This randomized controlled study aims to compare the acute effects of bench press (BP) and machine chest press (MCP) exercises on the mechanical properties of the pectoralis major muscle in resistance-trained bodybuilders. Sixteen male athletes are randomly assigned to BP or MCP groups. Both groups perform four sets of ten repetitions at 80% of one-repetition maximum with equalized volume load. Muscle mechanical properties, including oscillation frequency, stiffness, decrement, relaxation time, and creep, are measured using MyotonPRO before and immediately after exercise. The study hypothesizes that BP will induce greater stiffness due to higher stabilization demands, whereas MCP will produce greater increases in oscillation frequency due to more isolated loading.

Exercise selection is a key determinant of acute neuromuscular responses during resistance training. Bench press (BP) and machine chest press (MCP) are widely used exercises targeting the pectoralis major, but they differ biomechanically in stabilization demands and load distribution. While BP requires multi-joint stabilization and increased neuromuscular coordination, MCP provides a guided movement pattern that isolates the pectoralis major.

Despite similar muscle activation reported in previous electromyographic studies, the acute mechanical responses of muscle tissue to these exercises have not been directly compared. Muscle mechanical properties, including oscillation frequency, stiffness, decrement, relaxation time, and creep, provide objective insights into neuromuscular function and fatigue.

In this randomized controlled trial, sixteen male bodybuilders with at least five years of resistance training experience are assigned to BP or MCP groups. Both groups perform four sets of ten repetitions at 80% 1RM. MyotonPRO is used to assess mechanical properties of the pectoralis major before and immediately after exercise.

The primary aim is to determine whether biomechanical differences between BP and MCP produce distinct acute mechanical responses in muscle tissue.

Inclusion Criteria:

• Male participants
• Aged between 20 and 40 years
• Minimum of 5 years of regular resistance training experience
• Competitive bodybuilding athletes

Exclusion Criteria:

• History of musculoskeletal injury affecting the pectoralis major, shoulder, or upper extremity within the last 12 months
• History of upper extremity surgery
• Use of anabolic steroids or performance-enhancing substances within the last 12 months

Individual participant data (IPD) will not be shared due to the small sample size and to ensure participant confidentiality and data protection.

The outcome assessor and data analyst were blinded to group allocation. Participants and care providers were not blinded due to the nature of the exercise interventions.