No Changes In Lower-body Muscle Size And Force Characteristics Following Short-term Autoregulatory Progressive Resistance Exercise

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Autoregulatory progressive resistance exercise (APRE) programs dynamically adjust training intensity based on individual performance. The use of an APRE training program may provide further insight into the mechanisms that contribute to acceleration in strength gains and muscular hypertrophy. These mechanisms can be examined through the change in rate of force development (RFD) and cross-sectional area (CSA) following a mid-thigh pull. PURPOSE: The purpose of this study was to examine changes in muscle morphology, peak force, and RFD in the VL following a 4-week APRE training program. METHODS: Eight resistance trained males (age: 21.5 ± 2.3 yrs; height: 176.5 ± 6.8 cm; weight: 70.3 ± 17.8 kg) participated in a 4-week APRE training program. Resistance trained males were taken to absolute fatigue for 2 sets using approximately 85% of 1RM for compound lifts such as the squat, bench, deadlift, and overhead press. Pre and post measures were recorded during an isometric mid-thigh pull to compare RFD during the early phase of force production (0-50 ms, 50-100 ms, and 100-150 ms) and peak force. Ultrasound images were also taken to compare the changes in CSA in the VL following the training study. Paired samples t-test were used to compare the pre and post measurements for CSA and peak force. Furthermore, a mixed factorial analysis of variance (time [pre v post] x RFD [0-50 ms v 50-100 ms v 100-150 ms]) was used to compare RFD in 50 ms epochs during the early phase of the mid-thigh pull. RESULTS: There was not a significant difference in CSA from pre to post (p = 0.81; 27.39 ± 2.60 to 27.12 ± 1.91; mean ± SE). Additionally, there were no significant differences in peak force from pre to post (p = 0.58; 1860.76 ± 206.04 to 1908.71 ± 185.84; mean ± SE). Lastly, there were no significant time x RFD interactions (p = 0.735) or main effects for time (p = 0.956) or RFD (p = 0.077) between the early phase 50 ms epochs. CONCLUSIONS: The program did not yield significant changes in muscle morphology, peak force, or early-phase RFD, likely due to the participants' training style and brevity of training duration. For resistance training participants, future research should consider an intervention lasting ~8-12 weeks to better capture potential improvements in muscular performance.

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