1 and 2).

Table 1 Characteristics of trial groups, anthropometric and body composition measurements

Table 2 Aerobic and strength measurements

Training characteristics and adherence to the intervention

At the end of the study, the total dropout was 21% and 36% in the NW and W groups, respectively (Figure 1).

The monthly mean values of steps count (Figure S1) increased over time (P=0.001), with no time × group interaction (P=0.982) and no significant differences between the two groups (P=0.323). The HR_mean increased (P<0.001), without time × group interaction (P=0.370) and differ significantly among the two groups (p=0.015); the HR_mean was significantly higher in NW group in month 1 (P=0.008), month 2 (P=0.009), month 3 (P=0.009), month 5 (P=0.022), month 6 (P=0.023). The RPE values decreased over time (P<0.001), without any time × group interaction (P=0.111) and differ significantly among the two groups (P=0.045). RPE was significantly lower in the NW compared to W group at the end of month 1 (P=0.035), month 2 (P=0.051) and month 5 (P=0.049) of training.

The monthly mean values of HR and RPE recorded at the end of the training sessions in the NW and W groups are presented in Figure 2.

Figure 2 Monthly trend of the heart rate (HRmean, panel a) and RPE (panel b) during training sessions in NW and W groups. #P<0.05, ##P<0.01, significant differences between NW and W groups. Abbreviations: NW, Nordic walking; W, walking; RPE, rate of perceived exertion.

Anthropometry and body composition

A significant decrease in BMI was seen over time (P=0.001) without any time × group interaction (P=0.329). After 3 and 6 months of training, BMI significantly reduced in both NW (5% and 6%, respectively) and W (3% and 5%, respectively) group.

WC reduced over time (P=0.001) with a trend in time × group interaction (P=0.062). After 3 and 6 months, WC significantly decreased in both NW (9% and 5%, respectively) and W (3% and 4%, respectively) group.

BF_TOT, trunk fat and android fat reduced over time (P=0.001) without any time × group interaction (P=0.301; P=0.712; P=0.162, respectively). For the within-group analysis, after 3 and 6 months of training, only the NW group showed a significant reduction in BF_TOT (8%) and android fat (13% and 14%, respectively). For leg fat, there was a significant decrease over time (P=0.001) and a time × group interaction (P=0.022). After 3 months of training, a significant reduction was shown only in the NW group (9%) with no differences between the two groups (P=0.776). At the end of the intervention, both NW and W group reduced significantly leg fat (9% and 5%, respectively). The main changes in total and compartmental body fat are summarized in Figure 3.

Figure 3 Changes in total body fat (BFTOT, panel a), android fat (panel b) and leg fat (panel c) in NW and W groups after 3 and 6 months of training. *P<0.05, **P<0.01, significant differences from baseline and from 3 to 6 months. Abbreviations: NW, Nordic walking; W, walking.

No significant differences (P>0.05) were found in the two groups for BL_TOT, arm fat, arm lean mass, trunk and android lean mass and leg lean mass (Table 1).

Aerobic capacity

VO_2peak and peak power output (PPO) increased over time (P=0.009 and P=0.001, respectively) with no time × group interaction (P=0.382 and P=0.752, respectively). After 6 months, the VO_2peak increased significantly in the NW group (8%), while the W group had no significant changes (3%, P>0.05). After 3 and 6 months of training, the PPO increased significantly in both NW (6% and 12%, respectively) and W (7% and 10%, respectively) group.

PO_VT1 and PO_VT2 improved over time (P=0.001) with no time × group interaction (P=0.653; P=0.707, respectively). After 3 and 6 months, PO_VT1 increased significantly in NW (13% and 19%, respectively) and W (7% and 19%, respectively) group. Moreover, PO_VT2 increased in both NW (7% and 13%, respectively) and W (9% and 16%, respectively) group.

There was a significant increase in 6MWT over time (P=0.001) with a time × group interaction (P=0.050). After 3 months, only the NW group improved significantly 6MWT (7%), but no differences were observed between the two groups (P=0.347). At the end of the intervention, the 6MWT improved significantly in both NW (13%) and W (9%) group.

Muscular strength

MVC_BB and MVC_QF increased over time (P=0.001) with no time × group interaction (P=0.501; P=0.148, respectively). The within-group analysis revealed that after 3 and 6 months, only the NW group improved significantly MVC_BB (9% and 14%, respectively) and MVC_QF (23% and 17%, respectively).

There was an increase in AC over time (P=0.002) and a time × group interaction (P=0.013). After 6 months, only the NW group improved significantly AC (35%); however, no significant differences were found between the two groups (P=0.114). CS significantly increased over time (P=0.001) with no time × group interaction (P=0.539). After 3 months, a significant improvement in CS was found in both NW (29%) and W (37%) group. However, at the end of the intervention, no significant differences were observed in both groups (P>0.05).

Discussion

This study investigated the effects of a long period of NW plus diet compared with W plus diet, as well as analyzed cardiorespiratory changes and other aspects of health-related parameters (ie, body composition and muscular strength) in an overweight and obese population.

After 6 months of training, the dropout rate of the participants (21% and 36% in the NW and W groups, respectively) was higher when compared with rates reported by other studies.^34,35 The main reasons for this low compliance were the “lack of time” (as declared by the participants) and injuries not related to the exercise program. However, the participants that concluded the training period attended more than 80% of the training sessions. This is in keeping with results available in the literature.^20,23

In our study, we observed a significant reduction in BMI and WC in both groups after 3 months, with a further reduction after 6 months, in accordance to other studies.^21,34,36 However, we reported higher variations in BMI and WC indexes, and this might be because of the controlled diet, which is relevant for enhancing the chances of losing weight.⁴ Regarding the results of body composition, the statistical analysis did not find any significant differences between the two training modalities; however, over time only the NW group had a significant reduction in BF_TOT (8%), with a preferential loss in leg and android fat mass (9% and 14%, respectively). A possible explanation might be that the continuous emphasized movement of the shoulders and trunk in NW helps to mobilize and utilize fatty acid reserves with a positive effect on android fat.³⁷

The gain in VO_2peak (8% for NW) at the end of the intervention was smaller than that reported by others, eg, +10% in both NW and W groups after 13 weeks of training,³⁴ +20% and +14% in the NW and W groups, respectively, after 3 weeks.¹⁹ The differences might be explained by the different protocols used for the incremental test (cycle ergometer in our study vs treadmill).^19,34 Although walking on a treadmill is a more ecological test, we decided to use a cycling incremental test to focus on the improvements in the aerobic capacity while excluding any possible interference due to the habituation with walking pattern of motion. The increase in PPO in both groups, with a significant improvement on VO_2peak only in NW, can be the result of an enhanced capacity to tolerate fatigue.³⁸ Regarding the improvements in power at submaximal intensity (PO_VT1 and PO_VT2), we suggest that both forms of training can give enhancements in these exercise capacity parameters over a long period of time. However, the recruitment of the upper muscles in NW can raise the intensity of the stimulus during training sessions. NW group showed a higher HR_mean with a lower RPE compared with W, in line with other studies^10,12,21 that can accelerate the physiological adaptations at submaximal intensities.

After 3 months, only the NW group improved in 6MWT, whereas the W group showed an improvement only after 6 months. Other studies^19,20 reported an increase in 6MWT in both groups after 3 months of training. We speculate that the faster changes in the NW group might be due to the aerobic improvements and to the improved capacity in keeping a longer step length at higher locomotion speeds.^39,40

Although the results did not show significant differences among the two groups in terms of strength, only the NW improved maximal arm and leg strength compared with no significant changes in the W group. To our knowledge, only the study conducted by Ossowski et al (2016) investigated the effects in maximal leg strength after a period of NW training. Even though NW is mainly an aerobic exercise that can hardly lead to a gain in muscle strength, the process of learning the NW technique could be a stimulus for the neuromuscular component. Indeed, it has been reported that learning a new motor task may increase motor unit recruitment, making these more efficient.⁴¹ The increase in motor unit recruitment augments the maximal force production, explaining in part the improvements in MVC of the upper and lower limbs without changes in muscle mass.⁴⁰

After 6 months, we observed an increase in AC (35%) in the NW compared with the W group, in keeping with previous studies.^19,20,22 This may reinforce the idea that the use of poles can lead to a higher activation of the upper limb muscles compared with W,¹⁰ with positive effects on the arm resistance strength. Conversely, the significant effects on lower limbs resistance strength observed after 3 months of training (ie, 29% and 37% in NW and W, respectively) degraded in the last 3 months.

Conclusion

Our study showed that both forms of exercise may be well-tolerated for long-supervised training periods in overweight and obese adults. This is of relevance because in interventional studies in clinical populations, the main difficulty is to maintain a high level of adherence, even if the exercise program is supervised. However, the results revealed that when exercise program is associated to a diet, NW program may give additional benefits compared with diet plus W program in some key health-related parameters: 1) can be a suitable tool for patients with excess abdominal fat, therefore reducing the cardiovascular risks factors; 2) can increase the intensity of exercise with a tolerated fatigue, encouraging subjects with a low level of physical fitness to maintain the minimal dose of exercise recommended; 3) can increase muscle strength, while preserving muscle mass and counteracting the detrimental effects of aging/obese state on the maximal isometric strength; 4) can lead to faster changes in some exercise-related parameters.

Interventional studies where a specific comparison between NW and W is protracted and an unsupervised intervention is included should be encouraged. Particularly, studies investigating the effects on strength and compartmental fat with a greater sample of obese patients would be highly relevant for increasing the efficacy of interventions for overweight individuals.