Foot Progression Angle Phenotype Modulates Acute Vastus Medialis Contractile Responses During Leg Press Exercise in Resistance-Trained Athletes
Phase: NA
Conditions: Muscle Contractile Properties, Resistance Exercise, Foot Progression Angle
Sponsor: Giresun University

STUDY PROTOCOL
Official Title:
Foot Progression Angle Phenotype Modulates Acute Vastus Medialis Contractile
Responses During Leg Press Exercise in Resistance-Trained Athletes
NCT Number: Not Yet Assigned
Document Date: November 05, 2025
Document Version: 1.0
Principal Investigators:
Giresun University, Faculty of Sport Sciences
This document contains the complete study protocol including objectives, design, methods, scientific
background, and statistical considerations.

1. SCIENTIFIC BACKGROUND
Initial joint alignment in closed kinetic chain resistance exercises is a determinant factor for
load transfer and inter-segmental force transmission (Neumann, 2019; Straub and Powers,
2024). Among these exercises, the leg press is widely used in strength and hypertrophy-oriented
programs owing to its capacity to accommodate high mechanical loads while providing
external support for trunk stability (Martín-Fuentes et al., 2020). Foot placement on the
platform during leg press constitutes an important initial condition that may influence force
transmission and joint loading patterns along the lower extremity (Da Silva et al., 2008). Given
the natural inter-individual variability in the rotational alignment of the lower extremity,
whether standardized foot positions applied during leg press generate equivalent biomechanical
conditions across individuals represents an important consideration for the development of
individualized training strategies.
One of the key indicators that quantifies these natural rotational differences is the foot
progression angle (FPA). The FPA is an important biomechanical parameter that defines the
angular relationship between the longitudinal axis of the foot and the direction of progression
during gait, reflecting the rotational alignment of the lower extremity in the transverse plane
(Caderby et al., 2022; Cibulka et al., 2016). This angle, which may vary among individuals, is
regarded not only as a descriptive feature of gait pattern but also as a functional indicator of
habitual lower extremity alignment (Caderby et al., 2022; Shen et al., 2026). It has been
reported that inter-individual differences in FPA may be associated with tibial rotation and load
distribution at the knee joint (Bennour et al., 2017; Cibulka et al., 2016; Qiu et al., 2020), and
may also alter lower extremity muscle activation (Rutherford et al., 2010).
The effects of foot placement on lower extremity biomechanics during leg press exercise
have been examined in the literature through various manipulations. These studies have
focused on the effects of variables such as foot height on the platform, foot width, or fixed
internal–external rotation angles on muscle activation and joint loading (Da Silva et al., 2008;
Escamilla et al., 2001; Harandi et al., 2013; Martín-Fuentes et al., 2020; Martín-Fuentes et al.,
2022; Pereira et al., 2017). However, in these studies, standardized foot positions were applied
to all participants and rotational manipulations were performed using fixed angles. The absence
of FPA from the initial foot positioning suggests that these studies operated under the
assumption that applied foot positions generate similar biomechanical conditions across all
individuals.
Furthermore, biomechanical differences associated with foot position in previous research
have predominantly been assessed through electromyographic muscle activation and kinematic
parameters (Martín-Fuentes et al., 2020; Da Silva et al., 2008; Martín-Fuentes et al., 2022).
While electromyography provides information on the neural dimension of muscle activation
(Disselhorst-Klug,  2025),  tensiomyography  enables  assessment  of  contractile  properties
through the mechanical response of the muscle to electrical stimulation and can provide
important information regarding the functional state of the muscle (Rey et al., 2012; Fernández-
Baeza et al., 2024). The absence of tensiomyographic methods in the aforementioned studies
limits the direct assessment of the effects of initial foot positioning on skeletal muscle
contractile properties.
In this context, the existing literature presents a clear gap with respect to both the integration
of individual rotational alignment differences (FPA) into exercise starting position and the
evaluation of this interaction through muscle contractile properties.

2. STUDY OBJECTIVES AND HYPOTHESES
2.1. Primary Objective
To examine the effects of the interaction between rotational foot positioning during leg press
exercise and individuals’ habitual foot progression angle (FPA) phenotype on the acute
contractile response of the vastus medialis muscle.
2.2. Hypotheses
Primary hypothesis: When the foot rotation position applied during exercise is incongruent
with the individual’s habitual foot progression angle, the contractile responses of the vastus
medialis muscle would be more pronounced.
Secondary hypothesis: A neutral foot position in individuals with a habitually high FPA profile,
and an externally rotated foot position in individuals with a normal FPA profile, would be
associated with greater contractile responses.
3. STUDY DESIGN
This study was designed as a mixed-design, crossover experimental investigation. In the
study design, FPA phenotype (high FPA vs. normal FPA) was defined as the between-subjects
factor, while foot rotation protocol (0° neutral vs. 30° toe-out) and time (pre-exercise vs. post-
exercise) were defined as within-subjects factors.
All participants were assessed in two separate sessions, each involving one of the two foot
rotation protocols, with a 48-hour washout period applied between sessions to minimize
potential fatigue and carry-over effects. Within the crossover design, protocol order was fixed
on a group-specific basis to minimize learning effects. Accordingly, each group performed the
condition congruent with their habitual foot progression angle in the first session and the
incongruent condition in the second session.
Pre-exercise TMG values obtained prior to the second session were compared with baseline
measurements  to  confirm  return  to  baseline  levels.  All  experimental  procedures  were
conducted under controlled environmental conditions (24°C) and within the same time-of-day
window for each participant (±1 hour). Participants were instructed to avoid strenuous physical
activity and caffeine consumption for 48 hours prior to each measurement.
To minimize measurement bias, the researcher conducting TMG assessments was blinded
to participants’ phenotype group and the exercise condition applied (single-blind). Exercise
administration and data analysis were performed by different researchers, and group codes
were anonymized during the analysis process.
4. PARTICIPANTS
4.1. Study Population
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.
4.2. Inclusion Criteria

(a) Aged between 20 and 35 years; (b) a minimum of five years of regular resistance training
experience; (c) currently active participation in training; (d) measurements from both feet
required to meet the established threshold values for FPA classification.
4.3. Exclusion Criteria
(a) A history of lower extremity surgery or serious musculoskeletal injury within the past year;
(b) the presence of congenital or acquired foot deformity; (c) a history of neurological,
cardiovascular, or metabolic disease.
4.4. Group Classification
Participants were divided into two groups based on FPA values measured during gait analysis.
Participants with a mean FPA exceeding 13° for both feet were classified as the high FPA
(HFPA) group (n=12), while those with values between 0° and 13° were classified as the
normal FPA (NFPA) group (n=12). This threshold was established in accordance with
reference values recommended in the literature (Cibulka et al., 2016).
4.5. Sample Size Calculation
Sample size was calculated using G*Power 3.1.9.7 software based on a repeated measures
mixed-design ANOVA model (within–between interaction). Effect size estimation was based
on tensiomyographic  changes reported in the lower extremity muscles following acute
resistance exercise. Previous studies have reported large effect sizes (Cohen’s d ≈ 1.0–1.9)
particularly for Tc and Td parameters (Beato et al., 2021). Adopting a more conservative
approach, a medium-to-large effect size (f = 0.40) was assumed. With a significance level of α
= 0.05, statistical power of (1−β) = 0.80, and a correlation between repeated measures of r =
0.50, the minimum total sample size was calculated as 20 (n = 10 per group). Considering the
within-subject comparison advantage of the crossover design and to compensate for potential
data loss, 12 participants were included in each group.
5. METHODS
5.1. 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.
5.2. Assessment of Muscle Contractile Properties (TMG)
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 (Macgregor et al., 2018; Rey et al., 2012; Šimunič, 2012).
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.
5.3. TMG Measurement Reliability
Prior to the main experimental sessions, test–retest measurements were performed on 12
participants with a 48-hour interval. Reliability was assessed using the intraclass correlation
coefficient [ICC(3,1)] calculated with a two-way mixed-effects model. ICC values for TMG
parameters were 0.91 for Dm, 0.88 for Tc, and 0.83 for Td, indicating high reliability. The
standard  error  of  measurement  (SEM)  and  minimal  detectable  change  (MDC95)  were
calculated to quantify measurement error. SEM and MDC95 values were 0.31 mm and 0.86
mm for Dm, 0.49 ms and 1.36 ms for Tc, and 1.17 ms and 3.24 ms for Td, respectively.
5.4. Assessment of Foot Progression Angle
Habitual FPA values were assessed during dynamic gait analysis using a baropodometric
walkway platform (BTS P-Walk, BTS Bioengineering, Italy; 2.4 m). Measurements were
performed under standardized laboratory conditions. Participants were instructed to walk
across the platform at their natural walking speed, and data collection was initiated without
prior notification to preserve the naturalness of the gait pattern. FPA values were automatically
calculated by the device’s integrated software as the angle between the longitudinal axis of the
foot and the direction of progression during gait. FPA values for both feet were obtained
separately. A minimum of three valid walking trials were collected per participant, and mean
FPA values across trials were used in analyses (Caravaggi et al., 2017; Kawai et al., 2019).
5.5. FPA Measurement Reliability
Test–retest reliability of FPA measurements was assessed in 12 participants with a 48-hour
interval. The two-way mixed model intraclass correlation coefficient (ICC 3,1) was 0.92. The
minimal detectable change (MDC95) was calculated as 1.8°.
5.6. Leg Press Foot Positioning and Exercise Protocol
In the neutral protocol, participants’ feet were placed on the platform at shoulder-width apart
with foot rotation in a neutral (0°) position. In the toe-out protocol (30°), feet were placed at the
same shoulder-width distance with the forefoot rotated 30° outward. Foot positions were
measured using a standard goniometer at each session and verified by angle markings drawn on
the footplate (Da Silva et al., 2008; Escamilla et al., 2001; Martín-Fuentes et al., 2020).
All procedures were performed on a 45° inclined leg press machine (Technogym, Italy). Range
of motion was restricted from 90° of knee flexion to full extension. One-repetition maximum
(1RM) values were determined 48 hours prior to the experimental sessions.
In  the  experimental  session,  participants  performed  the  leg  press  exercise  following  a
standardized general warm-up. The exercise protocol consisted of 2 × 15 repetitions at 40%
1RM followed by 4 × 10 repetitions at 75–80% 1RM. Inter-set rest was standardized at 2
minutes. Tempo was controlled using a metronome with a 2-second eccentric phase and 1-
second concentric phase, and technical compliance was monitored by an experienced coach
(Ratamess et al., 2009; Nuzzo et al., 2024).
5.7. Outcome Variables
All outcome variables were determined from tensiomyographic (TMG) parameters obtained
from the vastus medialis muscle of the dominant leg before the leg press exercise protocol and
within  90  seconds  following  completion  of  the  final  repetition.  Pre-  and  post-exercise

measurements were analyzed using raw data within a repeated measures model. Outcome
variables were defined a priori.
Primary Outcomes: Changes in Dm and Tc. It was hypothesized that the acute effect of the
potential interaction between foot rotation position and habitual FPA phenotype on muscle
contractile dynamics would be most evident through Dm and Tc parameters. Accordingly, the
Protocol × Time interaction was evaluated primarily in terms of changes in Dm and Tc.
Secondary Outcomes: Change in the Td parameter.
6. STATISTICAL CONSIDERATIONS
Statistical analyses were performed using SPSS software (Version 27, IBM Corp., Armonk,
NY, USA). Descriptive statistics are presented as mean ± standard deviation (mean ± SD) and
the significance level was set at α = 0.05. Normality of continuous variables was assessed using
the Shapiro–Wilk test and homogeneity of variance was evaluated with Levene’s test.
To assess potential carry-over effects associated with the crossover design, pre-exercise
measurements obtained prior to the second session were compared using paired samples t-tests
within each group; no significant carry-over effect was observed (all p > 0.05).
A 2 (Group: HFPA vs. NFPA) × 2 (Protocol: congruent vs. incongruent) × 2 (Time: pre vs.
post) factorial repeated measures ANOVA were applied to examine changes in muscle
contractile parameters. Group was included as a between-subjects factor, while protocol and
time were included as within-subjects factors. Main effects and all two-way (Group × Protocol,
Group × Time, Protocol × Time) and three-way (Group × Protocol × Time) interactions were
evaluated. As each within-subject factor had two levels, the sphericity assumption was
automatically satisfied and no correction was applied.
Primary outcome variables were defined a priori as Dm and Tc. In line with the primary
hypothesis of the study, the Protocol × Time interaction was prioritized during analysis and
interpretation.
Where significant main effects or interactions were identified, pairwise comparisons were
conducted with Bonferroni correction. Additionally, 95% confidence intervals for mean
differences were calculated and reported for all post-hoc comparisons.
Effect sizes were reported as partial eta squared (ηp²) and interpreted as small (0.01),
medium (0.06), and large (0.14) (Richardson, 2011). The Td parameter was treated as a
secondary outcome variable and only significant effects are reported.
7. ETHICAL CONSIDERATIONS
The research protocol was approved by the relevant ethics committee and the study was
conducted in accordance with the Declaration of Helsinki. Prior to the study, participants were
provided with detailed information regarding the research protocol and written informed
consent was obtained from all participants.
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