Built for speed, the Zoom Fly SP ‘Dark Citron’ is also designed to be durable enough for everyday training. Mounted on the responsive Lunarlon midsole is a translucent, stretch-woven upper, accented with dark yellow detailing throughout. Within the midsole, a full-length carbon-infused nylon plate delivers an extra bit of spring during each stride. A digital clock graphic on the heel references Breaking2, the project undertaken by Nike to break the two-hour marathon barrier.