Metabolic flexibility includes the ability to perform fat and carbohydrate oxidation, as well as oxidative capacity, which is associated with mitochondrial function, energetic contributions, and physical health and performance. During a session of graded incremental exercise testing (GIET), we investigated metabolic flexibility, the contributions of three energy systems, and performances of individuals with different metabolic characteristics. Fifteen general population (GP; n = 15, male n = 7, female n = 8) and 15 national-level half-marathon and triathlon athletes (A; n = 15, male n = 7, female n = 8) participated in this study. During GIET, heart rate (HR), oxygen uptake (V˙O2mean and V˙CO2mean), metabolic equivalents (METs) in V˙O2mean, and blood glucose and lactate concentrations (La−) were measured. Furthermore, jogging/running speeds (S) at specific La−, fat and carbohydrate oxidations (FATox and CHOox), and energetic contributions (oxidative; WOxi, glycolytic; WGly, and phosphagen; WPCr) were calculated. The percentages of HRmax, relative V˙O2mean, V˙CO2mean, and METs in V˙O2mean were all lower in A than they were in GP. FATox values were lower in GP than in A, while CHOox and La− were higher in GP than in A. Negative correlations between La− and FATox were also observed in both groups. Contributions of WOxi, WGly, and WPCr were higher in GP than in A during GIET. Moreover, values of WGly, and WPCr were significantly lower and higher, respectively, in male GP than in female GP. Furthermore, S at specific La− were higher in A than in GP. It is suggested that an individualized low-intensity recovery exercise program be established, to achieve increased metabolic flexibility and oxidative capacity (aerobic base), such as public health improvements and a greater volume of higher exercise intensities; this is the type of exercise that elite athletes worldwide mostly perform during their training period and progression. This may prevent cardiac/metabolic diseases in GP.

The diagnostics of anaerobic glycolytic metabolism which play a subordinate role in elite rowing and parameters such as maximum lactate accumulation rate (νLa.max) have thus far not been associated with ergometer rowing performance. The aim of the study was to quantify the glycolytic energy metabolism (WGly) during a 2000 m ergometer rowing time trial (RTT) and νLa.max during a 10 s maximum ergometer rowing sprint test (RST) and to unravel associations between those variables and RTT performance. Combined post-exercise lactate measurements and oxygen uptake after RST and RTT were used to determine νLa.max and glycolytic energy contribution (WGly) in seven male and three female German U 23 national rowers (N = 10, 19.8 ± 0.9 years, 183.2 ± 7.0 cm height, 79.9 ± 13.3 kg body mass, 16.4 ± 5.1 % body fat). WGly during RTT ranged from 7 to 15.5% and νLa.max between 0.25 and 0.66 mmol∙L−1∙s−1. νLa.max correlated with WGly (p < 0.05, r = 0.74) and the mechanical power output (W) for the first 300 m (300first) during RTT (p < 0.05, r = 0.67). νLa.max further correlated with ∆300first−last (W) for the first and last 300 m (300last) during RTT (p < 0.01, r = 0.87) and also within the subgroup of male rowers. νLa.max displays a wide spectrum of individual differences in rowers. Due to this and its correlation to specific phases of RTT, it contributes to an individual energetic performance profile in rowing. Future studies must undermine the role of νLa.max for exercise performance and whether it serves as a marker that can be specifically targeted for a training-induced increase or decrease.