Abstract
Purpose: This study aimed to determine whether triceps surae’s muscle architecture and Achilles tendon parameters are related to running metabolic cost (C) in trained long-distance runners.Methods: Seventeen trained male recreational long-distance runners (mean age = 34 years) participated in this study. C was measured during submaximal steady-state running (5 min) at 12 and 16 km h–1 on a treadmill. Ultrasound was used to determine the gastrocnemius medialis (GM), gastrocnemius lateralis (GL), and soleus (SO) muscle architecture, including fascicle length (FL) and pennation angle (PA), and the Achilles tendon cross-sectional area (CSA), resting length and elongation as a function of plantar flexion torque during maximal voluntary plantar flexion. Achilles tendon mechanical (force, elongation, and stiffness) and material (stress, strain, and Young’s modulus) properties were determined. Stepwise multiple linear regressions were used to determine the relationship between independent variables (tendon resting length, CSA, force, elongation, stiffness, stress, strain, Young’s modulus, and FL and PA of triceps surae muscles) and C (J kg–1m–1) at 12 and 16 km h–1.Results: SO PA and Achilles tendon CSA were negatively associated with C (r2 = 0.69; p < 0.001) at 12 km h–1, whereas SO PA was negatively and Achilles tendon stress was positively associated with C (r2 = 0.63; p = 0.001) at 16 km h–1, respectively. Our results presented a small power, and the multiple linear regression’s cause-effect relation was limited due to the low sample size.Conclusion: For a given muscle length, greater SO PA, probably related to short muscle fibers and to a large physiological cross-sectional area, may be beneficial to C. Larger Achilles tendon CSA may determine a better force distribution per tendon area, thereby reducing tendon stress and C at submaximal speeds (12 and 16 km h–1). Furthermore, Achilles tendon morphological and mechanical properties (CSA, stress, and Young’s modulus) and triceps surae muscle architecture (GM PA, GM FL, SO PA, and SO FL) presented large correlations with C.
Highlights
Economical running is an important biological advantage in human evolution (Saibene and Minetti, 2003)
Endurance running performance is significantly related to some physiological factors, such as maximal oxygen uptake (V O2MAX), physiological transition thresholds, V O2MAX fractional utilization, and the net energy cost of running [the energy expended above the resting energy expenditure per unit of distance, running metabolic cost (C), measured in J kg−1 km−1]
The equation used to predict C at 16 km h−1 (C16) was: C16 = 5.187 + (−0.082) SO PA + (0.006) stress where C16 is the running metabolic cost at 16 km h−1 (J kg−1 m−1) and SO PA is the soleus pennation angle (◦) and stress is measured in MPa
Summary
Economical running is an important biological advantage in human evolution (Saibene and Minetti, 2003). Adaptations at the organismal level (e.g., lower limbs morphology) allowed humans to run greater distances with a lower energy cost compared to their primate relatives (Steudel-Numbers and Wall-Scheffler, 2009) In this regard, human running has been classified as an energy-saving mechanism, where part of the total mechanical energy associated with the body center of mass is stored as elastic strain energy by the lower limb elastic structures (Cavagna et al, 1964; Alexander, 1991; Saibene and Minetti, 2003). The triceps surae muscletendon unit (MTU) is very important for running performance, being responsible together with the quadriceps, for more than 70% of the total mechanical work during the stance phase (Sasaki and Neptune, 2006) It comprises three muscles (GM, gastrocnemius medialis; GL, gastrocnemius lateralis, SO, soleus) joined distally by a single tendon (i.e., the Achilles tendon). MTUs with short fibers and long tendons (e.g., triceps surae) reduce C due to the lower muscle work required to perform terrestrial locomotion (Holt et al, 2014)
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