. Introduction
In all recorded historical texts, the ability to generate power has fascinated man. Although modern technology has reduced the need for maximal strength levels for normal daily activities, from a scientific and clinical point of view muscle strength is of particular importance for health [1], optimal sports performance [2] and increased quality of life [3]. The history of organized weight training dates back to the late 1800s, however, the first scientific study of resistance training was reported in 1948 by Delorme and Watkins [1]. Delorme and Watkins demonstrated the importance of increasing resistance training compared to low-intensity long repetitions for strength gains and muscle hypertrophy. Since then, the study of the optimal way of training to increase strength, hypertrophy and power has occupied a large part of the scientific literature of sports sciences. Berger [2] conducted a series of studies between 1962 and 1984 to find the optimal training method to increase muscle strength [5-12]. The results of Berger's studies determined that performing 3-9 maximum repetitions in 3 consecutive times is the best way to increase muscle strength. However, the results reported by Berger have not been confirmed by subsequent studies.
Several training variables are central to the structure of a resistance training program. These training variables, including the number of turns of each movement, the number of repetitions of each turn, the number of movements performed in each training session, the rest period between turns, the intensity (load) of exercise in each turn, the type of muscle contraction used, and the number of training sessions per week, are expertly used to achieve the desired result [2]. Although these variables are well defined, there is much doubt about their utility for designing a resistance training program [13]. Obviously, determining the contribution of these variables in the structure of an optimal resistance training program, to increase strength and muscle size, depends to a large extent on the effort and initiative of researchers to conduct further studies. In this study, an attempt has been made to examine the changes in strength, anaerobic power, muscle mass, and acute responses to these two methods of exercise, considering the role of training load in each round of resistance training.
1-2. Statement of the problem
Strength training is widely used for the desired increase in strength, power and muscle hypertrophy in athletes. Although muscle strength and power, the key factors of muscle preparation for optimal performance of sports skills such as; Jumping[3], speed increase in minimum time, change of direction, and rotation[4] are the optimal training method to increase these muscle fitness factors.
There is a huge gap in the published literature about the role of training variables for increasing strength and muscle hypertrophy. Despite this, it is obvious that how the training variables are used in the structure of the resistance training program has an effect on the strength, power, hypertrophy and range of acquired neural adaptations [14,2]. Although it is well established that neural adaptations are the major factor in increasing strength in the early stages of resistance training [16,1], the interaction between training intensity and volume may play the greatest role in determining the optimal range of resistance training adaptations [2]. Despite this, relatively few studies have examined muscle adaptation in response to different methods of yielding [14]. Although it is recommended to perform maximum load bouts to increase maximal strength, it seems that how to apply maximal loads in macrocycle[5], microcycle[6], mesocycle[7] and even in the training session from one bout to the next bout is of particular importance to create the optimal training stimulus. In addition, it has been shown that the use of intensity and volume Variable training in the long term brings more adaptability to improve strength acquisition [17].
Generally, it is accepted that the training method of multiple rounds [8], for increasing strength and muscle hypertrophy, is superior to the training method of a single round [9] due to the greater volume of resistance training [19,18]. The most common training protocols
multiple bouts to increase strength and hypertrophy are using a constant load in each bout (flat pyramidal loading pattern; FPLP[10]), and gradually increasing the training load from one round to the next (slanted pyramidal loading pattern; [11]SPLP) [20]. It has been claimed that the use of the flat pyramidal yielding pattern, due to maintaining the intensity at the maximum level in each round of training, and preventing the body from confusing itself with several different training intensities, has created the greatest neural adaptation and is therefore superior to the oblique pyramidal yielding pattern for increasing strength and hypertrophy [21]. According to our knowledge, almost no study directly examines the role of maximal loads in multiple bouts of resistance training. However, studies that have examined different methods of resistance training by varying the training load in each protocol have reported a similar increase in strength. For example, by comparing two training methods Delorme (in which the load was gradually increased in each round) and Oxford [13] (in which the training load was maximal in the first round and decreased in the following rounds) reported 1RM and 10RM.
It has been found that strength training with maximal loads leads to improvement in strength by changing muscle neural activity [23]. Neural adaptation occurs naturally when the nervous system is under pressure caused by moving an unfamiliar load, fatigue and muscle inactivity [24]. This neuromuscular fatigue can be measured by the reduction in muscle force output by maximal isometric voluntary contraction (MVIC) [14], immediately after load displacement [26-24]. For example, Behm et al. [24] reported an average decrease of 21% in the MVIC of the brachial flexor muscle immediately after performing a single bout with 5RM, 10RM, and 20RM protocols. Several studies [27-31], acute responses such as; Neuromuscular fatigue and metabolite accumulation in a single resistance training session have been attributed to long-term adaptations in strength, along with regular resistance training. The results of the mentioned studies may suggest that the training protocol that results in greater muscle inactivity and glycolytic demand in response to a resistance training session is the appropriate training protocol for optimal increase in strength and muscle hypertrophy. For example, Takarada et al. [31], further increases in muscle strength and size along with a special training protocol; It has been attributed to the increased production and accumulation of metabolites during each training session, with the restriction of blood flow to the muscle increasing the metabolic demand in the active muscle. However, the results of the study by Brandenburg and Docherty [15] [13] do not support this theory. Brandenburg and Docherty [13] have reported a greater decrease and increase in MVIC and blood lactate test values ??(determinants of the acute response to resistance exercise) immediately after a session of a training protocol in which the load was reduced per turn (RL) [16], compared to a protocol with a constant load per turn (CL) [17]. This may suggest that maintaining intensity at a maximal level, by employing fewer repetitions per set, produces less neural fatigue and glycolytic demand in response to exercise, which is contrary to the initial claim of using maximal intensity to increase exercise stimulation and optimal neuromuscular adaptation. However, in this study the RL protocol had a higher training volume (more repetitions and time under tension), which is the reason for these reported findings [13]. However, after 8 weeks, both training protocols showed similar increases in 1RM strength of the arm flexors. The authors reported factors such as the short duration of the training period, the use of trained subjects and the use of a limited number of bouts (3 bouts) for each protocol as the reason for the similar increase in strength by the two protocols [4]. Also, in this study, subjects performed each turn until reaching complete paralysis regardless of the number of repetitions, it seems that this caused the same mechanism to call motor units in two different protocols, and as a result, it resulted in a similar increase in strength after 8 weeks [13].