Among the factors that can influence an athlete's performance, muscle strength stands out in relation to performance and risk of injuries in sports. As an alternative to quadriceps strength training, blood flow restriction (BFR) and neuromuscular electrical stimulation (NMES) are two techniques used to enhance muscle recruitment with less risk of mechanical damage and joint overload.

Evaluate the effects of strength training with BFR and BFR associated with NMES of the quadriceps muscle in physically active subjects on parameters of muscle thickness and lower limb performance.

This is a randomized clinical trial. The volunteers will sign the informed consent form. Will be recruited 60 individuals of both sexes, aged between 18 and 35 years, physically active according to the International Physical Activity Questionnaire (IPAQ). An initial anamnesis will be carried out to characterize the sample and anthropometric data will be collected, as well as thigh cytometry. Then, the volunteers will be randomized into three groups: Blood Flow Restriction Group (BFRG), Blood Flow Restriction Associated with Electrostimulation Group (BFREG) and Conventional Exercise Group (CEG). The evaluators will be blind in relation to the group that the individual was allocated, as well as the person responsible for the statistical analysis. Ultrasonography will be used in vascular Doppler mode to measure Total Occlusion Pressure (TOP) and in two-dimensional mode with a linear transducer to assess quadriceps muscle thickness. The performance of the lower limb will be evaluated from the height of the jump on the contact platform in the Counter Movement Jump (CMJ), Squat Jump (SJ) and Drop Jump (DJ) modes from an elevation of 30 and 60cm. The test of a maximum repetition (1MR) unilateral in the extension chair will be used to quantify the load during the interventions. The flow restriction protocols and the same combined with electrostimulation will have four sets of 30, 15, 15, 15 repetitions, with 1 minute of rest between sets of knee extension, with a load of 30% 1MR and 50% of the TOP, which will be adjusted by 5% each week of the protocol until reaching a TOP of 80%. In the CEG, conventional strengthening will be performed, with 70% 1MR in the leg extension, which will have three sets of 10 repetitions, with a 1-minute rest interval between sets. The training will be carried out twice a week, for a period of eight weeks, with reassessment of the 1RM test in the fourth week. At the end of the protocol, individuals will be reassessed.

It is expected that the findings of this study confirm the effectiveness of training with blood flow restriction compared to conventional exercise and that there is superiority in results when associated with neuromuscular electrostimulation.

In clinical practice, if proven effective, this strengthening program can be proposed as a muscle strengthening option for individuals who cannot tolerate high loads during conventional training.