Determining characteristics of the Achilles tendon properties on metabolic cost and 3000 m running performance

Abstract

Tendons play a fundamental role in storing and releasing elastic energy, minimizing metabolic cost (CMET) in distance running. This behavior is related to the tendon's ability to resist deformation (e.g. stiffness), which is controlled by changes in the tendon morphological [cross-sectional area (CSA)], and material (e.g. Young’s modulus) properties. However, the relationship between Achilles tendon properties, CMET, and running performance is still uncertain. This study aimed to correlate the Achilles tendon properties, CMET and 3000 m running performance. 7 trained male long-distance runners (31 ± 8 years) participated in this study (Ethics Committee approval number: 2.437.616). Ultrasound was used to determine the Achilles tendon CSA, length, and elongation as a function of plantar flexion torque during voluntary plantar flexion. Tendon force- elongation and stress-strain relationships were determined by maximum voluntary isometric contractions on a dynamometer. Then, the maximal incremental test was performed until exhaustion on a treadmill. After 24 hours, CMET was measured in the running economy test for 5 minutes at 12 and 16 km.h-1 on a treadmill. After 10 minutes at rest, the 3000 m running performance test on an athletics track was performed. The oxygen uptake was measured by spirometry. Correlations between Achilles tendon properties, CMET (12 and 16 km.h-1), and 3000 m running performance were obtained through Pearson’s test (p<0.05). Correlation coefficient was classified as null (0), low (0-0.3), moderate (0.3-0.6), high (0.6-0.9), very high (0.9-1), and perfect (1). CMET at 16 km.h-1 correlated with CSA (r=-0.834, p=0.02), stress (r=0.901, p=0.006) and Young’s modulus (r=0.880, p=0.009). Moreover, stress also correlated with CSA (r=- 0.886, p=0.008) and Young’s modulus (r=0.878, p=0.009). Tendon stiffness showed a very high correlation with strain (r=-0.931, p=0.002). Finally, 3000m running performance correlated with vVO2MAX (r=-0.781, p=0.038). There was no correlation with TL or TL-SL, plantar flexor force, CMET at 12 km.h-1, VO2MAX, first and second ventilatory threshold. We concluded that runners with lower Young’s modulus, mainly due to greater CSA (related to lower stress) and greater stiffness (related to lower strain), presented better RE at 16 km.h-1 due to the greater tendon work at this speed, minimizing the CMET. Moreover, RE at 16 km.h-1 is indirectly related to the 3000 m running performance, due to the high correlation between vVO2MAX and 3000 m running performance.