Purple Patch [colloq. ~ winning streak] (1). cycling high-performance period; a.k.a. peak form, flying, on fire, bombing, untouchable); (2). any part of an athletes training program where the top form is so good that it seems unexplainable (traditionally color-highlighted in 'purple' on the schedule sheet).
Experiencing a 'purple patch', as it has been called in recent decades by those before us, is a period of 'peak form-fitness' best known as racing form on the bicycle, and most typically lasting 2-3 weeks. The lucky Purple Patch rider is characteristically observed executing seemingly untiring turns at the front of fast bunches, leading out race-finishes as well as sprinting, recovering quickly enough from attacking that they can counter-attack themselves, repeated surging while climbing at high speed, and the ability to pedal any gear ratio at any rev range at any point in the ride.