Abstract
During prolonged running, the magnitude of Achilles tendon (AT) length change may increase, resulting in increased tendon strain energy return with each step. AT elongation might also affect the magnitude of triceps surae (TS) muscle shortening and shortening velocity, requiring greater activation and increased muscle energy cost. Therefore, we aimed to quantify the tendon strain energy return and muscle energy cost necessary to allow energy storage to occur prior to and following prolonged running. 14 trained male (n = 10) and female (n = 4) distance runners (24±4 years, 1.72±0.09 m, 61±10 kg, 64.6±5.8 ml•kg-1•min-1) ran 90 minutes (RUN) at approximately 85% of lactate threshold speed (sLT). Prior to and following RUN, AT stiffness and running energy cost (Erun) at 85% sLT were determined. AT energy return was calculated from AT stiffness, measured with dynamometry and ultrasound and estimated TS force during stance. TS energy cost was estimated on the basis of AT force and assumed crossbridge mechanics and energetics. Following RUN, AT stiffness was reduced from 328±172 N•mm-1 to 299±148 N•mm-1 (p = 0.022). Erun increased from 4.56±0.32 J•kg-1•m-1 to 4.62±0.32 J•kg-1•m-1 (p = 0.049). Estimated AT energy return was not different following RUN (p = 0.99). Estimated TS muscle energy cost increased significantly by 11.8±12.3 J•stride-1, (p = 0.0034), accounting for much of the post-RUN increase in Erun (8.6±14.5 J•stride-1,r2 = 0.31). These results demonstrate that a prolonged, submaximal run can reduce AT stiffness and increase Erun in trained runners, and that the elevated TS energy cost contributes substantially to the elevated Erun.
Citation: Fletcher JR, MacIntosh BR (2018) Changes in Achilles tendon stiffness and energy cost following a prolonged run in trained distance runners. PLoS ONE 13(8):
e0202026.
https://doi.org/10.1371/journal.pone.0202026
Editor: Hazel RC Screen, Queen Mary University of London, UNITED KINGDOM
Received: March 18, 2018; Accepted: July 26, 2018; Published: August 8, 2018
Copyright: © 2018 Fletcher, MacIntosh. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Data Availability: All relevant data are within the paper and its Supporting Information file.
Funding: JRF was supported by Natural Sciences and Engineering Research Council of Canada (NSERC PGSD2-391898-2010), and by Mitacs and Own the Podium through the Mitacs-Accelerate Program. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
Abbreviations:
ANOVA,
analysis of variance; AT,
Achilles tendon; dL,
tendon elongation; Erun,
energy cost of running; F,
force; Fz,
vertical ground reaction force; MG,
medial gastrocnemius; MVC,
maximal voluntary contraction; RUN,
prolonged 90 minute run; SD,
standard deviation; sLT,
speed of lactate threshold; SWC,
smallest worthwhile change; TS,
triceps surae; ,
maximal oxygen uptake
Description
Study investigates changes in Achilles tendon stiffness and energy cost in trained distance runners after prolonged running.