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VOLUME 3, ISSUE 2 

 2020 

 

RESEARCH ARTICLE 

Blakeley N., Silver-Thorn B., Cross J.A. Investigation of the effects of prosthetic knee condition for individuals with transfemoral amputation during attempted 

running. Canadian Prosthetics & Orthotics Journal. 2020; Volume 3, Issue 2, No.3. https://doi.org/10.33137/cpoj.v3i2.34481 

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https://doi.org/10.33137/cpoj.v3i2.34481


 

1 

Blakeley N., Silver-Thorn B., Cross J.A. Investigation of the effects of prosthetic knee condition for individuals with transfemoral amputation during attempted 
running. Canadian Prosthetics & Orthotics Journal. 2020; Volume 3, Issue 2, No.3. https://doi.org/10.33137/cpoj.v3i2.34481 

 

 

 
RESEARCH ARTICLE 

 

INVESTIGATION OF THE EFFECTS OF PROSTHETIC KNEE CONDITION FOR INDIVIDUALS 
WITH TRANSFEMORAL AMPUTATION DURING ATTEMPTED RUNNING  

 
Blakeley N.1*, Silver-Thorn B.1, Cross J.A.2 
 

1 Department of Biomedical Engineering, Marquette University, Milwaukee, USA.  
2 Department of Orthopaedic Surgery, Medical College of Wisconsin, Milwaukee, USA. 

 

 

 

 

 

  

 

 

 

 

 

 

 

 

 

 

 

INTRODUCTION   

When using a running specific prosthesis (RSP) at fixed 

speeds on a treadmill, individuals with a transfemoral 

amputation (TFA) consume 45-78% more oxygen than age-

matched able-bodied runners.1 Some individuals with TFA 

run in a prosthesis with an unlocked prosthetic knee, others 

choose to run without a prosthetic knee; their prosthetic 

socket and foot are linked via a non-articulating pylon (no-

knee condition).2,3 This non-articulating prosthesis will not 

buckle and collapse, regardless of load or runner fatigue, 

minimizing fall risk.3 Consequently, distance runners with 

TFA have reported decreased cognitive effort for the no-

knee condition.3 The lack of a knee joint, however, requires 

that the individuals with TFA circumduct their prosthetic limb 

to clear the ground during swing phase.4 Leg circumduction 

during swing shifts the center of gravity laterally, thus 

decreasing energy efficiency.5 

 
OPEN  ACCESS Volume 3, Issue 2, Article No.3. 2020 

 

 

Journal Homepage: https://jps.library.utoronto.ca/index.php/cpoj/index 

 

ABSTRACT 

BACKGROUND: A number of individuals with unilateral transfemoral amputation (TFA) run in a 

prosthesis with an unlocked prosthetic knee, while others choose to run with a locked prosthetic knee to 

increase stability. Research regarding running with an unlocked knee (UK) versus a locked knee (LK), 

with respect to energy efficiency, is limited and might be enhanced by characterization of the impact of 

knee condition on kinematics. 

OBJECTIVE: To investigate the effect of an UK versus LK on hip kinematics, energy efficiency, and 

running speed. 

METHODOLOGY: Five male novice runners with unilateral TFA completed one three-minute self-

selected running speed (SSRS) trial and three peak speed trials per knee condition. Hip kinematics, 

energy efficiency, and running speed were compared between conditions. 

FINDINGS: Four of the five subjects exhibited a fast walk, rather than a consistent run.  Hip flexion 

increased for all subjects and hip abduction decreased for four subjects during swing phase for the UK 

condition. Hip kinematic asymmetry was reduced for the UK condition in the sagittal plane for four 

individuals; hip kinematic asymmetry was also reduced in the frontal plane for the UK condition for three 

of these individuals. Mean energy efficiency was better for the UK condition (UK: 0.282 mLO2/kg/m, LK: 

0.328 mLO2/kg/m). Peak running speed did not differ significantly between knee conditions (UK: 1.47 

m/s, LK:1.32 m/s).  

CONCLUSIONS: For novice recreational runners with unilateral transfemoral amputation, the UK 

condition resulted in improved energy efficiency and enhanced kinematic symmetry, despite comparable 

peak speed relative to the LK condition. Therefore the UK condition may be advantageous for mid-range 

distance running.  

ARTICLE INFO 

Received: June 14, 2020 

Accepted: September 7, 2020 

Published: September 16, 2020 

CITATION 

Blakeley N., Silver-Thorn B., 

Cross J.A. Investigation of the 

effects of prosthetic knee 

condition for individuals with 

transfemoral amputation during 

attempted running. Canadian 

Prosthetics & Orthotics Journal. 

2020;Volume 3, Issue 2, No.3. 

https://doi.org/10.33137/cpoj.v3i

2.34481 

KEYWORDS 

Kinematic, Gait analysis, 

Amputation, Prosthesis, 

Running, Energy efficiency,  

Gait symmetry, Prosthetic knee, 

Lower limb amputation 

 

* CORRESPONDING AUTHOR: 
Natalie Blakeley,  
Department of Biomedical Engineering, Marquette University, 
Milwaukee, USA.  
E-mail: Blakeley.natalie@gmail.com 
ORCID: https://orcid.org/0000-0002-2066-4096  
 

https://doi.org/10.33137/cpoj.v3i2.34481
https://jps.library.utoronto.ca/index.php/cpoj/index
https://doi.org/10.33137/cpoj.v3i2.34481
https://doi.org/10.33137/cpoj.v3i2.34481
https://orcid.org/0000-0002-2066-4096
https://orcid.org/0000-0002-2066-4096


 

2 

Blakeley N., Silver-Thorn B., Cross J.A. Investigation of the effects of prosthetic knee condition for individuals with transfemoral amputation during attempted 
running. Canadian Prosthetics & Orthotics Journal. 2020; Volume 3, Issue 2, No.3. https://doi.org/10.33137/cpoj.v3i2.34481 

ISSN: 2561-987X EFFECTS OF PROSTHETIC KNEE CONDITION DURING ATTEMPTED RUNNING 
Blakeley et al. 2020 

 
CPOJ 

 
The effect of knee condition on oxygen consumption and 

running speed has been minimally investigated and results 

to date have been contradictory. For two experienced 

runners with TFA wearing RSPs, Wening and Stockwell 

reported that running without a prosthetic knee (no-knee 

condition) is more efficient based on level treadmill running 

trials at progressively increasing speeds.3 Both subjects ran 

for a prolonged period and achieved faster peak speeds 

when running in the no-knee condition. One subject 

demonstrated reduced peak VO2 and a faster speed for the 

no-knee condition, suggesting decreased energy efficiency. 

The other subject achieved a faster speed, but with an 

increased peak VO2, for the no-knee condition. Although 

Wening and Stockwell reported the no-knee condition was 

more energy efficient, as running speed was not controlled, 

this finding is inconclusive. In contrast, Highsmith et al. who 

tested  four experienced runners with TFA reported that the 

unlocked knee (UK) condition was more energy efficient 

than the no-knee condition.2 Both self-selected running 

speed (SSRS) and peak speed tended to increase for the 

UK condition, although not significantly.2 However, mean 

oxygen consumption was only reduced for five of eight 

running speeds for the UK condition and prosthesis mass 

was not controlled. The potential variation in oxygen 

consumption with knee condition for runners with unilateral 

TFA may be related to hip kinematics as circumduction and 

increased hip abduction decrease energy efficiency due to 

the lateral shift in the center of gravity.5 However, hip 

kinematics for individuals with unilateral TFA running with a 

RSP have not been reported to date.   

The goal of this study was to investigate whether a 

prosthetic knee unit should be unlocked or locked for 

individuals with unilateral TFA during recreational running 

on a treadmill based on hip kinematics, energy efficiency, 

and running speed. Running with a locked prosthetic knee 

is anticipated to introduce circumduction of the prosthetic 

limb for ground clearance. For the two knee conditions, the 

following results are anticipated: 1) increased prosthetic 

limb hip flexion and reduced hip abduction during swing 

when running in the UK condition, 2) reduced frontal and 

sagittal plane interlimb asymmetry of the hip during swing 

phase when running in the UK condition, 3) better energy 

efficiency when running with the UK, and 4) faster peak 

running speed for the UK condition. The population of TFA 

who currently run is small. To increase the sample size, our 

target population was novice runners, TFAs interested in 

extending their exercise regimen and potential fitness level, 

and trialing a running prosthesis. These individuals and their 

prosthetists might benefit from these trials and the related 

objective data acquired.   

METHODOLOGY 

Five male subjects participated in the study (Table 1). 

Subject inclusion criteria were: unilateral transfemoral 

amputation, K3 to K4 activity level, 18-65 years, good 

general health, novice runners or individuals with interest 

and capability (as assessed by their physician or 

prosthetist), and body weight less than 100 kg (weight limit 

for the running prosthesis6). Individuals with balance 

disorders or neurological conditions that would adversely 

impact running, residual limb skin breakdown, or elevated 

vacuum suspension (incompatible with RSP) were 

excluded. The study protocol was approved by the affiliated 

Institutional Review Board (approval number HR-3249) and 

written informed consent was solicited and obtained for 

each subject prior to study participation.  

An Ottobock (Duderstadt Germany) RSP consisting of the 

prosthetic socket, the 3S80 Modular Sport Knee Joint and 

either the IE90 Springlite Sprinter Foot (subjects 1, 2 and 4) 

or the IE91 Runner Foot (subjects 3 and 5) was used by all 

subjects. Each subject retained their original socket for both 

knee conditions. For subjects who did not own the Ottobock 

RSP, a fitting session was conducted by a collaborating 

certified prosthetist. The manual lock of the 3S80 knee was 

either locked (LK) or unlocked (UK), depending on the knee 

condition. 

Due to time constraints (participant, prosthetist, laboratory, 

and loaned RSP’s), a single training session (60-90 min) 

was conducted by the investigator to familiarize the subject 

with the equipment, test environment, and protocol as well 

as to determine the subject’s SSRS in the UK and LK 

conditions. The treadmill training session included walking 

in both knee conditions, gradually progressing to a run at a 

pace dictated by the subject. Running at a steady-state 

speed was practiced for 1 to 3 minutes. Peak speed trials in 

each knee condition were conducted to familiarize the 

subject with the protocol. Once the subject verbally 

acknowledged they felt comfortable running in both knee 

conditions, the training session was concluded. A minimum 

of 72 hours post training, a single 3-4 hour testing session 

was conducted. 

Running trials were conducted on an instrumented split-belt 

treadmill (Woodway, Waukesha, WI) while subjects were 

secured in a fall-arrest, safety harness. Subjects completed 

a warm-up period; the specific duration and activities (i.e., 

UK or LK, walking or running) were at the discretion of the 

subject. The warm-up period included a confirmatory 

determination of SSRS. The SSRS from the testing session 

was within 0.13 m/s of the training session SSRS for all 

subjects. Two three-minute running trials at SSRS were 

conducted (one per knee condition) followed by six peak 

speed running trials (three per knee condition) with a 

minimum of ten minutes rest between trials.7 Subjects were 

permitted a rest duration greater than 10 minutes, but all 

declined the extended time. For the three-minute running 

trials at SSRS, the treadmill was accelerated from rest to a 

comfortable walking speed and then increased to the 

subject’s SSRS for the respective knee condition at a rate 

dictated by the subject.  

https://doi.org/10.33137/cpoj.v3i2.34481


 

3 

Blakeley N., Silver-Thorn B., Cross J.A. Investigation of the effects of prosthetic knee condition for individuals with transfemoral amputation during attempted 
running. Canadian Prosthetics & Orthotics Journal. 2020; Volume 3, Issue 2, No.3. https://doi.org/10.33137/cpoj.v3i2.34481 

ISSN: 2561-987X EFFECTS OF PROSTHETIC KNEE CONDITION DURING ATTEMPTED RUNNING 
Blakeley et al. 2020 

 
CPOJ 

 

The peak speed trials commenced in a similar manner after 

the SSRS was achieved: the speed was increased by 0.089 

m/s every 3 seconds until the subject indicated they wanted 

to stop, pressed the emergency stop button, or engaged the 

safety harness.  

To minimize knee condition changes, the running trial order 

was not randomized. Switching knee conditions repeatedly 

would have increased the subjects’ time burden, and 

randomizing the knee condition test order may adversely 

affect the subject’s confidence. The UK condition was 

tested first as subjects routinely walk with an unlocked knee, 

thereby increasing their initial confidence and security 

during testing. Additionally, Highsmith et al. found the UK 

knee was more energy efficient,2 thus the UK condition 

sprints were completed last. The test order was SSRS UK, 

SSRS LK, peak speed LK, followed by peak speed UK 

(Figure 1). 

Three-minute running trials were conducted first to 

decrease the effect of fatigue on metabolic results. Three 

peak speed trials with the knee locked were completed prior 

to peak speed testing in the UK condition, as the subject 

had just completed sub-maximal running with this knee 

condition. Peak speed was determined by accelerating the 

treadmill from rest to a comfortable walking speed and then 

increasing speed to the subject’s SSRS for the associated 

knee condition. The speed then increased by 0.089 m/s 

every 3 seconds until the subject indicated they wanted to 

stop, pressed the emergency stop button, or engaged the 

safety harness. The final speed achieved prior to the 

occurrence of one of  these events was recorded as the 

trial’s peak speed. At the conclusion of the testing session, 

subjects were asked to identify the preferred knee condition 

(UK or LK) for distance running and sprinting.  

A 13-camera motion capture system (OptiTrack, Corvallis, 

OR) was used to acquire kinematic data (120 Hz, low pass 

filtered with a fourth order Butterworth, cut-off frequency of 

6 Hz 8,9) during the three-minute running trials. The filter cut-

off frequency was determined based on a fast Fourier 

transform of the left and right heel and anterior superior iliac 

spine marker position data.  Thirty five retro-reflective 

markers were secured to the subject based on a 

conventional gait model, modified for the prosthetic 

limb,4,10 using Visual 3D software (version 6, C-Motion, 

Germantown, MD). Consistent with the conventional gait 

model, the hip angle was defined as the thigh relative to the 

pelvis. Markers were placed on the sacrum and bilaterally 

positioned on the iliac crest, anterior superior iliac spine, 

greater trochanter, lateral femoral epicondyle, medial 

femoral epicondyle, tibial tuberosity, lateral malleolus, 

 Subject 1 Subject 2 Subject 3 Subject 4 Subject 5 Mean (SD) 

Age (years) 59 52 57 54 56 55.6 (2.42) 

Mass (without 

prosthesis, kg) 
72.8 93.0 87.4 82.5 93.4 85.2 (8.54) 

Height (with RSP, 

cm) 
184.0 186.0 178.0 185.5 176.5 182 (3.96) 

Residual Limb 

Length* (cm) 
21 16 38 31 39 29 (9.14) 

Amputated Side Right Left Left Right Left -  

Cause of 

Amputation 
Cancer Cancer Trauma Trauma Trauma - 

Time Post 

Amputation (years) 
49 47 5 6 6 22.6 (20.75) 

Running 

Experience 

Everyday 

Prosthesis 

Short sprints during 

various sports 

(volleyball, tennis, 

basketball) within 1 

month of testing, 

knee unlocked  

None None None 

Weekly fast walk 

1.5-2 miles, on 

treadmill within 1 

month of testing, 

knee unlocked 

- 

Everyday 

Prosthetic 

Componentry 

Suspension: 

Suction 

Knee: Genium 

Foot: Triton Vertical 

Shock 

Suspension: 

Suction 

Knee: X3 

Foot: Triton Vertical 

Shock 

Suspension: 

Suction 

Knee: C-Leg 

Foot: Triton 1C60 

Suspension: 

Elevated Vacuum 

Knee:  X3 

Foot: Triton 

Harmony 

Suspension: 

Suction 

Knee: Genium 

Foot: Trias Plus 

- 

Running 

Experience with 

RSP 

For the 2 weeks 

prior to testing, over 

ground running with 

knee unlocked and 

locked 

One day per year, 

over ground with 

knee unlocked and 

locked 

For the 3 months 

prior to testing, 3-

4x per week on 

AlterG anti-gravity 

treadmill with knee 

unlocked 

For the 3 months 

prior to testing, 

over ground with 

knee locked 

None - 

 

Table 1: Subject characteristics and running experience.  
* Distance from the greater trochanter to the most distal point on the femur (as determined by palpation). 

https://doi.org/10.33137/cpoj.v3i2.34481


 

4 

Blakeley N., Silver-Thorn B., Cross J.A. Investigation of the effects of prosthetic knee condition for individuals with transfemoral amputation during attempted 
running. Canadian Prosthetics & Orthotics Journal. 2020; Volume 3, Issue 2, No.3. https://doi.org/10.33137/cpoj.v3i2.34481 

ISSN: 2561-987X EFFECTS OF PROSTHETIC KNEE CONDITION DURING ATTEMPTED RUNNING 
Blakeley et al. 2020 

 
CPOJ 

 
medial malleolus, fifth metatarsal, second metatarsal, and 

calcaneus. Marker placements on the RSP are shown in 

Figure 2. A static trial was conducted for each subject and 

knee condition to define the local coordinate systems. 

 

Figure 1: Flow chart overview of the running trials for the test 

protocol. 

To determine stride cycle events, vertical force data were 

collected (1200 Hz) from the instrumented split belt 

treadmill, low pass filtered (zero phase 8th order 

Butterworth filter, cutoff of 12 Hz13), and down sampled to 

match the sampling frequency for the kinematic data; an 

amplitude threshold of 44.5 N was implemented to define 

heel strike (HS) and toe-off (TO) events.14 A custom 

MATLAB (version: 9.1.0.441655, The MathWorks, Inc., 

Natick, MA) script was written for vertical force data 

processing. 

Specific kinematic parameters, extracted bilaterally for 

analysis, included peak hip flexion and peak hip abduction 

during swing phase. To assess the asymmetry of these 

kinematic parameters between the prosthetic and intact 

limbs during each knee condition, the interlimb asymmetry 

(IA) index (Equation 1)15 was calculated using Microsoft 

Excel (Version 1908, Microsoft Corporation, Redmond, WA) 

for discrete stride cycles in the middle 45-second period of 

the three-minute SSRS trial. Stride cycles were excluded if 

marker drop-out exceeded 10 frames and affected the 

calculated kinematic parameter of interest. For a given 

subject and kinematic parameter, the number of stride 

cycles (6-17 cycles) retained for analysis was the same 

between knee conditions, randomly omitting the extra stride 

cycles for the knee condition with more cycles. For each 

subject and knee condition, the mean and standard 

deviations were calculated across all included stride cycles 

in the analyzed time period for IA for peak hip flexion and 

abduction during swing phase, respectively. 

Equation 1:    𝐼𝐴 = (
𝑋𝑖𝑛𝑡𝑎𝑐𝑡−𝑋𝑝𝑟𝑜𝑠𝑡ℎ𝑒𝑡𝑖𝑐 

𝑋𝑖𝑛𝑡𝑎𝑐𝑡 +𝑋𝑝𝑟𝑜𝑠𝑡ℎ𝑒𝑡𝑖𝑐 
) ∗ 100%                     

Xprosthetic and Xintact represent the specific kinematic 

measures (peak swing phase hip flexion and abduction) for 

the prosthetic and intact limbs, respectively. An IA index 

value of 0 represents symmetry; negative IA values indicate 

that the parameter value for the prosthetic limb exceeded 

that for the intact limb. The percentage of asymmetry is 

reflected by the IA magnitude (e.g. an IA index of -20 and 

+20 represent the same magnitude of asymmetry). 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 2: Marker placements on the 1E90 Sprinter foot (Top) and 

1E91 Runner foot (Bottom) (Figure adapted from Ottobock11,12). 

Not pictured: “heel” marker placed posteriorly at the most acute 

radius of the foot. 

• Kinematic data: 

middle 45 sec 

period only 

• SSRS 

• RE: during 

steady state 

period only, 

40-120 sec 

• Peak speed 

• Preferred knee 

condition for 

distance, 

sprinting  

3 min run with knee unlocked 

Max speed with knee unlocked 

3 min run with knee locked 

Max speed with knee locked 

Max speed with knee locked 

Max speed with knee locked 

Max speed with knee unlocked 

Max speed with knee unlocked 

Minimum 10 min. rest 

Minimum 10 min. rest 

Minimum 10 min. rest 

Minimum 10 min. rest 

Minimum 10 min. rest 

Minimum 10 min. rest 

Minimum 10 min. rest 

L Knee Lat. 

L Shank Sup. 

L Ankle 

L Tib. Tuberosity 

L Lat. Ankle Inf. 

L Med. Ankle Inf. 

L Foot Med. 

L Foot Lat. 

L Toe 
L Foot Ant. 

L Toe L Foot Lat. 

L Foot Med. 
L Foot Ant. 

L Lat. Ankle Inf. 

L Med. Ankle Inf. L Ankle 

L Shank Sup. 

L Tib. Tuberosity 

L Knee Lat. 

https://doi.org/10.33137/cpoj.v3i2.34481


 

5 

Blakeley N., Silver-Thorn B., Cross J.A. Investigation of the effects of prosthetic knee condition for individuals with transfemoral amputation during attempted 
running. Canadian Prosthetics & Orthotics Journal. 2020; Volume 3, Issue 2, No.3. https://doi.org/10.33137/cpoj.v3i2.34481 

ISSN: 2561-987X EFFECTS OF PROSTHETIC KNEE CONDITION DURING ATTEMPTED RUNNING 
Blakeley et al. 2020 

 
CPOJ 

 
VO2 measurements were collected breath-by-breath using 

the K4b2 portable metabolic system (Cosmed USA Inc, 

Chicago IL) during the full three-minute trials for both knee 

conditions. VO2 data were averaged over 20 second 

intervals for the entire data series. Running economy (RE), 

a measure of energy efficiency during running, was 

calculated from the steady-state VO2 portion of the trial. The 

steady-state portion of the VO2 was defined as a change in 

VO2 of less than 100 mL/min.16 Based on this definition, all 

participants achieved steady-state for both knee conditions 

with durations ranging from 40 to 120 seconds. RE was 

calculated as the ratio of the body-mass normalized steady-

state VO2 to the SSRS for the corresponding three-minute 

trial. RE was calculated both inclusive and exclusive of 

prosthesis mass. 

Statistical analyses 

Statistical analyses were conducted using SPSS (v 24.0, 

IBM Inc., Armonk, NY). The Shapiro-Wilk test (p=0.05) was 

used to assess data normality for all variables. The UK 

condition was anticipated to reduce hip kinematic 

pathologies during swing.  Swing phase peak prosthetic 

limb hip flexion, abduction, and hip frontal and sagittal plane 

interlimb asymmetry were tested with two-tailed paired t-

tests (p=0.05, if normally distributed data) or the Wilcoxon 

signed-rank test (p=0.05, if non-normally distributed data). 

All kinematic variables were assessed on a single-subject 

basis in a separate test for each knee condition, using all 

retained stride cycles. Thus, there were 6-17 data points per 

statistical test. The corresponding effect size was calculated 

using Cohen’s d (normally distributed data) and Equation 2 

(non-normally distributed data):  

Equation 2:                          r=Z/√N                      

where r represents effect size, Z represents the test statistic, 

and N represents the number of samples.  

 

In contrast to the kinematic parameters, single values of RE 

and peak speed were available for each knee condition and 

subject. These data were assessed on an inter-subject 

basis using a paired t-test (p=0.05). These group statistics, 

while statistically significant, are referred to as “trends” due 

to the small sample size. 

RESULTS 

Due to the novice running status of the recruited subjects, 

only subject 1 was able to run (i.e. exhibit periods where 

both feet were airborne simultaneously) consistently 

throughout the SSRS and peak running speed trials. 

Subjects 2-5 all exhibited a fast walk. Subjects 1 and 2 did 

not require the use of the handrails while subjects 3-5 used 

the handrails consistently throughout all the trials for both 

knee conditions. The UK condition was preferred for all 

subjects for distance running and subjects 2 and 4 preferred 

the LK condition for sprinting.  

Kinematics: 

Statistically significant single-subject differences in 

maximum hip flexion during swing were found between 

knee conditions across all subjects. Peak hip flexion of the 

prosthetic limb increased during swing with the UK condition 

for all subjects (Table 2, Figure 3, see Nelson17 for all 

kinematic graphs). A statistically significant difference in 

peak IA for the hip in the sagittal plane between knee 

conditions was found for each subject (Table 2).   

For four subjects (1-4), the prosthetic hip abduction during 

swing increased (greater negative angle) from the UK 

condition to the LK condition (Table 3, Figure 3, see Nelson17 

for all kinematic graphs). For all subjects, peak IA for the hip 

in the frontal plane during swing differed significantly 

between knee conditions (Table 3); in terms of magnitude, 

IA decreased for three subjects (1, 2, and 4) for the UK 

condition, reflecting increased symmetry for this knee 

condition.  

 

 

 
Subject 1 Subject 2 Subject 3 Subject 4 Subject 5 

UK LK UK LK UK LK UK LK UK LK 

Prosthetic Limb 
Peak Hip Flexion 
(°) 

45.7 
(1.05) 

27.4 
(1.34) 

48.2 
(2.72) 

31.8 
(2.22) 

60.3 
(2.03) 

57.2 
(4.25) 

53.5 
(1.50) 

40.6 
(1.76) 

53.8 
(1.57) 

51.8 
(1.72) 

+P <0.001, effect size: 
10.80 

[6 cycles] 

+P <0.001, effect size: 
4.29 

[7 cycles] 

+P =0.012, effect size: 
0.99 

[10 cycles] 

+P <0.001, effect size: 
6.52 

[17 cycles] 

+P = 0.001, effect 
size:0.26 

[17 cycles] 

IA for peak hip 
flexion (%) 

-2.87 
(1.35) 

25.90 
(2.54) 

-4.58 
(2.49) 

16.40 
(4.10) 

0.29 
(2.50) 

9.29 
(3.73) 

-3.58 
(1.67) 

9.10 
(2.37) 

-2.10 
(1.95) 

0.65 
(2.10) 

*P = 0.001, effect 
size:1.34 
[6 cycles] 

+P <0.001, effect 
size:3.36 
[7 cycles] 

+P = 0.006, effect 
size:1.84 
[6 cycles] 

+P <0.001, effect 
size:4.62 

[15 cycles] 

+P = 0.001, effect 
size:1.09 

[15 cycles] 

 

Table 2: Sagittal plane hip kinematics (mean (SD)) during swing phase for select strides in the middle 45 seconds of the three-minute self-

selected running speed trial for each subject for each knee condition. Bold values denote statistically significant single-subject differences 

(0.05 level) between knee conditions. + Denotes a two-tailed paired t-test was conducted (normally distributed data). * Denotes the Wilcoxon 

signed-rank test was conducted (non-normally distributed data). UK = Unlocked knee, LK = Locked Knee 

https://doi.org/10.33137/cpoj.v3i2.34481


 

6 

Blakeley N., Silver-Thorn B., Cross J.A. Investigation of the effects of prosthetic knee condition for individuals with transfemoral amputation during attempted 
running. Canadian Prosthetics & Orthotics Journal. 2020; Volume 3, Issue 2, No.3. https://doi.org/10.33137/cpoj.v3i2.34481 

ISSN: 2561-987X EFFECTS OF PROSTHETIC KNEE CONDITION DURING ATTEMPTED RUNNING 
Blakeley et al. 2020 

 
CPOJ 

 

E  

              

              

      Intact Limb 

       Prosthetic Limb 

Unlocked Knee Condition 

Unlocked Knee Condition 
Locked Knee Condition 

H
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) 

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-)
 (

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) 

H
ip

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Figure 3: Mean (middle 45 seconds) hip motion in the sagittal (Top) and frontal planes (Bottom) for Subject 1 during the self-selected running 

speed trial in the unlocked (left) and locked (right) knee conditions. Vertical lines denote toe-off. 

 
Subject 1 Subject 2 Subject 3 Subject 4 Subject 5 

UK LK UK LK UK LK UK LK UK LK 

Prosthetic 
Limb Peak Hip 
Abduction (°) 

-13.2 
(0.783) 

-20.7 
(0.968) 

-7.5  
(0.651) 

-18.4  
(1.27) 

-15.4 
(1.95) 

-18.4 
(2.63) 

-5.5 
(0.753) 

-16.1 
(1.38) 

-15.5 
(1.64) 

-13.7 
(1.48) 

+P <0.001               
effect size: 5.23 

*P = 0.018                     
effect size: 0.09 

+P = 0.017                 
effect size: 0.93 

+P <0.001                 
effect size: 6.41 

+P <0.001                
effect size:1.18 

IA for peak hip 
abduction (%) 

-19.4 
(4.53) 

-43.6 
(5.24) 

14.8 
(7.36) 

-20.9   
(8.93) 

-83.0 
(4.09) 

-65.0 
(4.30) 

22.5 
(6.52) 

-27.3 
(6.45) 

-32.4 
(9.73) 

-15.6 
(7.70) 

+P = 0.002                  
effect size:2.39 

*P = 0.001                      
effect size:1.24 

+P = 0.003                 
effect size:2.26 

+P <0.001                  
effect size:5.35 

*P <0.001                
effect size:1.40 

 

Table 3: Frontal plane hip kinematics (mean (SD)) during swing phase for select strides for the middle 45 seconds of the three-minute self-
selected running speed trial for each subject for each knee condition. Bold values denote statistically significant single-subject differences (0.05 
level) between knee conditions. + Denotes a two-tailed paired t-test was conducted (normally distributed data). * Denotes the Wilcoxon signed-
rank test was conducted (non-normally distributed data).UK = Unlocked knee, LK = Locked Knee 
 

Locked Knee Condition 

 
Subject 1 Subject 2 Subject 3 Subject 4 Subject 5 Group Mean (SD) 

UK LK UK LK UK LK UK LK UK LK UK LK 

RE 
(mLO2/kg/

m) 
0.301 0.348 0.290 0.286 0.266 0.305 0.332 0.430 0.223 0.270 

0.282 
(0.037) 

0.328 
(0.057) 

 

Table 4: Running economy during the three-minute SSRS trials; normalization is exclusive of prosthesis mass. 

https://doi.org/10.33137/cpoj.v3i2.34481


 

7 

Blakeley N., Silver-Thorn B., Cross J.A. Investigation of the effects of prosthetic knee condition for individuals with transfemoral amputation during attempted 
running. Canadian Prosthetics & Orthotics Journal. 2020; Volume 3, Issue 2, No.3. https://doi.org/10.33137/cpoj.v3i2.34481 

ISSN: 2561-987X EFFECTS OF PROSTHETIC KNEE CONDITION DURING ATTEMPTED RUNNING 
Blakeley et al. 2020 

 
CPOJ 

 

Energy Efficiency 

A trend was found for differences in RE between knee 

conditions, regardless of whether prosthesis mass was 

included or excluded in the normalization. Mean RE values 

were reduced for the UK condition for the RE calculated 

exclusive of prosthesis mass (Table 4, see Nelson17 for RE 

normalized inclusive of prosthesis mass). 

Running Speed 

SSRS ranged from 0.890 to 1.79 m/s (mean SSRS: 

UK=1.47(SD=0.260) m/s, LK=1.32 (SD=0.246) m/s). All five 

subjects exhibited faster SSRS for the UK condition  

(Table 5). Peak running speed ranged from 2.15 to 3.30 m/s 

(average peak speed: UK=2.72 (SD=0.450) m/s, LK=2.61 

(SD=0.320) m/s). 

DISCUSSION  

Research regarding the effect of knee condition on lower 

extremity kinematics for individuals with unilateral TFA is 

limited; the observed kinematic data cannot be contrasted 

with the literature. For novice runners with unilateral TFA, 

LK running can be characterized by reduced peak hip 

flexion of the prosthetic limb and increased hip abduction 

during swing (Table 2, Table 3). The more extended and 

abducted prosthetic hip during swing is likely attributed to 

circumduction of the prosthetic limb to provide floor 

clearance. In contrast to the UK condition for which knee 

flexion assists with floor clearance in the sagittal plane, LK 

running requires both sagittal and frontal plane hip motion 

to provide clearance. Future work might include an analysis 

of the bilateral knee kinematics to provide more insight into 

how foot clearance is accomplished. 

Although swing phase pelvic kinematic data were not 

presented, it was collected and can assist in the 

interpretation of the hip kinematic data. The pelvis was 

typically tilted anteriorly during running in the LK condition. 

For subjects 3-5, this may be attributed to their leaning on 

the handrails for support. Pelvic motion in the frontal plane 

was variable: subjects 1-3 exhibited ipsilateral tilt (pelvis 

tilted downwards on the prosthetic limb side) during LK 

running and subjects 4 and 5 exhibited contralateral tilt 

(pelvis tilted upwards on the prosthetic limb side) during LK 

running. All subjects exhibited external pelvic rotation 

(rotated away from center of body) on the prosthetic limb 

side. Specifically, subject 5 demonstrated approximately 

17° of external pelvic rotation compared to 3°-11° external 

pelvic rotation for subjects 1-4.  

Although all subjects exhibited a decrease in peak swing 

phase hip flexion during LK running, this difference was 

relatively small for subjects 3 and 5 (2-3°) relative to the 

other subjects (13-18°). During LK running, hip abduction of 

the prosthetic limb increased during the swing phase by 3° 

to 11° for subjects 1 and 4, potentially due to the 

circumduction of the prosthetic limb for floor clearance 

during LK running. It should be noted that because the hip 

angle was defined as the thigh relative to the pelvis, an 

increase in hip abduction may be attributed, at least in part, 

to upwards pelvic obliquity. Subject 5 did not exhibit an 

increase in swing phase hip abduction with the LK condition 

potentially due to adopting a different strategy to clear the 

prosthetic limb as he was one of the least experienced 

runners with an RSP. The unanticipated decrease in hip 

abduction with the LK condition may have been 

inadvertently masked by defining the hip angle as the thigh 

relative to pelvis. For example, if the trunk and pelvis were 

leaning away from the swing limb to aid foot clearance, no 

increased hip abduction would be observed. The 

anticipated increase in prosthetic limb hip flexion during 

swing was not observed, nor was the anticipated reduced 

hip abduction during swing observed with the UK condition. 

The UK condition resulted in better symmetry in peak hip 

flexion (maximum hip angle) for four subjects (1-4) as 

indicated by the reduced IA magnitude compared to the LK 

condition (Table 2).  

In the frontal plane, IA differed significantly on a single-

subject basis between knee conditions for peak hip 

abduction (minimum hip angle) during swing phase for all 

subjects. Three subjects (1, 2, 4) demonstrated improved 

symmetry during UK running. In contrast, subjects 3 and 5 

exhibited improved frontal plane hip symmetry during swing 

for the LK condition. The anticipated reduced hip IA in the 

frontal and sagittal planes when running in the UK condition 

was therefore not observed. A possible explanation for this 

unanticipated result is that subjects 3 and 5 adopted an 

altered circumduction pattern. For subjects 1, 2, and 4, 

prosthetic limb hip flexion occurred approximately 13-22% 

stride cycle later than hip abduction. Subjects 3 and 5, 

however, initiated hip flexion and abduction simultaneously. 

 
Subject 1 Subject 2 Subject 3 Subject 4 Subject 5 Group Mean (SD) 

UK LK UK LK UK LK UK LK UK LK UK LK 

SSRS 
(m/s) 

1.34 1.29 1.43 1.34 1.79 1.48 1.07 0.890 1.70 1.61 
1.47 

(0.260)  
1.32 

(0.246) 

Peak 
Speed 
(m/s) 

2.24 2.32 2.86 2.86 3.30 2.95 2.15 2.15 3.04 2.77 
2.72 

(0.450) 
2.61 

(0.320) 

 

Table 5: SSRS and peak speed (maximum value of three trials) for each knee condition. 

https://doi.org/10.33137/cpoj.v3i2.34481


 

8 

Blakeley N., Silver-Thorn B., Cross J.A. Investigation of the effects of prosthetic knee condition for individuals with transfemoral amputation during attempted 
running. Canadian Prosthetics & Orthotics Journal. 2020; Volume 3, Issue 2, No.3. https://doi.org/10.33137/cpoj.v3i2.34481 

ISSN: 2561-987X EFFECTS OF PROSTHETIC KNEE CONDITION DURING ATTEMPTED RUNNING 
Blakeley et al. 2020 

 
CPOJ 

 
For subject 3, this manifested as increased hip flexion and 

reduced hip abduction during circumduction, leading to a 

narrower circumduction path. This may be due to his 

experience with UK running (Table 1) leading to a habit of 

pulling the prosthetic limb directly underneath his body, as 

opposed to circumduction. In contrast, subject 5 externally 

rotated his pelvis on the prosthetic limb side just prior to toe-

off which may have facilitated the simultaneous hip flexion 

and abduction. This may be a technique to achieve 

circumduction with decreased hip abductor muscle activity 

on the intact limb.   

It is important to note that the socket design was kept 

consistent between knee conditions for each subject; 

therefore, the socket design did not influence results on an 

individual subject basis, but it may have influenced results 

between subjects. Additionally, the length of the prosthesis 

was not adjusted when switching between knee conditions. 

A prosthetist may elect to shorten the prosthesis when 

leaving the knee locked to assist in limb clearance during 

swing phase. Thus, the observed increased hip abduction 

during LK running may be attributed in part to overall 

prosthesis length.  

While not statistically significant, a trend was found for 

grouped-subject differences also observed in RE (Table 4) 

across subjects. Mean RE values were improved for the UK 

condition, indicating that for this population of novice 

runners with TFA, running with an UK was more efficient 

than running with a LK, as expected. These results are 

consistent with Highsmith et al.2 who observed reduced 

mean oxygen consumption for the UK condition for five of 

eight running speed stages (1.12- 2.01 m/s). The decreased 

energy efficiency observed for the LK condition is likely 

attributed to the pathologic prosthetic limb circumduction 

strategy adopted to provide floor clearance. The improved 

RE with the three-minute running trial also supports the UK 

condition preference for distance running for all five 

subjects.  

Finally, for the novice runners with unilateral TFA in this 

study, the average peak running speed was faster for the 

UK condition (unlocked: 2.72 ± 0.450 m/s, locked: 2.61 ± 

0.320 m/s). Contrary to initial expectations, only two 

subjects (3 and 5) ran faster in the UK condition. The results 

were consistent with Highsmith et al.2 who also observed no 

significant difference in peak running speed with knee 

condition for runners with unilateral TFA. These findings, 

however, contradict Wening and Stockwell3 who reported 

faster speeds for the no-knee condition. Neither study, 

however, included statistical analyses as the investigations 

included just two and one subject, respectively. These 

previous studies tested experienced runners with unilateral 

TFA for a much longer duration (10-17 minutes2,3 versus 30-

60 seconds). Their protocols therefore measured peak 

endurance speed rather than sprinting capacity.  

Similarly, the mean SSRS for the UK (1.47 (SD=0.260) m/s) 

was faster than for the LK condition (1.32 (SD= 0.240) m/s). 

The faster SSRS for the UK condition may indicate the UK 

is advantageous for treadmill running, provided that the 

subject has the endurance and cognitive focus to prevent 

knee buckling. In contrast, Highsmith et al. did not find 

significant differences in SSRS between knee conditions.   

Limitations 

A primary limitation of this study was the small sample size. 

Post hoc power analysis indicated the power associated 

with the peak speed parameter was only 16.8%. Given the 

lack of statistically significant differences in peak speed with 

knee condition, variations in test methodology between the 

current study and previous studies, definitive conclusions 

regarding which knee condition facilitates increased speed 

cannot be stated.  

Another limitation is the small magnitude of observed 

differences in hip kinematics between knee conditions. 

While these differences were statistically significant, they 

are likely not clinically relevant. A 2°-3° difference in peak 

hip flexion (subject 5) and peak hip abduction (subjects 3 

and 5) between knee conditions may have been 

imperceptible to the subject.   

Similarly, the relatively short duration (three minutes) of the 

SSRS trials likely limits the potential clinical and/or real-

world relevance of the study findings. While the differences 

in SSRS were modest, such differences may be relevant if 

sustained during increased duration running trials.  

Lastly, subject 1 was the sole participant who actually “ran”, 

exhibiting periods during which both feet were airborne 

simultaneously. The ambulation of the remaining subjects 

might be more accurately described as a “fast walk”, with a 

few cycles of true running interspersed. Future protocols 

might incorporate more extensive training for both knee 

conditions, prior to data collection, to more effectively 

assess subjects’ true running performance. Additionally, a 

second test session to determine repeatability of the novice 

runners’ performance would have been ideal; however, time 

constraints did not permit this. 

Clinical Recommendations: Running with a LK increases 

stability of the prosthesis, decreasing fall risk and cognitive 

load3; these factors are likely important during running for 

prolonged periods and longer distances. For recreational, 

short distance running on a treadmill, the results of this 

study suggest that the UK condition may be advantageous 

for novice runners with unilateral TFA. The LK condition 

resulted in decreased energy efficiency and a slower SSRS. 

The UK condition may also decrease risk of 

musculoskeletal injury, as this knee condition resulted in 

minimal gait pathologies. The LK condition required 

circumduction for floor clearance, a gait pathology that 

https://doi.org/10.33137/cpoj.v3i2.34481


 

9 

Blakeley N., Silver-Thorn B., Cross J.A. Investigation of the effects of prosthetic knee condition for individuals with transfemoral amputation during attempted 
running. Canadian Prosthetics & Orthotics Journal. 2020; Volume 3, Issue 2, No.3. https://doi.org/10.33137/cpoj.v3i2.34481 

ISSN: 2561-987X EFFECTS OF PROSTHETIC KNEE CONDITION DURING ATTEMPTED RUNNING 
Blakeley et al. 2020 

 
CPOJ 

 
impacts hip kinematics in multiple planes and may also 

affect pelvic and trunk motion. 

CONCLUSION 

Hip flexion decreased for all subjects and hip abduction 

increased for four subjects during swing when individuals 

with unilateral TFA ran with a LK due to compensatory 

circumduction to assist with foot clearance. This 

circumduction increased IA during swing for the peak hip 

flexion and peak hip abduction measures and may 

contribute to the decreased energy efficiency observed 

during LK running. Based on these results and the relatively 

short running duration in this study, the UK condition is 

recommended for novice runners with unilateral TFA when 

running short distances on a treadmill. 

ACKNOWLEDGEMENTS 

The authors would like to thank Ottobock, Duderstadt, Germany for 

providing the running specific prostheses for this study. The authors 

would also like to thank David Del Toro, MD for his assistance with 

study concept and subject recruitment, Paula Papanek, Ph.D. and 

Toni Uhrich, MS for assistance with energy cost methodology and 

analysis, and Molly Erickson, Scott Crawford, and Courtney Jack 

for their assistance with subject testing and data analysis. The 

authors would also like to thank collaborating prosthetists (Herb 

Bohn, CP, John Mooney, CPO, Tom Current, CPO, Joshua Dezek, 

CP, and Dennis Farrell, CP) for their active involvement in subject 

recruitment and prosthetic fitting. Lastly, the authors would like to 

acknowledge Laurens Holmes, MD, Ph.D, and Rebekah Walker, 

Ph.D for their expertise regarding statistical analysis. 

DECLARATION OF CONFLICTING 

INTERESTS 

The authors declare that there is no conflict of interest. 

AUTHOR CONTRIBUTION 

Natalie Blakeley: designed the study, acquired the data, analyzed 

the data, interpreted the data, and drafted the manuscript. 

Barbara Silver-Thorn: designed the study, interpreted the data, 

and revised the manuscript. 

Janelle A. Cross: assisted in the design of the study, interpreted 

the data, and revised the manuscript. 

SOURCES OF SUPPORT 

Clinical and Translational Science Institute Pilot Translational and 

Clinical Studies Program Start-up Project Award. This award is 

supported by grant UL1TR001436 from the Clinical and 

Translational Science Award (CTSA) program of the National 

Center for Research Resources and the National Center for 

Advancing Translational Sciences. 

ETHICAL APPROVAL 

The study protocol was approved by the affiliated Institutional 

Review Board (approval number HR-3249) and written informed 

consent was solicited and obtained for each subject prior to study 

participation. 

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Blakeley N., Silver-Thorn B., Cross J.A. Investigation of the effects of prosthetic knee condition for individuals with transfemoral amputation during attempted 
running. Canadian Prosthetics & Orthotics Journal. 2020; Volume 3, Issue 2, No.3. https://doi.org/10.33137/cpoj.v3i2.34481 

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