Effect of Achilles Tendon Mechanics on the Running Economy of Elite Endurance Athletes

Abstract

The Achilles tendon stores and releases strain energy, influencing running economy. The present study aims to verify the influence of the Achilles tendon tangent modulus, as a material property, on running economy by comparing two groups of elite endurance-performance athletes undergoing different running training volumes. Twelve athletes, six long-distance runners and six pentathletes, were studied. Long-distance runners had a higher weekly running training volume (116.7±13.7 vs. 58.3±20.4 km, p<0.05) and a better running economy (204.3±12.0 vs. 222.0±8.7 O2 mL ∙ kg−1 ∙ km−1, p<0.05) evaluated in a treadmill at 16 km·h–1, 1% inclination. Both groups presented similar VO2max (68.5±3.8 vs. 65.7±5.0 mL ∙ min−1 ∙ kg−1, p>0.05). Achilles tendon tangent modulus was estimated from ultrasound-measured deformations, with the ankle passively mobilized by a dynamometer. True stress was calculated from the measured torque. The long-distance runners had a higher maximum tangent modulus (380.6±92.2 vs. 236.2±82.6 MPa, p<0.05) and maximum true stress than pentathletes (24.2±5.1 vs. 16.0±3.5 MPa, p<0.05). The correlation coefficient between tangent modulus at larger deformations was R=–0.7447 (p<0.05). Quantifying tendon tissue adaptations associated with different running training volumes will support subject and modality-specific workouts prescription of elite endurance athletes.

Triceps Surae Muscle-Tendon Properties as Determinants of the Metabolic Cost in Trained Long-Distance Runners

“…A stronger muscle with shorter fascicles will demand a higher tendon mechanical capacity (i.e., higher stiffness), which is probably related to an improvement in the operating fascicle force-velocity profile, mainly during the tendon lengthening, improving the muscular work production efficiency ( Bohm et al, 2021a ). A stiffer Achilles tendon may reach higher elastic energy storage and release capacity ( Pinto et al, 2021 ). As the runners present similar Achilles tendon strain during running compared to the non-runners and the runners with different running economies ( Rosager et al, 2002 ; Arampatzis et al, 2006 ), a larger Achilles tendon CSA will require a greater amount of force to stretch the tendon, increasing the elastic strain energy stored ( Rosager et al, 2002 ).…”

“…This is interesting as trained runners present higher Achilles tendon stiffness compared with healthy non-runners ( Devaprakash et al, 2020 ). Furthermore, Pinto et al (2021) found that the Achilles tendon material (maximum tangent modulus and stress) of elite long-distance runners ( N = 6) is higher than that of pentathletes ( N = 6). Moreover, the authors suggest that higher Achilles tendon stiffness is presumably associated with the highest weekly running training volume and with a tendency to reach higher elastic energy storage and release capacity.…”

“…The elastic storage capacity of a deformable structure is the area below the force-elongation curve, or the stress-strain curve, in which case the elastic energy is normalized by material volume. Elastic energy depends on MTU’s force and length limits and on the fixed or variable force-elongation curve slope, defined as stiffness ( Pinto et al, 2021 ). Therefore, larger CSA tendons can store more elastic strain energy than thin tendons (minor CSA) at similar tendon elongation ( Geremia et al, 2018 ) and, therefore, have higher stiffness.…”

“…Moreover, the authors suggest that higher Achilles tendon stiffness is presumably associated with the highest weekly running training volume and with a tendency to reach higher elastic energy storage and release capacity. Finally, they found a significant negative correlation between running economy (RE) and Achilles tendon tangent modulus ( r = −0.74), suggesting that long-distance runners can generate a greater running propulsion tendon force, enabling more RE and, possibly, greater storage and release of elastic energy ( Pinto et al, 2021 ). These results agree with those found by Arampatzis et al (2006) who found greater Achilles tendon force and stiffness in a group of endurance runners with better RE, compared to runners with lower RE, without differences on GM muscle architecture parameters.…”

“…The conflicting results found in the literature between triceps surae muscle architecture and/or Achilles tendon’s morphological, mechanical, and material properties’ independent variables, related to running performance, RE or, more specifically, to C, can be explained by the studies’ methodological differences regarding training characteristics (e.g., volume and intensity) and/or specificity of recruited sample size ( Ooi et al, 2015 ; Pinto et al, 2021 ). Therefore, it is unclear which of the Achilles tendon parameters are associated with C. Similarly, although the triceps surae muscle generates tension actively, which suggests that the muscle is the dominant structure determining C ( Kram, 2000 ; Fletcher and MacIntosh, 2017 ; Bohm et al, 2021a ), we do not know which of the triceps surae muscle architecture parameters are related to C, and what is the relative contribution between the muscular and tendon parameters to C. Therefore, our goal was to determine whether triceps surae’s muscle architecture and Achilles tendon parameters are related to C in trained long-distance runners at different running speeds (12 and 16 km h –1 ).…”