Introduction Strength training improves running economy (RE) in a nonfatigued state and performance after prolonged exercise at moderate intensity. However, it is unknown if strength training improves RE durability at marathon race intensity, or high-intensity performance akin to the final stages of a competitive race. This study quantified the effect of a supplementary 10-wk strength training program on RE throughout 90 min of running in the heavy-intensity domain, and subsequent fatigued performance in runners. Methods Twenty-eight well-trained male runners (maximal oxygen uptake (VO2max) 58.6 mL·kg-1·min-1; 10 km 39:02 mm:ss) were performance-matched and randomly assigned to a habitual running-only control (E; n = 14) or supplementary strength training group (E + S; n = 14) that performed maximal strength and plyometric training twice weekly for 10 wk. Before the training, participants performed a 90-min run at 10% delta between lactate threshold 1 and 2 (13.1 ± 1.4 km·h-1, 79.7% VO2max). RE, quantified as oxygen cost (mL·kg-1·km-1), was recorded at 15-min intervals during the run, immediately thereafter, participants ran a time to exhaustion (TTE) at 95% pre-test VO2max (16.1 ± 1.6 km·h-1). The 90-min run and TTE were repeated after the training intervention. Results A large interaction effect of training-group-run time was found for RE (P = 0.003, np2 = 0.13), with E + S improving versus E at 90 min (-2.1% vs +0.6%; P = 0.04). For TTE, a large group-training interaction effect was detected (P = 0.004, np2 = 0.28), changing by +35% in E + S and -8% in E. Conclusions This study demonstrated that adding maximal strength and plyometrics training to a program of endurance running improved RE durability and substantially increased high-intensity TTE at the end of a 90-min run in the heavy-intensity domain in well-trained male runners.
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