Michelle M. Miller, Zachary K. Pope, Franklin M. Benik, Garrett M. Hester & Jason M. DeFreitas. Oklahoma State University, Stillwater, Oklahoma; e-mail: michelle.miller10@okstate.edu

Numerous studies have shown that resistance training can improve muscle size and quality over time; yet, it remains unknown how these muscle variables are influenced by the manipulation of training variables, such as rest period duration (i.e. time interval allotted between sets). PURPOSE: To determine the effects of rest period duration on muscle echogenicity and muscle cross-sectional area (CSA) following an 8 week (3 session/wk) resistance training program. METHODS: Twenty-one, college-aged males volunteered for, and completed, this IRB-approved research study. The participants were randomly assigned to 1 of 2 groups [SHORT (n=11); LONG (n=10)], before participating in 8 weeks of supervised, full-body, dynamic resistance training. All training variables were identical between groups (7 exercises, 3 sets, 10 reps, 10 RM load) with the only exception being rest period duration (SHORT = 1 min; LONG = 3 min). Before, and following, the resistance training program, ultrasound images were obtained from each participant’s dominant rectus femoris (RF) and vastus lateralis (VL) muscles. Using NIH Image-J software, CSA (cm2) and echogenicity (mean gray-scale value; 0 – 255) were calculated by carefully selecting as much of the muscle as possible, while avoiding any outer fascia. RESULTS: Following training, no significant differences were observed between groups (p>.05). However, with both groups collapsed (n=21), significant improvements were seen for 3 of the 4 variables: CSA of the RF (+6.62%; p<.05), CSA of the VL (+13.61%; p<.05), and echogenicity of the VL (-7.73%; p<.05). Echogenicity of the RF, however, was not significantly affected following training (-3.23%; p>.05). CONCLUSION: Resistance training can increase muscle size and may positively affect echogenicity of the quadriceps muscles in college-aged males. However, our findings indicate that these adaptations were not specific to the rest period duration utilized. Therefore, it was concluded that the resistance training program described in this investigation can elicit positive muscular adaptations (size and quality) using either 1 or 3 minute rest periods.

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