Detailed Answer
Speed drop over time (fatigue) is normal. Causes: mental focus wanes after 2-3 minutes; hand muscles tire; you stop reading ahead; posture degrades. To improve endurance: 1) Practice longer sessions (10-15 minutes) at 80% of your max speed. 2) Build physical stamina with hand stretches and breaks. 3) Use a keyboard with lighter switches. 4) Breathe deeply and relax shoulders. 5) Train with passages that include varied punctuation and numbers – they demand more cognitive load. If your 5-minute speed is >15% lower than your 1-minute speed, you have an endurance gap. Add one long practice daily.