Lower limb amputees competing in the 400m sprint at this year's Rio Paralympics could improve their chances of success by using stiffer prosthetics.

Stiffer prosthetics help improve sprinting economy for longer distance sprints and could theoretically lead to faster times, says Dr Lara Grobler from the Sport Physiology Laboratory in the Department of Sport Science at Stellenbosch University (SU). In her recent doctoral study at SU, Grobler focused on the mechanical aspects of Running Specific Prostheses (RSPs) and its effect on sprinting performance.

Having worked with athletes with physical impairments, Grobler says she realised the need for more knowledge regarding prosthetic selection as well as the interaction between mechanical components of prostheses and the biology of athletes.

She points out that while athletes with lower-limb amputations, cerebral palsy and visual impairments improved their sprinting performance over the years, those with lower-limb amputations showed greater improvement thanks to technological advances in the RSPs used at event such as the Paralympic Games.

As part of her study, Grobler completed athlete independent testing on eight (four categories of two models) different prosthetics.

She connected the RSPs to a custom-made prosthetic socket and attached them to a specific piece of gym equipment. She then loaded the machine with weight and dropped it onto a force plate while at the same time recording the drop and subsequent hops of the RSPs on a high-speed camera. This allowed her to determine the ground reaction force (force exerted by the RSP when dropped to the ground), contact time (length of time during which the foot is in contact with the ground) and jump time (length of time the RSP is in the air after hopping off the ground), as well as the compression of the prosthetic throughout the contact time.

Grobler says her study showed that there is a difference in the stiffness between the two models.

"We tested these two models of prosthetics on an athlete with a lower limb amputation and found that stiffer prosthetics cause improvements in sprinting economy. This was achieved by decreased contact time with stiffer prosthetics leading to decreases in work time and neuromuscular fatigue."

"We also found that the shorter distance sprint RSP was less stiff than the longer distance sprint prosthetic, which resulted in the ground reaction force of the longer distance sprint prosthetic being greater than the shorter distance sprint prosthetic," says Grobler.

"Furthermore, the contact time was shorter with the longer distance prosthetic and the compression of the prosthetic was greater with the shorter distance prosthetic."

Grobler says that while stiffer prosthetics could help athletes in longer sprints, it is unclear whether they would also be beneficial for shorter sprints since no studies have been done in this regard.

• Photo: Dr Lara Grobler testing the mechnical aspects of running prostheses.
  
• Photographer: Sarah Arnold
  

​FOR MEDIA ENQUIRIES ONLY

Dr Lara Grobler

Sport Physiology Laboratory

Department of Sport Science

Stellenbosch University

Tel: 021 808 3915

15028151@sun.ac.za