Dynamic elastic response prostheses alter approach angles and ground reaction forces but not leg stiffness during a start-stop task

Inspired by the springlike action of biological legs, running-specific prostheses are designed to enable athletes with lower-limb amputations to run. However, manufacturer’s recommendations for prosthetic stiffness and height may not optimize running performance. Therefore, we investigated the effects of using different prosthetic configurations on the metabolic cost and biomechanics of running. Five athletes with bilateral transtibial amputations each performed 15 trials on a force-measuring treadmill at 2.5 or 3.0 m/s. Athletes ran using each of 3 different prosthetic models (Freedom Innovations Catapult FX6, Össur Flex-Run, and Ottobock 1E90 Sprinter) with 5 combinations of stiffness categories (manufacturer’s recommended and ± 1) and heights (International Paralympic Committee’s maximum competition height and ± 2 cm) while we measured metabolic rates and ground reaction forces. Overall, prosthetic stiffness [fixed effect (β) = 0.036; P = 0.008] but not height ( P ≥ 0.089) affected the net metabolic cost of transport; less stiff prostheses reduced metabolic cost. While controlling for prosthetic stiffness (in kilonewtons per meter), using the Flex-Run (β = −0.139; P = 0.044) and 1E90 Sprinter prostheses (β = −0.176; P = 0.009) reduced net metabolic costs by 4.3–4.9% compared with using the Catapult prostheses. The metabolic cost of running improved when athletes used prosthetic configurations that decreased peak horizontal braking ground reaction forces (β = 2.786; P = 0.001), stride frequencies (β = 0.911; P < 0.001), and leg stiffness values (β = 0.053; P = 0.009). Remarkably, athletes did not maintain overall leg stiffness across prosthetic stiffness conditions. Rather, the in-series prosthetic stiffness governed overall leg stiffness. The metabolic cost of running in athletes with bilateral transtibial amputations is influenced by prosthetic model and stiffness but not height. NEW & NOTEWORTHY We measured the metabolic rates and biomechanics of five athletes with bilateral transtibial amputations while running with different prosthetic configurations. The metabolic cost of running for these athletes is minimized by using an optimal prosthetic model and reducing prosthetic stiffness. The metabolic cost of running was independent of prosthetic height, suggesting that longer legs are not advantageous for distance running. Moreover, the in-series prosthetic stiffness governs the leg stiffness of athletes with bilateral leg amputations.

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Sex and stride length impact leg stiffness and ground reaction forces when running with body borne load

Journal of Biomechanics ◽

10.1016/j.jbiomech.2019.01.048 ◽

2019 ◽

Vol 86 ◽

pp. 96-101 ◽

Cited By ~ 4

Author(s):

Nicholas J. Lobb ◽

AuraLea C. Fain ◽

Kayla D. Seymore ◽

Tyler N. Brown

Keyword(s):

Stride Length ◽

Ground Reaction Forces ◽

Leg Stiffness ◽

Reaction Forces

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Spring-like leg behaviour, musculoskeletal mechanics and control in maximum and submaximum height human hopping

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2010.0348 ◽

2011 ◽

Vol 366 (1570) ◽

pp. 1516-1529 ◽

Cited By ~ 23

Author(s):

Maarten F. Bobbert ◽

L. J. Richard Casius

Keyword(s):

Energy Expenditure ◽

Muscle Activation ◽

Mechanical Energy ◽

Reaction Force ◽

Ground Reaction Forces ◽

Centre Of Mass ◽

Leg Stiffness ◽

Reaction Forces ◽

And Control ◽

The Relationship

The purpose of this study was to understand how humans regulate their ‘leg stiffness’ in hopping, and to determine whether this regulation is intended to minimize energy expenditure. ‘Leg stiffness’ is the slope of the relationship between ground reaction force and displacement of the centre of mass (CM). Variations in leg stiffness were achieved in six subjects by having them hop at maximum and submaximum heights at a frequency of 1.7 Hz. Kinematics, ground reaction forces and electromyograms were measured. Leg stiffness decreased with hopping height, from 350 N m −1 kg −1 at 26 cm to 150 N m −1 kg −1 at 14 cm. Subjects reduced hopping height primarily by reducing the amplitude of muscle activation. Experimental results were reproduced with a model of the musculoskeletal system comprising four body segments and nine Hill-type muscles, with muscle stimulation STIM( t ) as only input. Correspondence between simulated hops and experimental hops was poor when STIM( t ) was optimized to minimize mechanical energy expenditure, but good when an objective function was used that penalized jerk of CM motion, suggesting that hopping subjects are not minimizing energy expenditure. Instead, we speculated, subjects are using a simple control strategy that results in smooth movements and a decrease in leg stiffness with hopping height.

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How do prosthetic stiffness, height and running speed affect the biomechanics of athletes with bilateral transtibial amputations?

Journal of The Royal Society Interface ◽

10.1098/rsif.2017.0230 ◽

2017 ◽

Vol 14 (131) ◽

pp. 20170230 ◽

Cited By ~ 9

Author(s):

Owen N. Beck ◽

Paolo Taboga ◽

Alena M. Grabowski

Keyword(s):

Treadmill Running ◽

Ground Reaction Forces ◽

Ground Contact ◽

Step Frequency ◽

Running Speed ◽

Leg Stiffness ◽

Reaction Forces ◽

Ground Contact Time ◽

Available Information ◽

Distance Running Performance

Limited available information describes how running-specific prostheses and running speed affect the biomechanics of athletes with bilateral transtibial amputations. Accordingly, we quantified the effects of prosthetic stiffness, height and speed on the biomechanics of five athletes with bilateral transtibial amputations during treadmill running. Each athlete performed a set of running trials with 15 different prosthetic model, stiffness and height combinations. Each set of trials began with the athlete running on a force-measuring treadmill at 3 m s −1 , subsequent trials incremented by 1 m s −1 until they achieved their fastest attainable speed. We collected ground reaction forces (GRFs) during each trial. Prosthetic stiffness, height and running speed each affected biomechanics. Specifically, with stiffer prostheses, athletes exhibited greater peak and stance average vertical GRFs ( β = 0.03; p < 0.001), increased overall leg stiffness ( β = 0.21; p < 0.001), decreased ground contact time ( β = −0.07; p < 0.001) and increased step frequency ( β = 0.042; p < 0.001). Prosthetic height inversely associated with step frequency ( β = −0.021; p < 0.001). Running speed inversely associated with leg stiffness ( β = −0.58; p < 0.001). Moreover, at faster running speeds, the effect of prosthetic stiffness and height on biomechanics was mitigated and unchanged, respectively. Thus, prosthetic stiffness, but not height, likely influences distance running performance more than sprinting performance for athletes with bilateral transtibial amputations.

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The biomechanics of the fastest sprinter with a unilateral transtibial amputation

Journal of Applied Physiology ◽

10.1152/japplphysiol.00737.2017 ◽

2018 ◽

Vol 124 (3) ◽

pp. 641-645 ◽

Cited By ~ 4

Author(s):

Owen N. Beck ◽

Alena M. Grabowski

Keyword(s):

Treadmill Running ◽

Ground Reaction Forces ◽

Functional Abilities ◽

Leg Length ◽

Transtibial Amputation ◽

Leg Stiffness ◽

Reaction Forces ◽

Vertical Ground ◽

Leg Amputation ◽

Vertical Ground Reaction Forces

People have debated whether athletes with transtibial amputations should compete with nonamputees in track events despite insufficient information regarding how the use of running-specific prostheses (RSPs) affect athletic performance. Thus, we sought to quantify the spatiotemporal variables, ground reaction forces, and spring-mass mechanics of the fastest athlete with a unilateral transtibial amputation using an RSP to reveal how he adapts his biomechanics to achieve elite running speeds. Accordingly, we measured ground reaction forces during treadmill running trials spanning 2.87 to 11.55 m/s of the current male International Paralympic Committee T44 100- and 200-m world record holder. To achieve faster running speeds, the present study’s athlete increased his affected leg (AL) step lengths ( P < 0.001) through longer contact lengths ( P < 0.001) and his unaffected leg (UL) step lengths ( P < 0.001) through longer contact lengths ( P < 0.001) and greater stance average vertical ground reaction forces ( P < 0.001). At faster running speeds, step time decreased for both legs ( P < 0.001) through shorter ground contact and aerial times ( P < 0.001). Unlike athletes with unilateral transtibial amputations, this athlete maintained constant AL and UL stiffness across running speeds ( P ≥ 0.569). Across speeds, AL step lengths were 8% longer ( P < 0.001) despite 16% lower AL stance average vertical ground reaction forces compared with the UL ( P < 0.001). The present study’s athlete exhibited biomechanics that differed from those of athletes with bilateral and without transtibial amputations. Overall, we present the biomechanics of the fastest athlete with a unilateral transtibial amputation, providing insight into the functional abilities of athletes with transtibial amputations using running-specific prostheses.NEW & NOTEWORTHY The present study’s athlete achieved the fastest treadmill running trial ever attained by an individual with a leg amputation (11.55 m/s). From 2.87 to 11.55 m/s, the present study’s athlete maintained constant affected and unaffected leg stiffness, which is atypical for athletes with unilateral transtibial amputations. Furthermore, the asymmetric vertical ground reaction forces of athletes with unilateral transtibial amputations during running may be the result of leg length discrepancies.

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Prosthetic model, but not stiffness or height, affects the metabolic cost of running for athletes with unilateral transtibial amputations

Journal of Applied Physiology ◽

10.1152/japplphysiol.00896.2016 ◽

2017 ◽

Vol 123 (1) ◽

pp. 38-48 ◽

Cited By ~ 10

Author(s):

Owen N. Beck ◽

Paolo Taboga ◽

Alena M. Grabowski

Keyword(s):

Lower Limb ◽

Metabolic Cost ◽

Ground Reaction Forces ◽

Ground Contact ◽

Limb Stiffness ◽

Leg Stiffness ◽

In Series ◽

Reaction Forces ◽

Vertical Ground ◽

Vertical Ground Reaction Forces

Running-specific prostheses enable athletes with lower limb amputations to run by emulating the spring-like function of biological legs. Current prosthetic stiffness and height recommendations aim to mitigate kinematic asymmetries for athletes with unilateral transtibial amputations. However, it is unclear how different prosthetic configurations influence the biomechanics and metabolic cost of running. Consequently, we investigated how prosthetic model, stiffness, and height affect the biomechanics and metabolic cost of running. Ten athletes with unilateral transtibial amputations each performed 15 running trials at 2.5 or 3.0 m/s while we measured ground reaction forces and metabolic rates. Athletes ran using three different prosthetic models with five different stiffness category and height combinations per model. Use of an Ottobock 1E90 Sprinter prosthesis reduced metabolic cost by 4.3 and 3.4% compared with use of Freedom Innovations Catapult [fixed effect (β) = −0.177; P < 0.001] and Össur Flex-Run (β = −0.139; P = 0.002) prostheses, respectively. Neither prosthetic stiffness ( P ≥ 0.180) nor height ( P = 0.062) affected the metabolic cost of running. The metabolic cost of running was related to lower peak (β = 0.649; P = 0.001) and stance average (β = 0.772; P = 0.018) vertical ground reaction forces, prolonged ground contact times (β = −4.349; P = 0.012), and decreased leg stiffness (β = 0.071; P < 0.001) averaged from both legs. Metabolic cost was reduced with more symmetric peak vertical ground reaction forces (β = 0.007; P = 0.003) but was unrelated to stride kinematic symmetry ( P ≥ 0.636). Therefore, prosthetic recommendations based on symmetric stride kinematics do not necessarily minimize the metabolic cost of running. Instead, an optimal prosthetic model, which improves overall biomechanics, minimizes the metabolic cost of running for athletes with unilateral transtibial amputations.NEW & NOTEWORTHY The metabolic cost of running for athletes with unilateral transtibial amputations depends on prosthetic model and is associated with lower peak and stance average vertical ground reaction forces, longer contact times, and reduced leg stiffness. Metabolic cost is unrelated to prosthetic stiffness, height, and stride kinematic symmetry. Unlike nonamputees who decrease leg stiffness with increased in-series surface stiffness, biological limb stiffness for athletes with unilateral transtibial amputations is positively correlated with increased in-series (prosthetic) stiffness.

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Stability in skipping gaits

Royal Society Open Science ◽

10.1098/rsos.160602 ◽

2016 ◽

Vol 3 (11) ◽

pp. 160602 ◽

Cited By ~ 7

Author(s):

Emanuel Andrada ◽

Roy Müller ◽

Reinhard Blickhan

Keyword(s):

Numerical Simulations ◽

Inverted Pendulum ◽

Ground Reaction Forces ◽

Fast Running ◽

Leg Stiffness ◽

Adult Humans ◽

Speed Range ◽

Reaction Forces ◽

System Energy ◽

Male Subjects

As an alternative to walking and running, humans are able to skip. However, adult humans avoid it. This fact seems to be related to the higher energetic costs associated with skipping. Still, children, some birds, lemurs and lizards use skipping gaits during daily locomotion. We combined experimental data on humans with numerical simulations to test whether stability and robustness motivate this choice. Parameters for modelling were obtained from 10 male subjects. They locomoted using unilateral skipping along a 12 m runway. We used a bipedal spring loaded inverted pendulum to model and to describe the dynamics of skipping. The subjects displayed higher peak ground reaction forces and leg stiffness in the first landing leg (trailing leg) compared to the second landing leg (leading leg). In numerical simulations, we found that skipping is stable across an amazing speed range from skipping on the spot to fast running speeds. Higher leg stiffness in the trailing leg permits longer strides at same system energy. However, this strategy is at the same time less robust to sudden drop perturbations than skipping with a stiffer leading leg. A slightly higher stiffness in the leading leg is most robust, but might be costlier.

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Lower Extremity Stiffness in Collegiate Distance Runners Pre- and Post-Competition

Journal of Human Kinetics ◽

10.2478/hukin-2019-0075 ◽

2020 ◽

Vol 71 (1) ◽

pp. 69-77

Author(s):

Jake P. Tavernite ◽

Matthew F. Moran

Keyword(s):

Ground Reaction Forces ◽

Distance Runners ◽

Countermovement Jump ◽

Squat Jump ◽

Leg Stiffness ◽

Main Effect ◽

Before And After ◽

Reaction Forces ◽

Cross Country ◽

Post Hoc

AbstractPrevious evidence has suggested that there is a relationship between leg stiffness and improved running performance. The purpose of this investigation was to determine how leg stiffness of runners was influenced in the 24 and 48 hour period following a cross country race. Twenty-two collegiate cross-country runners (13 males, 9 females, 19.5 ± 1.4 yr) were recruited and participated in the study. Leg stiffness was assessed 24 hours before and after a race as well as 48 hours post-race. Three jumping protocols were conducted: 1) a static jump, 2) a countermovement jump, and 3) a vertical hopping test. Two embedded force plates (1000 Hz) were utilized to measure ground reaction forces for each test and a metronome was utilized to maintain hopping frequency (2.2 Hz). A significant main effect was found for a static jump, a countermovement jump and leg stiffness. Leg stiffness was significantly reduced 24 hours post-race (pre-race 36.84 kN·m-1, 24h post 33.11 kN·m-1, p < 0.05), but not 48 hours post-race (36.30 kN·m-1). No significant differences were found in post-hoc analysis for the squat jump, countermovement jump height and the eccentric utilization ratio. Following a cross-country race, leg stiffness significantly declined in a group of collegiate runners in the immediate 24 hours post-race, but returned to baseline 48 hours post-race. Sport scientists and running coaches may be able to monitor leg stiffness as a metric to properly prescribe training regiments.

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Leg stiffness of sprinters using running-specific prostheses

Journal of The Royal Society Interface ◽

10.1098/rsif.2011.0877 ◽

2012 ◽

Vol 9 (73) ◽

pp. 1975-1982 ◽

Cited By ~ 54

Author(s):

Craig P. McGowan ◽

Alena M. Grabowski ◽

William J. McDermott ◽

Hugh M. Herr ◽

Rodger Kram

Keyword(s):

Ground Reaction Forces ◽

Mass Model ◽

Leg Stiffness ◽

Reaction Forces ◽

Vertical Ground ◽

Stiffness Characteristics ◽

And Performance ◽

Vertical Ground Reaction Forces ◽

Transtibial Amputees ◽

Running Mechanics

Running-specific prostheses (RSF) are designed to replicate the spring-like nature of biological legs (bioL) during running. However, it is not clear how these devices affect whole leg stiffness characteristics or running dynamics over a range of speeds. We used a simple spring–mass model to examine running mechanics across a range of speeds, in unilateral and bilateral transtibial amputees and performance-matched controls. We found significant differences between the affected leg (AL) of unilateral amputees and both ALs of bilateral amputees compared with the bioL of non-amputees for nearly every variable measured. Leg stiffness remained constant or increased with speed in bioL, but decreased with speed in legs with RSPs. The decrease in leg stiffness in legs with RSPs was mainly owing to a combination of lower peak ground reaction forces and increased leg compression with increasing speeds. Leg stiffness is an important parameter affecting contact time and the force exerted on the ground. It is likely that the fixed stiffness of the prosthesis coupled with differences in the limb posture required to run with the prosthesis limits the ability to modulate whole leg stiffness and the ability to apply high vertical ground reaction forces during sprinting.

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Running ground reaction forces across footwear conditions are predicted from the motion of two body mass components

Journal of Applied Physiology ◽

10.1152/japplphysiol.00925.2018 ◽

2019 ◽

Vol 126 (5) ◽

pp. 1315-1325 ◽

Cited By ~ 3

Author(s):

Andrew B. Udofa ◽

Kenneth P. Clark ◽

Laurence J. Ryan ◽

Peter G. Weyand

Keyword(s):

Ground Reaction Force ◽

Lower Limb ◽

Reaction Force ◽

Ground Reaction Forces ◽

Vertical Ground Reaction Force ◽

Time Patterns ◽

Foot Strike ◽

Reaction Forces ◽

Vertical Ground ◽

Force Time

Although running shoes alter foot-ground reaction forces, particularly during impact, how they do so is incompletely understood. Here, we hypothesized that footwear effects on running ground reaction force-time patterns can be accurately predicted from the motion of two components of the body’s mass (mb): the contacting lower-limb (m1 = 0.08mb) and the remainder (m2 = 0.92mb). Simultaneous motion and vertical ground reaction force-time data were acquired at 1,000 Hz from eight uninstructed subjects running on a force-instrumented treadmill at 4.0 and 7.0 m/s under four footwear conditions: barefoot, minimal sole, thin sole, and thick sole. Vertical ground reaction force-time patterns were generated from the two-mass model using body mass and footfall-specific measures of contact time, aerial time, and lower-limb impact deceleration. Model force-time patterns generated using the empirical inputs acquired for each footfall matched the measured patterns closely across the four footwear conditions at both protocol speeds ( r2 = 0.96 ± 0.004; root mean squared error = 0.17 ± 0.01 body-weight units; n = 275 total footfalls). Foot landing angles (θF) were inversely related to footwear thickness; more positive or plantar-flexed landing angles coincided with longer-impact durations and force-time patterns lacking distinct rising-edge force peaks. Our results support three conclusions: 1) running ground reaction force-time patterns across footwear conditions can be accurately predicted using our two-mass, two-impulse model, 2) impact forces, regardless of foot strike mechanics, can be accurately quantified from lower-limb motion and a fixed anatomical mass (0.08mb), and 3) runners maintain similar loading rates (ΔFvertical/Δtime) across footwear conditions by altering foot strike angle to regulate the duration of impact. NEW & NOTEWORTHY Here, we validate a two-mass, two-impulse model of running vertical ground reaction forces across four footwear thickness conditions (barefoot, minimal, thin, thick). Our model allows the impact portion of the impulse to be extracted from measured total ground reaction force-time patterns using motion data from the ankle. The gait adjustments observed across footwear conditions revealed that runners maintained similar loading rates across footwear conditions by altering foot strike angles to regulate the duration of impact.

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