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. 2023 Sep 1;22(3):582-590.
doi: 10.52082/jssm.2023.582. eCollection 2023 Sep.

Mechanics of The Medial Gastrocnemius-Tendon Unit in Behaving more Efficiently in Habitual Non-Rearfoot Strikers than in Rearfoot Strikers during Running

Liqin Deng  1 , Xini Zhang  1   2 , Boyi Dai  3 , Songlin Xiao  1 , Faning Zhang  1 , Weijie Fu  1
Affiliations

Mechanics of The Medial Gastrocnemius-Tendon Unit in Behaving more Efficiently in Habitual Non-Rearfoot Strikers than in Rearfoot Strikers during Running

Liqin Deng et al. J Sports Sci Med. .

Abstract

This study aims to quantify how habitual foot strike patterns would affect ankle kinetics and the behavior and mechanics of the medial gastrocnemius-tendon unit (MTU) during running. A total of 14 runners with non-rearfoot strike patterns (NRFS) and 15 runners with rearfoot strike patterns (RFS) ran on an instrumented treadmill at a speed of 9 km/h. An ultrasound system and a motion capture system were synchronously triggered to collect the ultrasound images of the medial gastrocnemius (MG) and marker positions along with ground reaction forces (GRF) during running. Ankle kinetics (moment and power) and MG/MTU behavior and mechanical properties (MG shortening length, velocity, force, power, MTU shortening/lengthening length, velocity, and power) were calculated. Independent t-tests were performed to compare the two groups of runners. Pearson correlation was conducted to detect the relationship between foot strike angle and the MTU behavior and mechanics. Compared with RFS runners, NRFS runners had 1) lower foot strike angles and greater peak ankle moments; 2) lower shortening/change length and contraction velocity and greater MG peak force; 3) greater MTU lengthening, MTU shortening length and MTU lengthening velocity and power; 4) the foot strike angle was positively related to the change of fascicle length, fascicle contraction length, and MTU shortening length during the stance phase. The foot strike angle was negatively related to the MG force and MTU lengthening power. The MG in NRFS runners appears to contract with greater force in relatively isometric behavior and at a slower shortening velocity. Moreover, the lengthening length, the lengthening velocity of MTU, and the MG force were greater in habitual NRFS runners, leading to a stronger stretch reflex response potentially.

Keywords: Foot strike pattern; medial gastrocnemius; muscle contraction; ultrasound.

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Figures

Figure 1.
Figure 1.
Experimental setup and probe placement.
Figure 2.
Figure 2.
Ultrasound image of the medial gastrocnemius and calculation of the medial gastrocnemius (MG) and the medial gastrocnemius–tendon unit (MTU) behavior. Lstrike, Le-m, Lm-t, Lp, and Ltoe-off are the fascicle length of touchdown, the end of the early stance phase and the start of the mid-stance phase, the end of the mid-stance phase and start of propulsion phase, the end of propulsion phase and toe-off moment. Lmax and Lmin are the maximum and minimum fascicle lengths. LMTUstrike, LMTUtoe-off, and LMTUmax are the length at touchdown, toe-off, and the maximum length of the medial gastrocnemius-tendon unit (MTU).
Figure 3.
Figure 3.
Effect of habitual foot strike patterns on foot strike angles and the 2nd peak GRF and ankle kinetics. GRF: ground reaction force, NRFS: non-rearfoot striker, RFS: rearfoot striker, * indicates significant differences.
Figure 4.
Figure 4.
Curve of the medial gastrocnemius fascicle length and the muscle tendon–unit (MTU) length habitual non rearfoot strike pattern (NRFS) and rearfoot strike pattern (RFS) during the stance phase.
Figure 5.
Figure 5.
Effect of habitual foot strike patterns on the behavior of the medial gastrocnemius (MG) of the stance phase. FL: fascicle length, NRFS: non-rearfoot striker, RFS: rearfoot striker, * indicates significant differences.
Figure 6.
Figure 6.
Correlations of foot strike angle with the mechanics and behavior of MTU.
Figure 7.
Figure 7.
Effect of habitual foot strike patterns on the behavior of the medial gastrocnemius–tendon unit (MTU) of the stance phase. NRFS: non-rearfoot striker, RFS: non-rearfoot striker, * indicates significant difference.
See this image and copyright information in PMC

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