Sensitivity of Load-Velocity Measures for Detecting Fatigue During Smith-Machine Squats (SLV)

Sensitivity of the Load-Velocity Relationship Variables to Discriminate the Level of Fatigue Induced by Multiple Sets of the Smith-Machine Squat Exercise

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.

Study Overview

• Status: Completed
• Conditions: Neuromuscular Fatigue; Load-velocity Variables
• Intervention / Treatment: Other: Control Protocol (No Training); Other: Moderate-fatigue; Other: High-fatigue

Detailed Description

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.

• Study Type: Observational
• Enrollment (Actual): 28

Contacts and Locations

Study Locations

• Turkey (Türkiye)
  • avcılar
    • Istanbul, avcılar, Turkey (Türkiye), 34310
      • Istanbul Gelisim University

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: Yes

• Sampling Method: Probability Sample

Study Population

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.

Description

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.

Study Plan

How is the study designed?

Number of groups / cohorts

3

Cohorts and Interventions

Group / Cohort	Intervention / Treatment
Control Condition; Control Protocol Arm: Participants completed no exercise between the pre- and post-session load-velocity tests.	Other: Control Protocol (No Training); This intervention consists of no training or exercise during the session. Participants assigned to the control arm rest for the entire duration between the pre-session and post-session load-velocity assessments. No fatigue-inducing activity, resistance exercise, or additional intervention is administered, allowing all observed changes to reflect normal variation without training-related fatigue.
Moderate-Fatigue Protocol; Participants performed 5 sets of the Smith-machine squat at 70% of their 1RM, completing half of the maximum possible number of repetitions in each set. This protocol was designed to induce a moderate level of fatigue while avoiding complete muscular failure.	Other: Moderate-fatigue; Participants performed five sets of Smith-machine squats at 70% of their 1-repetition maximum (1RM), completing half of the maximum possible repetitions in each set. This protocol was designed to induce a moderate level of neuromuscular fatigue without reaching complete exhaustion.
High-Fatigue Protocol; In the high-fatigue protocol, participants performed five sets of Smith-machine squats at 70% of their 1RM, completing each set to muscular failure. In every set, participants continued lifting until they could no longer complete a full repetition with proper technique. This protocol was designed to induce a high level of neuromuscular fatigue and to test the sensitivity of load-velocity variables under maximal fatigue conditions.	Other: High-fatigue; This intervention involves no training or fatigue-inducing activity. Participants do not perform any squat sets between the pre- and post-session incremental loading tests. This condition serves as a baseline to determine natural variations in load-velocity measures, thereby eliminating the influence of exercise-induced fatigue.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in Theoretical Maximal Load (L0) Derived From the Load-Velocity Relationship	Difference in theoretical maximal load (L0, kg) derived from the load-velocity relationship between baseline (pre-session) and immediately post-session incremental loading tests.	Baseline (pre-session) and immediately post-session (within 15 minutes)

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in Theoretical Maximal Velocity (v0) Derived From the Load-Velocity Relationship	Difference in theoretical maximal velocity (v0, m/s) derived from the load-velocity relationship between baseline (pre-session) and immediately post-session incremental loading tests.	Baseline (pre-session) and 15 minutes post-session
Change in Area Under the Load-Velocity Relationship Line (Aline)	Difference in area under the load-velocity relationship line (Aline, calculated as L0 × v0 / 2) between baseline (pre-session) and immediately post-session incremental loading tests.	Baseline (pre-session) and immediately post-session (within 15 minutes)
Change in One-Repetition Maximum (1RM) in the Smith-Machine Squat	Difference in one-repetition maximum (1RM, kg) in the smith-machine squat between baseline (pre-session) and immediately post-session incremental loading tests.	Baseline (pre-session) and immediately post-session (within 15 minutes)

Collaborators and Investigators

• Sponsor: Istanbul Gelisim University
• Investigators: Principal Investigator: Deniz Şentürk, PhD, Istanbul Gelisim University

Study record dates

Study Major Dates

• Study Start (Actual): May 5, 2024
• Primary Completion (Actual): May 10, 2024
• Study Completion (Actual): October 10, 2024

Study Registration Dates

• First Submitted: November 27, 2025
• First Submitted That Met QC Criteria: December 19, 2025
• First Posted (Actual): December 29, 2025

Study Record Updates

• Last Update Posted (Actual): December 29, 2025
• Last Update Submitted That Met QC Criteria: December 19, 2025
• Last Verified: December 1, 2025

More Information

Terms related to this study

• Keywords: fatigue; resistance training; velocity-based training
• Additional Relevant MeSH Terms: Pathological Conditions, Signs and Symptoms; Signs and Symptoms; Fatigue
• Other Study ID Numbers: 2024/04/67

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES
• IPD Plan Description: 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.
• IPD Sharing Time Frame: Individual participant data and supporting documents will become available 6 months after publication of the study results and will remain available for 5 years.
• IPD Sharing Access Criteria: 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.
• IPD Sharing Supporting Information Type: STUDY_PROTOCOL; SAP; ICF; CSR

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No