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Resistance Training/Periodization

(15) VOLUME-LOAD, MUSCLE DEOXYGENATION, AND MUSCLE FATIGUE DURING A BACKSQUAT SET TO FAILURE ON A DYNAMIC LOAD DIGITAL-WEIGHT SYSTEM AND FREE WEIGHTS

Thursday, July 13, 2023
2:00 PM – 3:30 PM East Coast USA Time
Location: Milano III-IV

    Poster Presenter(s)

  • Riley Melton

    Student
    Coastal Carolina University
    Conway, South Carolina, United States

    • Author(s)

  • JL

    Jakob D. Lauver

    Assistant Professor
    Coastal Carolina University
    Conway, South Carolina, United States

  • TR

    Timothy R. Rotarius

    Assistant Professor
    Coastal Carolina University
    Conway, South Carolina, United States

  • JG

    Justin P. Guilkey

    Assistant Professor
    Coastal Carolina University
    Conway, South Carolina, United States

Abstract Details: Volume-load (VL), metabolic stress and muscular fatigue can lead to muscle hypertrophy when performing resistance training to failure. A smart digital-weight system (DWS) that utilizes dynamic loads throughout the concentric and eccentric phases of contraction may exacerbate these responses compared to traditional free-weight exercise by optimally stressing the muscle throughout the movement.

Purpose: This study examined the VL, metabolic stress and muscular fatigue during a single set of back squats to failure using barbell free-weight (FREE) and dynamic resistance DWS.

Methods: Healthy adults (29.7 ± 7.1 yrs) who were not currently engaged in resistance training to failure participated. Prior to experimental conditions, a predicted one-repetition maximum (1-RM) for back squat was determined on the DWS. There were two experimental conditions (FREE and DWS) that were performed on separate days and assigned in a random order. In FREE, one set to failure of barbell back squat at 60% of 1-RM was performed. During DWS, one set to failure of back squats was performed on a DWS (Tonal Home Gym©, San Francisco, California) with dynamic load. During dynamic load, the load was 60% of 1-RM at the transition from eccentric to concentric phases and load increased during the concentric phase and decreased during eccentric phase.  In FREE, VL was calculated (repetitions x load), but VL during DWS was determined by the DWS software, due to the dynamic loading. Muscle deoxygenation (HHb) was measured by near-infrared spectroscopy placed on the vastus lateralis. The magnitude of the metabolic stress was assessed as the greatest change in HHb from the cycle warm up (HHbmax). Also, HHb data from the first repetition to the last repetition were normalized to a cycle warm up and plotted against time. The area under the curve (HHbAUC) was calculated via the trapezoidal rule to assess overall metabolic stress in each condition. Change in jump height from pre to post squat assessed muscular fatigue. Three countermovement jumps were performed before and immediately after the set. Jump heights were measured via a positional linear transducer and averaged. Differences between FREE and DWS were compared using paired T-tests. Significant differences were established if p</span> < 0.05.

Results: The predicted 1-RM for back squat was 174.0 ± 11.0 lbs and the load for each condition was 105.0 ± 5.5 lbs.  There were no significance differences between DWS and FREE for the number of repetitions to fatigue (37.0 ± 12.6 reps vs. 39.2 ± 7.9 reps) or VL (4267.4 ± 1494.6 lbs vs. 4108.0 ± 795.3 lbs). There were no differences in HHbmax between DWS (-7.8 ± 3.3 au) and FREE (-8.2 ± 3.5 au). During HOME, the HHbAUC was 618.6 ± 330.0 au2 and HHbAUC during FREE was 636.2 ± 463.5 au2. The differences were not significant. Additionally, the change in jump height was similar between DWS (-5.2 ± 1.4 in) and FREE (-5.7 ± 1.6 in). CONCLUSION: The dynamic load during DWS did not affect VL, metabolic stress, or muscular fatigue compared to free-weight exercise during one set of back squats to failure. PRACTICAL APPLICATION: Acute responses during resistance exercise to failure suggests a dynamic load DWS could be as effective as free-weight exercise in promoting muscle hypertrophy. However, the dynamic load in DWS may not enhance muscle hypertrophy when training to failure. A home smart DWS could be a safe and effective at-home resistance training system for resistance training to failure.  

Acknowledgements: None