I was reading the article Speed Play in Techniques magazine Volume 15, number 3 (February 2022) and encountered the following quote:
This explositivity is underpinned by a collection of neuromuscular factors including, but not limited to motor-unit typing, intra- and inter-muscular coordination, rate-coding and neural drive, whic hcollectively work to actualize sprint-movement characteristics. Because of their role in rate and magnitude of force development, these neuromuscular factors serve as prerequisites for proper mechanical actions within critical time frames. For example, sprinters who initiate GC with a stance phase that is more proximal to the center of mass at top-speed are more likely to conserve energy and prioritize elastic behavior through the SSC, a rapid and forceful lengthening of muscle-tendon complex followed by an immediate shortening or contraction (Komi, 2008).
What, exactly, are GC and SSC in this context?