Gastrocnemius’ role as an agonist or antagonist of the anterior cruciate ligament (ACL) is not 27 well understood. This study explored the use of ultrasound imaging to investigate how 28 gastrocnemius stimulation levels influenced anterior tibial translation. The gastrocnemii of 10 29 participants were stimulated to four different levels using electrical muscle stimulation. The 30 quadriceps were co-activated at a fixed level. Anterior tibial translation was determined using 31 ultrasound imaging. Intraclass correlation coefficient [ICC (2,1)] was used to assess the intra-32 rater reliability over two sessions. Intra-rater reliability was good at rest and under most 33 muscle stimulation levels (ICC = 0.84 to 0.92), and moderate with the lowest (ICC = 0.71) 34 and highest stimulation (ICC = 0.61). While anterior tibial translation was not significantly 35 different across simulation levels, ultrasound imaging recorded the anterior movement of the 36 tibia as the gastrocnemius was activated, thus supporting gastrocnemius’ role as an antagonist 37 of the ACL.

Purpose: Small knee flexion angles are associated with increased non-contact anterior cruciate ligament (ACL) injury risks. The purpose of this study was to provide insights into how ankle plantar flexion angles influenced knee flexion angles at initial contact during single-leg drop landings.

Method: Thirteen male recreational basketball players performed single-leg drop landings from a 30-cm high platform using three randomized foot-landing positions (natural, fore-foot, and flat-foot). A motion capture system and a force plate were used to measure lower extremity kinematics and vertical ground reaction force (VGRF). A one-way repeated measures Analysis of Variance and the Friedman test were conducted (α = .05).

Results: Foot-landing position had a significant effect on knee flexion angles at initial contact (p < .001). As compared to flat-foot landings (18° (SD 5°), significantly smaller knee flexion angles were found for natural (mean 12° (SD 5°), p = .004) and fore-foot landings (mean 12° (SD 3°), p = .001). There was however significantly smaller knee flexion range of motion in flat-foot landings (mean 42° (SD 3°), as compared to natural landings (mean 48° (SD 4°) (p < .001). Flat-foot landings also resulted in a 1.4 times higher maximum VGRF than fore-foot landings (p < .001) and 1.3 times higher than natural landings (p = .005).

Conclusions: Natural and fore-foot landings are better for force absorption but are associated with smaller knee flexion angles at initial contact. These findings have important implications for non-contact ACL injuries.

Fused deposition modeling printing is a material extrusion (MEX) process that has gained popularity over the years due to its increased affordability and greater versatility. There is a wide variety of MEX printing technologies and a broad spectrum of materials that can be 3D printed, ranging from metallic to non-metallic materials. MEX has emerged as the most common technology in consumer-grade, desktop 3D printers for printing thermoplastics, such as acrylonitrile butadiene styrene (ABS) and polylactic acid. High-density polyethylene (HDPE) is a widely used thermoplastic material for product packaging. The sheer availability of recyclable or recycled HDPE (rHDPE) from used packaging has led to efforts to apply it in MEX printing. However, rHDPE presents challenges as a filament material, including issues such as part detachment from the print bed and high warpage. The focus of this study is to determine the optimal conditions that can mitigate, if not eliminate, the print bed adhesion problems associated with printing rHDPE filaments. This was achieved by conducting a series of tests to address these challenges, including part removability relating to the shear strength of print bed adhesion to identify the necessary range of print bed adhesion and corresponding parameters.

Ankle braces typically restrict the functional range of motion. Braces should preferably allow a free functional range of motion during sport while protecting the foot at high-risk positions beyond that range. This could be achieved with 3D printed metamaterial structures that could have varying properties throughout an individual’s ankle range of motion. This paper aims to illustrate an exploratory methodology of using an affordable Fused Deposition Modelling 3D printing technology to develop an ankle brace using metamaterial structures. It also showcases the design, manufacturing processes and testing of 3D printed customised ankle brace prototype designs that incorporated metamaterial structures. Initial tests showed that as designed, the prototype braces maintained the full range of motion for plantar flexion angles. Results also showed that the prototypes required one of the lowest moments during functional range of motion while achieving almost twice to thrice the moment required beyond the functional range of motion.

Increased knee flexion angles are associated with reduced non-contact anterior cruciate ligament (ACL) injury risks. Ankle plantar flexion angles and internal risk factors could influence knee flexion angles, but their correlations are unknown. This study aimed to establish and validate a regression model to predict knee flexion angles using ankle plantar flexion angles, body mass index (BMI) and generalised joint laxity (GJL) at initial contact of single-leg drop landings. Thirty-two participants performed single-leg drop landings from a 30-cm-high platform. Kinematics and vertical ground reaction forces were measured using a motion capture system and force plate. A multiple regression was performed, and it was validated using a separate data set. The prediction model explained 38% (adjusted R2) of the change in knee flexion angles at initial contact (p = 0.001, large effect size). However, only the ankle plantar flexion angle (p < 0.001) was found to be a significant predictor of knee flexion angles. External validation further showed that the model explained 26% of knee flexion angles (large effect size). The inverse relationship between ankle plantar flexion and knee flexion angles suggests that foot landing strategies could be used to increase knee flexion angles, thereby reducing non-contact ACL injury risks.