@fitzuniversity: Why do you get tired so fast when you run? It comes down to energy systems. At lower intensities, you’re using your aerobic system (oxygen-based). It’s efficient and built for longer efforts. As you speed up, your body shifts toward the anaerobic system. Now you’re producing energy faster—but with less oxygen. That leads to a buildup of metabolites (like hydrogen ions), which interfere with muscle contraction. That’s the “burn” you feel. At the same time: • Force production drops • Ground contact time increases • Mechanics break down → That’s why your pace slows. Most runners make this mistake: They spend too much time in this high-fatigue zone. Research and experts like Andy Galpin emphasize building an aerobic base first—then layering in intensity. Simple fix: • Run easier more often (Zone 2) • Build your base • Add hard efforts strategically Train smarter—and running gets easier, faster. ⸻ #FitzUniversity #RunSmart #EnduranceTraining #VO2Max #PerformanceTraining

Coach Fitz | Fitz University

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Sunday 12 April 2026 15:58:06 GMT