Effects of Myo-Reps, Traditional, and Combined Resistance Training on Rectus Femoris Muscle Thickness and Acute IL-15 Responses in Resistance-Trained Men

Document Type : Research Paper

Authors

1 Department of Exercise Physiology, Faculty of Physical Education and Sport Sciences, Kharazmi University, Tehran, Iran.

2 Department of Exercise Physiology, Faculty of Physical Education and Sport Sciences, Allameh Tabataba’i University, Tehran, Iran.

10.22080/jaep.2026.31724.2255

Abstract

Background and Objective: The acute myokine response to resistance training and its relationship with muscle hypertrophy remain incompletely understood. This study aimed to investigate the effects of Myo-Reps, traditional, and combined resistance training protocols on serum interleukin-15 (IL-15) levels and rectus femoris muscle thickness in resistance-trained men.
Materials and Methods: Thirty-six resistance-trained men (mean age: 26.03 ± 4.22 years; body mass index: 24.83 ± 3.05 kg/m²) were recruited through purposive sampling and randomly assigned to three groups: traditional, Myo-Reps, and combined training. The intervention lasted 8 weeks, with three training sessions per week. One-repetition maximum (1RM) was assessed before the intervention, and the training program was structured as a three-day split routine targeting the lower limbs and triceps, chest and shoulders, and back and biceps. Training volume was equated across the three groups, while exercise intensity progressed from 75% to 85% of 1RM. Serum IL-15 levels were measured at baseline and immediately after the first training session of the first week. Rectus femoris muscle thickness was assessed using ultrasonography before and after the 8-week training intervention. Data were analyzed using paired-samples t-tests and analysis of covariance (ANCOVA), with statistical significance set at p < 0.05.
Results: None of the three resistance training protocols produced a statistically significant change in serum IL-15 levels. Rectus femoris muscle thickness increased significantly in the Myo-Reps (p = 0.024) and combined (p = 0.001) groups, whereas the increase in the traditional training group did not reach statistical significance (p = 0.07). A significant between-group difference was also observed in changes in muscle thickness (p = 0.016). Post hoc analysis indicated a statistically significant difference between the combined and traditional training groups (p = 0.018), whereas the other pairwise comparisons were not statistically significant.
Conclusion: The findings indicate that Myo-Reps, traditional, and combined resistance training protocols did not differentially affect the acute serum IL-15 response. However, combining Myo-Reps with traditional resistance training resulted in a significantly greater increase in rectus femoris muscle thickness compared with traditional resistance training alone.

Keywords

Journal of Applied Exercise Physiology
Volume 22, Issue 43
June 2026
Pages 93-114

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History

  • Receive Date: 10 May 2026
  • Revise Date: 02 July 2026
  • Accept Date: 21 July 2026

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