Downloaded from http://jramc.bmj.com/ on July 17, 2015 - Published by group.bmj.com
Original paper
Influence of running shoes and cross-trainers on Achilles tendon forces during running compared with military boots Jonathan Sinclair,1 P J Taylor,2 S Atkins1 1
Centre for Applied Sport and Exercise Sciences, University of Central Lancashire, Preston, UK 2 School of Psychology, University of Central Lancashire, Preston, UK Correspondence to Professor Jonathan Sinclair, Division of Sport, Exercise and Nutritional Sciences, School of Sport Tourism and Outdoors, Centre for Applied Sport and Exercise Sciences, University of Central Lancashire, Preston, Lancashire PR1 2HE, UK; [email protected] Received 14 April 2014 Revised 2 August 2014 Accepted 24 September 2014 Published Online First 26 November 2014
ABSTRACT Military recruits are known to be susceptible to Achilles tendon pathology. The British Army have introduced footwear models, the PT-03 (cross-trainer) and PT1000 (running shoes), in an attempt to reduce the incidence of injuries. The aim of the current investigation was to examine the Achilles tendon forces of the cross-trainer and running shoe in relation to conventional army boots. Ten male participants ran at 4.0 m/s in each footwear condition. Achilles tendon forces were obtained throughout the stance phase of running and compared using repeated-measures ANOVAs. The results showed that the time to peak Achilles tendon force was significantly shorter when running in conventional army boots (0.12 s) in comparison with the cross-trainer (0.13 s) and running shoe (0.13 s). Achilles tendon loading rate was shown to be significantly greater in conventional army boots (38.73 BW/s) in comparison with the crosstrainer (35.14 BW/s) and running shoe (33.57 BW/s). The results of this study suggest that the running shoes and cross-trainer footwear are associated with reductions in Achilles tendon parameters that have been linked to the aetiology of injury, and thus it can be hypothesised that these footwear could be beneficial for military recruits undertaking running exercises.
INTRODUCTION
To cite: Sinclair J, Taylor PJ, Atkins S. J R Army Med Corps 2015;161:140–143. 140
Military recruits are known to be susceptible to injury.1 These injuries are predominantly experienced in the lower extremities, with incidence ranging from 15% to 50%,2 though often higher in female recruits.3 Injury aetiology within military populations is associated with the high volume of physical training undertaken by recruits.4 5 The Achilles tendon, which serves to transfer forces from the gastrocnemius and soleus muscles to the calcaneus,6 has been shown to be a common injury site in military recruits with an occurrence rate of 14.5%.7 The aetiology and pathogenesis of Achilles tendinopathy have not been fully clarified scientifically; however, a key component for those involved in dynamic activities such as running is repetitive submaximal loading which creates microscopic tears in the tendons’ collagen fibres.8 In military recruits, the high volume of physical training aligned with inadequate footwear provision has been identified as a potential contributory mechanism.9 Military boots have frequently been implicated as a potential mechanism behind the high incidence of injuries among military recruits.10 Poor shock absorption characteristics have been identified in military boots when compared with running shoes.11 Indeed, the inclusion of neoprene shock absorbing
Key messages ▸ Running in military boots increases the load experienced by the Achilles tendon. ▸ Military recruits who are susceptible to Achilles tendon pathologies may wish to utilise running trainers and cross trainers for their running activities.
insoles to military boots has shown improvements in injury rates.12 In an attempt to attenuate the overall injury rate in their recruits, the British military introduced two footwear models, the PT-03 cross-trainer and PT1000 running shoe. These footwear were introduced to replace the traditional army boot when undertaking non-operational running activities. These more sophisticated footwear were designed in response to the frequent claims regarding inadequacies of traditional army boots. The influence of different footwear and running technique on the forces experienced by the Achilles tendon has received little attention. Kulmala et al13 showed that forefoot strike runners exhibited significant increases in Achilles tendon forces compared with those who exhibited a rearfoot strike pattern. In addition, Sinclair14 demonstrated that running barefoot and in minimalist footwear led to significant increases in the forces experienced by the Achilles tendon compared with conventional running trainers. Nonetheless, the influence of different military footwear types on the forces experienced by the Achilles tendon has not received any attention in clinical/footwear biomechanics literature. The aim of the current investigation was to examine the forces experienced by the Achilles tendon when running in the PT-03 cross-trainer and PT1000 trainer compared with conventional army boots. This study may serve to provide information to the military regarding the most appropriate footwear choice for recruits in order to attenuate the high incidence of lower limb injuries.
METHODS Participants Ten male runners took part in the current investigation. The mean characteristics of the participants were: age 23.41±6.29 years, height 174.72±5.38 cm and body mass 70.73±4.87 kg. Participants were active recreational runners engaging in training at least three times per week and were classified as
Sinclair J, et al. J R Army Med Corps 2015;161:140–143. doi:10.1136/jramc-2014-000308
Downloaded from http://jramc.bmj.com/ on July 17, 2015 - Published by group.bmj.com
Original paper rearfoot strikers as they exhibited a clear first peak in their vertical ground reaction force (GRF) time-curve. In accordance with the procedures outlined in the declaration of Helsinki, runners were all free from musculoskeletal pathology at the time of data collection and provided written informed consent. The procedure used for this investigation was approved by the University of Central Lancashire ethical committee.
Procedure Participants completed 10 trials running over a 22 m walkway at 4.0 m/s ±5% in each footwear condition. The participants struck an embedded piezoelectric force platform (Kistler Instruments) sampling at 1000 Hz with their right foot which was dominant in all runners.15 Running velocity was monitored using infrared timing gates (SmartSpeed UK). The stance phase of the running gait cycle was described as the period over which >20 N of vertical force was applied to the force platform.16 The order in which participants ran in each footwear was randomised and all data were collected within a single session. 3D kinematics of the foot and shank were collected using an eight camera optoelectric motion capture system (Qualisys Medical AB, Goteburg, Sweden) with a recording frequency of 250 Hz. Calibration of the system was performed before each data collection session. Only calibrations which produced average residuals of less than 0.85 mm for each camera for a 750.5 mm wand length and points above 4000 in all cameras were accepted prior to data collection.17 GRF and 3D kinematic information were obtained synchronously using Qualisys track manager software. The calibrated anatomical systems technique was used to model the body segments of interest.18 To define the anatomical frames of the right foot and shank, retroreflective markers (19 mm diameter) were positioned onto the calcaneus, 1st and 5th metatarsal heads, medial and lateral malleoli and medial and lateral femoral epicondyles. A rigid carbon-fibre tracking cluster was also positioned onto the shank segment. The foot was tracked using the calcaneus, 1st and 5th metatarsal markers. Static calibration trials were obtained in order for the positions of the anatomical markers to be referenced in relation to the tracking clusters/markers.
peak force divided by the time to peak force.14 In addition, GRFs at peak plantar flexion moment were also obtained in all three axes. The discrete variables extracted for statistical analysis were (1) peak plantarflexion moment, (2) peak Achilles tendon force, (3) time to peak Achilles tendon force and (4) Achilles tendon loading rate. These variables were extracted from each of the ten trials for all three footwear conditions and the data were then averaged within subjects for statistical analysis.
Statistical analysis Differences in Achilles tendon force parameters as a function of footwear were examined using one-way repeated-measures ANOVAs. The α criterion for statistical significance was adjusted to p=0.007 using a Bonferroni correction to control type I error. Effect sizes were calculated using a partial η2 ( pη2). Post-hoc pairwise comparisons were conducted on all significant main effects. All statistical actions were conducted using SPSS V.21.0 (SPSS, Chicago, Illinois, USA).
Data processing GRF and 3D kinematic data were filtered at 50 and 15 Hz respectively using a low pass Butterworth 4th order zero-lag filter using Visual 3D (C-Motion, Germantown, Maryland, USA).14 Ankle joint moments were calculated using Newton-Euler inverse-dynamics allowing the net internal ankle moments to be obtained. Net ankle moments were quantified using anthropometric, GRFs and angular kinematic data. Net ankle joint moments were normalised to body mass (kg N/m). To estimate the forces experienced by the Achilles tendon, a predictive algorithm was used.19 Previous analyses have shown this algorithm to be appropriately sensitive to determine alterations in Achilles tendon forces as a function of different running footwear.13 14 The force experienced by the Achilles tendon was determined by dividing the plantarflexion moment by the Achilles tendon moment arm (atMA). The moment arm was quantified as a function of the ankle sagittal plane ankle angle. Achilles tendon force ¼ plantarflexion moment=atMA atMA ¼ 0:5910 þ 0:08297 SAA 0:0002606 SAA2 The Achilles tendon force was normalised to bodyweight (BW) and Achilles tendon loading rate (BW/s) was also calculated as a function of the change in tendon force from initial contact to
Figure 1 Ankle kinematics, moments and Achilles tendon loads obtained as a function of footwear ((A) ankle angle; (B) ankle moment; (C) Achilles tendon load) (Black=boot, grey=trainer, dash=cross-trainer).
Sinclair J, et al. J R Army Med Corps 2015;161:140–143. doi:10.1136/jramc-2014-000308
141
Downloaded from http://jramc.bmj.com/ on July 17, 2015 - Published by group.bmj.com
Original paper Table 1
Achilles tendon force parameters (mean±SD) as a function of footwear Conventional military boot
Plantarflexion moment (N.m/kg) Peak Achilles tendon force (BW) Time to peak Achilles tendon force (s) Achilles tendon loading rate (BW/s) Medial force (BW) Anterior force (BW) Vertical force (BW)
Trainer
Cross-trainer
Mean
SD
Mean
SD
Mean
SD
2.48 4.73 0.12* 38.73* 0.08 0.21 2.01
0.32 0.62 0.01 5.33 0.07 0.13 0.46
2.42 4.52 0.13 35.14 0.09 0.20 2.03
0.29 0.45 0.01 3.31 0.06 0.10 0.51
2.38 4.41 0.13 33.57 0.08 0.20 2.03
0.39 0.34 0.01† 3.44† 0.06 0.11 0.53
*Significantly different from trainer and cross-trainer. †Significant main effect. BW, bodyweight.
RESULTS Figure 1 and Table 1 present the Achilles tendon forces obtained as a function of footwear. The results indicate that Achilles tendon force parameters were significantly influenced by the examined footwear. No significant difference (F(2, 18)=1.95, p>0.007, pη2=0.17) between footwear was found for the peak plantarflexion moment (Table 1: Figure 1B). There was also no significant difference (F(2, 18)=2.67, p>0.007, pη2=0.23) between footwear for the peak Achilles tendon force (Table 1: Figure 1C). A significant main effect (F(2, 18)=16.63, p0.007, pη2=0.04) and medial (F(2, 18)=1.13, p>0.007, pη2=0.06) GRFs at the instance of peak plantarflexion moment (Table 1).
DISCUSSION The aim of the current investigation was to examine the forces experienced by the Achilles tendon when running in the crosstrainer and running shoe compared with conventional army boots during running. This study represents the first to examine Achilles tendon forces in military footwear. A study of this nature may be beneficial as it details a potential mechanism by which Achilles tendon pathology may be mediated. The primary observation from the current investigation is that Achilles tendon loading rate parameters were reduced significantly when running in the trainer and cross-trainer conditions. This observation concurs with the findings of Kulmala et al13 and Sinclair14 who showed that different footwear can significantly influence the load experienced by the Achilles tendon. This finding may have clinical significance regarding the aetiology and pathogenesis of Achilles tendon injury in military recruits. Repetitive high magnitude tendon loads such as those experienced during running are linked to degradation of the tendon itself.8 With appropriate rest, loading can mediate a physiologically positive influence on the tendon through collagen synthesis, which produces hypertrophic alterations in the 142
tendon itself.8 20 However, with insufficient rest and applied loads that fall outside of tolerable levels, the extent of degradation outpaces collagen synthesis and the tendon ultimately becomes weakened and the susceptibility to injury increases.8 Our results may therefore provide insight into the mechanism by which appropriate footwear selection may be used to attenuate the biomechanical mechanisms linked to the aetiology of Achilles tendinopathy. Based on these observations, it appears that running in trainers and cross-trainers are most appropriate for recruits who are susceptible to Achilles tendon problems. It is likely that the increases in Achilles tendon loading rates observed in the army boot condition relate to the enhanced midsole cushioning associated with the trainer and cross-trainer. As observed in the current study (Figure 1A), when running with decreased midsole cushioning, runners use increased plantarflexion throughout the stance phase.17 21 Increases in ankle plantarflexion are associated with a shortening of the atMA, which leads to an increase in the force experienced by the tendon itself.13 19 A potential limitation of the current investigation is that only male participants were examined. Women exhibit distinct running mechanics in comparison with age-matched men22 23 that places them at an increased risk from the incidence of injury.24 Furthermore, Sinclair et al22 showed that female footwear requirements were different from men; thus, it is unlikely that the findings from this investigation can be generalised to women. It may therefore be prudent for the current investigation to be repeated using a female sample. That the current investigation quantified foot motion using shoe mounted markers may also serve as a limitation of the current investigation. There is likely to be movement of the foot within the shoe, and thus it is questionable as to whether markers positioned on the shoe provide comparable results with those placed on the foot itself.25 26 However, because cutting holes in the experimental footwear to attach markers to skin compromises the structural integrity of the upper and affects runners’ perception of the shoes,25 it was determined that the current technique was the most appropriate.
CONCLUSIONS The observations from the current investigation provide new information regarding the influence of military footwear on Achilles tendon forces during running. The findings from the current study show that running with trainers and cross-trainer mediates significant reductions in Achilles tendon loading rate parameters when compared with running in traditional military boots. Although the shoes examined during this study are not
Sinclair J, et al. J R Army Med Corps 2015;161:140–143. doi:10.1136/jramc-2014-000308
Downloaded from http://jramc.bmj.com/ on July 17, 2015 - Published by group.bmj.com
Original paper currently administered to military personnel, the findings provide insight into mechanisms by which Achilles tendon pathologies may be mediated through appropriate footwear intervention. This study suggests that the running shoes and cross-trainer footwear are associated with reductions in Achilles tendon parameters that have been linked to the aetiology of injury, and thus it can be hypothesised that footwear of this nature could be beneficial for military recruits undertaking running exercises. Acknowledgements We would like to thank Robert Graydon for his tecnical assistance during data collection. Contributors All named authors have made a significant and substantial contribution to all aspects of the study. Each of the named authors provided a meaningful contribution to the conception, design, execution and interpretation of the study data in addition to writing, drafting and revising the paper itself. This paper is submitted with the agreement and approval of both authors. Competing interests None.
8 9
10 11 12
13
14 15 16
Patient consent Obtained.
17
Ethics approval University of Central Lancashire Ethics committee.
18
Provenance and peer review Not commissioned; externally peer reviewed. 19
REFERENCES 1 2 3
4
5
6 7
Molloy JM, Feltwell DN, Scott SJ, et al. Physical training injuries and interventions for military recruits. Mil Med 2012;177:553–8. Popovich RM, Gardner JW, Potter R, et al. Effect of rest from running on overuse injuries in army basic training. Am J Prev Med 2000;18:147–55. Hauret K, Shippey D, Knapik J. The physical training and rehabilitation program: duration of rehabilitation and final outcome of injuries in basic combat training. Mil Med 2001;166:820–6. Bullock SH, Jones BH, Gilchrist J, et al. Prevention of physical training-related injuries recommendations for the military and other active populations based on expedited systematic reviews. Am J Prev Med 2010;38:156–18. US Department of the Army. Prevention and control of musculoskeletal injuries associated with physical training. Washington, DC: DA, 2006. Technical Bulletin Medical 592 (TB MED 592). Moore JS. Function, structure, and responses of components of the muscle-tendon unit. Occup Med 1992;7:713–40. Mahieu N, Witvrouw E, Stevens V, et al. Intrinsic risk factors for the development of achilles tendon overuse injury: a prospective study. Am J Sports Med 2006;34:226–35.
20 21
22
23 24 25 26
Sinclair J, et al. J R Army Med Corps 2015;161:140–143. doi:10.1136/jramc-2014-000308
Magnusson SP, Langberg H, Kjaer M. The pathogenesis of tendinopathy: balancing the response to loading. Nat Rev Rheumatol 2010;6:262–8. Owens BD, Wolf JM, Seelig AD, et al. Risk Factors for Lower Extremity Tendinopathies in Military Personnel. Orthop J Sports Med 2013. Published Online First. http://ojs.sagepub.com/content/1/1/2325967113492707 Paisis P, Hanley B, Havenetidis K, et al. Cypriot and Greek Army Military Boot Cushioning: Ground Reaction Forces and Subjective Responses. Mil Med 2013;178:e493–7. Kaufman K, Brodine S, Shaffer R. Military training-related injuries surveillance, research, and prevention. Am J Prev Med 2000;18:54–63. Schwellnus M, Jordaan G, Noakes T. Prevention of common overuse injuries by the use of shock absorbing insoles. A prospective study. Am J Sports Med 1990;18:636–41. Kulmala JP, Avela J, Pasanen K, et al. Forefoot strikers exhibit lower running-induced knee loading than rearfoot strikers. Med Sci Sports Exerc 2013;45:2306–13. Sinclair J. Effects of barefoot and barefoot inspired footwear on knee and ankle loading during running. Clin Biomech (Bristol, Avon) 2014;29:395–9. Sinclair J, Hobbs SJ, Taylor PJ, et al. The influence of different force measuring transducers on lower extremity kinematics. J App Biomech 2014;30:166–72. Sinclair J, Edmundson CJ, Brooks D, et al. Evaluation of kinematic methods of identifying gait Events during running. Int J Sports Sci Eng 2011;5:188–92. Sinclair J, Greenhalgh A, Edmundson CJ, et al. The efficacy of barefoot and shod running and shoes designed to mimic barefoot running. Footwear Sci 2013;5:45–53. Cappozzo A, Catani F, Leardini A, et al. Position and orientation in space of bones during movement: anatomical frame definition and determination. Clin Biomech 1995;10:171–8. Self BP, Paine D. Ankle biomechanics during four landing techniques. Med Sci Sports Exerc 2001;33:1338–44. Selvanetti A, Cipolla M, Puddu G. Overuse tendon injuries: basic science and classification. Op Tech Sports Med 1997;5:110–17. Sinclair J, Hobbs SJ, Currigan G, et al. A comparison of several barefoot inspired footwear models in relation to barefoot and conventional and conventional running footwear. Comp Ex Phys 2013;9:13–21. Sinclair J, Greenhalgh A, Edmundson CJ, et al. Gender Differences in the Kinetics and Kinematics of Distance Running: Implications for Footwear Design. Int J Sports Sci Eng 2012;6:118–28. Ferber R, Davis IM, Williams DS. Gender differences in lower extremity mechanics during running. Clin Biomech 2003;18:350–7. Taunton JE, Ryan MB, Clement DB, et al. A retrospective case–control analysis of 2002 running injuries. Br J Sports Med 2012;36:95–101. Sinclair J, Greenhalgh A, Taylor PJ, et al. Differences in tibiocalcaneal kinematics measured with skin-and shoe-mounted markers. Hum Mov 2013;14:64–9. Sinclair, J, Taylor PJ, Hebron, J, et al. Differences in multi-segment foot kinematics measured using skin and shoe mounted markers. FAOJ. doi: 10.3827/faoj.2014. 0701.0001 In press.
143
Downloaded from http://jramc.bmj.com/ on July 17, 2015 - Published by group.bmj.com
Influence of running shoes and cross-trainers on Achilles tendon forces during running compared with military boots Jonathan Sinclair, P J Taylor and S Atkins J R Army Med Corps 2015 161: 140-143 originally published online November 26, 2014
doi: 10.1136/jramc-2014-000308 Updated information and services can be found at: http://jramc.bmj.com/content/161/2/140
These include:
References Email alerting service
This article cites 23 articles, 2 of which you can access for free at: http://jramc.bmj.com/content/161/2/140#BIBL Receive free email alerts when new articles cite this article. Sign up in the box at the top right corner of the online article.
Notes
To request permissions go to: http://group.bmj.com/group/rights-licensing/permissions To order reprints go to: http://journals.bmj.com/cgi/reprintform To subscribe to BMJ go to: http://group.bmj.com/subscribe/
Original paper
Influence of running shoes and cross-trainers on Achilles tendon forces during running compared with military boots Jonathan Sinclair,1 P J Taylor,2 S Atkins1 1
Centre for Applied Sport and Exercise Sciences, University of Central Lancashire, Preston, UK 2 School of Psychology, University of Central Lancashire, Preston, UK Correspondence to Professor Jonathan Sinclair, Division of Sport, Exercise and Nutritional Sciences, School of Sport Tourism and Outdoors, Centre for Applied Sport and Exercise Sciences, University of Central Lancashire, Preston, Lancashire PR1 2HE, UK; [email protected] Received 14 April 2014 Revised 2 August 2014 Accepted 24 September 2014 Published Online First 26 November 2014
ABSTRACT Military recruits are known to be susceptible to Achilles tendon pathology. The British Army have introduced footwear models, the PT-03 (cross-trainer) and PT1000 (running shoes), in an attempt to reduce the incidence of injuries. The aim of the current investigation was to examine the Achilles tendon forces of the cross-trainer and running shoe in relation to conventional army boots. Ten male participants ran at 4.0 m/s in each footwear condition. Achilles tendon forces were obtained throughout the stance phase of running and compared using repeated-measures ANOVAs. The results showed that the time to peak Achilles tendon force was significantly shorter when running in conventional army boots (0.12 s) in comparison with the cross-trainer (0.13 s) and running shoe (0.13 s). Achilles tendon loading rate was shown to be significantly greater in conventional army boots (38.73 BW/s) in comparison with the crosstrainer (35.14 BW/s) and running shoe (33.57 BW/s). The results of this study suggest that the running shoes and cross-trainer footwear are associated with reductions in Achilles tendon parameters that have been linked to the aetiology of injury, and thus it can be hypothesised that these footwear could be beneficial for military recruits undertaking running exercises.
INTRODUCTION
To cite: Sinclair J, Taylor PJ, Atkins S. J R Army Med Corps 2015;161:140–143. 140
Military recruits are known to be susceptible to injury.1 These injuries are predominantly experienced in the lower extremities, with incidence ranging from 15% to 50%,2 though often higher in female recruits.3 Injury aetiology within military populations is associated with the high volume of physical training undertaken by recruits.4 5 The Achilles tendon, which serves to transfer forces from the gastrocnemius and soleus muscles to the calcaneus,6 has been shown to be a common injury site in military recruits with an occurrence rate of 14.5%.7 The aetiology and pathogenesis of Achilles tendinopathy have not been fully clarified scientifically; however, a key component for those involved in dynamic activities such as running is repetitive submaximal loading which creates microscopic tears in the tendons’ collagen fibres.8 In military recruits, the high volume of physical training aligned with inadequate footwear provision has been identified as a potential contributory mechanism.9 Military boots have frequently been implicated as a potential mechanism behind the high incidence of injuries among military recruits.10 Poor shock absorption characteristics have been identified in military boots when compared with running shoes.11 Indeed, the inclusion of neoprene shock absorbing
Key messages ▸ Running in military boots increases the load experienced by the Achilles tendon. ▸ Military recruits who are susceptible to Achilles tendon pathologies may wish to utilise running trainers and cross trainers for their running activities.
insoles to military boots has shown improvements in injury rates.12 In an attempt to attenuate the overall injury rate in their recruits, the British military introduced two footwear models, the PT-03 cross-trainer and PT1000 running shoe. These footwear were introduced to replace the traditional army boot when undertaking non-operational running activities. These more sophisticated footwear were designed in response to the frequent claims regarding inadequacies of traditional army boots. The influence of different footwear and running technique on the forces experienced by the Achilles tendon has received little attention. Kulmala et al13 showed that forefoot strike runners exhibited significant increases in Achilles tendon forces compared with those who exhibited a rearfoot strike pattern. In addition, Sinclair14 demonstrated that running barefoot and in minimalist footwear led to significant increases in the forces experienced by the Achilles tendon compared with conventional running trainers. Nonetheless, the influence of different military footwear types on the forces experienced by the Achilles tendon has not received any attention in clinical/footwear biomechanics literature. The aim of the current investigation was to examine the forces experienced by the Achilles tendon when running in the PT-03 cross-trainer and PT1000 trainer compared with conventional army boots. This study may serve to provide information to the military regarding the most appropriate footwear choice for recruits in order to attenuate the high incidence of lower limb injuries.
METHODS Participants Ten male runners took part in the current investigation. The mean characteristics of the participants were: age 23.41±6.29 years, height 174.72±5.38 cm and body mass 70.73±4.87 kg. Participants were active recreational runners engaging in training at least three times per week and were classified as
Sinclair J, et al. J R Army Med Corps 2015;161:140–143. doi:10.1136/jramc-2014-000308
Downloaded from http://jramc.bmj.com/ on July 17, 2015 - Published by group.bmj.com
Original paper rearfoot strikers as they exhibited a clear first peak in their vertical ground reaction force (GRF) time-curve. In accordance with the procedures outlined in the declaration of Helsinki, runners were all free from musculoskeletal pathology at the time of data collection and provided written informed consent. The procedure used for this investigation was approved by the University of Central Lancashire ethical committee.
Procedure Participants completed 10 trials running over a 22 m walkway at 4.0 m/s ±5% in each footwear condition. The participants struck an embedded piezoelectric force platform (Kistler Instruments) sampling at 1000 Hz with their right foot which was dominant in all runners.15 Running velocity was monitored using infrared timing gates (SmartSpeed UK). The stance phase of the running gait cycle was described as the period over which >20 N of vertical force was applied to the force platform.16 The order in which participants ran in each footwear was randomised and all data were collected within a single session. 3D kinematics of the foot and shank were collected using an eight camera optoelectric motion capture system (Qualisys Medical AB, Goteburg, Sweden) with a recording frequency of 250 Hz. Calibration of the system was performed before each data collection session. Only calibrations which produced average residuals of less than 0.85 mm for each camera for a 750.5 mm wand length and points above 4000 in all cameras were accepted prior to data collection.17 GRF and 3D kinematic information were obtained synchronously using Qualisys track manager software. The calibrated anatomical systems technique was used to model the body segments of interest.18 To define the anatomical frames of the right foot and shank, retroreflective markers (19 mm diameter) were positioned onto the calcaneus, 1st and 5th metatarsal heads, medial and lateral malleoli and medial and lateral femoral epicondyles. A rigid carbon-fibre tracking cluster was also positioned onto the shank segment. The foot was tracked using the calcaneus, 1st and 5th metatarsal markers. Static calibration trials were obtained in order for the positions of the anatomical markers to be referenced in relation to the tracking clusters/markers.
peak force divided by the time to peak force.14 In addition, GRFs at peak plantar flexion moment were also obtained in all three axes. The discrete variables extracted for statistical analysis were (1) peak plantarflexion moment, (2) peak Achilles tendon force, (3) time to peak Achilles tendon force and (4) Achilles tendon loading rate. These variables were extracted from each of the ten trials for all three footwear conditions and the data were then averaged within subjects for statistical analysis.
Statistical analysis Differences in Achilles tendon force parameters as a function of footwear were examined using one-way repeated-measures ANOVAs. The α criterion for statistical significance was adjusted to p=0.007 using a Bonferroni correction to control type I error. Effect sizes were calculated using a partial η2 ( pη2). Post-hoc pairwise comparisons were conducted on all significant main effects. All statistical actions were conducted using SPSS V.21.0 (SPSS, Chicago, Illinois, USA).
Data processing GRF and 3D kinematic data were filtered at 50 and 15 Hz respectively using a low pass Butterworth 4th order zero-lag filter using Visual 3D (C-Motion, Germantown, Maryland, USA).14 Ankle joint moments were calculated using Newton-Euler inverse-dynamics allowing the net internal ankle moments to be obtained. Net ankle moments were quantified using anthropometric, GRFs and angular kinematic data. Net ankle joint moments were normalised to body mass (kg N/m). To estimate the forces experienced by the Achilles tendon, a predictive algorithm was used.19 Previous analyses have shown this algorithm to be appropriately sensitive to determine alterations in Achilles tendon forces as a function of different running footwear.13 14 The force experienced by the Achilles tendon was determined by dividing the plantarflexion moment by the Achilles tendon moment arm (atMA). The moment arm was quantified as a function of the ankle sagittal plane ankle angle. Achilles tendon force ¼ plantarflexion moment=atMA atMA ¼ 0:5910 þ 0:08297 SAA 0:0002606 SAA2 The Achilles tendon force was normalised to bodyweight (BW) and Achilles tendon loading rate (BW/s) was also calculated as a function of the change in tendon force from initial contact to
Figure 1 Ankle kinematics, moments and Achilles tendon loads obtained as a function of footwear ((A) ankle angle; (B) ankle moment; (C) Achilles tendon load) (Black=boot, grey=trainer, dash=cross-trainer).
Sinclair J, et al. J R Army Med Corps 2015;161:140–143. doi:10.1136/jramc-2014-000308
141
Downloaded from http://jramc.bmj.com/ on July 17, 2015 - Published by group.bmj.com
Original paper Table 1
Achilles tendon force parameters (mean±SD) as a function of footwear Conventional military boot
Plantarflexion moment (N.m/kg) Peak Achilles tendon force (BW) Time to peak Achilles tendon force (s) Achilles tendon loading rate (BW/s) Medial force (BW) Anterior force (BW) Vertical force (BW)
Trainer
Cross-trainer
Mean
SD
Mean
SD
Mean
SD
2.48 4.73 0.12* 38.73* 0.08 0.21 2.01
0.32 0.62 0.01 5.33 0.07 0.13 0.46
2.42 4.52 0.13 35.14 0.09 0.20 2.03
0.29 0.45 0.01 3.31 0.06 0.10 0.51
2.38 4.41 0.13 33.57 0.08 0.20 2.03
0.39 0.34 0.01† 3.44† 0.06 0.11 0.53
*Significantly different from trainer and cross-trainer. †Significant main effect. BW, bodyweight.
RESULTS Figure 1 and Table 1 present the Achilles tendon forces obtained as a function of footwear. The results indicate that Achilles tendon force parameters were significantly influenced by the examined footwear. No significant difference (F(2, 18)=1.95, p>0.007, pη2=0.17) between footwear was found for the peak plantarflexion moment (Table 1: Figure 1B). There was also no significant difference (F(2, 18)=2.67, p>0.007, pη2=0.23) between footwear for the peak Achilles tendon force (Table 1: Figure 1C). A significant main effect (F(2, 18)=16.63, p0.007, pη2=0.04) and medial (F(2, 18)=1.13, p>0.007, pη2=0.06) GRFs at the instance of peak plantarflexion moment (Table 1).
DISCUSSION The aim of the current investigation was to examine the forces experienced by the Achilles tendon when running in the crosstrainer and running shoe compared with conventional army boots during running. This study represents the first to examine Achilles tendon forces in military footwear. A study of this nature may be beneficial as it details a potential mechanism by which Achilles tendon pathology may be mediated. The primary observation from the current investigation is that Achilles tendon loading rate parameters were reduced significantly when running in the trainer and cross-trainer conditions. This observation concurs with the findings of Kulmala et al13 and Sinclair14 who showed that different footwear can significantly influence the load experienced by the Achilles tendon. This finding may have clinical significance regarding the aetiology and pathogenesis of Achilles tendon injury in military recruits. Repetitive high magnitude tendon loads such as those experienced during running are linked to degradation of the tendon itself.8 With appropriate rest, loading can mediate a physiologically positive influence on the tendon through collagen synthesis, which produces hypertrophic alterations in the 142
tendon itself.8 20 However, with insufficient rest and applied loads that fall outside of tolerable levels, the extent of degradation outpaces collagen synthesis and the tendon ultimately becomes weakened and the susceptibility to injury increases.8 Our results may therefore provide insight into the mechanism by which appropriate footwear selection may be used to attenuate the biomechanical mechanisms linked to the aetiology of Achilles tendinopathy. Based on these observations, it appears that running in trainers and cross-trainers are most appropriate for recruits who are susceptible to Achilles tendon problems. It is likely that the increases in Achilles tendon loading rates observed in the army boot condition relate to the enhanced midsole cushioning associated with the trainer and cross-trainer. As observed in the current study (Figure 1A), when running with decreased midsole cushioning, runners use increased plantarflexion throughout the stance phase.17 21 Increases in ankle plantarflexion are associated with a shortening of the atMA, which leads to an increase in the force experienced by the tendon itself.13 19 A potential limitation of the current investigation is that only male participants were examined. Women exhibit distinct running mechanics in comparison with age-matched men22 23 that places them at an increased risk from the incidence of injury.24 Furthermore, Sinclair et al22 showed that female footwear requirements were different from men; thus, it is unlikely that the findings from this investigation can be generalised to women. It may therefore be prudent for the current investigation to be repeated using a female sample. That the current investigation quantified foot motion using shoe mounted markers may also serve as a limitation of the current investigation. There is likely to be movement of the foot within the shoe, and thus it is questionable as to whether markers positioned on the shoe provide comparable results with those placed on the foot itself.25 26 However, because cutting holes in the experimental footwear to attach markers to skin compromises the structural integrity of the upper and affects runners’ perception of the shoes,25 it was determined that the current technique was the most appropriate.
CONCLUSIONS The observations from the current investigation provide new information regarding the influence of military footwear on Achilles tendon forces during running. The findings from the current study show that running with trainers and cross-trainer mediates significant reductions in Achilles tendon loading rate parameters when compared with running in traditional military boots. Although the shoes examined during this study are not
Sinclair J, et al. J R Army Med Corps 2015;161:140–143. doi:10.1136/jramc-2014-000308
Downloaded from http://jramc.bmj.com/ on July 17, 2015 - Published by group.bmj.com
Original paper currently administered to military personnel, the findings provide insight into mechanisms by which Achilles tendon pathologies may be mediated through appropriate footwear intervention. This study suggests that the running shoes and cross-trainer footwear are associated with reductions in Achilles tendon parameters that have been linked to the aetiology of injury, and thus it can be hypothesised that footwear of this nature could be beneficial for military recruits undertaking running exercises. Acknowledgements We would like to thank Robert Graydon for his tecnical assistance during data collection. Contributors All named authors have made a significant and substantial contribution to all aspects of the study. Each of the named authors provided a meaningful contribution to the conception, design, execution and interpretation of the study data in addition to writing, drafting and revising the paper itself. This paper is submitted with the agreement and approval of both authors. Competing interests None.
8 9
10 11 12
13
14 15 16
Patient consent Obtained.
17
Ethics approval University of Central Lancashire Ethics committee.
18
Provenance and peer review Not commissioned; externally peer reviewed. 19
REFERENCES 1 2 3
4
5
6 7
Molloy JM, Feltwell DN, Scott SJ, et al. Physical training injuries and interventions for military recruits. Mil Med 2012;177:553–8. Popovich RM, Gardner JW, Potter R, et al. Effect of rest from running on overuse injuries in army basic training. Am J Prev Med 2000;18:147–55. Hauret K, Shippey D, Knapik J. The physical training and rehabilitation program: duration of rehabilitation and final outcome of injuries in basic combat training. Mil Med 2001;166:820–6. Bullock SH, Jones BH, Gilchrist J, et al. Prevention of physical training-related injuries recommendations for the military and other active populations based on expedited systematic reviews. Am J Prev Med 2010;38:156–18. US Department of the Army. Prevention and control of musculoskeletal injuries associated with physical training. Washington, DC: DA, 2006. Technical Bulletin Medical 592 (TB MED 592). Moore JS. Function, structure, and responses of components of the muscle-tendon unit. Occup Med 1992;7:713–40. Mahieu N, Witvrouw E, Stevens V, et al. Intrinsic risk factors for the development of achilles tendon overuse injury: a prospective study. Am J Sports Med 2006;34:226–35.
20 21
22
23 24 25 26
Sinclair J, et al. J R Army Med Corps 2015;161:140–143. doi:10.1136/jramc-2014-000308
Magnusson SP, Langberg H, Kjaer M. The pathogenesis of tendinopathy: balancing the response to loading. Nat Rev Rheumatol 2010;6:262–8. Owens BD, Wolf JM, Seelig AD, et al. Risk Factors for Lower Extremity Tendinopathies in Military Personnel. Orthop J Sports Med 2013. Published Online First. http://ojs.sagepub.com/content/1/1/2325967113492707 Paisis P, Hanley B, Havenetidis K, et al. Cypriot and Greek Army Military Boot Cushioning: Ground Reaction Forces and Subjective Responses. Mil Med 2013;178:e493–7. Kaufman K, Brodine S, Shaffer R. Military training-related injuries surveillance, research, and prevention. Am J Prev Med 2000;18:54–63. Schwellnus M, Jordaan G, Noakes T. Prevention of common overuse injuries by the use of shock absorbing insoles. A prospective study. Am J Sports Med 1990;18:636–41. Kulmala JP, Avela J, Pasanen K, et al. Forefoot strikers exhibit lower running-induced knee loading than rearfoot strikers. Med Sci Sports Exerc 2013;45:2306–13. Sinclair J. Effects of barefoot and barefoot inspired footwear on knee and ankle loading during running. Clin Biomech (Bristol, Avon) 2014;29:395–9. Sinclair J, Hobbs SJ, Taylor PJ, et al. The influence of different force measuring transducers on lower extremity kinematics. J App Biomech 2014;30:166–72. Sinclair J, Edmundson CJ, Brooks D, et al. Evaluation of kinematic methods of identifying gait Events during running. Int J Sports Sci Eng 2011;5:188–92. Sinclair J, Greenhalgh A, Edmundson CJ, et al. The efficacy of barefoot and shod running and shoes designed to mimic barefoot running. Footwear Sci 2013;5:45–53. Cappozzo A, Catani F, Leardini A, et al. Position and orientation in space of bones during movement: anatomical frame definition and determination. Clin Biomech 1995;10:171–8. Self BP, Paine D. Ankle biomechanics during four landing techniques. Med Sci Sports Exerc 2001;33:1338–44. Selvanetti A, Cipolla M, Puddu G. Overuse tendon injuries: basic science and classification. Op Tech Sports Med 1997;5:110–17. Sinclair J, Hobbs SJ, Currigan G, et al. A comparison of several barefoot inspired footwear models in relation to barefoot and conventional and conventional running footwear. Comp Ex Phys 2013;9:13–21. Sinclair J, Greenhalgh A, Edmundson CJ, et al. Gender Differences in the Kinetics and Kinematics of Distance Running: Implications for Footwear Design. Int J Sports Sci Eng 2012;6:118–28. Ferber R, Davis IM, Williams DS. Gender differences in lower extremity mechanics during running. Clin Biomech 2003;18:350–7. Taunton JE, Ryan MB, Clement DB, et al. A retrospective case–control analysis of 2002 running injuries. Br J Sports Med 2012;36:95–101. Sinclair J, Greenhalgh A, Taylor PJ, et al. Differences in tibiocalcaneal kinematics measured with skin-and shoe-mounted markers. Hum Mov 2013;14:64–9. Sinclair, J, Taylor PJ, Hebron, J, et al. Differences in multi-segment foot kinematics measured using skin and shoe mounted markers. FAOJ. doi: 10.3827/faoj.2014. 0701.0001 In press.
143
Downloaded from http://jramc.bmj.com/ on July 17, 2015 - Published by group.bmj.com
Influence of running shoes and cross-trainers on Achilles tendon forces during running compared with military boots Jonathan Sinclair, P J Taylor and S Atkins J R Army Med Corps 2015 161: 140-143 originally published online November 26, 2014
doi: 10.1136/jramc-2014-000308 Updated information and services can be found at: http://jramc.bmj.com/content/161/2/140
These include:
References Email alerting service
This article cites 23 articles, 2 of which you can access for free at: http://jramc.bmj.com/content/161/2/140#BIBL Receive free email alerts when new articles cite this article. Sign up in the box at the top right corner of the online article.
Notes
To request permissions go to: http://group.bmj.com/group/rights-licensing/permissions To order reprints go to: http://journals.bmj.com/cgi/reprintform To subscribe to BMJ go to: http://group.bmj.com/subscribe/
