The purpose of this study is to determine whether load-velocity (L-V) relationship variables (L0, v0, and Aline) are sensitive indicators of fatigue produced by different squat fatigue protocols. The study aims to answer how accurately these L-V measures reflect changes in performance, particularly changes in one-repetition maximum (1RM), after varying levels of induced fatigue. Twenty-eight resistance-trained men completed three sessions involving different fatigue protocols or no training. L-V variables measured before and after each protocol were compared. The findings will help determine whether L-V relationship parameters can be used as practical and sensitive tools for monitoring fatigue during resistance training.

This study investigates how different levels of fatigue influence the parameters of the load-velocity (L-V) relationship during the Smith-machine squat exercise. After an initial familiarization and baseline testing session used to establish 1-repetition maximum (1RM) and to perform a repetition-to-failure test at 70% 1RM, participants completed three separate experimental sessions. Each session implemented a distinct fatigue protocol, and all protocols were performed between two incremental loading tests to determine pre-session and post-session L-V profiles.

The moderate-fatigue condition consisted of five sets at 70% 1RM, with participants performing half of their maximal possible repetitions per set. The high-fatigue condition required five sets performed to volitional failure using the same relative load. A control condition with no exercise was also included to establish non-fatigue reference values. L-V variables of interest included L0, v0, and Aline (calculated as L0 × v0 / 2). These variables were compared across conditions to determine their responsiveness to increasing levels of fatigue and their association with changes in neuromuscular performance, particularly reductions in 1RM strength.

Inclusion Criteria:

Healthy males aged 18-40 years.

Resistance-trained (minimum 2 years of regular lower-body resistance training and ≥2 sessions/week).

Able to perform a proper smith-machine back squat with correct technique.

1-RM smith-machine squat measurable and ≥ bodyweight (or specify threshold used in study).

No musculoskeletal injury of lower limbs or back in the past 6 months.

Not using performance-enhancing drugs or anabolic steroids for the past 12 months.

Willing and able to attend all testing and training sessions and provide written informed consent.

Exclusion Criteria:

Any cardiovascular, pulmonary, metabolic, or neurological disease contraindicating intense exercise.

Recent (≤6 months) lower-extremity or spinal surgery or acute injury.

Current musculoskeletal pain or injury that limits squat performance.

Use of medications that affect neuromuscular performance (e.g., systemic corticosteroids) or stimulant drugs.

Regular participation in structured lower-body rehabilitation programs.

Failure to complete familiarization or preliminary 1-RM testing.

Inability or unwillingness to provide informed consent or follow study procedures.

Twenty-eight physically trained males, with an average age of 23.3 years (standard deviation [SD]: 3.0 years; range: 20-36 years), willingly enrolled in this research endeavor. The participants exhibited a mean body mass of 78.1 kg (SD: 9.3 kg), a body height of 177.2 cm (SD: 3.3 cm), and a one-repetition maximum (1RM) for smith-machine squat (SMS) exercise of 150.9 kg (SD: 12.5 kg). All subjects possessed prior RT experience, averaging 5.0 years (SD: 2.6 years), and demonstrated proficiency in executing the SMS exercise during the familiarization session.

Individual participant data (IPD) will be shared after de-identification. Data will be available to qualified researchers upon reasonable request for academic purposes. Access will be provided following publication of the primary results. Researchers will be required to submit a brief proposal describing the intended use of the data, and data will be shared through secure, controlled access. No identifiable information will be released.

Individual participant data and supporting documents will become available 6 months after publication of the study results and will remain available for 5 years.

Individual participant data (IPD) will be shared in anonymized form with qualified researchers for scientific purposes. The shared data will include de-identified performance measurements, load-velocity variables, and outcome measures relevant to the study.