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Olympics 2024: physicists are improving competitors' abilities

Paralympics: how to optimise jumping blades for long-jumper amputees

Fabien Szmytka, Researcher at ENSTA Paris (IP Paris), Jean-François Semblat, Professor at at ENSTA Paris, Head of mechanics and energy department at IP Paris and Élodie Doyen, research engineer at ENSTA Paris (IP Paris)
On January 3rd, 2023 |
4 min reading time
Fabien Szmytka
Fabien Szmytka
Researcher at ENSTA Paris (IP Paris)
Jean François Semblat
Jean-François Semblat
Professor at at ENSTA Paris, Head of mechanics and energy department at IP Paris
Elodie Doyen
Élodie Doyen
research engineer at ENSTA Paris (IP Paris)
Key takeaways
  • In the context of the 2024 Olympic and Paralympic Games, studies are being conducted to improve the performance of tibial prostheses.
  • The Paralympic athletes concerned use spring-like jumping blades to replace the amputated limb.
  • The main challenge is to convert the athlete's kinetic energy into “momentum”, in order to jump as far as possible.
  • In addition to improving performance, the aim is also to improve the comfort of athletes by avoiding skin-prosthesis friction as much as possible.
  • The study of static and dynamic forces is put to use for the benefit of the human being, in order to advance the “augmented human”.

The 2024 Paris Olympic and Par­a­lympic Games are fast approach­ing. As part of the SCIENCES2024 project, we are work­ing to improve the per­for­mance of the tib­ial pros­the­ses used by cer­tain Par­a­lympians for the long jump. There are sev­er­al cat­e­gories of amputees – low or high leg ampu­ta­tion, both limbs or one limb – but we are focus­ing on uni­lat­er­al amputees, i.e. those who have had one leg ampu­tat­ed below the knee.

Jumping further

The aim of our approach is to find solu­tions to opti­mise the resti­tu­tion of ener­gy at the crit­i­cal moment of the jump: it is the very moment of the impulse that allows the ath­lete to project him­self for­ward. In uni­lat­er­al amputees, the jump­ing blade – made of rigid but very slen­der car­bon – replaces the ampu­tat­ed limb and is like a large, almost per­fect spring.

The blade, which fits over the resid­ual limb, allows the ath­lete to take off by press­ing on it and thus com­press­ing it strong­ly at the moment of impulse. Dur­ing a long jump, an ath­lete makes a long run-up: the faster he or she runs, the more kinet­ic ener­gy he or she stores, which is then “trans­formed” into impulse dur­ing the final take-off. The main chal­lenge is to con­vert this kinet­ic ener­gy, linked to the speed of the run-up, into “impulse ener­gy” to enable the ath­lete to run as far as possible. 

The main chal­lenge is to con­vert the momen­tum into impulse ener­gy to allow the ath­lete to run as far as possible.

Cer­tain para­me­ters, such as an unsuit­able jump angle, a poor body posi­tion or the athlete’s own move­ments dur­ing the jump, can dis­si­pate this pre­cious ener­gy. In addi­tion, fric­tion in the sock­et or shock to the ath­lete’s body can lead to injury – even if the ges­ture or pros­the­sis is designed in the best pos­si­ble way for per­for­mance. We are there­fore look­ing at how to opti­mal­ly trans­fer this kinet­ic ener­gy to the impulse in a length-effi­cient man­ner with­out caus­ing injury that is detri­men­tal to performance. 

The sports ges­ture and the pros­the­sis are there­fore essen­tial for ener­gy con­ver­sion. To this end, we study the ener­gy accu­mu­lat­ed in the blade so that the ath­lete can project as far as pos­si­ble. We are more inter­est­ed in per­for­mance in this part of our work, and we work with the tech­ni­cal direc­tor of the French Han­d­is­port Fed­er­a­tion who puts us in con­tact with the ath­letes and their trainers.

Improving comfort 

So, in addi­tion to improv­ing per­for­mance, we also seek to improve the com­fort of the ath­letes, to lim­it their fatigue and, of course, their injuries. The jump­ing blade is an appendage that allows them to jump, but it also cre­ates vibra­tions and shocks when it hits the ground. These vibra­tions can cause fric­tion in the sock­et, lead­ing to dis­com­fort and even pain. We are look­ing to mea­sure these shocks through numer­i­cal mod­el­ling to analyse their trans­mis­sion to the athlete’s body.

We will be able to under­stand how the mate­ri­als mak­ing up the blade and the pros­the­sis can deform mechan­i­cal­ly and reduce the shock.

We have set up exper­i­men­tal pro­to­cols in the lab­o­ra­to­ry that will enable us to repro­duce the sport­ing ges­ture. With these, we will be able to under­stand the over­all defor­ma­tion of the blade, under the effect of com­pres­sion, dur­ing the impulse, but above all we will be able to under­stand how the mate­ri­als mak­ing up the blade and the pros­the­sis trans­mit the forces of the track to the ath­lete’s body. In addi­tion, we will iden­ti­fy their role both in the resti­tu­tion of ener­gy and in the reduc­tion of the risk of injury inher­ent in the practice.

To do this, we have devel­oped numer­ous lab­o­ra­to­ry exper­i­ments with var­i­ous instru­ments. High-speed cam­eras and sen­sors allow us to analyse dynam­ic phe­nom­e­na in detail and to mea­sure efforts and wave trans­fer. These mea­sure­ments allow us to move towards a glob­al opti­mi­sa­tion of the blade-pros­the­sis system.

We are also work­ing on the devel­op­ment of the mate­ri­als that make up the pros­the­sis and we are try­ing to find those that will give good over­all per­for­mance. These mate­ri­als are man­u­fac­tured by 3D print­ing, oth­er­wise known as addi­tive man­u­fac­tur­ing.

Understanding the forces 

To best analyse the impact of mate­ri­als and ath­let­ic move­ment, we are look­ing at two sce­nar­ios. In the first, when the ath­lete press­es on the blade slow­ly enough, this caus­es a pro­gres­sive defor­ma­tion. In this case, the infor­ma­tion can be analysed in a fair­ly sim­ple way through a sta­t­ic lab­o­ra­to­ry test pro­to­col. Since the blade is made of a rigid but slen­der mate­r­i­al, it deforms glob­al­ly but also local­ly at the sole and at the point of con­tact with the resid­ual limb via the sock­et. We are there­fore study­ing the local sta­t­ic defor­ma­tions, which allow us to under­stand how ener­gy is dis­si­pat­ed, and the nature of the pres­sures on the ampu­tat­ed limb, which can lead to pos­si­ble injuries.

Sec­ond sce­nario: the speed of the load is pro­gres­sive­ly increased to repro­duce the con­di­tions of the athlete’s last impulse on the blade. Thanks to our obser­va­tions dur­ing the ath­lete’s run and at the moment of his jump, we are able to mea­sure the defor­ma­tion speed of the blade and the sole. The trans­mis­sion of vibra­tions and shocks from the ground to the blade and then to the athlete’s limb is thus char­ac­terised by the­o­ret­i­cal mod­els. In this sec­ond sce­nario, it is also inter­est­ing to see the dynam­ic effects and forces that inter­act between the track, the blade, and the ath­lete. These forces vary rapid­ly at the moment of impulse and are rep­re­sen­ta­tive of the impact phe­nom­e­na that often lead to injuries.

In the first sce­nario, sta­t­ic forces are at work; in the sec­ond, dynam­ic or impulse forces are at work. These con­cepts are com­mon­ly used to study struc­tured mate­ri­als or meta­ma­te­ri­als in indus­try. We trans­pose them to the ser­vice of humans, to advance the field of “aug­ment­ed human” or the future medal-win­ning athlete!

Isabelle Dumé


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