Swing time is the amount of time the foot spends off the ground in the gait cycle, defined by the time from toe off to heel strike of the same foot. Swing time in sprinting is thought of as a “passive” stage of the gait cycle, in which the leg swings forward as a result of elastic energy transfer, rather than from direct muscle contractions.
Swing times for sprinters - Swing times are fairly consistent amongst elite sprinters, but tend to be longer than swing times of recreational runners.
Santos-Concejero, J.; Granados, C.; Irazusta, J., Bidaurrazaga-Letona, I.; Zabala-Lili, J.; Tam, N., & Gil, S.M. (2014). Influence of the biomechanical variables of the gait cycle in running economy. RICYDE. Revista internacional de ciencias del deporte, 36(10), 95-108 http://dx.doi.org/10.5232/ricyde2014.03601.
Running economy is negatively correlated with swing time - At 19.5 km/h, longer swing time was correlated to lower running efficiency, so it appears that swing time may be a discriminating factor of efficiency in well-trained runners.
Santos-Concejero J, Granados C, Irazusta J, et al. Differences in ground contact time explain the less efficient running economy in north african runners. Biol Sport. 2013;30(3):181-187. doi:10.5604/20831862.1059170