Negative split and descend training really helped my ability to deliver high efforts even towards the end of the race, or the end of each segment. On the bike, I would train hills up to 5 hours and then go ride for an hour, completing intervals at high watts with rest in between. This helped me be able to accelerate and pass at the final stretch of the bike, even when I was tired. For the run, I would descend my long 6 mile hill loops so that each loop was run faster than the last. This trained my muscles to not collapse after many miles, but to be able to still give more when I demanded more speed nearing the end. Thus, after 24 miles of maintaining pace, I was still able to accelerate at the end to have a strong finish.
Tiring your body out for a long stretch, and THEN picking up the pace at the end during training is painful, taxing, and hard, but extremely great training for not fading during a race and potentially even going faster at the end.