Bench Press and Machine Chest Press Elicit Distinct Acute Mechanical Responses in the Pectoralis Major: A Randomized Controlled Study
Phase: NA
Conditions: Muscle Mechanical Properties, Resistance Training
Sponsor: Nihat Sarıalioğlu

STUDY PROTOCOL 
Official Title: 
Acute Effects of Bench Press and Machine Chest Press Exercises on Pectoralis Major Muscle 
Mechanical Properties in Resistance-Trained Athletes 
NCT Number: Pending 
Document Date: April 14 2026 
Document Version: 1.0 
Principal Investigators: 
Giresun University, Faculty of Sport Sciences 
1. SCIENTIFIC BACKGROUND
Resistance training exercises are widely used to improve muscular strength and hypertrophy. 
Among these exercises, the bench press and machine chest press are commonly utilized for 
targeting the pectoralis major muscle. Although both exercises aim to activate similar muscle 
groups, differences in movement pattern, stabilization demand, and mechanical loading may 
result in distinct neuromuscular responses. 
Muscle mechanical properties such as stiffness and tone can be objectively assessed using 
myotonometry. These parameters provide valuable information regarding muscle function, 
viscoelastic behavior, and acute responses to exercise. However, the extent to which different 
chest press variations influence these mechanical properties remains unclear. 
Understanding the acute effects of these exercises on muscle mechanical characteristics may 
contribute to optimizing resistance training strategies and exercise selection. 
2. OBJECTIVES AND HYPOTHESES
2.1 Primary Objective
To compare the acute effects of bench press and machine chest press exercises on pectoralis 
major muscle stiffness and tone. 
2.2 Hypothesis 
It is hypothesized that different chest press variations will produce distinct acute changes in 
muscle mechanical properties, particularly stiffness and oscillation frequency. 
3. STUDY DESIGN
This study was designed as a randomized parallel-group experimental study. Participants were 
randomly assigned to either a bench press group or a machine chest press group. 
All participants completed a single-session resistance exercise protocol. Muscle mechanical 
properties were assessed before and immediately after the exercise intervention. 
The outcome assessor was blinded to group allocation. 
4. PARTICIPANTS
4.1 Study Population

A total of 16 male resistance-trained athletes participated in the study. 
4.2 Inclusion Criteria 
•
Male participants
•
Aged between 20 and 40 years
•
Minimum of 5 years of resistance training experience
4.3 Exclusion Criteria 
•
History of upper extremity injury within the last 12 months
•
Previous upper extremity surgery
•
Use of performance-enhancing substances
5. METHODS
5.1 Exercise Protocol
Participants performed a standardized resistance training protocol consisting of four sets of ten 
repetitions at 80% of one-repetition maximum (1RM), with 2-minute rest intervals. 
•
Bench Press Group: Barbell bench press exercise
•
Machine Chest Press Group: Machine chest press exercise
5.2 Assessment of Muscle Mechanical Properties 
Muscle mechanical properties of the pectoralis major were assessed using MyotonPRO. 
Measurements were performed before and within 90 seconds after completion of the exercise 
protocol. 
The following parameters were analyzed: 
•
Oscillation frequency (muscle tone)
•
Stiffness
•
Decrement
•
Relaxation time
•
Creep
6. OUTCOME MEASURES
Primary Outcomes
•
Change in muscle stiffness
•
Change in oscillation frequency (muscle tone)
Secondary Outcomes 
•
Change in muscle decrement
•
Change in relaxation time

•
Change in creep
7. STATISTICAL ANALYSIS
Data were analyzed using the SPSS 27.0 software package. The normality of the data 
distribution was assessed using the Shapiro-Wilk test; all parameters were found to exhibit a 
normal distribution (p > 0.05). To examine the effect of exercise type on muscle mechanical 
properties, a Mixed-Design Analysis of Variance (ANOVA) was applied, where time (pre-
test, post-test) was defined as a within-subject variable and group (BP, MCP) was defined as 
an between-subject variable. The primary focus of the analysis was the Time × Group 
interaction effect, reflecting whether the two exercise protocols produced different changes in 
muscle mechanical properties from pre-test to post-test. For parameters where a significant 
Time × Group interaction was detected, within-group pre-test–post-test differences were 
examined using a paired-samples t-test, and Bonferroni correction was applied for multiple 
comparisons. For ANOVA, effect sizes were reported as partial eta squared (ηp²) and 
interpreted as small (ηp² = 0.01), moderate (ηp² = 0.06), and large (ηp² ≥ 0.14) (Richardson, 
2011). For within-group paired comparisons, effect sizes were calculated as Hedges' g and 
interpreted as small (< 0.35), moderate (0.35–0.80), and large (> 0.80) (Rhea, 2004). The 
statistical significance level was set at p < 0.05.
8. ETHICAL CONSIDERATIONS
The study protocol was approved by the Giresun University Ethics Committee for Social 
Sciences, Natural Sciences, and Engineering Research (Approval No: 09/17). The study was 
conducted in accordance with the Declaration of Helsinki, and all participants provided 
written informed consent prior to participation.