Running mechanics in amputee runners using ...

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Running mechanics in amputee runners using running-specific prostheses Hiroaki Hobara1,2), Brian S Baum2), Hyun Joon Kwon2), Jae Kun Shim2)

As described above, the recent technical developments

1. Introduction

of running-specific carbon-fiber prostheses with energy storing capabilities have allowed individuals with lower

International debates were fueled when a South

extremity amputation (ILEA) to compete at levels

African double amputee sprinter took part in the 2011

never before achieved. Additionally, running-specific

World Championships and 2012 Olympics in London. In

prostheses (RSPs) have attracted more and more ILEA

July 2011, he ran the 400-meter race in 45.07 seconds

to running as a form of exercise and athletic competition.

in Lignano, Italy, passing the qualifying standard that

Development of improved rehabilitation techniques

allowed him to represent South Africa alongside the best

and prosthesis designs to promote running within this

able-bodied athletes at the 2011 World Championships in

population requires a detailed understanding of ILEA

August 2011. At the 2012 Summer Olympics, the double

running biomechanics and the biomechanical function

amputee sprinter became the first amputee runner to

of prostheses during this activity. However, due to

compete at an Olympic Games. In the 400-meter sprint

the lack of running studies in ILEA and the dearth of

race, he advanced to the semifinals by taking second

information on RSPs, quantification of biomechanical

place in the first heat of five runners (45.44 seconds). He

parameters during ILEA running using the RSPs is

ran in the second semifinal where he finished eighth with

scarce. Furthermore, the advent of RSPs raised a debate

a time of 46.54 seconds. He did not advance to the final,

in the scientific community regarding whether the

but his performance surprised many people.

RSPs provide potential advantages or disadvantages

The double amputee sprinter also took part in the

for ILEA as compared with able-bodied counterparts in

2012 Summer Paralympics, where he entered the men’s

running (Adamczyk PG, 2010; Brüggemann et al., 2008;

100-meter, 200-meter and 400-meter races in the T44

Brüggemann, 2009; Buckley and Juniper, 2010; Cavagna,

classification, along with the T42–T46 4 × 100-meter

2010; Chockalingam et al., 2011; Fuss, 2008; Kram et

relay. He won gold medals in the men’s 400-meter race

al., 2010a,b; Morin, 2010; Weyand and Bundle, 2010a,b;

in a Paralympic record time of 46.68 seconds and in

Weyand et al., 2009; Zelik, 2010).

the 4 × 100-meter relay in a world record time of 41.78

In this article, we review previous literature regarding

seconds. He also received a silver medal in the 200-meter

running mechanics in ILEA using RSPs and discuss the

race, while setting a world record of 21.30 seconds in the

role of technology. This paper consists of four parts:

semifinal.

Introduction, History, Mechanics, and Injury. In the second part, we briefly review the history of RSPs. In the

HOBARA Hiroaki, BAUM Brian S, KWON Hyun Joon and SHIM Jae Kun 1) Research Fellow of the Japan Society for the Promotion of Science, Tokyo, Japan 2） Department of Kinesiology, University of Maryland, College Park, MD, US

third part, we examine the debate regarding advantages and disadvantages of RSPs while reviewing previous literature and our own data. After a discussion on the relationship between using RSPs and injury risk in the fourth part, we summarize this article with several 1

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suggestions for future studies.

Flex-Sprint I (Figure 2-C; Össur, Reykjavik, Iceland), was developed by eliminating the heel portion and altering

2. History of running-specific prostheses

the stiffness configuration with the lay-up sequence of the carbon while still maintaining the J-shaped outline of

After the invention of the SACH foot (Solid Ankle and

the carbon forefoot. As reviewed by Nolan (2008), there

Cushioned Heel; Ohio Willow Wood, Ohio, USA) in the

are now several different sprint foot designs available, all

late 1950s, prosthetic foot designs and materials changed

with a similar basic shape (Figure 2-A to M), which has

little for approximately 20-30 years (Nolan, 2008).

changed little since 1992.

According to Aruin (2000), the usefulness of lower-

According to Brüggemann et al. (2009), the

limb prostheses improved tremendously in the 1980s,

advent of carbon-fiber prostheses and RSPs shortened

when advances in composite materials flooded into the

approximately 1.5 seconds off the world record of

prosthetics industry. Carbon composite materials, used

100-meter races in the T44 class (transtibial amputees)

extensively in the aerospace industry, brought lightness,

within 10 years (from 1988 to 1998). One of the major

durability and strength to the design of prosthetic feet,

examples in this context is the Paralympic Games in

pylons and sockets (Aruin, 2000; Nolan, 2008; Scholz et

Atlanta, GA, in 1996. Tony Volpentest, an American

al., 2011). In 1984, Van Phillips, an American inventor of

Paralympian athlete, was born with short malformed

prostheses, created the “Flex-Foot ” (Figure 1) made of

legs and arms. When he initiated running using walking

carbon graphite. The innovative artificial foot allowed

prostheses, his personal record in the 100-meter race was

users to store and then return elastic energy during the

only 14.38 s (in 1989). Later, when provided with Flex-

ground contact phase of gait.

Foot prostheses, he won the gold medal at the Atlanta

®

The Flex-Foot was first seen in elite sport at the 1988

Paralympic Games in the men’s 100-meter race by setting

Paralympic Games (Pailler et al., 2004). Four years later, the prosthetic heel was absent for some athletes (Pailler et al., 2004) creating the first sprint prosthesis (Nolan et al., 2008). In fact, the first specialized running foot, the

Figure 1.  Flex-Foot (provided by Department of Prosthetics and Orthotics, Research Institute of National Rehabilitation Center for Persons with Disabilities, Tokorozawa, Japan). 2

Figure 2.  Typical examples of running-specific prostheses (A to F were adapted from from Lechlar and Lilja, 2008). A: Flex-Foot® (Modular III; Össur), B: Flex-Sprint II (Össur), C: Flex-Sprint I (Össur), D: Flex-Sprint III® (Cheetah; Össur), E: Flex-RunTM (Össur), F: Symes-Sprint (Össur), G: Cheetah Xtreme ® (Össur, https://www.ossur.com), H: Cheetah Xtend® (Össur, https://www.ossur.com), I: 1E90 (Sprinter, OttoBock, http://www.ottobockus.com), J: 1C2 (C-Sprint®, http://www.ottobockus.com), K: Nitro (Freedom Innovation, http://www.freedom-innovations.com), L: Catapult TM (Freedom Innovation, http://www.freedom-innovations. com), M: SP1100 (KATANA, IMASEN Engineering Corporation).

Running mechanics in amputee runners using running-specific prostheses

a world record with a time of 11.36 seconds. Furthermore,

3. Running mechanics using RSPs

he also took gold medal in the 200-meter race in the time of 23.28 seconds. As just described, the recent devices along with hard training now enable athletes with

As previously mentioned in the Introduction, the

amputations to run 100-meters in just under 11 seconds.

advent of the RSPs raised a debate in the scientific

The current world records in the 100-meter, 200-meter

community

and 400-meter sprints in T43 and T44 classes compared

advantages or disadvantages to ILEA during running

with the able-bodied world records are shown in Table 1.

compared to able-bodied runners. According to Weyand

For the last 15 years, technical advances in prostheses

et al. (2000 and 2010), top speed during constant-speed

have been a main factor in the increased performance

running is the product of step frequency, contact length

of athletes with lower-limb amputations. The use of

and the average mass-specific force applied to the

materials such as carbon fiber, titanium, and graphite has

running surface during the foot-ground contact period.

provided added strength and energy-storage capabilities

Therefore, Weyand and Bundle (2010a) advocated that

to prostheses while decreasing the weight of prosthetic

there were three mechanical variables which constrained

components (Webster et al., 2001). Today, the carbon

the speed of human runners: 1) how quickly the limbs

fiber prostheses are most popular in elite running and

can be repositioned for successive steps, 2) the forward

jumping events. These prostheses allow lower-limb

distance the body travels while the foot is in contact with

amputees to actively participate in sporting activities

the ground, and 3) how much force the limbs can apply

including competitive sports (Scholz et al., 2011).

to the ground in relation to the body’s weight. Weyand

whether

RSPs

can

provide

potential

and Bundle (2010a) also insisted that if one or more of

Table 1.  Current world records in the 100-meter, 200-meter and 400-meter sprints in able-bodied (AB), T43 and T44 classes (as of 4 March 2013). Data were adapted from the International Association of Athletics Federations (IAAF) website, http:// www.iaaf.org, and the International Paralympic Committee (IPC) website, http://www. paralympic.org/Home. Men’s 100 m

Women’s 100 m

Men’s 200 m

Women’s 200 m

Men’s 400 m

Women’s 400 m

Class Name AB Usain Bolt Oscar Pistorius T43 Blake Leeper T44 Jonnie Peacock AB Florence Griffith-Joyner T43 Marlou van Rhijn T44 April Holmes AB Usain Bolt T43 Oscar Pistorius T44 Arnu Fourie AB Florence Griffith-Joyner T43 Marlou van Rhijin T44 Marie-Amelie Le Fur AB Michael Johnson T43 Oscar Pistorius T44 David Prince AB Marita Koch T43 Shea Cowart T44 Marie-Amelie Le Fur

Country JAM RSA USA GBR USA NED USA JAM RSA RSA USA NED FRA USA RSA USA GRD USA FRA

Time 9.58 10.91 10.91 10.85 10.49 13.27 12.98 19.19 21.30 22.49 21.34 26.18 26.76 43.18 45.39 50.61 47.60 01:09.61 01:02.42

Date 2009/8/16 2007/4/4 2012/7/14 2012/7/1 1988/7/16 2012/9/1 2006/7/1 2009/8/20 2012/9/1 2012/9/2 1988/9/29 2012/9/6 2012/9/6 1999/8/26 2011/8/28 2012/9/8 1985/10/6 2001/8/10 2007/6/22

*T43: Double below knee anputeesand other athletes with impairments that are comparable to a double below knee amputation (definition ofIntemational Paralympic Committee). *T44: A ny athletewith al ower limb impairment/st hatmeets minimum disabilityc riteria for:l ower limb deficiency; impaired lower limb passive range of motion ;im paired lower limb muscle power; or leg length difference (definition of Intemational Paralympic Committee). 3

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these variables could be improved, running speeds would

Games. Although the low number of subjects may have

be enhanced. In this section, we review past findings

limited their statistical power, there were no significant

and present related research regarding the issue of

differences in the swing time among the runners.

advantages/disadvantages of using RSPs.

Furthermore, Grabowski et al. (2010) also found that

3.1  Stride frequency and swing time

added prosthesis mass (100 or 300 g) did not significantly change swing time during running at top speeds. From

Weyand et al., (2009) compared stride frequency and

these results, Grabowski et al. (2010) concluded that the

swing time during treadmill running between one double

low mass and inertia of RSPs did not facilitate unnaturally

transtibial amputee runner and four able-bodied runners.

fast leg swing times, and that fast leg swing times could

The authors found that the stride frequencies attained

result from learning and/or training. However, Grabowski

by the double amputee sprinter at top speed were 15.8%

et al. (2010)’s data using video recordings were based

and 9.3% greater than those of the able-bodied athletes

on 30-Hz television footage, which could have led to

and elite sprinters, respectively. Furthermore, Weyand

large measurement errors (Epstein, 2012; Morin, 2010).

et al., (2009) and Weyand and Bundle (2010a) showed

Therefore, caution should be taken when interpreting or

that the swing times in the double transtibial amputee

comparing the swing times obtained from this study.

runner at top speed were 21% and 17.4% shorter than those of able-bodied athletes and the first two finishers

3.2  Contact length

in the 100-meter dash at the 1987 World Track and Field

Contact length is defined as the forward distance the

Championships (Moravec et al., 1988), respectively.

body travels while the foot is in contact with the ground

Based on the results, Weyand and Bundle (2010a)

(Weyand et al., 2000; Weyand and Bundle, 2010a). Weyand

claimed that the extreme stride frequencies of the double

et al., (2009) compared contact length during treadmill

transtibial amputee runner were the direct result of how

running between one double-transtibial amputee runner

rapidly the double transtibial amputee runner was able to

and able-bodied runners. The authors found that the

reposition his limbs. It was also reported that RSPs were

contact length (normalized to leg length) of the double-

characterized as having lower mass and smaller moments

transtibial amputee runner was 9.6% greater than those

of inertia compared with intact human legs (Brüggemann

of the track athletes. Even when the contact length was

et al., 2008; Baum et al., In Press). These characteristics

normalized to body height, the contact length in the

might have allowed unnaturally fast leg swing times in

double-transtibial amputee runner was 16.2% greater

the double transtibial amputee runner using the RSPs.

than those of the elite able-bodied sprinters (Moravec

Grabowski et al. (2010) compared the step frequency

et al., 1988). Consequently, Weyand and Bundle (2010a)

and swing time between intact and prosthetic legs in

claimed that the greater contact lengths at top speed

six unilateral transtibial runners using a treadmill. The

would also be advantageous for speed.

authors found that the step frequency was 8% greater in

Grabowski et al. (2010) compared the contact length

the intact leg than the prosthetic leg at top speeds, but

between intact and prosthetic legs in six unilateral

the swing time was not significantly different between

transtibial runners using treadmill. The authors found

the intact and prosthetic legs at any speeds, including top

that the subjects in their study increased the contact

speeds. Grabowski et al. (2010) also used high definition

length at faster speeds for both the intact and prosthetic

digital video recordings of the 2008 Beijing Paralympic

leg, but there were no significant differences in the contact

Games men’s T43/T44 events to determine the swing

length between legs. Similar to the stride frequency and

time for the top five 100-meter and top two 200-meter

swing time described in the previous section, the results

competitors (one bilateral and five unilateral amputees).

for contact length are also inconclusive. However, one

Next, they analyzed video from the 2008 Beijing Olympics

should pay careful attention to the fact that these studies

(in the men’s 100-meter final) to determine the swing

examined different amputation types (e.g. bilateral or

time for top three finishers, and compared their swing

unilateral amputee runners).

time with those of amputee runners in the Paralympic 4

Running mechanics in amputee runners using running-specific prostheses

3.3  Ground reaction force

lower for prosthetic legs in ILEA compared with control legs in able-bodied runners. Our group also compared the

Vertical ground reaction force (vGRF) is an important

peak vGRF of the intact and prosthetic legs of ILEA and

factor for determining top running speed (Weyand et

the control legs of able-bodied persons during overground

al., 2000); however, a very limited number of published

running at 2.5 to 3.5 m/s (Figure 3; Baum et al., 2012).

studies are available in the literature investigating vGRF

We found that intact limb peak vGRFs were greater than

while using RSPs. Brüggemann et al. (2008) compared

prosthetic and control limbs. Taken together, the results

the vGRF between one double-transtibial athlete and

of these studies commonly show that the RSP limits

five able-bodied sprinters in maximal overground sprint

vGRF production during running in a range of running

running (achieved running velocities between 9.2 and 9.5

speeds (including maximal sprinting). As suggested

m/s). They found that the vGRF was significantly higher

by Grabowski et al. (2010), the RSP would impair force

in the able-bodied athletes than in the double amputee

generation and thus likely limit top speeds.

sprinter. Weyand et al. (2009) also investigated vGRF

For other GRF components such as braking and

in one double-transtibial athlete and five able-bodied

propulsive forces, only three publications are currently

runners using a customized high-speed treadmill at 3.0

available. Brüggemann et al. (2008) compared the

to 10.0 m/s. The authors also demonstrated that the vGRF

anterior-posterior GRF (AP-GRF) between one double-

was significantly higher in the able-bodied runners than

transtibial athlete and five able-bodied sprinters in

in the double amputee sprinter. Further, Grabowski et al.

maximal overground sprint running. They found that

(2010) compared vGRF between intact and prosthetic legs

the braking force and impulse was significantly higher

in six unilateral transtibial runners using a treadmill. The

in the able-bodied athletes than in the double amputee

results showed that the average vGRF was approximately

sprinter. Further, Weyand et al. (2009) reported that

9% lower in the prosthetic leg compared with the intact

horizontal impulses and peak forces were substantially

leg across a range of speeds including the top speed.

lower for one double-transtibial athlete compared to able-

Recently, McGowan et al. (2012) reported comprehensive

bodied subjects at every speed. Recently, Baum (2012)

data for the vGRF during treadmill running in able-

demonstrated that peak AP-GRFs in the prosthetic limbs

bodied runners and unilateral and bilateral transtibial

of eight unilateral transtibial subjects were significantly

amputees. At 9.5 m/s, peak vGRF was on average 18%

lower than in intact limbs and control subject limbs across

Figure 3.  Upper panel: schematic representation of one amputee subject during the contact, aerial, and swing phases of a stride while running. Stance and swing time (Tstance and Tswing) is indicated by band area. Lower panel: vertical ground reaction force (vGRF) in prosthetic and intact leg. As highlighted by two dotted lines, the intact limb peak vGRFs (normalized to body weight; BW) were greater than prosthetic and control limbs. 5

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a range of running speeds (from 2.5 to 3.5 m/s). Therefore,

abnormal lower extremity loading during running with

similar to vGRF, RSP use seems to be associated with

RSPs may put ILEA at increased risk for physical injuries

decreased abilities to produce AP-GRFs when compared

and degenerative joint diseases (Buckwalter and Lane,

to able-bodied runners.

1997; Buckwalter and Brown, 2004; Fink-Bennett and Benson, 1984; Lehmann et al., 1993), little is known about

4. RSPs and Injury

loading rate in ILEA during running using RSPs. To investigate loading rates of the vertical ground

The development of carbon fiber RSPs has allowed

reaction force in ILEA runners using RSPs, we instructed

ILEA to regain the functional capability of running

eight ILEA with unilateral transtibial amputations and

(Nolan, 2008), which is one of the most difficult everyday

eight control subjects to perform overground running

motor tasks for ILEA (Kegal et al., 1978). In spite of this

at three speeds (2.5, 3.0, and 3.5 m/s). Each ILEA used

positive trait, RSPs have not been thoroughly evaluated

their own RSP. From vGRF, we measured vertical average

regarding potential injury risks due to the abnormal

loading rates, defined as the change in force divided by

loading during running, specifically in unilateral

the time of the interval between 20 and 80% of the first

amputees.

impact peak (Figure 4-A and B). We found that loading

Current RSPs are made from carbon fiber, a material

rate in both ILEA and control limbs increased with

known to generate high-frequency vibrations when

running speed (Figure 5). Further, the loading rate in

used (Lehmann et al., 1993). According to previous

ILEA’s intact limbs was 45% and 30% greater than their

studies, high impact forces of short duration associated

prosthetic limbs and control limbs, respectively (Figure

with running can result in a reticence to participate

5). In 2008, Brüggemann et al. (2008) investigated

in exercise due to skin discomfort and possible pain in

the loading rate during maximal sprinting in both one

the residual limb-socket interface (Dudek et al., 2005;

double transtibial amputee using RSP and five able-

Pitkin, 1997; Waetjen et al., 2012). Furthermore, lower

bodied sprinters. They found that the average loading

extremity injuries are more common in amputee athletes

rate (the linear gradient to the maximum vGRF) was

and typically occur during running activities (Ferrara

significantly higher in the able-bodied athletes than in

and Peterson, 2000). Specifically, the most common

a bilateral amputee sprinter (Brüggemann et al., 2008).

musculoskeletal injuries among amputee athletes are

The differences in the results between our study and the

tibial stress fractures, sprains and strains to the lumbar

previous study may be explained by the differences in

spine and sacroiliac joint in the intact side (Feldman et

running speeds (submaximal vs. maximal), computation

al., 2010; Laboute et al., 2008). Although these injuries are thought to mainly be attributed to the mechanical stress of the ground reaction forces during running (Aruin 2000; Feldman et al., 2010), evidence regarding the abnormal loading in ILEA during running has not been reported. It has been shown that abnormal lower extremity loading may be evaluated by vertical average loading rate (VALR) using vertical ground reaction force (vGRF). The VALR is an indication of how fast vGRF rises to its first peak at early stance phase (Zadpoor and Nikooyan, 2011). Indeed, greater loading rates are often considered as the cause of overuse running injuries such as tibial stress fractures in able-bodied runners (Davis et al., 2004; Milner et al., 2006; Pohl et al., 2008; Zadpoor and Nikooyan, 2011; Zifchock et al., 2006). Although the 6

Figure 4.  Vertical ground reaction force (vGRF) during the stance phase, recorded from the prosthetic (A) and intact limb (B) of a single ILEA at 2.5 m/s. Vertical average loading rate (VALR) was determined at early stance phase between 20% and 80% before the first GRF peak. When no distinct impact peak existed, the loading rate was measured at the same percentage of stance as determined for each condition in the trials with an impact transient (Lieberman et al., 2010).

Running mechanics in amputee runners using running-specific prostheses

For example, despite the fact that running on curvature is one of the challenging tasks for amputee runners using RSPs (Lechler and Lilja, 2008), little is known about medio-lateral GRF data during curve running in this population. Furthermore, running mechanics using RSPs may depend on several factors, such as design and category of stiffness (Lechler and Lilja, 2008; Nolan, 2008; Wilson et al., 2009), inertial properties (Baum et al., In Press; Brüggemann et al., 2008), length (Wilson et al., 2009), alignment (Tominaga et al., 2012; Webster et al., 2001), and any combinations Figure 5.  Vertical average loading rates (VALR) for the prosthetic (white) and intact limbs (gray) of ILEA as well as for the limbs of the control group (black) at three running speeds, 2.5m/s, 3.0m/s, and 3.5ms. An asterisk (*) indicates statistically significant differences between limbs at p