## 1 Introduction  
Musculoskeletal disorders (MD) are common injuries characterized by clinical features such as pain, limited mobility, functional disability, and reduced quality of life [1]. In recent years, the prevalence of these injuries has increased by 58% [2], mainly affecting the lower limbs in all types of populations [3, 4], and they are currently the main cause of disability worldwide [5]. One of the most widely used treatments for MD is trauma surgery [6], which is a surgical procedure frequently performed in hospitalized and outpatient settings in the USA, France, Germany, and Spain [7]. However, these invasive procedures can have negative consequences. Muscle Weakness (MW), muscle atrophy (MA) and sometimes arthrogenic muscle inhibition (AMI) -especially after ACL reconstruction--are the most common consequences after musculoskeletal surgery [8; 9; 10]. During the postoperative period, MW, MA, and AMI can develop rapidly; for example, even short periods of immobilization can cause a 20-30% decrease in thigh volume after knee arthroscopy [11; 12]. Therefore, it is essential for physical therapists to incorporate analytical strength work in the early stages of the rehabilitation process [13; 14]. Thus, if there are no post-surgical complications, it is imperative to minimize the extent of knee extensor weakness during the early-stage post-ACL reconstruction [15]. Moreover, knee extensor maximal and explosive strength at 6-weeks post-ACL reconstruction has been shown to predict hop and jump performance at 6-months post-ACL surgery [16]. For these reasons, post-operative strength training should be initiated as soon as possible. Over the last few decades, some studies have suggested the potential for low-load exercise (i.e., <25% maximal capacity) to stimulate significant muscular adaptations when the blood flow to a muscle or muscle group is restricted or fully occluded [17]. In fact, comparing blood flow-restricted exercise to a non-occluded exercise control group, a 14% increase in knee extensor strength of young subjects engaging in strength training at 50% of maximal capacity was observed [18]. Thus, Blood Flow Restriction therapy, combined with low-load strength exercise (<30% Maximum Repetition (RM) [19]--Low-Load Blood Flow Restriction Training (LLBFRT) -, has emerged as a therapeutic alternative with great clinical potential, as it causes neuromuscular adaptations and improves muscle volume in a manner similar to Heavy Load Training (HLT) [13; 20; 21]. The basis of the adaptations caused by the use of LLBFRT are all the physiological changes, which comprise the increase in cellular swelling, systemic hormone production (GH, IGF1, and MGF), myogenic stem cell proliferation, protein synthesis (mTOR and MAPK signalling pathways), and recruitment of type II fibers [22; 23; 24; 25]. These changes result from metabolic cascades activated by mechanical tension and metabolic stress, the primary factors of hypertrophy [14; 18; 19; 20; 21; 22; 23; 24; 25; 26], which occur after the ischemic situation produced during the method application. LLBFRT has increased its use in rehabilitation and injury recovery areas [8; 24], since the above-mentioned responses and adaptations lead to mitigate MA and MW [23; 27] without overloading the tissue that must heal [16] and reducing the stress suffered by joints and bones [28]. Furthermore, it has a positive effect on postoperative pain management, as it has been shown to produce generalized hypoalgesia [29]. Research supports this, suggesting that working with this methodology favors strength and muscle mass increase, improves muscle and joint function, and sometimes reduces pain during exercise [8; 27; 28; 30; 31]. It is also known as a safe practice [11; 26; 32] that does not have more risks than traditional endurance training methods [8; 10]. In recent years, clinicians have started to implement LLBFRT in musculoskeletal postoperative settings [32; 33], where patients normally do not allow them to work with high exercise loads [22; 24].