Energy cost of running and Achilles tendon stiffness in man and woman trained runners

Abstract

The energy cost of running (E run), a key determinant of distance running performance, is influenced by several factors. Although it is important to express E run as energy cost, no study has used this approach to compare similarly trained men and women. Furthermore, the relationship between Achilles tendon (AT) stiffness and E run has not been compared between men and women. Therefore, our purpose was to determine if sex-specific differences in E run and/or AT stiffness existed. E run (kcal kg(-1) km(-1)) was determined by indirect calorimetry at 75%, 85%, and 95% of the speed at lactate threshold (sLT) on 11 man (mean ± SEM, 35 ± 1 years, 177 ± 1 cm, 78 ± 1 kg, [Formula: see text]1 = 56 ± 1 mL kg(-1) min(-1)) and 18 woman (33 ± 1 years, 165 ± 1 cm, 58 ± 1 kg, [Formula: see text]2 = 50 ± 0.3 mL kg(-1) min(-1)) runners. AT stiffness was measured using ultrasound with dynamometry. Man E run was 1.01 ± 0.06, 1.04 ± 0.07, and 1.07 ± 0.07 kcal kg(-1) km(-1). Woman E run was 1.05 ± 0.10, 1.07 ± 0.09, and 1.09 ± 0.10 kcal kg(-1) km(-1). There was no significant sex effect for E run or RER, but both increased with speed (P < 0.01) expressed relative to sLT. High-range AT stiffness was 191 ± 5.1 N mm(-1) for men and 125 ± 5.5 N mm(-1), for women (P < 0.001). The relationship between low-range AT stiffness and E run was significant at all measured speeds for women (r (2) = 0.198, P < 0.05), but not for the men. These results indicate that when E run is measured at the same relative intensity, there are no sex-specific differences in E run or substrate use. Furthermore, differences in E run cannot be explained solely by differences in AT stiffness.

Keywords: Allometric scaling; economy of locomotion; oxygen uptake; respiratory exchange ratio; running economy.

Figure 1.

Oxygen cost at the three measured relative speeds in both men and women. Speed is expressed relative to the speed at lactate threshold (sLT). Vertical bars represent SD.

Figure 2.

E_run as a function of absolute running speed. Energy of running was measured at 75% (A), 85% (B), and 95% (C) of sLT.

Figure 3.

The relationship between Achilles tendon (AT) stiffness and the energy cost of running for men and women. Open and closed dots represent each man and woman subject, respectively. E_run is represented as mean ± SD for all measured speeds. AT stiffness is shown as the stiffness representing the slope from 50 to 100% MVC of the force‐elongation curve for each subject. Solid and dashed lines represent the linear regression for woman and man subjects, respectively.