Running Title: Heel lifts lower Achilles tendon loading
The effect of an in-shoe orthotic heel lift on loading of the Achilles tendon during shod walking
Mathias Wulf1,2, Scott C. Wearing2,3, Sue L. Hooper4, Simon Bartold5, Lloyd Reed2 and Torsten
Brauner1
1Faculty of Sports and Health Sciences, Technische Universität München, Munich, Germany.
2Institute of Health & Biomedical Innovation, Queensland University of Technology, Brisbane, Australia.
3Division of Neurophysiology in the Center of Rare Diseases, Ulm University, Ulm, Germany.
4Office of Health and Medical Research, Queensland Health, Brisbane, Australia.
5University of Melbourne, Melbourne, Australia.
Financial Disclosure
This research received financial support from the Queensland Government.
Conflict of Interest Statement
The authors declare no conflicts of interest, financial or otherwise.
Ethics Statement
This study received approval from the University Human Research Ethics Committee.
* Correspondence, proof reading, and reprint requests to:
Scott C. Wearing
Institute of Health and Biomedical Innovation
Queensland University of Technology
60 Musk Avenue,
Kelvin Grove, Qld 4059
Australia
t: +61 7 3138 6444
f: +61 7 3138 60330
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The effect of an in-shoe orthotic heel lift on loading of the Achilles tendon during shod walking
ABSTRACT
Study Design: Controlled laboratory study 1
Objective: To investigate the effect of a 12–mm in–shoe orthotic heel lift on Achilles tendon 2
loading during shod walking using transmission–mode ultrasonography. 3
Background: Orthotic heel lifts are thought to lower tension in the Achilles tendon but evidence 4
for this effect is equivocal. 5
Methods: The propagation speed of ultrasound, which is governed by the elastic modulus and 6
density of tendon and is proportional to the tensile load to which it is exposed, was measured in 7
the right Achilles tendon of twelve recreationally–active males during shod treadmill walking 8
at matched speeds (3.4±0.7 km/h), with and without addition of a heel lift. Vertical ground 9
reaction force and spatiotemporal gait parameters were simultaneously recorded. Data were 10
acquired at 100Hz during 10s of steady–state walking. Statistical comparisons were made 11
using paired t–tests (α=.05). 12
Results: Ultrasound transmission speed in the Achilles tendon was characterized by two maxima 13
(P1, P2) and minima (M1, M2) during walking. Addition of a heel lift to footwear resulted in a 14
2% increase and 2% decrease in the first vertical ground reaction force peak and the local 15
minimum, respectively (P<.05). Peak ultrasonic velocity in the Achilles tendon (P1, P2, M2) was 16
significantly lower with addition of an orthotic heel lift (P<.05). 17
Conclusions: Peak ultrasound transmission speed in the Achilles tendon was lower with the 18
addition of a 12–mm orthotic heel lift, indicating the heel lift reduced tensile load in the 19
Achilles tendon, thereby counteracting the effect of footwear. These findings support the 20
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addition of orthotic heel lifts to footwear in the rehabilitation of Achilles tendon disorders 21
where management aims to lower tension within the tendon. 22
Level of Evidence: Therapy, level 2a 23
24
Key Terms: Soft tissue, Quantitative ultrasound, Speed of sound, Footwear, Orthoses 25
26
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27 Dz, Cohen’s effect size statistic for repeated measures 28
EVA, Ethylene–Vinyl Acetate 29
F1–F3, Vertical ground reaction force maxima (F1 & F3) and local minimum (F2) 30
FTI, Total–foot impulse (force–time integral) 31
M1–M2, Minimum axial transmission speed of ultrasound in the Achilles tendon 32
P1–P2, Peak axial transmission speed of ultrasound in the Achilles tendon 33
PFLR, Peak force loading rate 34
TF1–TF3, Timing of vertical ground reaction force maxima and local minimum35
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INTRODUCTION 36
In–shoe orthotic heel lifts are often used as a key therapeutic intervention in rehabilitation of the 37
Achilles tendon post–injury and have been suggested to be an effective treatment for Achilles 38
tendon disorders based on self–reported clinical outcomes.15, 25 The clinical rationale for use of 39
in–shoe orthotic heel lifts is based on two premises. The first is that heel lifts may attenuate 40
shock associated with heel strike.24 The second is that elevation of the heel results in 41
plantarflexion of the ankle joint and shortens the muscle–tendon unit, thereby decreasing the load 42
in the Achilles tendon during gait.32 Contradictory evidence exists for the use of heel lifts in 43
patients with Achilles tendinopathy5 and supporting evidence for a tension lowering effect in the 44
Achilles tendon remains equivocal. Elevation of the heel, in the order of 15 to 18 mm, has been 45
estimated to either increase,9 decrease,12 or have no effect 4, 10, 32 on peak tensile loading of the 46
Achilles tendon during gait and has been shown to have inconsistent effects on external ground 47
reaction forces, joint kinematics and lower limb muscle activity during walking.19, 20, 21, 24, 25, 42, 43 48
49
To date studies evaluating the effect of heel lifts on Achilles tendon loading have specifically 50
focused on running gait and used inverse dynamic models, to indirectly estimate tendon loads.9, 51
10, 12, 32 Although insightful, indirect estimation of internal tendon loads using the inverse 52
approach is not without limitation. As noted by Gregor et al.14 in comparing direct and indirect 53
estimates of Achilles tendon loading during cycling, inverse dynamic models likely over–54
estimate tendon loads by as much as 50%. Recently, we have shown that ultrasound transmission 55
techniques have the potential to provide direct non–invasive estimates of human tendon loading 56
under dynamic conditions.39 In contrast to indirect measurement techniques, measures of 57
acoustic velocity are neither predicated on estimates of the Achilles tendon moment arm, nor 58
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require assumptions regarding the contribution of agonist and antagonist muscles to the net ankle 59
joint moment, both of which have been shown to induce substantial errors in estimates of tendon 60
loading.14, 37 Rather, the speed of transmission of ultrasound is dependent on the modulus and 61
density of the material through which it propagates, and in tendon is governed by the classic 62
Newtonian–Laplace equation with some adjustment for Poisson’s effects in elastic media.7, 29 63
With application of physiological tensile load, the tangent or instantaneous elastic modulus of 64
tendon increases as does the speed of axial transmission of ultrasound along the tendon. 7, 29, 38 65
Thus, the change in ultrasound transmission speed is related to the magnitude of load applied to 66
the tendon. We went on to use this technique and demonstrate, somewhat unexpectedly, that 67
standard running shoes with an inherent 10–mm heel lift induced changes in ground reaction 68
force and temporospatial gait parameters that increased tensile load in the Achilles tendon in 69
healthy adults.39 The aim of this study, therefore, was to advance this work and investigate 70
whether an orthotic heel lift when used in combination with the same standard running shoes, 71
as typically employed in the management of Achilles tendon disorders,15, 25 had an influence on 72
loading of the Achilles tendon during walking. 73
74
Given that the axial transmission of ultrasound in tendon is governed by its elastic modulus and 75
density and is proportional to the tensile load in tendon,7, 16, 20, 26, 29 we hypothesized that 76
ultrasonic velocity in the Achilles tendon would be lower in standard running shoes with the 77
addition of an in–shoe orthotic heel lift. 78
79
MATERIALS & METHODS 80
Participants 81
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A detailed description of the participants, materials and methods used in this study have been 82
described elsewhere.39 In brief, 12 healthy adult males, recruited from university faculty, 83
participated in the project. The mean (± SD) age, height, body mass, foot length and shoe size 84
(US) of participants was 31 ± 9 years (range, 20 – 47 years), 1.78 ± 0.06 m, 81.0 ± 16.9 kg, 85
26.4 ± 0.9 cm and 10.5 ± 0.7, respectively. Participants were non–smokers, non–medicated and 86
recreationally active based on self–report. None reported a medical history of diabetes, 87
inflammatory joint disease, familial hypercholesterolemia or Achilles tendon pain or pathology. 88
Participant numbers were based on previously published data for human Achilles tendon,35 and 89
were sufficient to detect a 5% difference in the peak axial velocity of ultrasound (α = .05, β = 90
.20). All participants gave written informed consent prior to participation in the research, which 91
was undertaken according to the principles outlined in the Declaration of Helsinki and received 92
approval from the University Human Research Ethics Committee. 93
94
Equipment 95
A flexible strain–gauge electrogoniometer (SG110A, Penny and Giles, Biometrics, Gwent, UK) 96
was used to estimate the active range of non–weightbearing ankle dorsiflexion and plantarflexion 97
using a standard protocol 28 and the change in ankle flexion during quiet bipedal stance with and 98
without the addition of an in–shoe heel raise. The end–blocks of the electrogoniometer were 99
fixed to the skin overlying the lateral calcaneus and the distal aspect of the fibula of the right 100
ankle using double sided adhesive tape,36 and placed to ensure it did not interfere with the collar 101
of the shoe. The electrogoniometer had a resolution of 1° and is reportedly accurate to within 102
1.5% over its measurement range of 100°.35 103
104
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Vertical ground reaction force and temporospatial gait parameters were determined during 105
walking using an instrumented treadmill system, which housed a capacitance–based pressure 106
platform (FDM–THM–S, Zebris Medical GmbH, Isny, Germany). The pressure platform had a 107
sensing area of 108.4 x 47.4 cm and incorporated 7168 sensors, each approximately 0.85 x 0.85 108
cm. The treadmill had a contact surface of 150 x 50 cm and its belt speed could be adjusted 109
between 0.2 and 22 km.hr-1, at intervals of 0.1 km.hr-1. Reported within–subject coefficients of 110
variation for the majority of temporospatial gait parameters are typically below 10% for repeated 111
measures.31 112
113
A custom–built ultrasound device, which incorporated a five element ultrasound probe, was 114
used to synchronously measure axial transmission speed of ultrasound within the right Achilles 115
tendon (FIGURE 1). The probe consisted of a 1MHz broadband pulse emitter and four 116
regularly spaced receivers (range, 7.5 mm), which was maintained in close contact with the 117
skin by means of a coupling medium and elasticized straps. The received ultrasonic signals 118
were digitized at 20 MHz and the time of flight of the first arriving transient signal between 119
receivers was determined using the first zero crossing criterion.3 The average speed of axial 120
transmission of ultrasound waves was subsequently calculated given the known distance 121
between receivers and the measured time of flight. The mean within–subject coefficient of 122
variation for acoustic maxima and minima during steady-state walking is reportedly <1%,39 123
while the accuracy in predicting applied tensile force in tendon from direct measures of 124
ultrasonic velocity typically <2%.7 125
126
< Insert FIGURE 1 around here > 127
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128
Footwear and Heel Lift 129
A standard running shoe (Oregon, Adidas, Herzogenaurach, Germany) ranging in three sizes 130
between US 9.5 and 11.5 (length 29.4–30.9 cm) and mass between 359 and 396 g, with 131
identical, flexible mesh uppers and incorporating a single density EVA midsole (Shore A 132
Durometer, 60 ± 1) and rubber outsole (Shore A Durometer, 88 ± 1) were used (FIGURE 2). 133
All shoes were made by the same manufacturer and incorporate an intrinsic heel offset 134
(elevation) of 10 mm (forefoot height, 17.0 – 19.5 mm; heel height, 27.0 – 29.5 mm). 135
136
< Insert FIGURE 2 around here > 137
138
Two commercially available orthotic heel lifts (Foot Science International, Christchurch, New 139
Zealand) were added to the insole of the rearfoot of each shoe using double–sided adhesive 140
tape. Each wedge–shaped heel lift weighed 5 grams and was made of a single density EVA 141
(Shore A Durometer, 41 ± 1) which tapered over its 8.2 cm length from a height of 7 mm 142
posteriorly to finish flush anteriorly (FIGURE 2). According to the manufacturer, each 143
orthotic heel wedge was 6mm thick at the center of the heel and, since two heel raises were 144
added to each shoe, resulted in an effective heel lift of 12mm at the center of the heel. 145
146
Protocol 147
Participants reported to the gait laboratory having abstained from vigorous physical activity on 148
the day of testing. The skin overlying the posterior Achilles tendon was shaved and cleaned 149
using standard alcohol abrading methods. Following fixation of the probe to the right leg, 150
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participants were afforded a 10–minute treadmill acclimatization session. During the 151
acclimatization session, participants were instructed to adjust the speed of the treadmill to a 152
“comfortable” walking pace using a previously outlined method.31 The defined gait speed was 153
subsequently used to evaluate ultrasonic velocity in the Achilles tendon during two gait 154
conditions; (1) shod with the addition of an in–shoe orthotic heel raise, and (2) shod only. 155
Following five minutes of steady–state walking at the defined speed in each condition, the speed 156
of axial transmission of ultrasound in the right Achilles tendon, vertical ground reaction force 157
and basic temporospatial gait data were synchronously sampled over a 10–second period and at a 158
rate 100 Hz. The order of each gait condition was randomized between participants and each 159
was followed by a rest period in which ankle angle was measured during quiet bipedal stance. 160
161
< Insert FIGURE 3 around here > 162
163
Data Reduction and Statistical Analysis 164
Proprietary software (Zebris Medical GmbH, Isny, Germany) was used to calculate mean 165
temporospatial gait parameters including cadence, step length, step width, stance and swing 166
phase durations and single and double support times (TABLE 1). With the exception of stance 167
phase and swing phase durations, temporal data were expressed as a percentage of the stance 168
phase duration (SPD). Vertical ground reaction force data were exported in ASCII format and 169
custom computer code (Matlab R2012a, MathWorks, Natick, MA) was subsequently used to 170
identify the magnitude (F1–3) and timing (TF1–3) of conventional vertical ground reaction force 171
peaks for each step (FIGURE 3). The relative time to each force maxima and local minimum 172
was expressed as a percentage of the stance phase duration. Peak force loading rate (PFLR), 173
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defined as the greatest rate of force change during the first 20 ms of the gait cycle, was 174
calculated using previously outlined methods,33 while the total–foot impulse (FTI) was estimated 175
by numerical integration of the vertical ground reaction force with respect to time.40 Ultrasound 176
transmission speed in the Achilles tendon is characterized by two maxima (P1, P2) and two 177
minima (M1, M2) during steady–state treadmill walking (FIGURE 4),39 which were analyzed 178
similarly using custom computer code. The range in ultrasound transmission speed in tendon was 179
also calculated as the difference between the maximum and minimum values over the gait cycle. 180
Mean values were calculated for all steps recorded within the 10–second data capture period and 181
only data for the right limb have been presented. 182
183
< Insert FIGURE 4 around here > 184
185
The Statistical Package for the Social Sciences (IBM SPSS Statistics Version 21, Chicago, IL, 186
USA ) was used for all statistical procedures. Shapiro Wilkes tests were used to evaluate data for 187
underlying assumptions of normality. Outcome variables were determined to be normally 188
distributed, so means and standard deviations were used as summary statistics. Paired t–tests 189
were used to evaluate potential differences in ultrasonic, vertical ground reaction force and basic 190
temporospatial gait parameters including cadence, step length, step width, double support and 191
stance duration. Effect sizes were estimated using Cohen’s D for repeated measures (Dz), in 192
which the difference between mean values were standardized by the deviation of the difference.6 193
As a general guideline, Dz in the range of 0.20–0.50 was considered to be a small effect, 0.50–194
0.80 a medium effect, and a value of more than 0.80 as a large effect.6 An alpha level of .05 was 195
used for all tests of significance. 196
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197
RESULTS 198
Average active ankle plantarflexion and dorsiflexion range of motion of participants were 34° ± 199
6° and 15° ± 9°, respectively. Compared with unshod stance, footwear with a 10–mm heel offset 200
increased mean ankle plantarflexion by 4° ± 2° during quiet bipedal stance, which was further 201
increased to 8° ± 3° with addition of a 12–mm in–shoe heel raise (t11 = 7.0, P = .01). 202
203
< Insert Table 1 around here > 204
205
As demonstrated in TABLE 1, there were no statistically significant differences in 206
temporospatial gait parameters between conditions. Similarly there were no statistically 207
significant differences in the majority of kinetic parameters (TABLE 2), with the exceptions of a 208
statistically significant increase in the magnitude of the first vertical ground reaction force 209
maximum (t11 = 3.4, P = .02) and minimum (t11 = -4.1, P = .01). Although the orthotic heel raise 210
was associated with only a 2% increase in F1 and a 2% decrease in F2, the effect size exceeded 211
Cohen’s convention for a large effect (Dz = 0.80), suggesting the increase in F1 and decrease in 212
F2 was relatively consistent across participants (TABLE 2). 213
214
< Insert Table 2 around here > 215
216
Ultrasound transmission speed in the Achilles tendon was highly reproducible during steady–217
state treadmill walking; with a mean within–subject coefficient of variation of ultrasonic maxima 218
and minima ranging between 0.2% ± 0.1% and 1.0 ± 0.6%. Inclusion of an orthotic heel raise 219
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within the shoe lowered peak ultrasound transmission speeds within the Achilles tendon, with a 220
12m/s reduction noted in the magnitude of P1 (t11 = -2.3, P = .04), a 14m/s reduction in P2 (t11 = -221
3.5, P = .01) and a 50m/s reduction noted in M2 (t11 = -3.3, P = .01). Although the heel raise also 222
tended to lower the magnitude of M1 (t10 = -2.0, P = .07), the effect was not significant at the .05 223
level (TABLE 3). Effect sizes for the difference in ultrasonic transmission velocity with heel lifts 224
exceeded Cohen’s convention for moderate (Dz= 0.50–0.79) to large (Dz> 0.80) effects. 225
226
< Insert Table 3 around here > 227
228
DISCUSSION 229
This study used transmission-mode ultrasonography to evaluate the pattern of loading of the 230
Achilles tendon in standard running shoes and with the addition of a commercially available in–231
shoe orthotic heel lift. We have previously shown that a traditional running shoe design which 232
incorporated an intrinsic 10–mm heel offset induced global changes in vertical ground reaction 233
force and temporospatial gait parameters in healthy adults that acted to increase tensile load in 234
the Achilles tendon, as defined by an increase in ultrasound transmission speed (≈ 25 m/s) in the 235
tendon during walking.39 Here we advanced this work to show that the addition of a 12–mm 236
orthotic heel lift added to this standard shoe had negligible effect on basic gait parameters but 237
resulted in a significant reduction in ultrasound transmission speed in the Achilles tendon (12–50 238
m/s), suggesting that the heel lift resulted in reduced loading of the Achilles tendon during 239
walking; thereby counteracting, in part, the shoe–induced increase in tendon loading observed in 240
our earlier work.39 241
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It is noteworthy that the in–shoe heel raise used in this study had no significant effect on any of 243
the recorded temporospatial gait parameters compared with the shoe only condition, although it 244
did induce small but statistically significant alterations in vertical ground reaction force. While, 245
on average, F1 was increased by 2% and F2 decreased by 2% with the addition of the heel raise, 246
the effect was large according to Cohen’s convention (Dz > 0.80), suggesting the change in F1 247
and F2 although clinically small was relatively consistent across participants. While similar 248
alterations in F1 and F2 have been reported previously, albeit only in shoes with a heel height 249
greater than 5.1cm and accompanied by changes in temporospatial gait parameters,11 the reason 250
for a selective increase in F1 and decrease in F2 with use of the orthotic heel raise in the current 251
study is unknown. With an effective mass of just 10 g, it is unlikely that the 20N change in F1 252
and F2 reflect inertial effects associated with the orthotic device itself. 253
254
In the current study, the axial transmission speed of ultrasound in the Achilles tendon was 255
comparable to that reported previously for human tendon (≈ 1900–2050 m.s-1),29, 30, 41 and was of 256
a similar pattern to direct measures of force in the Achilles tendon during walking when recorded 257
by implanted force transducers.13, 18 As described by Komi et al.,18 force in the Achilles tendon is 258
typically reduced after heel contact prior to increasing again during the first part of stance. In the 259
current study both the first and second peaks in ultrasound velocity (P1, P2) were highly 260
reproducible during steady–state walking (mean within–subject coefficient of <1%), which is 261
consistent with earlier observations that the peak–to–peak amplitude of Achilles tendon force is 262
invariant across a range of walking speeds (1.1–1.8 m.s-1).13 Interestingly, use of the orthotic heel 263
lift in the current study, was associated with a lower peak magnitude of the speed of ultrasound 264
transmission in the Achilles tendon but increased the change (range) in ultrasonic velocity 265
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without influencing the duration of the gait cycle. Hence the in–shoe heel lift was associated with 266
a reduced magnitude but greater change in loading of the Achilles tendon throughout a gait cycle. 267
Interestingly, the peak change in ultrasound velocity with heel lifts (≈50 m/s) is similar to the 268
absolute difference in range noted between walking and running (≈54 m/s) over the entire gait 269
cycle.41 Thus, assuming that in–shoe orthotic heel lifts represent an effective treatment option 270
for Achilles tendon disorders based on self-reported outcomes,15, 25 this observation raises the 271
intriguing possibility that a reduction in the magnitude of load within the Achilles tendon, rather 272
than the rate of loading within the tendon, may be more important in achieving symptomatic 273
benefit for Achilles tendinopathy. Moreover, it may be argued that the load–reducing effect of an 274
in–shoe orthotic heel lift may be clinically counter–intuitive in management of tendinopathy, as 275
Achilles tendinopathy is often associated with reduced muscle activity in the Triceps Surae,2 and 276
heavy eccentric and/or concentric exercise is currently advocated for the management of 277
tendinopathy.17 Nonetheless, use of an in–shoe orthotic heel lift (12 mm) combined with 278
footwear that already incorporates a positive heel offset (10 mm) may be clinically useful, 279
particularly early in an progressive–loading intervention program, in which management is often 280
initially aimed at lowering tension within the Achilles tendon.25, 34 281
282
Study Limitations 283
The use of acoustic transmission techniques to investigate Achilles tendon loading is not without 284
limitations. The propagation of acoustic waves in soft tissue media is influenced by several 285
factors, including the structure, temperature, and density of the tissue through which it passes.26 286
Although tendon density and temperature were reasonably assumed to be stable during gait 287
conditions in the current study, there is evidence, albeit in animal models, that the composition of 288
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the Achilles tendon may vary along its length.8 Thus it is unknown whether the effects observed 289
in the current study were uniform across the entire tendon structure. Similarly, the mechanical 290
properties and response of the Achilles tendon to load may differ between sexes, with 291
tendinopathy and over the life–span.1, 19, 23 While gender–differences in tendon properties are not 292
universally reported,27 it is important to note that this study was limited to a small sample of 293
healthy adult males walking at one (preferred) gait speed, in a single shoe design and on the 294
same day. Thus, while it is pertinent to hypothesize about the effects of an in–shoe orthotic heel 295
lift on Achilles tendon disorders, it is unclear whether the results are directly applicable to 296
populations with Achilles tendon injury. Further studies exploring Achilles tendon loading 297
patterns in those with mid-portion and insertional tendinopathy and in repaired tendons following 298
rupture are warranted. Similarly, the effect of the in–shoe orthotic heel lift observed in the 299
current study may have represented only a transient response and may not be directly 300
transferable to Achilles tendon loading with habitual use, in children, females, older aged 301
cohorts, different shoe designs, or at markedly faster or slower gait speeds. Moreover, treadmill 302
systems are known to induce both spatial and temporal constraints on gait. While some studies 303
have observed that treadmills have no significant effect on fascicle behavior of the Triceps Surae 304
compared to over–ground walking, others have noted alter neuromuscular co–ordination and 305
subsequent lower extremity joint moments and powers during walking, which may mitigate the 306
effects of orthotic heel lifts.21, 22 Hence, the findings of this study may not be representative of 307
unconstrained walking in settings outside of the laboratory. 308
309
Nonetheless, the findings of the current study suggest that the addition of a 12–mm orthotic heel 310
lift to standard running shoes, which already have an intrinsic 10–mm heel offset, effectively 311
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counteracts the influence of footwear, to lower tensile load in the Achilles tendon. Although 312
further research into potential mechanisms underpinning the observed effect is required, the 313
findings of this study tend to support the addition of orthotic heel lifts to footwear for the 314
rehabilitation of Achilles tendon disorders where management is aimed at lowering tension 315
within the tendon. 316
317
CONCLUSIONS 318
The addition of an effective 12mm in–shoe orthotic heel lift to standard running shoes lowered 319
the speed of axial transmission of ultrasound in the Achilles tendon. Hence orthotic heel lifts 320
appear to counteract the increase in Achilles tendon loading noted with use of a standard 321
running shoe alone. These findings support the continued clinical use of in–shoe orthotic heel 322
lifts in the rehabilitation of Achilles tendon disorders in which the management plan aims to 323
lower tension within the tendon. 324
325
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KEY POINTS 326
327
Findings: 328
Addition of a 12mm in–shoe orthotic heel lift to standard running shoes lowered the speed 329
of axial transmission of ultrasound and thus tensile load, in the Achilles tendon. 330
Implications: 331
Addition of in–shoe orthotic heel lifts to standard running shoes reduced loading of the 332
Achilles tendon during walking and are appropriate in the rehabilitation of Achilles tendon 333
disorders where management aims to lower tension within the tendon. 334
Caution: 335
This study evaluated the immediate response of healthy adults to a 12mm in–shoe orthotic 336
heel lift during treadmill walking in a single shoe design and may not be directly transferable 337
to Achilles tendon loading with habitual use, in older or pathological cohorts, different shoe 338
designs or at markedly faster or slower gait speeds. 339
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437
438
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439
FIGURE LEGENDS 440
FIGURE 1. Ultrasound transmission speed was measured in the right Achilles tendon using a 441
custom built ultrasonic device (U), which was maintained in close contact with the skin by 442
means of an acoustic coupling medium and elasticized straps (omitted for illustrative purposes). 443
The endblocks of a strain–gauge electrogoniometer (G) were fixed to the skin over the lateral 444
aspect of the fibula and calcaneus using double sided adhesive tape and further fixed with 445
surgical tape. Inset: Close up image of five element ultrasound probe. 446
447 FIGURE 2. Commercially available in–shoe orthotic heel lifts (inset) were added to the 448
rearfoot of a standard running shoe design, which incorporated a single density EVA midsole 449
and an intrinsic heel offset (elevation) of 10 mm. 450
451 FIGURE 3. Vertical ground reaction force parameters derived from the instrumented treadmill 452
system. The force–time integral (FTI), or total foot impulse, is represented by the area under the 453
curve (shaded), while the peak force loading rate (PFLR) was the maximum rate of force change 454
within the first 20ms of the gait cycle. The time to force maxima and local minimum was 455
expressed as a percentage of the stance phase duration. 456
457 FIGURE 4. A typical curve for ultrasound transmission speed (solid lines) and vertical ground 458
reaction force (dashed lines) recorded for two gait cycles from the right Achilles tendon during 459
shod walking with (gray line) and without (black line) an orthotic heel lift at matched speed. 460
Note that the acoustic velocity in the Achilles tendon was characterized by two maxima (P1, P2) 461
and two minima (M1, M2) during each step. 462
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U
G
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0
100
200
300
400
500
600
700
800
900
0 20 40 60 80 100
TF3
TF2
TF1
F2F1 F3
Time (% stance phase duration)
For
ce (
N)
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port
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Time
Axia
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(m/s)
Ver
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, 201
6. F
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ourn
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f O
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paed
ic &
Spo
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Phys
ical
The
rapy
®. A
ll ri
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res
erve
d.
TABLE 1. Mean (SD) temporal and spatial gait parameters during shod walking with and without an additional 12mm heel raise.
Footwear Heel Raise Dz
n 12 12
Speed (km/h) 3.4 3.4 -0.37 (0.7) (0.7)
Cadence (steps/min) 96.7 96.2 0.22 (12.9) (13.2)
Step width (cm) 10.6 10.8 -0.19 (2.1) (1.9)
Step length (cm) 57.2 57.3 0.01 (4.4) (5.8)
Stance phase duration (% GC) 68 68 -0.40 (3) (3)
Load response (%SPD) 18 18 -0.42 (3) (3)
Single support (%SPD) 32 32 0.55 (3) (2)
Pre-swing (% SPD) 18 18 -0.51 (3) (2)
Swing phase duration (%GC) 32 32 0.40 (3) (3)
Note there are no statistically significant differences between conditions Dz, Cohen’s effect size statistic for repeated measures n, Sample size GC, Gait cycle SPD, Stance phase duration
Jour
nal o
f O
rtho
paed
ic &
Spo
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Phys
ical
The
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®
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from
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spt.o
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Janu
ary
17, 2
016.
For
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sona
l use
onl
y. N
o ot
her
uses
with
out p
erm
issi
on.
Cop
yrig
ht ©
${y
ear}
Jou
rnal
of
Ort
hopa
edic
& S
port
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ysic
al T
hera
py®
. All
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ts r
eser
ved.
TABLE 2. Mean (SD) kinetic gait parameters during shod walking with and without an additional 12mm heel raise.
Footwear Heel Raise Dz
n 12 12
F1 (BW) 1.14 1.16 * 0.98 (0.09) (0.10)
TF1 (% SPD) 30 30 -0.29 (4) (3)
F2 (BW) 0.92 0.90 * -1.18 (0.07) (0.09)
TF2 (% SPD) 49 49 -0.26 (3) (3)
F3 (BW) 1.14 1.13 -0.39 (0.10) (0.10)
TF3 (% SPD) 72 72 -0.36 (5) (5)
FTI (BWs) 0.65 0.65 -0.17 (0.07) (0.08)
PFLR (BW/S) 108 98 -0.36 (46) (29)
* statistically significant difference between conditions (P <.05) n, Sample size Dz, Cohen’s effect size statistic for repeated measures F1–F3, Vertical ground reaction force maxima (F1 & F3) and topic minimum (F2) TF1–TF3, Timing of vertical ground reaction force maxima and topic minimum FTI, Total–foot impulse (force–time integral) PFLR, Peak force loading rate BW, Body weights SPD, Stance phase duration
Jour
nal o
f O
rtho
paed
ic &
Spo
rts
Phys
ical
The
rapy
®
Dow
nloa
ded
from
ww
w.jo
spt.o
rg a
t on
Janu
ary
17, 2
016.
For
per
sona
l use
onl
y. N
o ot
her
uses
with
out p
erm
issi
on.
Cop
yrig
ht ©
${y
ear}
Jou
rnal
of
Ort
hopa
edic
& S
port
s Ph
ysic
al T
hera
py®
. All
righ
ts r
eser
ved.
TABLE 3. Mean (SD) ultrasonic velocity in the Achilles tendon during shod walking with and without an additional 12mm heel raise.
Footwear Heel Raise Dz
n 12 12
M1 1867 1834 -0.61 (60) (56)
P1 2047 2035 * 0.65 (71) (62)
M2 1844 1794 * -1.04 (51) (70)
P2 1943 1929 * 1.00 (55) (48)
Range 202 244 * 0.76 (34) (65)
* statistically significant difference between conditions (P <.05) n, Sample size Dz, Cohen’s effect size statistic for repeated measures M1–M2, Minimum axial transmission speed of ultrasound in the Achilles tendon P1–P2, Peak axial transmission speed of ultrasound in the Achilles tendon
Jour
nal o
f O
rtho
paed
ic &
Spo
rts
Phys
ical
The
rapy
®
Dow
nloa
ded
from
ww
w.jo
spt.o
rg a
t on
Janu
ary
17, 2
016.
For
per
sona
l use
onl
y. N
o ot
her
uses
with
out p
erm
issi
on.
Cop
yrig
ht ©
${y
ear}
Jou
rnal
of
Ort
hopa
edic
& S
port
s Ph
ysic
al T
hera
py®
. All
righ
ts r
eser
ved.