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An emerging area of research in resistance training (RT) is the development of low-intensity training methods aimed at reducing the mechanical stress of muscle joints and maintaining or improving the positive adaptability observed in traditional RT practices. This trend is due to the need to increase the number of potential RT users by reducing the risks associated with their practice.
Several studies confirm the health benefits of conventional RT, including reduced obesity in children and adolescents (56) (32,41,55), reduced risk of metabolic syndrome (9,15), and delayed sarcopenia (5,7,22 ).
However, the use of all of these RTs requires the work of individuals from different age groups who require continuous supervision, adherence to strict safety guidelines, and careful selection of intensity levels.
Even on athletes, it is sometimes necessary to reduce the intensity of the training load, because mechanical stresses on the joints associated with regular training activities (such as lifting and bearing weights) may increase the risk of injury if not performed in a progressive manner ( 3, 10, 19, 36).
Recent studies have shown that training by using blood flow resistance training (BFRRT) for RT can reduce training intensity, taking advantage of neuromuscular and metabolic conditions created by the application of external wrapping devices such as pressure cuffs or tourniquets.
Therefore, the purpose of this article is to propose the major neuromuscular and metabolic advantages associated with BFRRT, and to propose alternative methods of reducing muscle blood flow by adjusting the rate of contraction.
Resistance training from clinical ischemia to blood flow limitation
The term "ischemia" comes from the Greek (ischein 5 to suppress; haimas 5 blood) and refers to an absolute or relative lack of blood supply to the organ. The ability to tolerate ischemia is organ-specific: human muscles can tolerate ischemia for 2 to 4 hours at normal body temperature (13).
In 1904, Cushing introduced the pneumatic tourniquet, a device that compresses blood vessels by using a gas source to compress a cylindrical bladder. This replaces Esmarch's bandages, which can sometimes cause nerve paralysis. The use of pneumatic tourniquets is essential to restrict blood flow during lower limb surgery. Although safety has increased significantly compared to previous techniques, it is important to study human metabolism during and after ischemia of the tourniquet, especially to understand that the few reported complications are the direct pressure exerted by the tourniquet on the nerves Consequences or consequences organizational change.
In 1975, Hal Hama and Engel (21) first studied the cellular metabolism of human skeletal muscle during clinical ischemia. They found that during surgery, a significant reduction in high-energy phosphate pools and lactic acid accumulation were observed in occluded legs compared to non-ischemic control limbs. Larsson and Hultman (26) used percutaneous biopsy to study the energy metabolism of 16 patients with knee injury after 1.5-2.5 hours of ischemia. They show a decrease in energy substrates during BFRRT, leading to a decrease in adenosine triphosphate and creatine phosphate, accompanied by an increase in monoadenosine phosphate, adenosine diphosphate, creatine and lactate. Sjo¨holm et al. (43), using the same technique as Larsson, reported that after 2 hours of quadriceps muscle occlusion in 13 patients undergoing knee injury surgery, the pH decreased by 7.1 to 6.8. However, the metabolic changes observed during the ischemia of the surgery-related tourniquet remain small.
In 1992, Moritani et al. (35) studied the neuromuscular response in handshake muscles during normal blood circulation and arterial occlusion during 20% repetitive contractions of maximum voluntary contraction (MVC). The metabolic state of active muscles is involved in the recruitment of motor units (MU) and the regulation of rate-coding patterns during exercise, as they observe a significant increase in the average MU stimulation amplitude and frequency during systole during arterial occlusion. These findings suggest that fast muscle (FT) fibers are recruited when oxygen availability is reduced, even with low intensity training. Sundberg (44) found that compared with the control group, fast muscle fibers experienced a higher glycogen reduction than slow muscle fibers in training legs with reduced blood flow, confirming that glycolytic fibers must be activated to maintain hypoxia Intramuscular conditions.
Takarada et al. (46) suggested that if muscles are forced to contract during blood flow restriction, thereby reducing the clearance of metabolites in the blood, even low-intensity exercise will increase the accumulation of intramuscular metabolites. In their study, six young male athletes performed 5 sets of knee extensions at 20% of a repetitive maximum (1RM) with a 30-second interval break, and a specially designed tourniquet was applied to the proximal end of the thigh. Plasma concentrations of lactic acid, norepinephrine, and growth hormone (GH) increased significantly under restricted blood flow (46).
In the same study, a comprehensive electromyographic activity analysis of the exercise concentric phase showed that the value under BFRRT conditions was 1.8 times higher compared to RT without blood flow restriction. This confirms that even if the same force is generated, BFRRT produces greater levels of activation in muscle, consistent with previous findings by Moritani et al. (35). BFRRT is a safe training mode (31, 37) that can be adopted by people of different ages and has been shown to increase the number of elderly women (48), trained athletes (47) and healthy athletes (47) Cross-sectional area (CSA) men (2,61). Abe et al. (1) studied daily changes in muscle CSA and strength, twice a week, twice a day, with a blood glucose limit of 20%.
They increased 3.5% and 17% in CSA, respectively, and increased maximum voluntary isometric strength in the quadriceps, respectively. Despite 1 week of RT twice a day, levels of muscle injury markers did not increase. The authors conclude that low-intensity BFRRT allows faster recovery, allowing RT to be performed more frequently, resulting in a faster hypertrophic response.
Subsequent studies confirmed that the use of BFRRT (16, 38, 45, 49) significantly increased plasma GH, leading some authors to speculate that the rapid increase in muscle fiber CSA that is often observed after such training is mediated by the action of GH. Like growth factor 1 (IGF-1) (2). However, some recent studies are questioning the role of GH in enhancing myofibrillar protein synthesis (59,60), suggesting that this hormone is more relevant to matrix collagen synthesis in skeletal muscle and tendons (11,14). Therefore, factors other than the increase in GH and IGF-1 appear to be related to the increase in muscle strength and size observed after BFRRT. These include mammals that activate the rapamycin signaling pathway (16, 20) and reduced myostatin (12, 27, 25).
In addition, it is speculated that rapid recruitment of fast muscle fibers (b) (29, 33) and failed training (29) and cell swelling (28) may be key factors explaining the positive training-induced fitness observed by BFRRT. Most studies that study BFRRT use blood flow limitation using external mechanical pressure, using wrapping devices such as pneumatically restricted cuffs, in training the proximal portion of the muscle. However, by taking into account the physiological effects of intramuscular pressure (IP) and relaxation time, the blood flow of muscles can be reduced without the need for external devices.