Background and Objectives: This study compared the effects of blood flow restriction resistance exercise (BFR-RE) and high-load resistance exercise (HL-RE) in voluntary exhaustion on quadriceps muscle adaptations in untrained young males. Materials and Methods: This study used a randomized controlled design that included 30 untrained young males (age = 21.42 ± 2.51). The BFR-RE group performed leg extension exercises with 60% occlusion pressure and 30% of one maximum repetition in volitional exhaustion. The same exercise was conducted at 70% 1RM in the HL-RE group. Fourteen variables were used to evaluate the intervention efficacy, including muscle thickness, stiffness, strength, cross-sectional area (CSA), and subcutaneous fat thickness. Analyses were reported using frequentist and Bayesian approaches. The Bayes factor (BF10 and BFincl) was interpreted based on negative and positive values. Results: The results revealed that the main effect of time was statistically significant for muscle strength, thickness, CSA, and stiffness (p < 0.05, BFincl > 1) and, in intragroup comparisons, both groups showed improvements in these parameters (p < 0.05, BF10 > 1). A statistically significant decrease in subcutaneous fat thickness was observed in the BFR-RE group (p < 0.05, BF10 > 1), while this change was not observed in the HL-RE group (p > 0.05, BF10 < 1). Similarly, a statistically significant increase in right rectus femoris muscle stiffness was detected in the BFR-RE group (p < 0.05, BF10 > 1) but not in the HL-RE group (p > 0.05, BF10 < 1). Furthermore, time’s main effect was statistically insignificant for thigh circumference (p > 0.05, BFincl < 1). The group × time interaction was statistically significant only for peak power leg flexion left (p < 0.05, BFincl > 1), and a statistically significant difference in favor of the BFR-RE group was observed in the intergroup comparisons (p < 0.05, BF10 > 1). Conclusions: In conclusion, BF-RE exercise with voluntary exhaustion may be as effective as HL-RE for hypertrophic adaptations in untrained young males.

The nature of exercise induced skeletal muscle hypertrophy is still a controversial phenomenon today. Various factors and limitations at the center of the process, such as muscle hypertrophy measurement methods and the training methods used, have prevented the correct definition of hypertrophic adaptation and mechanisms in the past. Along with the innovations and developments in sports science, long-term studies comparing various training methods with different measurement techniques raise doubts about the accuracy of hypertrophy definitions in previous sources. The largest lack of these definitions is related to the phenomenon of serial hypertrophy. In this respect, this review aims to examine many factors affecting skeletal muscle hypertrophy and to compile the effects of these factors on serial hypertrophy. In this review, a new and up-to-date approach to the definition of hypertrophy and hypertrophic adaptations has been tried to be brought together with the literature. In this direction, 62 studies and resources made between 1969 and 2020 were researched. As a result, it was emphasized that full range of motion, eccentric training and fast eccentric training caused more serial hypertrophy within the scope of increases in fiber and fascicle length, while partial range of motion, concentric training and slow eccentric training caused greater increases in fiber diameter. Research shows that different morphological adaptations may occur with muscle fiber hypertrophy during resistance training periods.