The Acute Effect Of Foot Strike Pattern On The Morphological And Mechanical Properties Of Medial Gastrocnemius-Tendon Unit During Running

Purpose:Forefoot strike pattern(FFS)has been shown to have the advantage of reducing impact force and impact-related running injuries.The effect of foot strike pattern on kinematics,kinetics,and EMG of the lower extremity was well explored However,there were few studies focusing on the muscle-tendon unit.The movement of medial gastrocnemius-tendon-unit(MTU)is important for the propulsion phase of running.Therefore,based on the motion capture system synchronizing with ultrasound system,the morphological and mechanical properties of MTU were collected during running in real-time,in order to explore the acute effects of footstrike pattern on the morphological and mechanical properties of MTU providing the biomechanical evidence for the effects of footstrike pattern on muscular mechanical and propulsion efficiency,especially at the muscle mechanics level in vivo.Methods:15 healthy recreational runners wearing cushioned shoes with rearfoot strike pattern(RFS)were recruited to run at 9 km/h with RFS and FFS.An uSmart 3300 ultrasound system was used to capture the real-time ultrasound video of the medial gastrocnemius.The Vicon three-dimensional motion capture system and the Bertec instrumented treadmill were utilized to capture the kinematics and ground reaction force during running.The kinetics and mechanical properties of the medial gastrocnemius-Achilles tendon complex was calculated.The paired t-test was used to compare the parameters between FFS and RFS.The significance level was set at 0.05.Results:Compared with RFS:1)The striking angle of FFS was significantly smaller(FFS:-6.28±3.38° vs.RFS:14.18±4.90°);2)the ground reaction force during the push-off stage(FFS:-6.28±3.38° vs.RFS:14.18±4.90°),the peak ankle power and torque of FFS was significantly greater,the plantarflexion angle of striking of RFS was smaller;3)the muscle force of FFS was significantly higher(FFS:1.19±0.18 BW vs.RFS:0.96±0.14 BW),the gastrocnemius fascicle length at the time of striking and toe-off of FFS was significantly smaller(FFS:4.72±0.88 cm vs.RFS:5.56±0.79 cm;FFS:3.57±0.60 cm vs.RFS:4.11 ±0.80 cm),the change of the fascicle length during the stance phase and toe-off phase(FFS:0.04±0.04 vs.RFS:0.07±0.03)of FFS was significantly smaller,and the peak shortening speed of FFS was lower(FFS:15.01±7.26 cm·s-1)vs.RFS:19.65±7.97 cm·s-1);4)the MTU length at the striking of FFS was significantly smaller,the shortening length,speed and power of shortening and lengthening,the lengthening length(FFS:2.32±0.60 cm vs.RFS:1.45±0.25 cm),speed(FFS:37.15±8.45 cm·s-1 vs.RFS:22.69±5.94 cm·s-1),and power of lengthening were significantly greater in FFS.Conclusion:Compared to RFS,the production of propulsion force was greater in FFS During FFS,the greater the plantarfl exion force,the smaller the fascicle shortening length amount and slower shortening speed in the stance phase and toe-off phase of FFS suggested that the muscle contraction was more energy-saving and produce greater force,that is,the efficiency of contraction is higher.The MTU stretching length,stretching and contraction power of RFS were significantly lower than that of FFS,which indicated that the tendon made better use of the elongation shortening cycle,improving its ability to store and release energy.From the perspective of muscle mechanics,compared with RFS,after acute conversion to FFS,the morphological and mechanical properties of MTU was optimized,so as to produce better propulsion efficacy.