This article was downloaded by: [Univ of Louisiana at Lafayette] On: 21 December 2014, At: 01:46 Publisher: Routledge Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Research Quarterly for Exercise and Sport Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/urqe20
Differences in Ground Reaction Forces and Shock Impacts Between Nordic Walking and Walking a
b
Alberto Encarnación-Martínez , Pedro Pérez-Soriano & Salvador Llana-Belloch a
b
Catholic University of Murcia
b
University of Valencia, Published online: 11 Nov 2014.
Click for updates To cite this article: Alberto Encarnación-Martínez, Pedro Pérez-Soriano & Salvador Llana-Belloch (2014): Differences in Ground Reaction Forces and Shock Impacts Between Nordic Walking and Walking, Research Quarterly for Exercise and Sport, DOI: 10.1080/02701367.2014.975178 To link to this article: http://dx.doi.org/10.1080/02701367.2014.975178
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
Research Quarterly for Exercise and Sport, 00, 1–6, 2014 Copyright q SHAPE America ISSN 0270-1367 print/ISSN 2168-3824 online DOI: 10.1080/02701367.2014.975178
RESEARCH NOTE
Differences in Ground Reaction Forces and Shock Impacts Between Nordic Walking and Walking Downloaded by [Univ of Louisiana at Lafayette] at 01:46 21 December 2014
Alberto Encarnacio´n-Martı´nez Catholic University of Murcia
Pedro Pe´rez-Soriano and Salvador Llana-Belloch University of Valencia
The regular practice of Nordic walking (NW) has increased in recent years, in part thanks to the health benefits described by the scientific literature. However, there is no consensus on the effects of shock-impact absorption during its practice. Purpose: The aim of this study was to compare the levels of impact and ground reaction forces (GRF) between NW and walking (W). Method: Twenty physically active and experienced participants were assessed using a dynamometric platform and accelerometry analysis. Results: The results show statistically significantly higher levels of acceleration in the tibia (12%) and head (21%) during NW compared with W. Equally, GRF were significantly higher (27%) at the instant of strike compared with W, and a reduction of the forces at the instant of takeoff (8%) was observed. Conclusions: During NW, shock impacts and GRF levels increased compared with W, an aspect that should be considered when prescribing health improvement programs. Keywords: biomechanics, kinetics, walking
Nordic walking (NW) is a cyclical activity, whose introduction into the world of physical activity and sport dates back to the early 1930s. Since its birth in Finland, the number of practitioners has greatly increased worldwide (Morgulec-Adamowicz, Marszałek, & Jagustyn, 2011). NW has internationally spread, despite its short career as a healthy physical sport activity, partly due to the benefits obtained by its regular practice (Fritschi, Brown, Laukkanen, & van Uffelen, 2012; Tschentscher, Niederseer, & Niebauer, 2013) on oxygen consumption, heart rate, and caloric expenditure parameters compared with walking (W; Church, Earnest, & Morss, 2002; Fritschi et al., 2012; Porcari, Hendrickson, Walter, Terry, & Walsko, 1997; Rodgers, VanHeest, & Schachter, 1995; Tschentscher et al., 2013). Submitted October 2, 2013; accepted May 3, 2014. Correspondence should be addressed to Alberto Encarnacio´n-Martı´nez, Department of Sport Sciences and Physical Education, Catholic University of Murcia, Campus de Los Jero´nimos, s/n. Guadalupe, 30107, Murcia, Spain. E-mail: [email protected]
From a biomechanical perspective, there is an almost unanimous consensus regarding the biomechanical response during NW compared with W, based on the observed increase in the stride length and speed during gait and in the muscle activity of the upper body as well as a reduction of the effort perception (Hagen, Henning, & Stieldorf, 2011; Stief et al., 2008). However, the consensus is not the same regarding ground reaction forces (GRF). Some studies indicate that shock-impact forces, treated as GRF at the heel strike with the ground, are lower during NW (Schwameder & Ring, 2006), while others show an increase (Brunelle & Miller, 1998; Hagen et al., 2011; Stief et al., 2008). A shock wave is produced as a result of the first heel strike with the ground during W that is then transmitted from the heel to the upper limbs. This has been linked to soft-tissue, bone, lower-limb, and vertebral column damage along with degradation of the biomechanical properties of the joint cartilage (Voloshin, 2001). Despite the evidence, only one study (Hagen et al., 2011) has ever analyzed this shock wave and the impacts produced during NW. These impacts were recorded by an accelerometer located in the
Downloaded by [Univ of Louisiana at Lafayette] at 01:46 21 December 2014
2
´ N-MARTI´NEZ ET AL. A. ENCARNACIO
wrists, and researchers concluded that those shock-impact levels received during NW are very high and represent a risk for suffering overuse injuries in the upper extremities. As previously discussed, the use of poles provokes a walking speed higher than usual, standing between walking and running (Hagen et al., 2011), an aspect that we hypothesize leads to increased levels of impact that have not yet been analyzed by any research. Other studies have shown a relationship between repeated impacts during running and the occurrence of degenerative joint injuries (Radin, 1987), with this aspect magnified by the occurrence of fatigue, because a positive correlation has been found between the magnitude of repeated impacts and the onset of inherent fatigue of aerobic activities like W, NW, and running (Mercer, Vance, Hreljac, & Hamill, 2002; Mizrahi, Voloshin, Russek, Verbitsky, & Isakov, 1997). The objectives of this study were to compare GRF and impact transmission along the locomotor system between NW and W.
METHODS Participants and Inclusion Criteria All participants, which included 20 healthy participants (10 men and 10 women), were instructors of NW (M age ¼ 25.9 ^ 4.54 years; M weight ¼ 69.4 ^ 6.5 kg; M height ¼ 1.73 ^ 0.52 m; M bodymassindex ¼ 23.2 ^ 1.8; Mexperience ¼ 6.4 ^ 2.6 years). Very different methodologies have been used for previous studies, and the degree of experience of participants has varied as well. For this reason, we chose experienced participants as in previous studies (Hagen et al., 2011; Hansen, Henriksen, Larsen, & Alkjaer, 2008; Stief et al., 2008). Inclusion criteria were that participants had no current injuries and were physically active (exercise practice three times a week for at least 30 min per session). Participants were excluded if they had an existing orthotics prescription or if they had had a lower-limb injury within the previous 3 months. All participants were informed of the characteristics of the study and provided informed consent according to the Declaration of Helsinki (1964 – 2000). Also, the institutional review board approved the research. Experimental Protocol There were two speed conditions: freely chosen speed (preferred speed or V1) and fast speed (fast speed or V2 ¼ V1 plus 20%; Pe´rez-Soriano, Llana-Belloch, Encarnacio´nMartı´nez, Martı´nez-Nova, & Morey-Klapsing, 2011). To calculate the V1 condition, all participants were asked to walk along the runway at a normal speed for as long as
necessary until they felt comfortable for both gait conditions (NW and W). Volunteers walked along the runway where walking speed was measured along the 5 central meters of the way—that is, leaving 3 m at the beginning and the end to allow acceleration and deceleration of each repetition. Volunteers were not asked to walk at any particular speed and then the process was repeated to calculate the freely chosen speed for both modalities, W and NW. After the participants had had sufficient practice trials to familiarize themselves with the testing procedure, five trials for both NW and W were performed. A maximal deviation of ^5% between the trials was accepted for each condition. Participants were told to hit the poles located on both sides of the platform. If any of the poles touched the platform, the test was repeated. A trial was considered valid when a full foot strike was captured by the force platform. Then, this step was selected for further analysis. Participants rested for 2 min between repetitions. NW and W order was randomized. All participants performed the test using the diagonal technique (Regelin & Mommert, 2005), which is the most common technique of NW worldwide and is characterized by a contralateral legs –arms coordination. During its practice, the body moves leaning slightly forward. Biomechanical Setup All participants were asked to walk and Nordic walk along a 12-m long, 2-m wide runway. Embedded in the runway was a Kistlerw (600 mm £ 400 mm £ 100 mm, Kistler AG, Winterthur, Switzerland) force platform. Both W and NW speeds were measured by two photocells connected to an electronic timer (Chronomasterw, Sportmetrics 2008, Valencia, Spain, with an accuracy of .001 s) located 5 m apart from each other. Vertical shock impacts were recorded by two uniaxial accelerometers (SMAA02-1 model, Sportmetricsw; the equivalents were: ^ 9.81 m/s2 , 1 g), located on the tibial tuberosity (measurement range of ^ 10 g) and the frontal bone (measurement range of ^ 5 g). The accelerometers were connected and synchronized with an analog cable to the amp box of the dynamometric platform. All data were synchronized and registered at a frequency rate of 500 Hz. The accelerometer of the tibia was placed on the dominant leg, which was the foot recorded by the dynamometric platform. The accelerometers were fixed to the skin with double-sided tape and were reinforced with tape and an elastic band. All variables were extracted using a program made with the help of Matlab Version 7.4. A filter was applied to data with a low pass cutoff frequency of 50 Hz. Peak acceleration of shank (PAS) and peak acceleration of head (PAH) were obtained. GRF (normalized to body weight [BW]) in the vertical (Z) and anterior-posterior (X) axes at the instants of heel strike (FZH and FXH) and takeoff phases (FZT and FXT), vertical force impact at heel strike (FZI), and
3
GRF AND IMPACTS IN NORDIC WALKING AND WALKING TABLE 1 Descriptive Values for Ground Reaction Forces of the Analyzed Variables: Level of Significance of the Two-Way Analysis of Variance (Main Effect of Speed and Condition) Walking (W) Preferred Speed
Downloaded by [Univ of Louisiana at Lafayette] at 01:46 21 December 2014
Variable Speed (m/s) Vertical force impact heel strike (N/kg) Vertical force heel strike (N/kg) Vertical force takeoff (N/kg) AP force heel strike (N/kg) AP force takeoff (N/kg) Braking impulse (N·s) Propulsive impulse (N·s)
Nordic Walking (NW)
Fast Speed
Preferred Speed
Level of Significance
Fast Speed
Speed
Condition
M
SD
M
SD
M
SD
M
SD
p
p
1.72 1.11 1.45 1.32 0.31 0.33 30.52 30.99
0.16 0.13 0.13 0.12 0.05 0.04 4.30 4.66
2.04 1.43 1.62 1.29 0.39 0.34 31.55 30.23
0.19 0.20 0.14 0.14 0.05 0.05 5.97 5.26
1.92 1.41 1.62 1.25 0.42 0.35 38.87 32.66
0.13 0.17 0.13 0.14 0.05 0.05 4.10 4.82
2.22 1.55 1.71 1.15 0.48 0.34 37.42 28.98
0.15 0.14 0.11 0.18 0.09 0.07 8.17 6.80
.000* .001* .001* .045** .002* .846 .738 .013**
.000# .002# .002# .003# .000# .911 .004# .721
Note. AP force ¼ anteroposterior force. *(p , .01) Preferred speed versus fast speed. **(p , .05) Preferred speed versus fast speed. # ( p , .01) W versus NW.
mechanical impulse of braking impulse (BIM) and propulsive impulse (PIM) were also obtained (Figure 1).
Data Analysis Statistical analysis was performed using the Statistical Package for the Social Sciences Version 17. First, normality of the data was verified using the Shapiro-Wilk test, homoskedasticity by the Levene test, and sphericity by the Mauchly test. A student’s t test was performed to determine whether there were differences between men and women.
Then, a two-way analysis of variance (ANOVA) test was performed to analyze whether there were differences between the means of the variables analyzed while taking into account the types of walking (NW vs. W) and speeds (V1 and V2). The level of significance was set at p # .05.
RESULTS The results of the t test showed no statistically significant differences (F ¼ 0.870, p ¼ .503, h 2 ¼ .029) regarding
FIGURE 1 Variables analyzed in the research. GRF ¼ ground reaction forces; NW ¼ Nordic walking; W ¼ walking; N/BW ¼ newtons/body weight; FZI ¼ vertical force impact; FZH ¼ vertical force at heel strike; FXH ¼ anterior-posterior force at heel strike; FZT ¼ vertical force at takeoff; FXT ¼ anterior-posterior force at takeoff; BIM ¼ braking impulse (area under the curve); PIM ¼ propulsive impulse (area under the curve).
´ N-MARTI´NEZ ET AL. A. ENCARNACIO
gender for any of the variables analyzed. So during this study, all subsequent statistical analyses were conducted jointly and included men and women as one sample (n ¼ 20). The results found by the two-way ANOVA showed statistically significant differences in the GRF and shockimpact levels received depending on the speed (V1 vs. V2) and type of walk (NW vs. W; Table 1). The results obtained for the variables of the GRF show statistically significant differences ( p , .05) between W and NW for the V1 condition. The values of the variables analyzed in NW were 10.5% higher on average. Specifically, the results show significant differences ( p , .05) depending on the walking condition (NW vs. W), on the GRF at FZI (F ¼ 27.1, p , .02, h 2 ¼ .730), at FZH (F ¼ 21.7, p , .01, h 2 ¼ .731), at FXH (F ¼ 47.0, p , .01, h 2 ¼ .825), and at BIM (F ¼ 31.7, p , .01, h 2 ¼ .760; Figure 2) being 15.6%, 8.9%, 29.9%, and 23.0%, respectively, higher during NW. In contrast, GRF at FZT (F ¼ 46.6, p , .01, h 2 ¼ .823) showed an important reduction of 8.2% during NW (Figure 2A). Regarding shock-impact transmission (see Figure 2B), statistically significant differences (F ¼ 10.4, p , .01, h 2 ¼ .536) between W and NW were found for both speeds’ PAS (V1, W ¼ 4.17 ^ 0.4 g vs. NW ¼ 4.87 ^ 0.7 g; V2, W ¼ 5.82 ^ 0.5 g vs. NW ¼ 6.32 ^ 0.8 g). In V2, only differences between conditions for PAH (F ¼ 13.7, p , .01, h 2 ¼ .633) were observed (fast speed, W ¼ 0.65 ^ 0.1 g vs. NW ¼ 0.77 ^ 0.1 g).
Analyzing the speed effects (V1 vs. V2), the results show a significant increase at FZI (F ¼ 68.8, p , .01, h 2 ¼ .873), at FZH (F ¼ 308.1, p , .01, h 2 ¼ .975), and at FXH (F ¼ 29.8, p , .01, h 2 ¼ .749), showing an increase in the force values during the V2 condition. By contrast, a significant reduction was observed at V2 FZT (F ¼ 5.8, p ¼ .045, h 2 ¼ .368) and at PIM (F ¼ 9.3, p ¼ .013, h 2 ¼ .483) (Table 1). Regarding the effect of the studied speed (Figure 2B), significant differences were noted for PAS (F ¼ 93.3, p , .01, h 2 ¼ .912) and PAH (F ¼ 24.5, p , .01, h 2 ¼ .754) during V2 (PAS, V1 ¼ 4.52 g vs. V2 ¼ 6.07 g; PAH, V1 ¼ 0.68 g vs. V2 ¼ 0.77 g) for both study conditions.
DISCUSSION The number of NW practitioners has considerably increased in recent years, mainly because it has been shown that regular practice of this activity provides important benefits such as improved general health, short-and long-term effects on the cardiopulmonary system, and improvements in a wide range of individuals with diseases. It has also proven to be a safe and accessible activity (Tschentscher et al., 2013). This research analyzed the biomechanical response of a group of expert practitioners to describe the GRF and impact levels received during NW compared with W.
B
A FZI (N/kg)
8
#
*
#
7 FZH (N/kg)
#
6 Acceleration (g)
Downloaded by [Univ of Louisiana at Lafayette] at 01:46 21 December 2014
4
#
FZT (N/kg)
#
FXH(N/kg)
Walking Nordic walking
#
5 4 3
0
0.5 #
1
1.5
2 2
Force (N/kg)
*
BIM (N·s)
1
#
#
0 0
10
20
30
Impulse (N·s)
40
50
Preferred Speed
Fast Speed
Peak acceleration shank (g)
Preferred Speed
Fast Speed
Peak acceleration head (g)
FIGURE 2 Results of the two-way analysis of variance. A) Ground reaction forces results, where FZI ¼ vertical force impact; FZH ¼ vertical force at heel strike; FXH ¼ anterior-posterior force at heel strike; FZT ¼ vertical force at takeoff; BIM ¼ braking impulse. B) Peak accelerations results. #Statistically significant difference ( p , .01) between walking and Nordic walking. *Statistically significant differences ( p , .01) between speeds (preferred vs. fast speed).
Downloaded by [Univ of Louisiana at Lafayette] at 01:46 21 December 2014
GRF AND IMPACTS IN NORDIC WALKING AND WALKING
Participants in this study walked about 10% faster with poles in the preferred condition, similar to other studies (Stief et al., 2008). It is important to highlight that the preferred chosen speed by the participants for NW corresponds to the speed described for the walking –running transition (Nilsson & Thorstensson, 1989), an aspect that could justify the differences found in the physiological and biomechanical response compared with W. Impact acceleration and maximum GRF peaks during walking are highly correlated to the walking speed, an aspect that is consistent with the results. As speed increases in both conditions (W and NW), the values of the GRF also increase, except at FXT and at BIM. Lee and Hidler (2008) showed that at speeds from 0.95 m/s to 1.33 m/s, the maximum vertical force during walking is 1.1 BW and 1.5 BW. Values obtained by this research are slightly more (, 1.4 BW to , 1.7 BW). These differences are probably due to the fact that the walking speeds are slightly higher (, 1.7 m/s to , 2.2 m/s). Despite the speed increase observed at V2 during NW, there is a significant reduction at FZT and at PIM. These results are consistent with a previous study where a trend is described toward a reduction of the vertical forces during takeoff (Stief et al., 2008). It could be interpreted that the increase in speed is partly due to a more active use of poles that consequently help reduce those parameters related to takeoff. Looking at the low size effect found in the differences between V1 and V2, we could conclude that this low size effect supports this interpretation of more active use of the poles rather than an increase in speed. On the contrary, during the initial phase of strike, the foot and pole force directions have opposite orientations, so a reduction in the GRF is not expected at that moment of the walking cycle (Hagen et al., 2011; Stief et al., 2008). There was a significant increase in both vertical and anterior-posterior forces (FZI, FZH, and FXH) at heel strike in NW compared with W. This entails an average GRF increase from , 9% to , 30% during NW. Likewise, a significant increase in the BIM was detected during NW; this indicates high load levels at heel strike. Results are consistent with previous studies (Brunelle & Miller, 1998; Hagen et al., 2011), like those of Brunelle and Miller (1998), reporting an increase of 25.7% on vertical forces and 5.8% on the anterior-posterior forces at heel strike during NW, indicating a strong braking component. Some previous studies have concluded that none of the kinetic parameters during NW suggest a biomechanical advantage compared with W during the stance phase in relation to joint load reduction. However, many studies have shown the beneficial and/or preventive effect of those shock impacts produced during the physical activity regarding the onset of osteoporosis (Nguyen, Center, & Eisman, 2000). However, it has also been shown that shock impacts received during normal walking are not enough to prevent osteoporosis (Martyn-St & Carroll, 2009); thus, the higher intensity on
5
impacts during NW could be considered a most appropriate exercise for the prevention of this illness. On the contrary, during NW, an important reduction (, 9%) was produced in FZT, associated with a more active use of poles, in line with previous trends (Stief et al., 2008). The magnitude of the impact increased with increasing walking (Rios, Andrade, & Vargas, 2010; Voloshin, 2001) or running speed (Mercer et al., 2002), which is consistent with results that have shown an increase of the impacts with the increase of the speed (mean PAS increase, V1 ¼ 4.54 ^ 0.61 g vs. V2 ¼ 6.07 ^ 0.71 g). Such studies have shown that the impact magnitude increases from 2.26 g to 5.56 g in a range of speed from 0.89 m/s to 1.79 m/s during the walk (Mercer et al., 2002; Rios et al., 2010; Voloshin, 2001). The results show that during NW, the acceleration levels increase in the tibia at preferred speed and in the head at fast speed. The results show an increase of the accelerations on the tibia and on the head during NW. However, there were no differences between conditions (NW vs. W) for the head peak acceleration at preferred speed. This responds to that protective behavior described by several authors (Voloshin, 2001) and coincides with the values obtained by other studies that have employed similar speeds (Jo¨llenbeck, Gru¨neberg, Leyser, Mull, & Classen, 2006; Kavanagh, Barrett, & Morrison, 2004; Voloshin, 2001). Significantly higher acceleration values were recorded for the head during NW compared with W at fast speed. Such an increase is linked to the speed employed during NW, which was close to the speed defined as a walk – run transition point—that is, the transition speed threshold (Nilsson & Thorstensson, 1989). These values are ranked among the intermediate values recorded during walking and running (Voloshin, 2001). This aspect can justify the differences found with the accelerations received during W. As limitations of the study, it should be noted that the choice of preferred walking speeds makes the interpretation of the results more complicated because several variables are largely dependent on the speed of practice. This aspect should be taken into consideration for the interpretation of the results. In the same way, all the volunteers who took part in the study showed a high experience in NW, as all of them were instructors trained by the same association; therefore, we do not know the effects that the use of a technique different from the one employed by the volunteers of this research could have on the biomechanical response. In summary, the GRF during the initial phase of strike in NW are higher compared with W. In contrast, compared with W, there was a reduction in the vertical forces during takeoff while, on the other hand, the accelerations received in the head and tibia during NW were significantly higher than during W. This is an aspect that should be taken into consideration when applying NW as part of a healthimprovement program with special populations.
6
´ N-MARTI´NEZ ET AL. A. ENCARNACIO
Downloaded by [Univ of Louisiana at Lafayette] at 01:46 21 December 2014
WHAT DOES THIS ARTICLE ADD? This article aims to provide more information on the biomechanical response during the practice of NW compared with W in real conditions. Although it is true that there are several studies that have described the biomechanical response (GRF, kinematics, kinetics, etc.), no study has analyzed the NW practice under real conditions (except Pe´rez-Soriano et al., 2011). This article describes the impact levels received during NW at real speed, an aspect that does not allow us to establish the cause and effect of the differences between NW and W. As this is a descriptive study, we can be sure that during NW higher levels of impact on the initial phase of the gait cycle and reduced GRF in the takeoff phases were recorded. Both aspects must be taken into account in future studies or intervention plans in which NW will be used as a means to improve health. The results mainly have a practical and clinical application because thanks to these results, we can ensure that the real stimulus during NW practice is significantly higher, and future research will determine whether it is beneficial or not for certain population groups.
REFERENCES Brunelle, E. A., & Miller, M. K. (1998). The effects of walking poles on ground reaction forces. Research Quarterly for Exercise and Sport, 69(Suppl. 1), A30. Church, T. S., Earnest, C. P., & Morss, G. M. (2002). Field testing of physiological responses associated with Nordic walking. Research Quarterly for Exercise and Sport, 73, 296 –300. Fritschi, J. O., Brown, W. J., Laukkanen, R., & van Uffelen, J. G. (2012). The effects of pole walking on health in adults: A systematic review. Scandinavian Journal of Medicine & Science in Sport, 22, e70–e78. Hagen, M., Henning, E. M., & Stieldorf, P. (2011). Lower and upper extremity loading in Nordic walking in comparison with walking and running. Journal of Applied Biomechanics, 27, 22–31. Hansen, L., Henriksen, M., Larsen, P., & Alkjaer, T. (2008). Nordic walking does not reduce the loading of the knee joint. Scandinavian Journal of Medicine & Science in Sports, 18, 436 –441. Jo¨llenbeck, T., Gru¨neberg, C., Leyser, D., Mull, M., & Classen, C. (2006). Nordic walking versus walking: Field testing to determine biomechanical loading of the lower limb. Journal of Biomechanics, 39(Suppl. 1), S185. Kavanagh, J. J., Barrett, R. S., & Morrison, S. (2004). Upper body accelerations during walking in healthy young and elderly men. Gait and Posture, 20, 291 –298.
Lee, S. J., & Hidler, J. (2008). Biomechanics of overground vs. treadmill walking in healthy individuals. Journal of Applied Physiology, 104, 747–755. Martyn-St, J. M., & Carroll, S. (2009). A meta-analysis of impact exercise on postmenopausal bone loss: The case for mixed loading exercise programmes. British Journal of Sports Medicine, 43, 898 –908. doi:10. 1136/bjsm.2008.052704 Mercer, J. A., Vance, J., Hreljac, A., & Hamill, J. (2002). Relationship between shock attenuation and stride length during running at different velocities. European Journal of Applied Physiology, 87, 403–408. Mizrahi, J., Voloshin, A., Russek, D., Verbitsky, O., & Isakov, E. (1997). The influence of fatigue on EMG and impact acceleration in running. Basic and Applied Myology, 7, 111 –118. Morgulec-Adamowicz, N., Marszałek, J., & Jagustyn, P. (2011). Nordic walking as an adapted physical activity. Human Movement, 12, 124–132. Nguyen, T. V., Center, J. R., & Eisman, J. A. (2000). Osteoporosis in elderly men and women: Effects of dietary calcium, physical activity, and body mass index. Journal of Bone and Mineral Research, 15, 322–331. Nilsson, J., & Thorstensson, A. (1989). Ground reaction forces at different speeds of human walking and running. Acta Physiologica Scandinavica, 136, 217 –227. Pe´rez-Soriano, P., Llana-Belloch, S., Encarnacio´n-Martı´nez, A., Martı´nezNova, A., & Morey-Klapsing, G. (2011). Nordic walking practice might improve plantar pressure distribution. Research Quarterly for Exercise and Sport, 82, 593–599. Porcari, J. P., Hendrickson, T. L., Walter, P. R., Terry, L., & Walsko, G. (1997). The physiological responses to walking with and without Power Poles on treadmill exercise. Research Quarterly for Exercise and Sport, 68, 161 –166. Radin, E. L. (1987). Osteoarthrosis: What is known about prevention. Clinical Orthopaedics and Related Research, 222, 60– 65. Regelin, P., & Mommert, P. (2005). Nordic-walking—aber richtig! [Nordic walking—the right way!]. Munich, Germany: Blv Buchverlag. Rios, J. L., Andrade, M. C., & Vargas, A. O. (2010). Analysis of peak tibial acceleration during gait in different cadences. Human Movement, 11, 132–136. Rodgers, C. D., VanHeest, J. L., & Schachter, C. L. (1995). Energy expenditure during submaximal walking with exerstriders. Medicine and Science in Sports and Exercise, 27, 607– 611. Schwameder, H., & Ring, S. (2006). Knee joint loading and metabolic energy demand in walking, Nordic walking and running. Journal of Biomechanics, 39(Suppl. 1), S185. Stief, F., Kleindienst, F. I., Wiemeyer, J., Wedel, F., Campe, S., & Krabbe, B. (2008). Inverse dynamic analysis of the lower extremities during Nordic walking, walking, and running. Journal of Applied Biomechanics, 24, 351 –359. Tschentscher, M., Niederseer, D., & Niebauer, J. (2013). Health benefits of Nordic walking. A systematic review. American Journal of Preventive Medicine, 44, 76–84. Voloshin, A. S. (2001). Impact propagation and its effects on the human body. In V. M. Zatsiorsky (Ed.), Biomechanics in sport: Performance enhancement and injury prevention (pp. 577–587). Oxford, England: Blackwell Science.
Research Quarterly for Exercise and Sport Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/urqe20
Differences in Ground Reaction Forces and Shock Impacts Between Nordic Walking and Walking a
b
Alberto Encarnación-Martínez , Pedro Pérez-Soriano & Salvador Llana-Belloch a
b
Catholic University of Murcia
b
University of Valencia, Published online: 11 Nov 2014.
Click for updates To cite this article: Alberto Encarnación-Martínez, Pedro Pérez-Soriano & Salvador Llana-Belloch (2014): Differences in Ground Reaction Forces and Shock Impacts Between Nordic Walking and Walking, Research Quarterly for Exercise and Sport, DOI: 10.1080/02701367.2014.975178 To link to this article: http://dx.doi.org/10.1080/02701367.2014.975178
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
Research Quarterly for Exercise and Sport, 00, 1–6, 2014 Copyright q SHAPE America ISSN 0270-1367 print/ISSN 2168-3824 online DOI: 10.1080/02701367.2014.975178
RESEARCH NOTE
Differences in Ground Reaction Forces and Shock Impacts Between Nordic Walking and Walking Downloaded by [Univ of Louisiana at Lafayette] at 01:46 21 December 2014
Alberto Encarnacio´n-Martı´nez Catholic University of Murcia
Pedro Pe´rez-Soriano and Salvador Llana-Belloch University of Valencia
The regular practice of Nordic walking (NW) has increased in recent years, in part thanks to the health benefits described by the scientific literature. However, there is no consensus on the effects of shock-impact absorption during its practice. Purpose: The aim of this study was to compare the levels of impact and ground reaction forces (GRF) between NW and walking (W). Method: Twenty physically active and experienced participants were assessed using a dynamometric platform and accelerometry analysis. Results: The results show statistically significantly higher levels of acceleration in the tibia (12%) and head (21%) during NW compared with W. Equally, GRF were significantly higher (27%) at the instant of strike compared with W, and a reduction of the forces at the instant of takeoff (8%) was observed. Conclusions: During NW, shock impacts and GRF levels increased compared with W, an aspect that should be considered when prescribing health improvement programs. Keywords: biomechanics, kinetics, walking
Nordic walking (NW) is a cyclical activity, whose introduction into the world of physical activity and sport dates back to the early 1930s. Since its birth in Finland, the number of practitioners has greatly increased worldwide (Morgulec-Adamowicz, Marszałek, & Jagustyn, 2011). NW has internationally spread, despite its short career as a healthy physical sport activity, partly due to the benefits obtained by its regular practice (Fritschi, Brown, Laukkanen, & van Uffelen, 2012; Tschentscher, Niederseer, & Niebauer, 2013) on oxygen consumption, heart rate, and caloric expenditure parameters compared with walking (W; Church, Earnest, & Morss, 2002; Fritschi et al., 2012; Porcari, Hendrickson, Walter, Terry, & Walsko, 1997; Rodgers, VanHeest, & Schachter, 1995; Tschentscher et al., 2013). Submitted October 2, 2013; accepted May 3, 2014. Correspondence should be addressed to Alberto Encarnacio´n-Martı´nez, Department of Sport Sciences and Physical Education, Catholic University of Murcia, Campus de Los Jero´nimos, s/n. Guadalupe, 30107, Murcia, Spain. E-mail: [email protected]
From a biomechanical perspective, there is an almost unanimous consensus regarding the biomechanical response during NW compared with W, based on the observed increase in the stride length and speed during gait and in the muscle activity of the upper body as well as a reduction of the effort perception (Hagen, Henning, & Stieldorf, 2011; Stief et al., 2008). However, the consensus is not the same regarding ground reaction forces (GRF). Some studies indicate that shock-impact forces, treated as GRF at the heel strike with the ground, are lower during NW (Schwameder & Ring, 2006), while others show an increase (Brunelle & Miller, 1998; Hagen et al., 2011; Stief et al., 2008). A shock wave is produced as a result of the first heel strike with the ground during W that is then transmitted from the heel to the upper limbs. This has been linked to soft-tissue, bone, lower-limb, and vertebral column damage along with degradation of the biomechanical properties of the joint cartilage (Voloshin, 2001). Despite the evidence, only one study (Hagen et al., 2011) has ever analyzed this shock wave and the impacts produced during NW. These impacts were recorded by an accelerometer located in the
Downloaded by [Univ of Louisiana at Lafayette] at 01:46 21 December 2014
2
´ N-MARTI´NEZ ET AL. A. ENCARNACIO
wrists, and researchers concluded that those shock-impact levels received during NW are very high and represent a risk for suffering overuse injuries in the upper extremities. As previously discussed, the use of poles provokes a walking speed higher than usual, standing between walking and running (Hagen et al., 2011), an aspect that we hypothesize leads to increased levels of impact that have not yet been analyzed by any research. Other studies have shown a relationship between repeated impacts during running and the occurrence of degenerative joint injuries (Radin, 1987), with this aspect magnified by the occurrence of fatigue, because a positive correlation has been found between the magnitude of repeated impacts and the onset of inherent fatigue of aerobic activities like W, NW, and running (Mercer, Vance, Hreljac, & Hamill, 2002; Mizrahi, Voloshin, Russek, Verbitsky, & Isakov, 1997). The objectives of this study were to compare GRF and impact transmission along the locomotor system between NW and W.
METHODS Participants and Inclusion Criteria All participants, which included 20 healthy participants (10 men and 10 women), were instructors of NW (M age ¼ 25.9 ^ 4.54 years; M weight ¼ 69.4 ^ 6.5 kg; M height ¼ 1.73 ^ 0.52 m; M bodymassindex ¼ 23.2 ^ 1.8; Mexperience ¼ 6.4 ^ 2.6 years). Very different methodologies have been used for previous studies, and the degree of experience of participants has varied as well. For this reason, we chose experienced participants as in previous studies (Hagen et al., 2011; Hansen, Henriksen, Larsen, & Alkjaer, 2008; Stief et al., 2008). Inclusion criteria were that participants had no current injuries and were physically active (exercise practice three times a week for at least 30 min per session). Participants were excluded if they had an existing orthotics prescription or if they had had a lower-limb injury within the previous 3 months. All participants were informed of the characteristics of the study and provided informed consent according to the Declaration of Helsinki (1964 – 2000). Also, the institutional review board approved the research. Experimental Protocol There were two speed conditions: freely chosen speed (preferred speed or V1) and fast speed (fast speed or V2 ¼ V1 plus 20%; Pe´rez-Soriano, Llana-Belloch, Encarnacio´nMartı´nez, Martı´nez-Nova, & Morey-Klapsing, 2011). To calculate the V1 condition, all participants were asked to walk along the runway at a normal speed for as long as
necessary until they felt comfortable for both gait conditions (NW and W). Volunteers walked along the runway where walking speed was measured along the 5 central meters of the way—that is, leaving 3 m at the beginning and the end to allow acceleration and deceleration of each repetition. Volunteers were not asked to walk at any particular speed and then the process was repeated to calculate the freely chosen speed for both modalities, W and NW. After the participants had had sufficient practice trials to familiarize themselves with the testing procedure, five trials for both NW and W were performed. A maximal deviation of ^5% between the trials was accepted for each condition. Participants were told to hit the poles located on both sides of the platform. If any of the poles touched the platform, the test was repeated. A trial was considered valid when a full foot strike was captured by the force platform. Then, this step was selected for further analysis. Participants rested for 2 min between repetitions. NW and W order was randomized. All participants performed the test using the diagonal technique (Regelin & Mommert, 2005), which is the most common technique of NW worldwide and is characterized by a contralateral legs –arms coordination. During its practice, the body moves leaning slightly forward. Biomechanical Setup All participants were asked to walk and Nordic walk along a 12-m long, 2-m wide runway. Embedded in the runway was a Kistlerw (600 mm £ 400 mm £ 100 mm, Kistler AG, Winterthur, Switzerland) force platform. Both W and NW speeds were measured by two photocells connected to an electronic timer (Chronomasterw, Sportmetrics 2008, Valencia, Spain, with an accuracy of .001 s) located 5 m apart from each other. Vertical shock impacts were recorded by two uniaxial accelerometers (SMAA02-1 model, Sportmetricsw; the equivalents were: ^ 9.81 m/s2 , 1 g), located on the tibial tuberosity (measurement range of ^ 10 g) and the frontal bone (measurement range of ^ 5 g). The accelerometers were connected and synchronized with an analog cable to the amp box of the dynamometric platform. All data were synchronized and registered at a frequency rate of 500 Hz. The accelerometer of the tibia was placed on the dominant leg, which was the foot recorded by the dynamometric platform. The accelerometers were fixed to the skin with double-sided tape and were reinforced with tape and an elastic band. All variables were extracted using a program made with the help of Matlab Version 7.4. A filter was applied to data with a low pass cutoff frequency of 50 Hz. Peak acceleration of shank (PAS) and peak acceleration of head (PAH) were obtained. GRF (normalized to body weight [BW]) in the vertical (Z) and anterior-posterior (X) axes at the instants of heel strike (FZH and FXH) and takeoff phases (FZT and FXT), vertical force impact at heel strike (FZI), and
3
GRF AND IMPACTS IN NORDIC WALKING AND WALKING TABLE 1 Descriptive Values for Ground Reaction Forces of the Analyzed Variables: Level of Significance of the Two-Way Analysis of Variance (Main Effect of Speed and Condition) Walking (W) Preferred Speed
Downloaded by [Univ of Louisiana at Lafayette] at 01:46 21 December 2014
Variable Speed (m/s) Vertical force impact heel strike (N/kg) Vertical force heel strike (N/kg) Vertical force takeoff (N/kg) AP force heel strike (N/kg) AP force takeoff (N/kg) Braking impulse (N·s) Propulsive impulse (N·s)
Nordic Walking (NW)
Fast Speed
Preferred Speed
Level of Significance
Fast Speed
Speed
Condition
M
SD
M
SD
M
SD
M
SD
p
p
1.72 1.11 1.45 1.32 0.31 0.33 30.52 30.99
0.16 0.13 0.13 0.12 0.05 0.04 4.30 4.66
2.04 1.43 1.62 1.29 0.39 0.34 31.55 30.23
0.19 0.20 0.14 0.14 0.05 0.05 5.97 5.26
1.92 1.41 1.62 1.25 0.42 0.35 38.87 32.66
0.13 0.17 0.13 0.14 0.05 0.05 4.10 4.82
2.22 1.55 1.71 1.15 0.48 0.34 37.42 28.98
0.15 0.14 0.11 0.18 0.09 0.07 8.17 6.80
.000* .001* .001* .045** .002* .846 .738 .013**
.000# .002# .002# .003# .000# .911 .004# .721
Note. AP force ¼ anteroposterior force. *(p , .01) Preferred speed versus fast speed. **(p , .05) Preferred speed versus fast speed. # ( p , .01) W versus NW.
mechanical impulse of braking impulse (BIM) and propulsive impulse (PIM) were also obtained (Figure 1).
Data Analysis Statistical analysis was performed using the Statistical Package for the Social Sciences Version 17. First, normality of the data was verified using the Shapiro-Wilk test, homoskedasticity by the Levene test, and sphericity by the Mauchly test. A student’s t test was performed to determine whether there were differences between men and women.
Then, a two-way analysis of variance (ANOVA) test was performed to analyze whether there were differences between the means of the variables analyzed while taking into account the types of walking (NW vs. W) and speeds (V1 and V2). The level of significance was set at p # .05.
RESULTS The results of the t test showed no statistically significant differences (F ¼ 0.870, p ¼ .503, h 2 ¼ .029) regarding
FIGURE 1 Variables analyzed in the research. GRF ¼ ground reaction forces; NW ¼ Nordic walking; W ¼ walking; N/BW ¼ newtons/body weight; FZI ¼ vertical force impact; FZH ¼ vertical force at heel strike; FXH ¼ anterior-posterior force at heel strike; FZT ¼ vertical force at takeoff; FXT ¼ anterior-posterior force at takeoff; BIM ¼ braking impulse (area under the curve); PIM ¼ propulsive impulse (area under the curve).
´ N-MARTI´NEZ ET AL. A. ENCARNACIO
gender for any of the variables analyzed. So during this study, all subsequent statistical analyses were conducted jointly and included men and women as one sample (n ¼ 20). The results found by the two-way ANOVA showed statistically significant differences in the GRF and shockimpact levels received depending on the speed (V1 vs. V2) and type of walk (NW vs. W; Table 1). The results obtained for the variables of the GRF show statistically significant differences ( p , .05) between W and NW for the V1 condition. The values of the variables analyzed in NW were 10.5% higher on average. Specifically, the results show significant differences ( p , .05) depending on the walking condition (NW vs. W), on the GRF at FZI (F ¼ 27.1, p , .02, h 2 ¼ .730), at FZH (F ¼ 21.7, p , .01, h 2 ¼ .731), at FXH (F ¼ 47.0, p , .01, h 2 ¼ .825), and at BIM (F ¼ 31.7, p , .01, h 2 ¼ .760; Figure 2) being 15.6%, 8.9%, 29.9%, and 23.0%, respectively, higher during NW. In contrast, GRF at FZT (F ¼ 46.6, p , .01, h 2 ¼ .823) showed an important reduction of 8.2% during NW (Figure 2A). Regarding shock-impact transmission (see Figure 2B), statistically significant differences (F ¼ 10.4, p , .01, h 2 ¼ .536) between W and NW were found for both speeds’ PAS (V1, W ¼ 4.17 ^ 0.4 g vs. NW ¼ 4.87 ^ 0.7 g; V2, W ¼ 5.82 ^ 0.5 g vs. NW ¼ 6.32 ^ 0.8 g). In V2, only differences between conditions for PAH (F ¼ 13.7, p , .01, h 2 ¼ .633) were observed (fast speed, W ¼ 0.65 ^ 0.1 g vs. NW ¼ 0.77 ^ 0.1 g).
Analyzing the speed effects (V1 vs. V2), the results show a significant increase at FZI (F ¼ 68.8, p , .01, h 2 ¼ .873), at FZH (F ¼ 308.1, p , .01, h 2 ¼ .975), and at FXH (F ¼ 29.8, p , .01, h 2 ¼ .749), showing an increase in the force values during the V2 condition. By contrast, a significant reduction was observed at V2 FZT (F ¼ 5.8, p ¼ .045, h 2 ¼ .368) and at PIM (F ¼ 9.3, p ¼ .013, h 2 ¼ .483) (Table 1). Regarding the effect of the studied speed (Figure 2B), significant differences were noted for PAS (F ¼ 93.3, p , .01, h 2 ¼ .912) and PAH (F ¼ 24.5, p , .01, h 2 ¼ .754) during V2 (PAS, V1 ¼ 4.52 g vs. V2 ¼ 6.07 g; PAH, V1 ¼ 0.68 g vs. V2 ¼ 0.77 g) for both study conditions.
DISCUSSION The number of NW practitioners has considerably increased in recent years, mainly because it has been shown that regular practice of this activity provides important benefits such as improved general health, short-and long-term effects on the cardiopulmonary system, and improvements in a wide range of individuals with diseases. It has also proven to be a safe and accessible activity (Tschentscher et al., 2013). This research analyzed the biomechanical response of a group of expert practitioners to describe the GRF and impact levels received during NW compared with W.
B
A FZI (N/kg)
8
#
*
#
7 FZH (N/kg)
#
6 Acceleration (g)
Downloaded by [Univ of Louisiana at Lafayette] at 01:46 21 December 2014
4
#
FZT (N/kg)
#
FXH(N/kg)
Walking Nordic walking
#
5 4 3
0
0.5 #
1
1.5
2 2
Force (N/kg)
*
BIM (N·s)
1
#
#
0 0
10
20
30
Impulse (N·s)
40
50
Preferred Speed
Fast Speed
Peak acceleration shank (g)
Preferred Speed
Fast Speed
Peak acceleration head (g)
FIGURE 2 Results of the two-way analysis of variance. A) Ground reaction forces results, where FZI ¼ vertical force impact; FZH ¼ vertical force at heel strike; FXH ¼ anterior-posterior force at heel strike; FZT ¼ vertical force at takeoff; BIM ¼ braking impulse. B) Peak accelerations results. #Statistically significant difference ( p , .01) between walking and Nordic walking. *Statistically significant differences ( p , .01) between speeds (preferred vs. fast speed).
Downloaded by [Univ of Louisiana at Lafayette] at 01:46 21 December 2014
GRF AND IMPACTS IN NORDIC WALKING AND WALKING
Participants in this study walked about 10% faster with poles in the preferred condition, similar to other studies (Stief et al., 2008). It is important to highlight that the preferred chosen speed by the participants for NW corresponds to the speed described for the walking –running transition (Nilsson & Thorstensson, 1989), an aspect that could justify the differences found in the physiological and biomechanical response compared with W. Impact acceleration and maximum GRF peaks during walking are highly correlated to the walking speed, an aspect that is consistent with the results. As speed increases in both conditions (W and NW), the values of the GRF also increase, except at FXT and at BIM. Lee and Hidler (2008) showed that at speeds from 0.95 m/s to 1.33 m/s, the maximum vertical force during walking is 1.1 BW and 1.5 BW. Values obtained by this research are slightly more (, 1.4 BW to , 1.7 BW). These differences are probably due to the fact that the walking speeds are slightly higher (, 1.7 m/s to , 2.2 m/s). Despite the speed increase observed at V2 during NW, there is a significant reduction at FZT and at PIM. These results are consistent with a previous study where a trend is described toward a reduction of the vertical forces during takeoff (Stief et al., 2008). It could be interpreted that the increase in speed is partly due to a more active use of poles that consequently help reduce those parameters related to takeoff. Looking at the low size effect found in the differences between V1 and V2, we could conclude that this low size effect supports this interpretation of more active use of the poles rather than an increase in speed. On the contrary, during the initial phase of strike, the foot and pole force directions have opposite orientations, so a reduction in the GRF is not expected at that moment of the walking cycle (Hagen et al., 2011; Stief et al., 2008). There was a significant increase in both vertical and anterior-posterior forces (FZI, FZH, and FXH) at heel strike in NW compared with W. This entails an average GRF increase from , 9% to , 30% during NW. Likewise, a significant increase in the BIM was detected during NW; this indicates high load levels at heel strike. Results are consistent with previous studies (Brunelle & Miller, 1998; Hagen et al., 2011), like those of Brunelle and Miller (1998), reporting an increase of 25.7% on vertical forces and 5.8% on the anterior-posterior forces at heel strike during NW, indicating a strong braking component. Some previous studies have concluded that none of the kinetic parameters during NW suggest a biomechanical advantage compared with W during the stance phase in relation to joint load reduction. However, many studies have shown the beneficial and/or preventive effect of those shock impacts produced during the physical activity regarding the onset of osteoporosis (Nguyen, Center, & Eisman, 2000). However, it has also been shown that shock impacts received during normal walking are not enough to prevent osteoporosis (Martyn-St & Carroll, 2009); thus, the higher intensity on
5
impacts during NW could be considered a most appropriate exercise for the prevention of this illness. On the contrary, during NW, an important reduction (, 9%) was produced in FZT, associated with a more active use of poles, in line with previous trends (Stief et al., 2008). The magnitude of the impact increased with increasing walking (Rios, Andrade, & Vargas, 2010; Voloshin, 2001) or running speed (Mercer et al., 2002), which is consistent with results that have shown an increase of the impacts with the increase of the speed (mean PAS increase, V1 ¼ 4.54 ^ 0.61 g vs. V2 ¼ 6.07 ^ 0.71 g). Such studies have shown that the impact magnitude increases from 2.26 g to 5.56 g in a range of speed from 0.89 m/s to 1.79 m/s during the walk (Mercer et al., 2002; Rios et al., 2010; Voloshin, 2001). The results show that during NW, the acceleration levels increase in the tibia at preferred speed and in the head at fast speed. The results show an increase of the accelerations on the tibia and on the head during NW. However, there were no differences between conditions (NW vs. W) for the head peak acceleration at preferred speed. This responds to that protective behavior described by several authors (Voloshin, 2001) and coincides with the values obtained by other studies that have employed similar speeds (Jo¨llenbeck, Gru¨neberg, Leyser, Mull, & Classen, 2006; Kavanagh, Barrett, & Morrison, 2004; Voloshin, 2001). Significantly higher acceleration values were recorded for the head during NW compared with W at fast speed. Such an increase is linked to the speed employed during NW, which was close to the speed defined as a walk – run transition point—that is, the transition speed threshold (Nilsson & Thorstensson, 1989). These values are ranked among the intermediate values recorded during walking and running (Voloshin, 2001). This aspect can justify the differences found with the accelerations received during W. As limitations of the study, it should be noted that the choice of preferred walking speeds makes the interpretation of the results more complicated because several variables are largely dependent on the speed of practice. This aspect should be taken into consideration for the interpretation of the results. In the same way, all the volunteers who took part in the study showed a high experience in NW, as all of them were instructors trained by the same association; therefore, we do not know the effects that the use of a technique different from the one employed by the volunteers of this research could have on the biomechanical response. In summary, the GRF during the initial phase of strike in NW are higher compared with W. In contrast, compared with W, there was a reduction in the vertical forces during takeoff while, on the other hand, the accelerations received in the head and tibia during NW were significantly higher than during W. This is an aspect that should be taken into consideration when applying NW as part of a healthimprovement program with special populations.
6
´ N-MARTI´NEZ ET AL. A. ENCARNACIO
Downloaded by [Univ of Louisiana at Lafayette] at 01:46 21 December 2014
WHAT DOES THIS ARTICLE ADD? This article aims to provide more information on the biomechanical response during the practice of NW compared with W in real conditions. Although it is true that there are several studies that have described the biomechanical response (GRF, kinematics, kinetics, etc.), no study has analyzed the NW practice under real conditions (except Pe´rez-Soriano et al., 2011). This article describes the impact levels received during NW at real speed, an aspect that does not allow us to establish the cause and effect of the differences between NW and W. As this is a descriptive study, we can be sure that during NW higher levels of impact on the initial phase of the gait cycle and reduced GRF in the takeoff phases were recorded. Both aspects must be taken into account in future studies or intervention plans in which NW will be used as a means to improve health. The results mainly have a practical and clinical application because thanks to these results, we can ensure that the real stimulus during NW practice is significantly higher, and future research will determine whether it is beneficial or not for certain population groups.
REFERENCES Brunelle, E. A., & Miller, M. K. (1998). The effects of walking poles on ground reaction forces. Research Quarterly for Exercise and Sport, 69(Suppl. 1), A30. Church, T. S., Earnest, C. P., & Morss, G. M. (2002). Field testing of physiological responses associated with Nordic walking. Research Quarterly for Exercise and Sport, 73, 296 –300. Fritschi, J. O., Brown, W. J., Laukkanen, R., & van Uffelen, J. G. (2012). The effects of pole walking on health in adults: A systematic review. Scandinavian Journal of Medicine & Science in Sport, 22, e70–e78. Hagen, M., Henning, E. M., & Stieldorf, P. (2011). Lower and upper extremity loading in Nordic walking in comparison with walking and running. Journal of Applied Biomechanics, 27, 22–31. Hansen, L., Henriksen, M., Larsen, P., & Alkjaer, T. (2008). Nordic walking does not reduce the loading of the knee joint. Scandinavian Journal of Medicine & Science in Sports, 18, 436 –441. Jo¨llenbeck, T., Gru¨neberg, C., Leyser, D., Mull, M., & Classen, C. (2006). Nordic walking versus walking: Field testing to determine biomechanical loading of the lower limb. Journal of Biomechanics, 39(Suppl. 1), S185. Kavanagh, J. J., Barrett, R. S., & Morrison, S. (2004). Upper body accelerations during walking in healthy young and elderly men. Gait and Posture, 20, 291 –298.
Lee, S. J., & Hidler, J. (2008). Biomechanics of overground vs. treadmill walking in healthy individuals. Journal of Applied Physiology, 104, 747–755. Martyn-St, J. M., & Carroll, S. (2009). A meta-analysis of impact exercise on postmenopausal bone loss: The case for mixed loading exercise programmes. British Journal of Sports Medicine, 43, 898 –908. doi:10. 1136/bjsm.2008.052704 Mercer, J. A., Vance, J., Hreljac, A., & Hamill, J. (2002). Relationship between shock attenuation and stride length during running at different velocities. European Journal of Applied Physiology, 87, 403–408. Mizrahi, J., Voloshin, A., Russek, D., Verbitsky, O., & Isakov, E. (1997). The influence of fatigue on EMG and impact acceleration in running. Basic and Applied Myology, 7, 111 –118. Morgulec-Adamowicz, N., Marszałek, J., & Jagustyn, P. (2011). Nordic walking as an adapted physical activity. Human Movement, 12, 124–132. Nguyen, T. V., Center, J. R., & Eisman, J. A. (2000). Osteoporosis in elderly men and women: Effects of dietary calcium, physical activity, and body mass index. Journal of Bone and Mineral Research, 15, 322–331. Nilsson, J., & Thorstensson, A. (1989). Ground reaction forces at different speeds of human walking and running. Acta Physiologica Scandinavica, 136, 217 –227. Pe´rez-Soriano, P., Llana-Belloch, S., Encarnacio´n-Martı´nez, A., Martı´nezNova, A., & Morey-Klapsing, G. (2011). Nordic walking practice might improve plantar pressure distribution. Research Quarterly for Exercise and Sport, 82, 593–599. Porcari, J. P., Hendrickson, T. L., Walter, P. R., Terry, L., & Walsko, G. (1997). The physiological responses to walking with and without Power Poles on treadmill exercise. Research Quarterly for Exercise and Sport, 68, 161 –166. Radin, E. L. (1987). Osteoarthrosis: What is known about prevention. Clinical Orthopaedics and Related Research, 222, 60– 65. Regelin, P., & Mommert, P. (2005). Nordic-walking—aber richtig! [Nordic walking—the right way!]. Munich, Germany: Blv Buchverlag. Rios, J. L., Andrade, M. C., & Vargas, A. O. (2010). Analysis of peak tibial acceleration during gait in different cadences. Human Movement, 11, 132–136. Rodgers, C. D., VanHeest, J. L., & Schachter, C. L. (1995). Energy expenditure during submaximal walking with exerstriders. Medicine and Science in Sports and Exercise, 27, 607– 611. Schwameder, H., & Ring, S. (2006). Knee joint loading and metabolic energy demand in walking, Nordic walking and running. Journal of Biomechanics, 39(Suppl. 1), S185. Stief, F., Kleindienst, F. I., Wiemeyer, J., Wedel, F., Campe, S., & Krabbe, B. (2008). Inverse dynamic analysis of the lower extremities during Nordic walking, walking, and running. Journal of Applied Biomechanics, 24, 351 –359. Tschentscher, M., Niederseer, D., & Niebauer, J. (2013). Health benefits of Nordic walking. A systematic review. American Journal of Preventive Medicine, 44, 76–84. Voloshin, A. S. (2001). Impact propagation and its effects on the human body. In V. M. Zatsiorsky (Ed.), Biomechanics in sport: Performance enhancement and injury prevention (pp. 577–587). Oxford, England: Blackwell Science.
