Effects of Fatigue on Running Mechanics: Spring-Mass Behavior in Recreational Runners After 60 Seconds of Countermovement Jumps

The purpose of this study was to investigate the effects of acute fatigue on spring-mass model (SMM) parameters among recreational runners at different speeds. Eleven participants (5 males and 6 females) performed running trials at slower, self-selected, and faster speeds on an indoor track before and after performing a fatigue protocol (60 s of countermovement jumps). Maximal vertical force (F-max), impact peak force (F-peak), loading rate (LR), contact time (Tc), aerial time (Ta), step frequency (SF), step length (SL), maximal vertical displacement of the center of mass (Delta Z), vertical stiffness (K-vert), and leg work (W-ieg) were measured using a force plate integrated into the track. A significant reduction (-43.1 +/- 8.6%; P < .05) in mechanical power during jumps indicated that the subjects became fatigued. The results showed that under fatigue conditions, the runners adjusted their running mechanics at slower (approximate to 2.7 ms(-1); Delta Z -12% and SF +3.9%; P < .05), self-selected (approximate to 3.3 ms(-1); SF +3%, SL -6.8%, Ta -16%, and F-max -3.3%; P < .05), and faster (approximate to 3.6 ms(-1) SL-6.9%, Ta-14% and F-peak-9.8%; P < .05) speeds without significantly altering K-vert (P>.05). During constant running, the previous 60 s of maximal vertical jumps induced mechanical adjustments in the spatiotemporal parameters without altering K-vert.