Foot Progression Angle Phenotype Modulates Acute Vastus Medialis Contractile Responses During Leg Press Exercise in Resistance-Trained Athletes

Participants A total of 24 male athletes (age: 27.5 ± 3.76 years) who were licensed and actively competing in bodybuilding with a minimum of five years of regular resistance training experience volunteered to participate. Prior to the study, participants were provided with detailed information regarding the research protocol and written informed consent was obtained.

Inclusion criteria were aged between 20 and 35 years, a minimum of five years of regular resistance training experience, and currently active participation in training. Additionally, measurements from both feet were required to meet the established threshold values for participants to be classified according to their FPA. Exclusion criteria were a history of lower extremity surgery or serious musculoskeletal injury within the past year, the presence of congenital or acquired foot deformity, and a history of neurological, cardiovascular, or metabolic disease.

Assessment of Demographic and Physical Characteristics A personal information form was used to obtain demographic data. Body height and mass were measured using standard procedures.

Assessment of Muscle Contractile Properties Muscle contractile properties were assessed using tensiomyography (TMG-BMC Ltd., Ljubljana, Slovenia) on the vastus medialis muscle of the dominant leg. Participants were positioned in supine with the knee supported at approximately 30° of flexion. The muscle belly was identified by palpation, and surface electrodes were placed proximal and distal to the motor point. The measurement probe was positioned perpendicular (90°) to the skin surface. Electrical stimulation was incrementally increased until maximal radial displacement of the muscle was obtained. Participants were instructed to keep their muscles fully relaxed throughout the measurements.

The following TMG parameters reflecting muscle contractile properties were analyzed: maximal radial deformation (Dm), contraction time (Tc), and delay time (Td). These parameters have been reported to demonstrate high relative reliability, with intraclass correlation coefficients of 0.97 for Dm, 0.92 for Tc, and 0.86 for Td, along with low measurement error (CV ≈ 2.7-4.7%) (Loturco et al., 2016; Tous-Fajardo et al., 2010). All measurements were performed before the exercise protocol and within 90 seconds following completion of the final repetition.