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Running-specific prostheses limit ground-force during sprinting

The Royal Society
Biology Letters
Authors:
Alena M Grabowski at University of Colorado Boulder
Alena M Grabowski
Craig P McGowan at University of Idaho
Craig P McGowan
Bill Mcdermott at The Orthopedic Speialty Hospital
Bill Mcdermott
  • The Orthopedic Speialty Hospital
Matthew Thomas Beale at University of Colorado Boulder
Matthew Thomas Beale
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Abstract

Running-specific prostheses (RSP) emulate the spring-like behaviour of biological limbs during human running, but little research has examined the mechanical means by which amputees achieve top speeds. To better understand the biomechanical effects of RSP during sprinting, we measured ground reaction forces (GRF) and stride kinematics of elite unilateral trans-tibial amputee sprinters across a range of speeds including top speed. Unilateral amputees are ideal subjects because each amputee's affected leg (AL) can be compared with their unaffected leg (UL). We found that stance average vertical GRF were approximately 9 per cent less for the AL compared with the UL across a range of speeds including top speed (p < 0.0001). In contrast, leg swing times were not significantly different between legs at any speed (p = 0.32). Additionally, AL and UL leg swing times were similar to those reported for non-amputee sprinters. We infer that RSP impair force generation and thus probably limit top speed. Some elite unilateral trans-tibial amputee sprinters appear to have learned or trained to compensate for AL force impairment by swinging both legs rapidly.
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... These concepts become essential, especially in the present conversation, as some have speculated that prosthetics may enhance an amputee's ability to produce ground reaction forces. For example, it has been reported that some prosthetics might compensate for these limitations better than others, although the deficiency in ground force reactions could be a limiting factor for transtibial athlete running performance [16]. One way in which prosthetics may yield a better performance could stem from their customizable structure. ...
... For instance, a prior study indicated that J-shaped blades were able to reduce the ground contact time with higher forces at the point of contact than C-shaped blades, and the values These concepts become essential, especially in the present conversation, as some have speculated that prosthetics may enhance an amputee's ability to produce ground reaction forces. For example, it has been reported that some prosthetics might compensate for these limitations better than others, although the deficiency in ground force reactions could be a limiting factor for transtibial athlete running performance [16]. One way in which prosthetics may yield a better performance could stem from their customizable structure. ...
... Grabowski et al. [16] 6 (29.2 ± 5.3) Male (n = 4) and female (n = 2) unilateral transtibial amputee runners -Type of running prosthetic significantly affects force generation. ...
Biological or Prosthetic Limb—Which Is More Advantageous for Running Performance? A Narrative Review
Article
Full-text available
  • Mar 2025
As the field of prosthetic engineering advances, questions around whether these new prosthetics hold the ability to outperform biological limbs become more relevant. To further clarify such a debate and discover gaps in our understanding, a narrative review of the present literature on this topic is needed. The purpose of the present review was to explore whether prosthetic legs grant amputee athletes an unfair advantage over traditional athletes by reviewing 11 articles pertaining to the running performance and potential among athletes with transtibial amputations. The findings of the included articles were categorized into three domains of running performance, chosen due to their precedence in the current literature: propulsion forward, limb repositioning, and physiological limitations. Our review indicated that the present literature alludes to transtibial amputee runners having a potential competitive advantage over able-bodied runners, with the caveat that some performance domains appear not to be differentiated. The present findings offer a unique perspective on understanding the impact of prosthetics on the running performance among para-athletes and suggest future research directions. As the depth of this area of literature increases, future systematic reviews and meta-analyses may be able to answer with greater certainty whether transtibial prosthetics allow for supra-biological running performances.
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... It has been shown that leg stiff- ness and stride frequency are related to each other in running, either directly [36] or via contact time length [98]. However, studies on sprinters with unilateral below the knee amputation (BKA) [50,62,86] have shown that the fixed stiffness of the RSP and the associated differences to the biological leg restrict the ability to regulate the stiffness of the entire leg affected by the amputation and thereby achieving top speed. Our simulation seems to confirm these results: When required to maximize step frequency, the amputee model can only generate slower average velocities. ...
... Nevertheless, for other objective functions the amputee model is able to generate higher average velocities than the non-amputee model. This result is in accordance with observations that running velocity is not only determined by step frequency [50,62,86], hence amputee athletes might adjust other parameters to achieve high velocities (compare the ranking of similarity measures: Max. Velocity and Max. ...
... Another research question with respect to velocities is raised by the observation that the amputee athlete runs faster than the non-amputee athlete only up to a certain velocity and then this behavior reverses. Here, further research would be interesting to compare our results, which suggest that the RSP may have a more hindering effect above a certain velocity threshold, with those of Grabowski et al. [50], which assume that the RSP fundamentally hinders force production and thus top speeds. In this context, there is also another issue raised by the results presented here: Compared to the measured reference movements, the amputee athlete makes better use of the RSP, but also shows greater knee flexion. ...
Towards a Simulator Tool for Predicting Sprinting and Long Jump Motions with and without Running-Specific Prostheses: An Optimization-Based Approach
Thesis
  • Jan 2023
The performances of sprinters and long jumpers with below the knee amputation (BKA) have improved continuously since the development of prostheses specifically for athletic movements. In the last years, a number of athletes with BKA have attempted to compete in non-amputee competitions. Due to the specific shape and material properties of the running-specific prosthesis (RSP), concerns exist that it may give athletes an advantage over non-amputee athletes. In this work, we investigate and compare sprinting and long jump movements of athletes with and without unilateral BKA using accurate computer models. In this context, the aim of the work is to describe similarities and differences between the athletes’ movements and to show that the employed model- and optimization-based computations are useful for this purpose. We created subject-specific multi-body models for five different athletes (four non-amputee athletes, one athlete with unilateral BKA) in order to be able to investigate the different movements. Depending on the research question, the models vary in the number of degrees of freedom (DOFs), from 16 DOFs for a two-dimensional model in the sagittal plane to 31 DOFs for a three-dimensional model. For the athlete with BKA, we created a three-segment model of the RSP with one rotational DOF in the sagittal plane. The respective motion is described by a sequence of several phases, which differ by the type of ground contact. Each of these phases is described by its own set of ordinary differential equations (ODEs) or differential algebraic equations (DAEs). We use multi-phase optimal control problems (OCPs) with discontinuities to generate sprint and long jump motions. Three different formulations of OCPs are adopted in this work. (1) We formulate a least squares OCP to reconstruct the dynamics of sprint and long jump motion capture recordings of the individual athletes. (2) For the generation of realistic motions, which can be used for prediction, we formulate a synthesis OCP; this optimizes an objective function consisting of a weighted combination of chosen optimization criteria. (3) Last, in the study of sprint movements, we use an inverse optimal control problem (IOCP): this consists of an inner loop, in which a synthesis OCP is solved, and an outer loop, which adjusts the weights of the individual optimization criteria such that the distance between the inner loop solution and a reference movement becomes minimal. We have successfully applied these three optimization problem formulations to the computation of two sprint steps of three athletes without and one athlete with unilateral transtibial amputation. Here, the movements of the non-amputee athletes differ from that of the amputee athlete in a large number of variables. In particular, the athletes use different actuation strategies for running with and without a RSP. We have observed lower torques in the amputee athlete in the leg affected by the amputation than in the non-amputee control group. In contrast, significantly larger torques occurred in the joints of the upper extremity in the amputee athlete. Furthermore, the comparison has shown that the asymmetry created by the RSP is reflected throughout the body and affects the entire movement. Using the OCPs for motion reconstruction (1) and synthesis (2), we have successfully computed the last three steps of the approach and the jump of a long jump for an athlete without and an athlete with unilateral amputation. In the reconstructed solutions, the amputee athlete achieves a greater jump distance compared to the non-amputee athlete, despite a slower approach velocity, because his take-off is more efficient. In the synthesis solutions, on the other hand, the non-amputee athlete achieves the greater jump distance because he generates a greater vertical force during the take-off and achieves a better ratio of gain of vertical to loss of horizontal velocity. Finally, we have presented our idea of a simulator tool to compare the amputee athlete with himself without amputation and have demonstrated it using the sprint and long jump movements. For this purpose, we have kept the model of the athlete with unilateral transtibial amputation from the previous studies and have created a non-amputee version of the same model by mirroring the biological leg. We have selected one objective function each for sprinting and for long jump and have solved the OCP for motion synthesis (2) for both model versions. Using the differences to the solutions based on the models of two real athletes, we have highlighted the importance of the simulator tool in the evaluation of advantages and disadvantages due to the use of the RSP.
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... Each athlete with UTTA or BTTA was aligned with 1E90 Sprinter RSPs (Ottobock, Duderstadt, Germany) at the manufacturer recommended stiffness category by a certified prosthetist 4 . For athletes with UTTA, the prosthetist first used a tape measure to measure the BioL leg length as the distance from the greater trochanter to the floor during standing, and then set the recommended RSP height so that unloaded ProsL length, measured from the greater trochanter to the distal end of the unloaded RSP, was 2-8 cm longer than standing BioL length based on the athlete's and prosthetist's preference 6,17 . For athletes with BTTA, the prosthetist set the recommended RSP height so that standing height followed the 2014 IPC competition guideline maximum height (IPC max ) for each athlete 25 . ...
... If the trial was successful, we increased speed by 1 m/s in each subsequent trial until the athlete approached their maximum speed, at which point we employed smaller speed increments. A trial was deemed successful if the participant maintained forward position on the treadmill for at least 8 consecutive strides 1,6,20 . If unsuccessful, participants could try again or deem their most recent successful speed as their maximum. ...
Equivalent running leg lengths require prosthetic legs to be longer than biological legs during standing
Article
Full-text available
  • May 2023
We aimed to determine a method for prescribing a standing prosthetic leg length (ProsL) that results in an equivalent running biological leg length (BioL) for athletes with unilateral (UTTA) and bilateral transtibial amputations (BTTA). We measured standing leg length of ten non-amputee (NA) athletes, ten athletes with UTTA, and five athletes with BTTA. All athletes performed treadmill running trials from 3 m/s to their maximum speed. We calculated standing and running BioL and ProsL lengths and assessed the running-to-standing leg length ratio (Lratio) at three instances during ground contact: touchdown, mid-stance, and take-off. Athletes with UTTA had 2.4 cm longer standing ProsL than BioL length (p = 0.030), but their ProsL length were up to 3.3 cm shorter at touchdown and 4.1 cm shorter at mid-stance than BioL, at speed 3–11.5 m/s. At touchdown, mid-stance, and take-off, athletes with BTTA had 0.01–0.05 lower Lratio at 3 m/s (p < 0.001) and 0.03–0.07 lower Lratio at 10 m/s (p < 0.001) in their ProsL compared to the BioL of NA athletes. During running, ProsL were consistently shorter than BioL. To achieve equivalent running leg lengths at touchdown and take-off, athletes with UTTA should set their running-specific prosthesis height so that their standing ProsL length is 2.8–4.5% longer than their BioL length, and athletes with BTTA should set their running-specific prosthesis height so that their standing ProsL lengths are at least 2.1–3.9% longer than their presumed BioL length. Setting ProsL length to match presumed biological dimensions during standing results in shorter legs during running.
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... However, moments of most muscle moments (PF, KF and DF during stance, and KF during swing) and CoA were, greater during walking, suggesting that increased muscle moments and co-contractions do not determine NCo. Studies have shown that the vertical oscillation of the centre of mass is more pronounced during running than during walking due to a higher hip extension during the stance phase [65,66]. This additional oscillation requires more work from gluteal muscles, therefore increasing NCo [67,68]. ...
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... We used a 20 N perpendicular GRF threshold to determine ground contact and analysed at least 15 steps from each leg per trial. A step was defined as ground contact and the subsequent aerial phase for the same leg [25]. All steps were resampled to 101 data frames and represented as a percentage. ...
The contribution of lower-limb joint quasi-stiffness to theoretical leg stiffness during level, uphill and downhill running at different speeds
Article
Full-text available
  • Apr 2024
Humans change joint quasi-stiffness (k joint ) and leg stiffness (kleg) when running at different speeds on level ground and during uphill and downhill running. These mechanical properties can inform device designs for running such as footwear, exoskeletons and prostheses. We measured kinetics and kinematics from 17 runners (10 M; 7 F) at three speeds on 0°, ±2°, ±4° and ±6° slopes. We calculated ankle and knee k joint , the quotient of change in joint moment and angular displacement, and theoretical leg stiffness (klegT) based on the joint external moment arms and k joint . Runners increased k ankle at faster speeds (p < 0.01). Runners increased and decreased the ankle and knee contributions to klegT, respectively, by 2.89% per 1° steeper uphill slope (p < 0.01) during the first half of stance. Runners decreased and increased ankle and knee joint contributions to klegT, respectively, by 3.68% during the first half and 0.86% during the second half of stance per 1° steeper downhill slope (p < 0.01). Thus, biomimetic devices require stiffer k ankle for faster speeds, and greater ankle contributions and greater knee contributions to klegT during the first half of stance for steeper uphill and downhill slopes, respectively.
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... From the vertical GRFs data, the maximum number of consecutive steps on the left and right belts was analysed. In addition, a threshold of 40 N was used for the vertical components of the GRF in each belt to determine the beginning (heelstrike) and ending (toe-off) of the stance [25,31]. The variability of GRFs against time (0-100% stance) for intact and prosthetic limbs of both TFSim and TFAmp groups is shown in figure 2. The pairwise variability in GRFs between the TFSim and TFAmp groups based on knee joints can be found in electronic supplementary material, figure S1. ...
Transfemoral prosthetic simulators versus amputees: ground reaction forces and spatio-temporal parameters in gait
Article
Full-text available
  • Mar 2024
This study aimed to compare the ground reaction forces (GRFs) and spatio-temporal parameters as well as their asymmetry ratios in gait between individuals wearing a transfemoral prosthetic simulator (TFSim) and individuals with unilateral transfemoral amputation (TFAmp) across a range of walking speeds (2.0–5.5 km h⁻¹). The study recruited 10 non-disabled individuals using TFSim and 10 individuals with unilateral TFAmp using a transfemoral prosthesis. Data were collected using an instrumented treadmill with built-in force plates, and subsequently, the GRFs and spatio-temporal parameters, as well as their asymmetry ratios, were analysed. When comparing the TFSim and TFAmp groups, no significant differences were found among the gait parameters and asymmetry ratios of all tested metrics except the vertical GRFs. The TFSim may not realistically reproduce the vertical GRFs during the weight acceptance and push-off phases. The structural and functional variations in prosthetic limbs and components between the TFSim and TFAmp groups may be primary contributors to the difference in the vertical GRFs. These results suggest that TFSim might be able to emulate the gait of individuals with TFAmp regarding the majority of spatio-temporal and GRF parameters. However, the vertical GRFs of TFSim should be interpreted with caution.
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... The GRF data were filtered using a low-pass Butterworth filter with a cutoff frequency of 25 Hz. From the filtered vertical GRF data, the touchdown and takeoff instants were detected using a threshold of 40 N [16][17][18][19] . This vertical threshold was used for all the GRF variables except the COP trajectory data. ...
Mediation of the mediolateral ground reaction force profile to maintain straight running among unilateral transfemoral amputees
Article
Full-text available
  • May 2023
The mediolateral ground reaction force (M-L GRF) profile that realizes a symmetrical mediolateral ground reaction impulse (M-L GRI) between both limbs is essential for maintaining a straight movement path. We aimed to examine the M-L GRF production across different running speeds in unilateral transfemoral amputees (TFA) to identify strategies for maintaining straight running. The average medial and lateral GRF, contact time (tc), M-L GRI, step width, and center of pressure angle (COPANG) were analyzed. Nine TFAs performed running trials at 100% speed on an instrumented treadmill. Trials were set at 30–80% speed with an increment of 10%. Seven steps from the unaffected and affected limbs were analyzed. Overall, the unaffected limbs exhibited a higher average medial GRF than the affected limbs. The M-L GRI were similar between both limbs at all speeds, implying that the participants were able to maintain a straight running path. The affected limb exhibited a longer tc and a lower M-L GRF profile than the unaffected limb. The results showed that unilateral TFAs adopted limb-specific strategies to maintain a straight running path, and that these limb-specific strategies were consistent across different running speeds.
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A systematic review of energy storing dynamic response foot for prosthetic rehabilitation
Article
  • Nov 2024
  • P I MECH ENG H
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Prosthetic Stiffness and Added Mass Affect Metabolic Power and Asymmetry in Female Runners with a Leg Amputation
Article
  • Jun 2024
  • J APPL PHYSIOL
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Adaptive Running
Chapter
  • Feb 2024
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Article
Full-text available
  • Jul 2009
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Fast Running Tracks
Article
Full-text available
  • Jan 1979
“Fast Running Tracks”, Scientific American, 239(6), 12/78, 148-163. Thomas A. McMahon, Peter R. Greene Harvard University, Div. Applied Sciences, Cambridge, Mass. ABSTRACT - On a springy new indoor track at Harvard University runners can run faster than they can on standard tracks. The design of the track was arrived at through a close analysis of the mechanics of human running. Last year Harvard University opened a new indoor sports facility housing a six-lane 220-yard running track. The track has a supporting substructure consisting primarily of wood and a synthetic surface covering. Most people find running on the track a pleasant and unusual experience. It feels particularly springy and therefore is comfortable to run on, and members of the Harvard track team have sustained considerably fewer injuries since they began practicing on the track. What is most remarkable, however, is that an analysis of the 1977-78 records of Harvard runners and their competitors shows that the track substantially enhances a runner's performance, reducing the time of, say, a well-run mile by several seconds. By all estimations the new track is fast. One of the most important parameters of track design is compliance, and it is mainly in this respect that the new track differs from other indoor tracks . . .
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Biomechanics of Sprint Running
Article
Full-text available
  • Jul 1992
Understanding of biomechanical factors in sprint running is useful because of their critical value to performance. Some variables measured in distance running are also important in sprint running. Significant factors include: reaction time, technique, electromyographic (EMG) activity, force production, neural factors and muscle structure. Although various methodologies have been used, results are clear and conclusions can be made. The reaction time of good athletes is short, but it does not correlate with performance levels. Sprint technique has been well analysed during acceleration, constant velocity and deceleration of the velocity curve. At the beginning of the sprint run, it is important to produce great force/ power and generate high velocity in the block and acceleration phases. During the constant-speed phase, the events immediately before and during the braking phase are important in increasing explosive force/power and efficiency of movement in the propulsion phase. There are no research results available regarding force production in the sprint-deceleration phase. The EMG activity pattern of the main sprint muscles is described in the literature, but there is a need for research with highly skilled sprinters to better understand the simultaneous operation of many muscles. Skeletal muscle fibre characteristics are related to the selection of talent and the training-induced effects in sprint running. Efficient sprint running requires an optimal combination between the examined biomechanical variables and external factors such as footwear, ground and air resistance. Further research work is needed especially in the area of nervous system, muscles and force and power production during sprint running. Combining these with the measurements of sprinting economy and efficiency more knowledge can be achieved in the near future.
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The spring in the arch of the human foot
Article
Full-text available
  • Jan 1995
Large mammals, including humans, save much of the energy needed for running by means of elastic structures in their legs and feet. Kinetic and potential energy removed from the body in the first half of the stance phase is stored briefly as elastic strain energy and then returned in the second half by elastic recoil. Thus the animal runs in an analogous fashion to a rubber ball bouncing along. Among the elastic structures involved, the tendons of distal leg muscles have been shown to be important. Here we show that the elastic properties of the arch of the human foot are also important.
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Accounting for elite indoor 200 m sprint results
Article
Full-text available
Times for indoor 200 m sprint races are notably worse than those for outdoor races. In addition, there is a considerable bias against competitors drawn in inside lanes (with smaller bend radii). Centripetal acceleration requirements increase average forces during sprinting around bends. These increased forces can be modulated by changes in duty factor (the proportion of stride the limb is in contact with the ground). If duty factor is increased to keep limb forces constant, and protraction time and distance travelled during stance are unchanging, bend-running speeds are reduced. Here, we use results from the 2004 Olympics and World Indoor Championships to show quantitatively that the decreased performances in indoor competition, and the bias by lane number, are consistent with this 'constant limb force' hypothesis. Even elite athletes appear constrained by limb forces.
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Biomechanics of double transtibial amputee sprinting using dedicated sprinting prostheses
Article
  • Jan 2008
The purpose of this study was to examine the overall kinetics and the kinetics at the joints of the lower limb while sprinting at maximum speed, and to compare the data of a double transtibial amputee and able‐bodied controls running at the same level of performance. One double transtibial amputee, using dedicated sprinting prostheses, and five able‐bodied sprinters participated in the study. The athletes performed submaximal and maximal sprints (60 m) on an indoor track. All of the participants ran three times at each speed (maximal and submaximal). The athletes’ kinematics were recorded using the Vicon 624 system with 12 cameras operating at 250 Hz. Four Kistler force plates (1250 Hz) were used to record ground reaction forces (GRF). External joint moments, joint work, and joint power were calculated from the GRF and the kinematic data. The analysis of total body kinetics revealed lower mechanical work during the stance phase for the double transtibial amputee using Cheetah prostheses than for the able‐bodied athletes running at the same speed. The joint kinetics showed lower external joint moments and joint power at the hip and the knee joints and higher values of joint power at the (prosthetic) ankle joint of the amputee than for the able‐bodied athletes. The ratio of the mechanical work at the ankle joint in the negative and the positive phase during stance was 0.907 for the carbon keels of the prostheses and 0.401 for the healthy ankle joints of the controls. The mechanical work at the knee joints was 11 times higher in the negative phase and 8.1 times higher in the positive phase during stance in the able‐bodied athletes than in the double transtibial amputee sprinter. It was assumed that due to reduced work at the joints of the lower limbs and less energy loss in the prosthetic leg, running with the dedicated prostheses allows for maximum sprinting at lower metabolic costs than in the healthy ankle joint complex.
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Biomechanics of double transtibial amputee sprinting using dedicated sprint prostheses
Article
  • Jan 2009
The purpose of this study was to examine the overall kinetics and the kinetics at the joints of the lower limb while sprinting at maximum speed, and to compare the data of a double transtibial amputee and able-bodied controls running at the same level of performance. One double transtibial amputee, using dedicated sprinting prostheses, and five able-bodied sprinters participated in the study. The athletes performed submaximal and maximal sprints (60 m) on an indoor track. All of the participants ran three times at each speed (maximal and submaximal). The athletes' kinematics were recorded using the Vicon 624 system with 12 cameras operating at 250 Hz. Four Kistler force plates (1250 Hz) were used to record ground reaction forces (GRF). External joint moments, joint work, and joint power were calculated from the GRF and the kinematic data. The analysis of total body kinetics revealed lower mechanical work during the stance phase for the double transtibial amputee using Cheetah prostheses than for the able-bodied athletes running at the same speed. The joint kinetics showed lower external joint moments and joint power at the hip and the knee joints and higher values of joint power at the (prosthetic) ankle joint of the amputee than for the able-bodied athletes. The ratio of the mechanical work at the ankle joint in the negative and the positive phase during stance was 0.907 for the carbon keels of the prostheses and 0.401 for the healthy ankle joints of the controls. The mechanical work at the knee joints was 11 times higher in the negative phase and 8.1 times higher in the positive phase during stance in the able-bodied athletes than in the double transtibial amputee sprinter. It was assumed that due to reduced work at the joints of the lower limbs and less energy loss in the prosthetic leg, running with the dedicated prostheses allows for maximum sprinting at lower metabolic costs than in the healthy ankle joint complex. © 2008 John Wiley and Sons Asia Pte Ltd
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Groucho Running
Article
  • Jul 1987
An important determinant of the mechanics of running is the effective vertical stiffness of the body. This stiffness increases with running speed. At any one speed, the stiffness may be reduced in a controlled fashion by running with the knees bent more than usual. In a series of experiments, subjects ran in both normal and flexed postures on a treadmill. In other experiments, they ran down a runway and over a force platform. Results show that running with the knees bent reduces the effective vertical stiffness and diminishes the transmission of mechanical shock from the foot to the skull but requires an increase of as much as 50% in the rate of O2 consumption. A new dimensionless parameter (u omega 0/g) is introduced to distinguish between hard and soft running modes. Here, omega 0 is the natural frequency of a mass-spring system representing the body, g is gravity, and u is the vertical landing velocity. In normal running, this parameter is near unity, but in deep-flexed running, where the aerial phase of the stride cycle almost disappears, u omega 0/g approaches zero.
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Energy transfer mechanisms as a compensatory strategy in below knee amputee runners
Article
  • Jul 1996
  • J BIOMECH
Below knee amputee runners exhibit abnormalities in the mechanical work characteristics of the lower extremity musculature during stance phase. The most significant abnormality is a marked reduction in the mechanical work done in the stance phase prosthetic limb. Energy transfer across the hip joint to the trunk during deceleration of the swing phase leg may be an important energy distribution mechanism to compensate for the reduced work done during prosthetic stance phase. Five unilateral below knee amputee runners wearing the SACH prosthetic foot and 5 normal subjects were studied. All subjects ran at a controlled velocity of 2.8 ms(-1) while kinematic and ground reaction force data were collected. Using a four segment linked segment model and an inverse dynamics approach joint moments, muscle power outputs, mechanical work values and energy transfers across the hip were calculated. The total amount of energy transferred during swing phase and the energy transferred out of the swing phase leg into the trunk were both significantly greater than normal. Energy transfer mechanisms are important in influencing the lower extremity energetics during swing phase. In addition, the 74 percent increase in energy transfer out of the intact swing phase limb combined with the temporal characteristics of this energy flow suggests that energy transfer may be an adaptive mechanism that allows energy redistribution to the trunk which may partially compensate for the reduced power output of the stance phase prosthetic limb.
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Faster top running speeds are achieved with greater ground forces not more rapid leg movements
Article
  • Dec 2000
We twice tested the hypothesis that top running speeds are determined by the amount of force applied to the ground rather than how rapidly limbs are repositioned in the air. First, we compared the mechanics of 33 subjects of different sprinting abilities running at their top speeds on a level treadmill. Second, we compared the mechanics of declined (-6 degrees ) and inclined (+9 degrees ) top-speed treadmill running in five subjects. For both tests, we used a treadmill-mounted force plate to measure the time between stance periods of the same foot (swing time, t(sw)) and the force applied to the running surface at top speed. To obtain the force relevant for speed, the force applied normal to the ground was divided by the weight of the body (W(b)) and averaged over the period of foot-ground contact (F(avge)/W(b)). The top speeds of the 33 subjects who completed the level treadmill protocol spanned a 1.8-fold range from 6.2 to 11.1 m/s. Among these subjects, the regression of F(avge)/W(b) on top speed indicated that this force was 1.26 times greater for a runner with a top speed of 11.1 vs. 6.2 m/s. In contrast, the time taken to swing the limb into position for the next step (t(sw)) did not vary (P = 0.18). Declined and inclined top speeds differed by 1.4-fold (9.96+/-0.3 vs. 7.10+/-0.3 m/s, respectively), with the faster declined top speeds being achieved with mass-specific support forces that were 1.3 times greater (2.30+/- 0.06 vs. 1.76+/-0.04 F(avge)/ W(b)) and minimum t(sw) that were similar (+8%). We conclude that human runners reach faster top speeds not by repositioning their limbs more rapidly in the air, but by applying greater support forces to the ground.
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