Introduction
Resistance training with blood flow restriction can have the same effects as traditional resistance training. On the other hand, the type of rest between resistance exercises affects muscle adaptation and aerobic muscle fitness. Active rest is likely to increase heart rate, vasodilators such as nitric oxide, and duration of activity in the minimum training time increase the training intensity, which can cause more adaptations [12]. The current study aimed to determine the effect of six weeks of selected resistance training with active and passive rest, with and without blood flow restriction, on young men’s C Reactive Protein (CRP), Lactate Dehydrogenase (LDH), and muscle endurance.
Materials & Methods 
From the available and voluntary samples, 24 healthy young soldiers of the Islamic Republic of Iran Air Force were divided into 3 groups of 8 subjects: traditional resistance training, resistance training with blood flow restriction, and passive rest and resistance training with blood flow restriction and active rest. The occlusion pressure was about 160 to 180 mm Hg for the legs and 140 to 160 mm Hg for the arms, depending on the systolic pressure of each person. Exercise programs were performed for 6 weeks, 3 sessions per week with an intensity of 70-80% One-repetition maximum (1RM) for the traditional resistance group (3 sets of 10), 20-30% 1RM for the passive rest group (30-15-15-15), and 20 -30% 1RM was administered for the active rest group (30-7-15-7-15). Before and after six weeks, physiological and anthropometric characteristics, muscle endurance, and hormonal levels were measured, and ELISA measured blood samples. Data were analyzed using covariance and Bonferroni post hoc tests and paired t-test for comparison within groups.
Results
Results showed that 6 weeks of exercise had a significant effect on Muscle endurance (P=0.001) but on the levels of C-reactive protein (P=0.43) and Lactate dehydrogenase (P=0.44) showed no significant difference. Paired t-test results also showed that at the levels of reactive protein C (Passive rest: P=0.020) and (active rest P=0.017), lactate dehydrogenase (Passive rest: P=0.007) and (Active rest P=0.001). The difference was significant only in the 2 groups with restricted blood flow. Restricted blood flow training with passive and active rest caused a significant reduction (42.30%) in CRP levels and (7.59%) in LDH levels. Also, a significant decrease (38.74%) in CRP and (11.20%) in LDH levels, respectively. But there is no significant difference between pre-test and post-test of CRP and LDH in the traditional resistance training group. There was a significant difference between the pre-test and post-test of all groups in muscle endurance (P=0.001) (Figure 1, 2) (Table 1).

Discussion
Clarkson and Thompson reported that regular physical activity reduced levels of muscle damage markers, including LDH [18]. Probably the reason for the conflict between the previous and present studies is the adaptation due to training. The type and intensity of training, recovery time, age, sex, physical fitness, season, and training with increasing fluctuations affect the concentration of this enzyme [26]. 
Studies show that the enzyme LDH has an effective role in causing inflammatory conditions for muscle cells. Some researchers have reported increased levels after physical activity due to damage to muscle fibers [27]. The 6-weeks training leads to adaptation; this training period will not lead to muscle damage. In addition, CRP is a sensitive inflammatory marker produced by liver cells in response to inflammatory agents and secreted by the liver. Physical activity reduces inflammation by improving endothelial function and has also been shown to reduce CRP production by reducing or inhibiting cytokines [28].
Previous research has shown a significant reduction in inflammatory factors after long-term exercise [29]. It has been shown that regular physical activity has the potential to reduce circulating levels of inflammatory markers [30]. Studies show a positive relationship between CRP and body mass index. The homogeneity of the body mass index of the groups can be considered another reason for the lack of statistically significant differences between the mentioned groups [40]. On the other hand, training with restricted blood flow enhances angiogenesis, increases the recruitment of type 2 fibers [44], increases muscle glycogen storage, improves the glycolytic capacity of type 2 fibers [45], and leads to improved muscle endurance. 
According to the results of this study, it seems that a combination of resistance training with restriction of blood flow and Interval training (active rest) can be a good alternative to traditional training and, in some cases, replace resistance training with occlusion and passive rest.

Ethical Considerations
Compliance with ethical guidelines
The Ethics Committee approved all experimental procedures of the Sport Sciences Research Institute of Iran (Code: I.R.SSRC.REC.1398.129) Clinical Trial Code from Iran Clinical Trial Registration Center (ID IRCT20191207045644N1) and were conducted in accordance with the Declaration of Helsinki.

Funding
This article was the result of a research project by Mr. Vahid Fekri Kourabbaslou, which was implemented under the supervision of the Physical Education Department of the Air Force of the Islamic Republic of Iran.

Authors' contributions
The main designer of the project: Vahid Fekri Kourabbaslou; the guide and consultants in designing and modifying the study: Ali Fakourian & Mohsen Heydarian; preparing the study draft and modifying it participated in this study: Seyes Masoud Kashfi.

Conflicts of interest
The authors declared no conflict of interest.

References