Author(s): MALINEN, T., NUUTTILA, O.P., MATOMÄKI, P., UUSITALO, A., KYRÖLÄINEN, H., Institution: UNIVERSITY OF JYVÄSKYLÄ, Country: FINLAND, Abstract-ID: 1836

INTRODUCTION:
Endurance performance is considered to be determined by maximal oxygen uptake (VO₂max), movement economy (e.g., running economy, RE), and lactate/ventilatory thresholds (LTs and VTs). These variables are commonly assessed using incremental tests, in which the maximal speed achieved (sPeak), reflecting both VO₂max and economy, is strongly associated with endurance performance. During prolonged exercise, however, these variables deteriorate; the ability to preserve them is termed physiological resilience. The determinants of physiological resilience remain unclear, although overall aerobic fitness, muscle fiber type distribution, and neuromuscular characteristics have been suggested as contributing factors. The purpose of this study was to investigate the relationship between physiological resilience, quantified as the decline (Δ%) in VO₂max, sPeak, VTs, and RE during and after prolonged exercise, and other variables associated with endurance performance.
METHODS:
33 well-trained endurance runners (18 females) participated in the study. On three separate testing days, they completed a peak fat oxidation test (measured variables: peak fat oxidation [PFO], and fatmax), a maximal anaerobic running test (measured variables: maximal power and maximal blood lactate concentration [LAmax]), an isometric leg press test (measured variable: maximal voluntary contraction [MVC]), a VO2max-test (measured variables: VO2max, sPeak and speed at VTs [sVTs]) and a 138-min physiological resilience test at ~90% of VT1 (including three 30 min moderate intensity running bouts divided by submaximal incremental tests) followed by a fatigued state VO2max-test (measured variables: physiological resilience). Associations between selected variables and physiological resilience were analyzed using Pearson’s or sex-adjusted partial correlations. Partial correlations were applied to variables influenced by sex (VO₂max, sPeak, VTs, MVC, PFO, and Pmax).
RESULTS:
Overall, VO2max (-2.3 %), sPeak (-6.4 %), sVTs (-4.4 and -5.5 %) and RE (5.0 %) all deteriorated during the physiological resilience test (p < 0.002). Δ%sPeak was negatively associated with LAmax (r = -0.37) and positively with VO2max (r = 0.37). Δ%sVT1 was associated with VO2max (r = 0.37), sVT2 (r = 0.52), sVT1 (r = 0.48) and sPeak (r = 0.44). Δ%RE was negatively associated with RE (r = -0.49) and MVC (r = -0.40). Δ%VO2max was associated with RE (r = 0.42). No significant correlations were observed for Δ%sVT2.
CONCLUSION:
Greater maximal strength of the leg extensor appears to be related to better ability to sustain RE. In contrast, higher aerobic fitness is related to the ability to sustain sVT1 and sPeak, whereas higher LAmax is associated with larger decline in sPeak. These findings suggest that high aerobic fitness and maximal strength of leg extensors seem to be key determinants of physiological resilience, while greater anaerobic capacity is associated with poorer resilience. Interventional studies are needed to establish causality.