Weyand - 2009 - The fastest runner on artificial legs: different limbs, similar function

Citation

Weyand PG, Bundle MW, McGowan CP, Grabowski A, Brown MB, Kram R, Herr H. The fastest runner on artificial legs: different limbs, similar function? J Appl Physiol. 2009 Sep;107(3):903-11. PUBMED - FULL TEXT

10 Word Summary

Amputees have similar metabolic costs, but different mechanics when running.

Abstract

The recent competitive successes of a bilateral, transtibial amputee sprint runner who races with modern running prostheses has triggered an international controversy regarding the relative function provided by his artificial limbs. Here, we conducted three tests of functional similarity between this amputee sprinter and competitive male runners with intact limbs: the metabolic cost of running, sprinting endurance, and running mechanics. Metabolic and mechanical data, respectively, were acquired via indirect calorimetry and ground reaction force measurements during constant-speed, level treadmill running. First, we found that the mean gross metabolic cost of transport of our amputee sprint subject (174.9 ml O(2).kg(-1).km(-1); speeds: 2.5-4.1 m/s) was only 3.8% lower than mean values for intact-limb elite distance runners and 6.7% lower than for subelite distance runners but 17% lower than for intact-limb 400-m specialists [210.6 (SD 13.2) ml O(2).kg(-1).km(-1)]. Second, the speeds that our amputee sprinter maintained for six all-out, constant-speed trials to failure (speeds: 6.6-10.8 m/s; durations: 2-90 s) were within 2.2 (SD 0.6)% of those predicted for intact-limb sprinters. Third, at sprinting speeds of 8.0, 9.0, and 10.0 m/s, our amputee subject had longer foot-ground contact times [+14.7 (SD 4.2)%], shorter aerial [-26.4 (SD 9.9)%] and swing times [-15.2 (SD 6.9)%], and lower stance-averaged vertical forces [-19.3 (SD 3.1)%] than intact-limb sprinters [top speeds = 10.8 vs. 10.8 (SD 0.6) m/s]. We conclude that running on modern, lower-limb sprinting prostheses appears to be physiologically similar but mechanically different from running with intact limbs.

Notes

• Assumptions about amputee
  • Smaller muscle volumes active during running requiring lower metabolic cost
  • Prostheses don't fatigue, so peak speed could be maintained longer
  • Mechanics of prostheses and lower limbs are similar
• Metabolic measures
  • Rate of oxygen uptake
    • Similar to that of distance runners
  • Maximal aerobic power
    • Almost identical to sprinter even though lower rate of oxygen uptake and lower cost of transport
  • Metabolic cost of transport
    • 175 mL-O2/kg/km for amputee
    • 182 mL-O2/kg/km for distance runners
• Sprinting endurance
• Sprinting mechanics
  • Top speed
    • Same as intact subjects, the relatively slow starts are likely due to the fact that HE DOESN'T HAVE ANKLES!!!!
  • Treadmill force data
    • Ground reaction forces lower and over longer period of time for amputee compared to intact-limb subject.
    • Swing time of leg shorter in amputee
    • Aerial phase shorter in amputee
• Running is physiologically similar, but mechanically dissimilar between amputee and intact-limb subjects.
• The specific absence of bi- and polyarticular muscles disallows the transfer of muscularforce possible from the knee to the ankle and foot of an intactlimb. The lesser ground reaction forces observed in theprosthetic vs. intact-limbs of unilateral, transtibial amputees provide direct evidence of a force impairment.