This study determined Maximal Aerobic Speed (MAS) at a speed that utilizes maximal aerobic and minimal anaerobic contributions. This method of determining MAS was compared between endurance (ET) and sprint (ST) trained athletes. Nineteen and 21 healthy participants were selected for the determination and validation of MAS respectively. All athletes completed five exercise sessions in the laboratory. Participants validating MAS also ran an all-out 5000 m at the track. Oxygen uptake at MAS was at 96.09 ± 2.51% maximal oxygen consumption (\documentclass[12pt]{minimal}
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				\begin{document}$${{\dot{\rm{V}}}}\text{O}_{\text{2max}}$$\end{document}V˙O2max). MAS had a significantly higher correlation with velocity at lactate threshold (vLT), critical speed, 5000 m, time-to-exhaustion velocity at delta 50 in addition to 5% velocity at\documentclass[12pt]{minimal}
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				\begin{document}$${{\dot{\rm{V}}}}\text{O}_{\text{2max}}$$\end{document}V˙O2max(TlimυΔ50 + 5%v\documentclass[12pt]{minimal}
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				\begin{document}$${{\dot{\rm{V}}}}\text{O}_{\text{2max}}$$\end{document}V˙O2max), and Vsub%95 (υΔ50 or υΔ50 + 5%v\documentclass[12pt]{minimal}
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				\begin{document}$${{\dot{\rm{V}}}}\text{O}_{\text{2max}}$$\end{document}V˙O2max) compared with v\documentclass[12pt]{minimal}
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				\begin{document}$${{\dot{\rm{V}}}}\text{O}_{\text{2max}}$$\end{document}V˙O2max, and predicted 5000 m speed (R2= 0.90,p< 0.001) and vLT (R2= 0.96,p< 0.001). ET athletes achieved significantly higher MAS (16.07 ± 1.58 km·h−1vs. 12.77 ± 0.81 km·h−1,p≤ 0.001) and maximal aerobic energy (EMAS) (52.87 ± 5.35 ml·kg−1·min−1vs. 46.42 ± 3.38 ml·kg−1·min−1,p= 0.005) and significantly shorter duration at MAS (ET: 678.59 ± 165.44 s; ST: 840.28 ± 164.97 s,p= 0.039). ST athletes had significantly higher maximal speed (35.21 ± 1.90 km·h−1,p< 0.001) at a significantly longer distance (41.05 ± 3.14 m,p= 0.003) in the 50 m sprint run test. Significant differences were also observed in 50 m sprint performance (p< 0.001), and peak post-exercise blood lactate (p= 0.005). This study demonstrates that MAS is more accurate at a percentage of v\documentclass[12pt]{minimal}
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				\begin{document}$${{\dot{\rm{V}}}}\text{O}_{\text{2max}}$$\end{document}V˙O2maxthan at v\documentclass[12pt]{minimal}
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				\begin{document}$${{\dot{\rm{V}}}}\text{O}_{\text{2max}}$$\end{document}V˙O2max. The accurate calculation of MAS can be used to predict running performances with lower errors (Running Energy Reserve Index Paper).