The Effects of Habitual Foot Strike Patterns on the Morphology and Mechanical Function of the Medial Gastrocnemius–Achilles Tendon Unit

Abstract

As a crucial and vulnerable component of the lower extremities, the medial gastrocnemius–Achilles tendon unit (gMTU) plays a significant role in sport performance and injury prevention during long-distance running. However, how habitual foot strike patterns influence the morphology of the gMTU remains unclear. Therefore, this study aimed to explore the effects of two main foot strike patterns on the morphological and mechanical characteristics of the gMTU. Long-distance male runners with habitual forefoot (FFS group, n = 10) and rearfoot strike patterns (RFS group, n = 10) and male non-runners (NR group, n = 10) were recruited. A Terason uSmart 3300 ultrasonography system was used to image the medial gastrocnemius (MG) and Achilles tendon, Image J software to analyze the morphology, and a dynamometer to determine plantar flexion torque during maximal voluntary isometric contractions. The participants first performed a 5-minute warm up; then, the morphological measurements of MG and AT were recorded in a static condition; finally, the MVICs test was conducted to investigate the mechanical function of the gMTU. One-way ANOVA and nonparametric tests were used for data analysis. The significance level was set at a p value of <0.05. The muscle fascicle length (FL) (FFS: 67.3 ± 12.7, RFS: 62.5 ± 7.6, NRs: 55.9 ± 2.0, η2 = 0.187), normalized FL (FFS: 0.36 ± 0.48, RFS: 0.18 ± 0.03, NRs: 0.16 ± 0.01, η2 = 0.237), and pennation angle (PA) (FFS: 16.2 ± 1.9, RFS: 18.9 ± 2.8, NRs: 19.3 ± 2.4, η2 = 0.280) significantly differed between the groups. Specifically, the FL and normalized FL were longer in the FFS group than in the NR group (p < 0.05), while the PA was smaller in the FFS group than in the NR group (p < 0.05). Conclusion: Long-term running with a forefoot strike pattern could significantly affect the FL and PA of the MG. A forefoot strike pattern could lead to a longer FL and a smaller PA, indicating an FFS pattern could protect the MG from strain under repetitive high loads.

Effects of 12-week gait retraining on plantar flexion torque, architecture, and behavior of the medial gastrocnemius in vivo

“…The study found that the normalized FL increased significantly in the GR group after training, and the FL of the MG increased significantly in both groups after training. A prior study has also provided evidence that long-term running with FFS could significantly influence the architecture of MG, resulting in runners having a longer FL ( Li et al, 2023 ). Compared with running with RFS, running with FFS requires more active involvement from the MG ( Lin et al, 2021 ).…”

“…The FL was defined as the length of the fascicular pathway between the superficial and deep fascias, and it was determined by calculating the average length of three fascicles in an ultrasound image ( Geremia et al, 2019 ). The normalized FL was obtained by dividing the FL by the shank length ( Li et al, 2023 ). The PA was defined as the angle formed between the muscle fascicle and deep fascia, the mean value of which was calculated according to the three ultrasound images of each participant ( Geremia et al, 2019 ).…”

“…Moreover, the excessive eccentric loading during ground contact in FFS may affect the stretch-shortening cycle of the triceps surae muscle–tendon unit, which in turn affects the ability to resist impact force during landing and return elastic energy ( Jewell et al, 2017 ). Significant differences in MG morphology have been found among different habitual foot strike patterns ( Li et al, 2023 ). Specifically, FFS runners have longer FL and smaller PA; these changes increase maximal shortening velocity and efficiency of force transmission.…”