Thursday, December 29, 2011

Rb @Jeffie: "Rb @scotlandlover: Sugarloaf - "Green-Eyed Lady"" ♫
RB @Jeffie: "The Beach Boys – "When I Grow Up (To Be A Man)"" ♫
listening to "Count On Me - Bruno Mars - Lyrics" ♫

Tuesday, October 11, 2011

listening to "Amy Winehouse - Cupid (Live)" ♫

Thursday, March 17, 2011

listening to "Macy Gray - I Try" ♫
listening to "Gracedigger - Irregular" ♫

Tuesday, March 15, 2011

I was a ghost before you came.... ♫

Exercise for Amputees

Welcome to my blog,

I have started this blog in order to let the world know the importance of exercise to amputees.

As an amputee myself since 1985, I have a fairly good understanding of the way that general fitness and body strength affects mobility for amputees.

From something as simple as a weight change, that completely changes the fit of the prosthetic limb to not having strength to support myself on down hill slopes.

To get an understanding of my inside knowledge, I will explain a little about my life and what inspired me to share my story with you.

In 1985 I was in a car crash in which I was the guy on the motorbike, as a result I lost my right leg 7 inches below the knee.

Complications developed within 12 months. Growth of bone spurs, had occurred, causing significant pain and eventually needing surgery.

On closer exploration a large cyst was discovered and removed.The following year, still unable to walk the bone spurs were removed.

I spent almost 6 years in some state of incapacity and most of it on crutches.

I went this whole time without any fixed rehabilitation or Exercise programme implemented. (This sort of thing doesn't happen as much these days)

This meant when I came to walk with my new prosthesis, my residual limb was so weak that i was suffering from muscle fatigue and would regularly trip and stumble.(I really needed some sort of muscle building exercise)

The best I was offered was a piece of elastic band off a large roll. The problem with this was my now short stump would not allow for this giant rubber band to be attached to me in an effective way.

Finding there was no Amputee Exercise Equipment available to me but wanting to get fit, I started research, Learning about what was happening to me and looking for methods of overcoming it.

This lead to the conducting of Literature Reviews, the design of several Amputee Specific Exercise Machines and clinical trials, finally in 2002"Hydraujoint(TM) Ltd" was founded.

Hydraujoint(TM)Ltd is a company that was set up specifically to research, develop and test exercise equipment specifically for amputees.

I will be sharing my findings over the next few weeks and look forward to your feedback.

If you have any literature you would like to submit on the topic, I would love to read it and share it.

Below is the first Literature Review I organised through Massey University with the assistance of Vision Manawatu and Prof Alan Warmsley

A copy of the first literature review is below.

IF you have any literature you would like to add to this subject or if you would just like to make a comment please do so at the bottom of the page.

Exercise for Trans-tibial Amputees.


In late 2002, Stephen Kemp, Managing Director of Hydraujoint Ltd, himself a trans-tibial amputee, approached John Henley-King of Massey University Research Services about the possibility of obtaining some assistance with the design and prototyping of an exercise device to improve muscle strength and functional capacity of amputees.

The device is intended to be used by amputees in their own home in an unsupervised setting, and so must be inherently safe and easy to use.

As a first step in this process, this literature review has been compiled to provide a basis for design and development.

The review will address the issues of the relationship between muscle strength and functional capacity in trans-tibial amputees, and will touch briefly on the incidence and control of phantom pain.

Literature review

Reduction in thigh muscle strength in trans-tibial amputees has been shown to be highly correlated with muscle atrophy and reduction in clinical function (Renstorm, Grimby, & Larsson, 1983).

In this study,thirty-two trans-tibial amputees participated in examinations of the isometric and isokinetic knee extension and flexion strength, and a degree of atrophy of the thigh muscles were measured in trans-tibial amputees.

The muscle strength in the amputated leg with and without prosthesis was significantly lower than the strength of the non amputated leg.

Knee extension strength was correlated to the mean muscle fibre area of the vastus lateralis, but there was no correlation between strength and the cross sectional area of the quadriceps muscles.

The reduction in knee extension and flexion strength in the amputated leg both with and without prosthesis compared with the non amputated leg was larger than the reduction in cross sectional areas of the quadriceps and hamstring muscles, which could indicate that other factors such as changes in motor unit recruitment patterns are important in the reduction of muscle strength.

Isometric and isokinetic knee extension and flexion strength values in the amputated leg with prosthesis were significantly correlated to step length, maximal walking speed and circumference of thigh.

Because step length is a major determinant of walking speed and efficiency, this result indicates that trans-tibial amputees with improved thigh muscle strength will have better walking capacity.

Muscle strength has been shown to be an important factor in fall prevention in the elderly.

Hurley and Roth (Hurley & Roth, 2000) indicate that strength training in the elderly, among other things:

1. produces substantial increases in the strength, mass, power and quality of skelatal muscle;

2. can increase endurance performance;

3. normalises blood pressure in those with high normal values;

4. reduces insulin resistance;

5. decreases both total and intra-abdominal fat;

6. reduces risk factors for falls; and

7. may reduce pain and improve function in those with osteoarthritis in the knee region.

In recent studies in New Zealand (Campbell,Borrie, & Spiers, 1989) it has been shown that a low intensity, community based exercise program including strength training reduces the risk of falling in adults.

The incidence and fear of falling is pervasive among amputees, and Miller and co-workers (Miller, Deathe, Speechley, & Koval, 2001; Miller, Speechley, & Deathe, 2001) showed that balance confidence was a major protective factor.

Thigh muscle strength is a major determinant of balance confidence, and so improvement of thigh muscle strength in amputees would be expected to improve balance, and so reduce the incidents of falls.

The gait of the trans-tibial amputees is significantly different from that of non-amputees, in particular, stride length is lower, and preferred walking speed is slower.

These differences have been shown to resemble the effect of additional load on the ankle of a normal walker (Eke-Okoro, 1999).

That is, the knee flexor and extensor muscles must exert larger forces in the amputee to compensate for the lack of ankle torques.

There is some rather inconsistent evidence that a slightly increased moment of inertia reduces the work required by the knee extensors during late swing phase of gait (Hillery & Wallace, 2000).

In normal walking, the gait on left and right sides is highly symmetrical.

This symmetry is not observed in amputees. In general, step length, step time and swing time are significantly longer on the amputated side, while stance time and single support time are significantly shorter on the amputated side (Isakov, Keren, & Benjuya, 2000).

Isakov et al also found large differences in muscle timing and relative activation between the sound and amputated limbs which they attributed to the prosthetic foot impeding forward motion in early swing phase and the need to support the knee on the amputated side in early stance (Isakov, Burger, Krajnik, Gregoric, & Marincek, 2001).

The absence of ankle plantar-flexion muscles has been considered a major disability in amputee gait because these are the major producers of forward propulsion.

The amputee overcomes this problem by using other muscles or changing the characteristics of gait (Michel & Do, 2002).

One of the strategies most often observed to achieve this is “Hip-hiking” (increasing the angle of the pelvis in the frontal plane during swing phase). This strategy has quite serious consequences for walking duration because it rapidly fatigues the hip abductor muscles.

It has been shown that those amputees with strong hip abductor muscles display increased weight bearing on the amputated limb, improved gait parameters, and reduced medio-lateral excursion of the centre of pressure under the amputated limb (Nadollek, Brauer, & Isles, (2002). Nadollek at al conclude that:

This research confirms the asymmetrical nature of amputee stance and demonstrates symmetry of strength and gait measures between limbs. The correlations between hip and abductor strength, weight distribution and gait measures illustrates the importance of training these muscles.

It is generally accepted that the energy cost of walking with a lower-limb prosthesis is higher than that of normal walking, and that the extra energy required may be reduced by appropriate physical conditioning (Ward & Meyers, 1995).

Endurance has been shown to be effective in increasing VO2max, anaerobic threshold, and maximum workload for amputees, to a point where there is no significant difference from normal control subjects.

An appropriate programme based on individual anaerobic threshold has been shown to be effective in this respect (Chin et al., 2001). Because the metabolic cost of walking is high for amputees, and they are generally less fit than normal control subjects, amputee walking endurance is much lower than that of a non-amputee.

Walking endurance is a useful measure of functional capacity in lower-limb amputees, and is often measured usin the two-minute walk test.

This is a simple test that measures the total distance walked in two minutes at a self-selected pace, and been proven reliable and sensitive to the effects of rehabilitation and physical training (Brooks et al., 2002; Brooks, Parsons, Hunter, Delvin, & Walker, 2001)

Strength training of the knee muscles in trans-tibial amutees at several fixed angular speeds has demonstrated increases in both size of knee extensor and flexor muscles and their ability to produce force (Klingenstierna, Renstorm, Grimby, & Morelli, 1990).

In this study, the intact leg was also trained, but did not demonstrate the magnetude of chabges found in the amputated limb.

The subjects reported that they could walk more than twice the distance achieved before training and could manage better without mobility aids.

The study also indicated a larger increase in the size and strength of type II (fast twitch, anaerobic) fibres compared with type I fibres, which indicates that the training forces were sufficient to activate almost all the motor units in the muscle.

In a similar study, Moirenfield et al (Moirenfield, Ayalon, Ben-Sira, & Isakov, 2000) measured concentric strength and endurance of the thigh muscles using an isokinetic dynamometer.

They found that peak tourque for extension and flexion was significantly higher in the sound limb, and that the fatigue index for flexion torque was significantly higher in the sound limb(p<0.01)>They concluded that:

It is of great importance to reduce the bilateral deficit and the degree of atrophy as soon as possible in order to improve the level of performance.

By choosing a correct strength and endurance training programme, one may expect to get a significant and good reaction from the muscles of the amputated limb as is expected from training the muscles of a sound limb.

Many exercise regimes and training programmes have been found helpful in the process of rehabilitation of amputees and reintegration to the workforce.

These may be divided into four main components: flexibility, muscle strength, cardiovascular training, and balance gait (Esquenazi & DiGiacomo, 2001).

Kegal at al (Kegal, Burgess, Starr, & Daly, 1981) showed that the use of biofeedback in a controlled isometric exercise program produced increase in muscle bulk below the knee.

Isokentic (constant speed) exercise has been shown to be effective in increasing strength of debilitated muscles.

However, this is usually achieved using specific, and usually very expensive, isokinetic dynamometer that was designed for use by non-amputees.

Consequently, amputees find this device difficult to us, even if they are able to gain access to one. Modifications to an isokinetic dynamometer to allow use by trans-tibial amputees with short stumps were described by Marin and co-workers (Marin, Spellman, Kenyon, & Belandres, 1992) and it appears that most practitioners would consider modification of existing exercise equipment as a first step in achieving an appropriate exercise regime for trans-tibial amputees.

There is a large body of literature on the incidence of phantom pain and stump pain in amputees, but there appears to be very little published research dealing with the effect of exercise on either phantom pain or stump pain.

A recent study (Nikoljsen & Staehelin Jenson, 2000) concludes:

Phantom pain is experienced by 60% to 80% of patients following limb amputation but is only severe in about 5% to 10% of cases. The mechanisms underlying pain in amputees are not fully understood, but factors in both the peripheral and central nervous system play a role.

A recent paper (Vichitrananda & Pausawasdi, 2001) has reported relief from severe phantom limb pain using Midazolam (a benzodiazepine) which acts to enhance the action of the glycine (also an inhibitory neurotransmitter) on receptors in the spinal neurons.

This result may indicate that the pain results from the imbalance of self-sustaining neural activity exceeding inhibitory control.

Consequently, it is feasible that an appropriate exercise regime could ameliorate the incidence of both phantom pain and stump pain by affecting cortical reorganisation and peripheral neural circuits involved in physical activity.


1. Trans-tibial amputees would benefit from both general physical fitness training and strength endurance training of knee flexor and extensor muscles and hip abductor muscles.

2. Reduction in gait asymmetry may be achieved by increasing muscular strength and endurance in the amputated limb.

3. Improvements in muscular strength and endurance will result in enhanced functional capacity in trans-tibial amputees as measured by the two minute walk test.

4. The design of any exercise device to improve muscular and endurance must allow for use by amputees with short stumps and must accommodate training of the hip abductor muscles in addition to the knee flexors and extensors.

5. The effect of any strength or exercise programme on the incidence and severity of phantom pain is, at present, unknown.

Alan Walmsley PhD
Massey University
28 April 2003

Brooks, D., Hunter, J. P., Parsons, J., Livsey, E., Quirt., J., & Devlin, M. (2002). Reliability of the two-minute walk test in individuals with trans-tibial amputation. Archives of Physical Medicine and Rehabilitation, 83(11),1562-1565. Brooks, D., Parsons, J., Hunter, J. P., Devlin, M., & Walker, J.(2001). The 2-minute walk test as a measure of functional improvement in persons with lower limb amputation. Archives of Physical Medicine & Rehabilitation, 82(10),1478-1483. Campbell, A. J., Borrie, M.J., & Spears, G. F.(1989). Risk factors for falls in a community-based prospective study of people 70 years and older. Journal of gerontology, 44(4), M112-117. Chin, T., Sawamura, S., Fujita, H., Nakajima, S., Ojima, I., Oyabu, H., et al.(2001). Effect of endurance training program based on anaerobic threshold (AT) for lower-limb amputees. Journal of Rehabilitation Research & Development., 38(1),7-11. Eke-okoro, S. T.(1999). Exploration of paretic gait by differential loading in normals. Clinical Biomechanics, 14(2), 136-140. Esquenazi, A., & DiGiacomo, R. (2001). Rehabilitation after amputation. Journal of the American Podiatric Medical Association, 91(1), 13-22. Hillery, S. C., & Wallace, E.S. (2000). Trans-tibial amputee gait adaptations as a result of prosthetic inertial manipulation. Disability & Rehabilitation, 22(8), 383- 386. Hurley, B. F., & Roth, S. M. (2000). Strength training in the elderly: effects on risk factors for age-related diseases. sports medicine. 30(4). 249-268.
Isakov, E., Burger, H., Krajnik, J., Gregoric, M., & Marincek, C. (2001). Knee muscle activity during ambulation of trans-tibial amputees. Journal of Rehabilitation Medicine, 33(5), 196-199.
Isakov, E., Keren, O., & Benjuya, N. (2000). Trans-tibial amputee gait: time-distance parameters and EMG activity. Prosthetics & Orthotics International, 24(3), 21-220.
Kegel, B., Burgess, E. M., Starr, T. W., & Daly, W. K (1981). Effects of isometric muscle training on residual limb volume, strength, and gait of below-knee amputees. Physical Therapy, 61(10), 1419-1426. Klingenstierna, U., Renstrom, P., Grimby, G., & Morelli, B. (1990). Isokinetic strength training in below-knee amputees. Scandinavian Journal Of Rehabilitation Medicine, 22(1), 39-43. Marin, R., Spellman, N., Kenyon, M., & Belandres, P. V. (1992) Isokinetic exercise system modification for short below-the-knee residual limbs. Archives of Physical Medicine & Rehabilitation., 73(9) 883-885. Michel, V., & Do, M. C. (2002). Are stance ankle plantar flexor muscles necessary to generate propulsive force during human gait initiation? Neuroscience Letters, 325(2), 139-143. Miller, W. C., Deathe, A. B., Speechley, M., & Koval, J. (2001). The influence of falling, fear of falling and balance confidence on prosthetic mobility and activity among individuals with a lower extremity amputation. Archives of Physical Medicine and Rehabilitation, 82(9), 12-38-1244. Miller, W. C., Speechley, M., & Deathe, B. (2001). The Prevalence and risk factors of falling and fear of falling among lower extremity amputees. Archives of physical Medicine and Rehabilitation, 82(8), 1031-1037. Moirenfeld, I., Ayalon, M., Ben-Sira, D., & Isakov, E. (2000). Isokinetic strength and endurance of the knee extensors and flexors in trans-tibial amputees. Prosthetics & Orthotics International, 24(3), 221-225. Nadollek, H., Brauer, S., & Isles, R. (2002). Outcomes after trans-tibial amputation: the relationship between quiet stance ability, strength of hip abductor muscle and gait. Physiotherapy Research International, (4), 203-214. Nikolajsen, L., & Staehelin Jensen, T. (2000). Phantom limb pain. Current Review of pain, 4(2), 166-170. Renstrom, P., Grimby, G., & Larsson, E. (1983). Thigh muscle strength in below-knee amputees. Scandinavian Journal of Rehabilitation Medicine- Supplementum, 9, 163-173. Vichitrananda, C., & Pausawasdi, S. (2001). Midazolam for the treatment of phantom limb pain exacerbation: preliminary reports. Journal of the Medical Association of Thailand, 84(2), 299-302. Ward, K. H., & Meyers, M. C. (1995). Exercise performance of lower-extremity amputees. Sports Medicine., 20(4), 207-214.



Student Number: 99110283POR31PGA
Pathological Gait Analysis
Subject coordinator: Tim Bach
WORD COUNT: ~ 2010

Biomechanics of trans-tibial amputee running gait compared to normalrunning

Ilse VermeulenPOR31PGA2001


I certify that the attached material is my original work.
No other persons' work has been used without due acknowledgment.
Except where I have clearly stated that I have used some of this material elsewhere, I have not presented it for examination in any other course or subject at this or any other institution.


The loss of part of a limb, as experienced by the trans-tibial amputee (TTA) would be expected to have a significant influence on the biomechanics of the person’s walking and running gait.

The TTA seem to adapt for this and after a period of rehabilitation TTA’s appear to walk and run with improved temporal and kinematic symmetry (Hurley, Mckenney, Robinson, Zadravec, Pierrynowski, 1990).

The aim of this assignment is a greater understanding of the biomechanical adaptations used by TTA runners.

Knowledge in this field could aid in the development of rehabilitation strategies as well as enable us to objectively evaluate the influence of prosthetic componentry on the running gait of TTA’s.The normal (non-amputee) runner show a uniform gain in the amplitude of hip, knee and ankle joint moments, as running speed is increases.

In contrast to a non-uniform increase in joint moments for the sound and prosthetic sides in the TTA (Sanderson and Martin, 1996). Enoka, Miller, Burgess, (1982) reported that 60% of TTA runner’s temporal and kinematic patterns were similar to that of a normal runner.

They also suggested that the differences in the remaining 40%, could be removed with prosthetic adjustments and training.

A study by Smith (1990) indicated that with increasing TTA cadence, less variability in kinematic data was observed in contrast to a greater variability in the kinetics results.


The trend in normal speed seems to favour an increase in step length at slower speeds and an increase in step frequency where higher speeds are demanded (Saito, Kobayashi, Miyashita and Hoshikawa, 1974 and Vaughan, 1985).

This same trend seems to be followed in TTA running. Sanderson (1996) reported an increase in step length, with increased running speed.

While Enoka et al. (1982) subjects’ were running at higher speeds, an increase in step frequency was noted.

An increase in step frequency correlates with an increase in non-support phase for the prosthetic side, but not on the sound side.

This period of non-support meets the criterion for running, which is to experience alternating periods of single support and complete non-support (Enoka et al., 1982).

Buckley (1999) reported the average duration of TTA stance phase to be 31% of the running gait cycle.

Biomechanics of trans-tibial amputee running gait compared to normalrunning


The duration and magnitude for prosthetic side hip extensor moment is greater than that of the sound side during its corresponding stance phase (Miller, 1987; Miller et. al., 1979).

In the normal running a brief concentric hip extensor moment is followed by an eccentric hip flexor moment which slows hip extension (Mann 1981, Winter 1983).

The sound and prosthetic sides follow the same sequence, although the eccentric hip flexor moment is abbreviated on the prosthetic side.

This extensor moment also provides some assistance to the quadriceps muscle in controlling the knee immediately following foot strike.

It then helps with knee extension from mid stance, rotating the thigh backward in relation to the hip, causing either a slowing of knee flexion or promotion knee extension.

A delayed transition from extension to flexion at the hip joint, occurred at around 26% of stride for the prosthetic side, whereas this change occurred at around the15% mark for both the normal and sound side hips.

A study by Sanderson (1996) showed that the prosthetic side hip joint underwent less extension during stance phase than the sound side hip.


The slow running gait of TTA’s is similar to that of the TTA walking gait, and is characterised by a restricted range of knee flexion of the sound side during swing phase.

This causes the sound side foot to always be close to the floor (Enoka et al., 1982). As velocity increases the sound side more closely resembles the normal gait with the characteristic knee flexion and extension. (Buckley, 1999).

During normal running the stance phase starts with an eccentric knee extensor moment to control knee flexion and is followed by a concentric knee extensor moment as the knee changes from flexion to extension (Mann, 1981 and Winter, 1983).

The TTA gait differs from this kinematic pattern in that the knee on the prosthetic side begin stance phase slightly more extended and experience a smaller flexion and extension moment.

Enoka et al. (1982) and Miller (1987) also remarked that some below-knee amputees maintain a straight or hyperextended knee on the prosthetic side throughout stance phase, with the sound side almost a mirror image.

Generally a knee flexion moment is still present, evidenced by a concentric knee flexor power output immediately after heel contact (Winter and Sienko, 1988; Czerniecki, Gitter, Munro, 1991).

The knee flexor – extensor pattern for a TTA running at 2.8m/s.


In normal running, heel contact commences with a dorsiflexion moment that continues through the first third of stance phase.

The TTA runner’s ankle on the sound side acts similar to that of the normal runner, except for the earlier termination of plantarflexion during the late phase of swing, which is similar to that of the prosthetic side (Miller, 1987; Sanderson, 1996).

As expected the ankle joint on the prosthetic side has a smaller range of motion.

The TTA runner also lacks a talocalcaneal joint to help achieve plantigrade, like in normal running.

As compensation the TTA can experience frontal plane rotation and translation of the leg or assume a position with the knee, ankle and foot directly underneath the hip.

To accommodate for this increase Biomechanics of trans-tibial amputee running gait compared to normal running in angular momentum in the legs, a change of alignment is necessary in the upper body.

These changes will obviously have a negative effect on running performance (Engsberg & Allinger, 1990).

Further research in this direction is of paramount importance.


In normal running the ankle plantarflexors are the major sources of energy generation, the knee extensors the major energy absorbers, while the hip musculature plays a minor role in energy absorption or generation(Winter a+b; Czerniecki and Gitter, 1992).

The amputee compensates by using the hip extensors as the major source of energy generation and interestingly enough becomes the predominant energy absorbers.

Czerniecki (1996) suggested that energy transfer across the hip joint to the trunk during deceleration of the swing phase leg might be an important energy distribution mechanism to partially compensate for reduced power output during stance phase of the prosthetic side.

A study done by Czerniecki and Gitter (1992) showed that the total muscle work on the prosthetic limb during stance phase is only 42 % of normal energy generation.

In addition Czerniecki et al. (1991) showed in their study that the total amount of energy transferred into the trunk, during swing phase was 74% greater than that of normal running.

These results support the importance of such an adaptive mechanism, to the TTA’s lower extremity energetics during swing phase.

For energy generated in late stance phase is critical to the acceleration of the trunk.


Peak forces for breaking, vertical and propulsion components are lower for the prosthetic limb in comparison with the sound and non-amputee limbs.

Miller (1987) measured an average vertical ground reaction force (VGRF) of 1.0 times body weight (BW) during stance phase for the prosthetic side, and 1.2 BW on the sound side, with the subject running at a speed of 2.6m/s. Sanderson (1996) measured 2.15 BW on the prosthetic side compared to 2.39 BW on the sound side, at a running speed of 3.5m/s. Brower, Allard, Labelle (1989) noted a VGRF of 2.44 BW for children running at an average running speed of 2.10m/s and a VGRF of 2.55 BW at 3.03m/s, for the sound side.

For the prosthetic side he measured 2.0 BW at 2.10m/s and 2.25 BW at 3.03m/s. Increasing speed consequently increases peak forces for sound and non-amputee limbs.

On the prosthetic side a substantial increase in propulsion force and a less marked increase in the breaking force was experienced (Sanderson, 1996).


The biomechanical analysis of a TTA’s running gait is valuable in many ways. One very important outcome is the development of improved prosthetic componentry.

One such development field is that of dynamic elastic response (DER) or energy storing feet (Wing & Hittenberger, 1989).

The Flex-Foot (FF) is the most widely prescribed and clinically popular prosthetic foot at present for the TTA runner.

Total work done by the lower extremity while running with a FF is 70% of normal comparing to the SACH foot’s 49.5% (Czerniecki et al., 1991). Czerniecki et al. (1991) also reported 84% energy return for the FF, which is significantly higher than other prosthetic feet tested.

The FF is a J-shaped carbon fibre leaf spring (CarbonX Active HeelTM)that deforms during loading.

This creates controlled dorsiflexion as the shank rotates forward over the planted foot and in turn allows flexion of the knee. Plantar and dorsiflexion similar to the sound limb is observed, leading to greater gait symmetry (Buckley, 1999).

Unlike other DER feet which generally make use of an four inch keel and attach to the ankle by a rigid pylon, the FF has a graphite composite keel that extends to the prosthetic socket, and therefore increasing the working leaver arm (Edelstein, 1989).

Not only does it result in a very responsive and resilient component, it also significantly improves the mass distribution of the prosthesis.

Most of the weight is situated in the socket and attachment cone, with the rest uniformly distributed across the pylon.

The inverted pendulum mechanism gives the patient a feel of a lighter prosthesis as it is propelled through space (Michael, 1987).

The effectiveness of the FF can be demonstrated in its ability to propel the body forward in combination with reducing heel strike load on the sound side (Lehmann, 1993).

Although the SACH foot shows more heel compliance, the FF shows more forefoot compliance, resulting in a greater ankle angle range (Torburn. Perry, Ayappa, Shanfield, 1990) and a shorter push off phase. Lehmann (1993), Hsu, Nielsen, Yack, Shurr, Lin (2000) and Torburn et al. (1990) didn’t find any significant increase in step length onto the sound limb, change in self-selected walking velocity or energy expenditure, as would be expected with the greater propulsion of the FF

(Note: Tests done at walking speed).

Lehmann (1993) suggested that this phenomenon could have been caused by the incorrect timing of the energy storage-release cycle of the FF, relative to the kinematic requirements of ambulation.

In contrast Macfarlane, Nielsen, Shurr, Meier (1992) and Menard et al. (1992) did find an increase in step length of the sound limb as well as an increase in self-selected walking speed in their study on TTA walking.

A more symmetrical gait was observed when walking with the Flexfoot, because larger more normal steps could be taken.

Macfarlane et al. (1992) explained changes in step length due to the longer support in stance phase of the prosthetic side when using a Flexfoot, resulting in a shorter short push-off with a greater impulse force.

Most subjects preferred to utilise this late ‘kick’ for sport activities rather than everyday living (Menard et al., 1992).

Mean =1SD stance phase power outputs of the hip, knee and ankle in four amputee subjects wearing the FF (solid lines) and five normal subjects (dotted lines) running a 2.8m/s. (Concentric power output = positive; eccentric power output = negative.)

Although cosmetic finishing for the FF is difficult and time-consuming, it has the advantage of resulting in a very highly water-resistant structure.

Distribution of total stance phase concentric muscle work between hip extensors, knee extensors and ankle plantarflexors in five normal and five amputee subjects running at 2.8m/s.

Distribution of total stance phase eccentric muscle work between hip extensors, knee extensors and ankle plantarflexors in five normal and five amputee subjects running at 2.8m/s.A more advanced type of FF is the Re-Flex Vertical Shock Pylon (VCP).

The Re-Flex VCP is the first prosthesis to successfully integrate a shock absorption system.

It uses a carbon fibre compression spring, and telescoping tubes that provide up to an inch of vertical compression.

Greater movement of the pylon occurs as speed increases, which results into greater energy storage and release (Miller & Childress, 1997).

Energy storing-releasing properties were showed to be more pronounced in the Re-Flex VCP than in the FF (Hsu, Nielsen, Yack, Shurr, 1999). Hsu et al. (1999) also suggested that the Re-Flex VCP a positive effect on energy cost, gait efficiency, and relative exercise intensity comparing to other prosthetic foot types.

Although limited testing has been performed on the Re-Flex VCP it has proven superior to the SACH and the FF.


Below knee amputees seem to demonstrate different coping mechanics to the increase in speed demand.

Although symmetry in stride frequency and support phase is demonstrated, asymmetry in ankle, knee and hip moments is marked.

During the stance phase less ankle motion, a decrease in the flexion- extension at the knee and less extension at the hip joint.


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