The Valid Measurement of Running Economy in Runners
Participant Characteristics. Participant characteristics are shown in Table 1. The well-trained status of the participants was emphasized by the high V̇O2max and vLTP values for both males and females. On average, the four stages before vLTP were 12.4–15.4 km·h for females and 13.8–16.8 km·h for males.
Allometric Modeling. Plots of BM against EC (Fig. 1) and OC (Fig. 2) were fitted with both power and linear functions. The results of the regression analyses with a power function fit between absolute EC and BM revealed exponents close to unity (males, b = 0.90, CI = 0.75–1.05; females, b = 0.88, CI = 0.66–1.10) and for OC (males, b = 0.93, CI = 0.79–1.06; females, b = 0.95, CI = 0.73–1.16). Similar but marginally higher R and lower RMSE values were observed for linear ratio scaling compared with power functions for both OC an EC (Table 2). The appropriateness of the linear model was confirmed by the absence of any relationship when BM was replotted against ratio scaled EC (kcal·kg·km) and OC (mL·kg·km) for both males (R = 0.017, P = 0.19 and R = 0.011, P = 0.30, respectively) and females (R = 0.012, P = 0.36 and R = 0.001, P = 0.77, respectively). Consequently, relative expressions of EC and OC were scaled to BM in all further analysis.
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Figure 1.
Absolute energy cost versus body mass. A. Females (n = 71) fitted with linear (solid line; y = 1.087x + 4.323) and power functions (dashed line; y = 1.888x ). B. Males (n = 101) fitted with linear (solid line; y = 1.052x + 6.506) and power functions (dashed line; y = 1.746x ).
(Enlarge Image)
Figure 2.
Absolute oxygen cost versus body mass. A. Females (n = 71) fitted with linear (solid line; y = 0.218x + 0.063) and power functions (dashed line; y = 0.271x ). B. Males (n = 101) fitted with linear (solid line; y = 0.202x + 0.841) and power functions (dashed line; y = 0.290x ).
Running Speed. No interaction effect was evident between speed and sex for EC, OC, and RER. Thus, both cohorts were combined to analyze the influence of speed on these parameters. ANOVA revealed increases in RER with increments in running speed (P < 0.001; Fig. 3). Increases in EC were also observed with increments in running speed (ANOVA, P < 0.001; Fig. 3). No differences in OC were seen across the four monitored speeds (ANOVA, P = 0.54).
(Enlarge Image)
Figure 3.
Physiological measures at the four speeds before lactate turn point (LTP; n = 151). *Significant difference from all other speeds (ANOVA with Bonferroni post hoc adjustments; P < 0.001).
Results
Participant Characteristics. Participant characteristics are shown in Table 1. The well-trained status of the participants was emphasized by the high V̇O2max and vLTP values for both males and females. On average, the four stages before vLTP were 12.4–15.4 km·h for females and 13.8–16.8 km·h for males.
Allometric Modeling. Plots of BM against EC (Fig. 1) and OC (Fig. 2) were fitted with both power and linear functions. The results of the regression analyses with a power function fit between absolute EC and BM revealed exponents close to unity (males, b = 0.90, CI = 0.75–1.05; females, b = 0.88, CI = 0.66–1.10) and for OC (males, b = 0.93, CI = 0.79–1.06; females, b = 0.95, CI = 0.73–1.16). Similar but marginally higher R and lower RMSE values were observed for linear ratio scaling compared with power functions for both OC an EC (Table 2). The appropriateness of the linear model was confirmed by the absence of any relationship when BM was replotted against ratio scaled EC (kcal·kg·km) and OC (mL·kg·km) for both males (R = 0.017, P = 0.19 and R = 0.011, P = 0.30, respectively) and females (R = 0.012, P = 0.36 and R = 0.001, P = 0.77, respectively). Consequently, relative expressions of EC and OC were scaled to BM in all further analysis.
(Enlarge Image)
Figure 1.
Absolute energy cost versus body mass. A. Females (n = 71) fitted with linear (solid line; y = 1.087x + 4.323) and power functions (dashed line; y = 1.888x ). B. Males (n = 101) fitted with linear (solid line; y = 1.052x + 6.506) and power functions (dashed line; y = 1.746x ).
(Enlarge Image)
Figure 2.
Absolute oxygen cost versus body mass. A. Females (n = 71) fitted with linear (solid line; y = 0.218x + 0.063) and power functions (dashed line; y = 0.271x ). B. Males (n = 101) fitted with linear (solid line; y = 0.202x + 0.841) and power functions (dashed line; y = 0.290x ).
Running Speed. No interaction effect was evident between speed and sex for EC, OC, and RER. Thus, both cohorts were combined to analyze the influence of speed on these parameters. ANOVA revealed increases in RER with increments in running speed (P < 0.001; Fig. 3). Increases in EC were also observed with increments in running speed (ANOVA, P < 0.001; Fig. 3). No differences in OC were seen across the four monitored speeds (ANOVA, P = 0.54).
(Enlarge Image)
Figure 3.
Physiological measures at the four speeds before lactate turn point (LTP; n = 151). *Significant difference from all other speeds (ANOVA with Bonferroni post hoc adjustments; P < 0.001).
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