Should I wear lighter shoes only in races?
It’s wise to do some of your training in them, too. You may experience more impact fatigue in a race if you’re not accustomed to shoes with less cushioning.
Wearing lighter shoes will also help to get you in better race shape by enabling higher quality training. A lighter, more responsive shoe will slightly decrease the energy cost of running. This should enable you to quicken your cadence, which will boost your race preparation. Use them only twice a week, on non-consecutive days, for your speed/interval work.