Feasibility of Velocity Loss-Based Volume Prescription During Constant-Load and Chain-Based Smith Machine Back Squats

NCT07719010 | Completed DMC

• 1 other identifier: SCNU-SPT-2025-055
• Study Type: observational
• Target: 26
• Locations: 1 country
• Sites: 1

Brief Summary

The goal of this observational study was to evaluate the feasibility of percentage of velocity loss (%VL)-based approaches for prescribing training volume during constant-load and chain-based Smith machine back squats. The study aimed to answer whether %VL can be expressed as the maximum number of repetitions (%Rep) in constant-load and chain-based Smith machine squats. Twenty-six resistance-trained men performed repetitions-to-failure tests under variable (VRT) and constant resistance training (CRT). The %Rep attained before reaching different levels of effort were compared between VRT and CRT across various loads and sessions. Furthermore, this study evaluated the influence of different factors on the predictive accuracy of the %Rep-%VL relationships. These findings will provide evidence-based evidence in prescribing and monitoring intra-set volume.

Conditions

Loading Configuration; Levels of Effort

Keywords

level of effort; lifting velocity; training volume; velocity-based training; variable resistance training

Outcome Measures

Primary Outcomes (2)

• The %Rep attained before reaching the 10%, 20%, and 30% VL thresholds

  The %Rep attained before reaching the 10%, 20%, and 30% VL thresholds was recorded across all loads, sessions, and loading configurations.

  April 1st, 2026

• The %rep predictive accuracy

  To assess predictive accuracy, second-order polynomial regression equations were generated from the first session of each loading configuration using all repetitions within a set, setting %Rep as the dependent variable and %VL as the independent variable. These equations were constructed using different regression types (individual vs. general), load specificities (load-specific vs. multiple-load), and loading configurations (CRT vs. VRT). During the second session, the actual %VL recorded after reaching the 10%, 20%, and 30% VL thresholds was substituted into the corresponding first-session equations to derive the predicted %Rep. Then, the absolute estimation error was calculated as (\|actual %Rep - predicted %Rep\|). In cases where muscular failure occurred before a specific %VL threshold was reached (e.g., 30% VL), the %VL of the final completed repetition was recorded, and the corresponding actual %Rep was defined as 100%.

  April 1st, 2026

Interventions

variable resistance training OTHER

Participants initially completed a standardized general warm-up and a specific warm-up. The specific warm-up protocol included 3 repetitions at approximately 40% 1RM, 2 repetitions at 65% 1RM, and 1 repetition at 90% 1RM using constant-load to ensure adequate neuromuscular activation for the subsequent testing sets. After a 3-minute rest, participants performed three sets to momentary muscular failure with 40% of total external loads provided by chains. To minimize fatigue from higher-repetition sets influencing the repetitions completed in subsequent loads, the loads were not tested in a randomized order. Instead, participants performed the tests in a descending order of 85%, 75%, and 65% 1RM.

constant resistance training OTHER

Participants initially completed a standardized general warm-up and a specific warm-up. The specific warm-up protocol included 3 repetitions at approximately 40% 1RM, 2 repetitions at 65% 1RM, and 1 repetition at 90% 1RM using constant-load to ensure adequate neuromuscular activation for the subsequent testing sets. After a 3-minute rest, participants performed three sets to momentary muscular failure with 0% of total external loads provided by chains. To minimize fatigue from higher-repetition sets influencing the repetitions completed in subsequent loads, the loads were not tested in a randomized order. Instead, participants performed the tests in a descending order of 85%, 75%, and 65% 1RM.

Eligibility Criteria

• Age: 18 Years+
• Sex: male
• Healthy Volunteers: Yes
• Age Groups: Adult (18-64), Older Adult (65+)
• Sampling Method: Non-Probability Sample

Study Population

Participant characteristics (mean ± standard deviation \[range\]) included: age, 20.4 ± 2.1 (18-25) years; body height, 1.78 ± 0.05 (1.68-1.87) m; body mass, 71.7 ± 7.5 (60.0-91.4) kg; training experience, 3.5 ± 1.8 (1-10) years; and constant-load 1RM, 135.4 ± 17.4 (95-163) kg, corresponding to 1.89 ± 0.21 (1.58-2.28) times body mass.

You may qualify if:

• at least 1 year of resistance training experience, performing back squats at least once per week.
• proficiency in the Smith machine back squat executed at maximal intended velocity.
• a constant-load 1RM of ≥ 1.5 times their body mass.
• no reported musculoskeletal injuries in the past three months.

You may not qualify if:

• Voluntary withdrawal or injury.

Sponsors & Collaborators

• South China Normal University: lead

Study Sites (1)

School of Physical Education and Sports Science, South China normal university

Guangzhou, Guangdong, 510006, China

Location

Related Links

• Related Info

Study Design

• Study Type: observational
• Observational Model: CASE CROSSOVER
• Time Perspective: CROSS SECTIONAL
• Sponsor Type: OTHER
• Responsible Party: PRINCIPAL INVESTIGATOR
• PI Title: Principal Investigator

Study Record Dates

• First Submitted: July 15, 2026
• First Posted: July 22, 2026
• Study Start: October 7, 2025
• Primary Completion: January 10, 2026
• Study Completion: May 1, 2026
• Last Updated: July 22, 2026

Record last verified: 2026-07

Data Sharing

• IPD Sharing: Will share
• Shared Documents: STUDY PROTOCOL, SAP, CSR
• Time Frame: Individual participant data and supporting documents will become available after publication of the study results and will remain available for 5 years.
• Access Criteria: Individual participant data (IPD) will be shared in anonymized form with qualified researchers for scientific purposes. The shared data will include lifting velocity of each repetition completed.

Locations

CN (1)