Acute Neuromuscular Responses to Combined Electrical Stimulation and Blood Flow Restriction: Effects on Quadriceps Torque, Fatigue, and Pain

Background and objective Neuromuscular electrical stimulation (NMES) combined with blood flow restriction (BFR) offers a promising therapeutic strategy for enhancing muscle strength in clinical populations who are unable to engage in high-intensity voluntary exercise. However, the optimal combination of NMES intensity and BFR pressure remains unclear, especially in terms of achieving an effective therapeutic outcome while maintaining patient tolerability. In this study, we sought to investigate how varying NMES intensities (medium-to-high) combined with different BFR pressures may affect quadriceps muscle torque generation, fatigue development, and pain perception. Methods Sixteen healthy individuals (10 females and six males; mean age: 19.3 ± 2.9 years) underwent six randomized experimental conditions combining two NMES intensities (50% and 75% of maximum tolerable intensity) with three different BFR pressures: unrestricted flow (0 mmHg), moderate restriction (50 mmHg), and severe restriction (250 mmHg). Each condition consisted of one set of five isometric contractions. Outcome measures included evoked torque (assessed via isokinetic dynamometry), fatigue slope (calculated through linear regression analysis), and pain perception (evaluated using a visual analog scale (VAS). Results Evoked torque significantly decreased during the fourth and fifth repetitions under severe BFR conditions relative to initial repetitions (p = 0.016). The rate of fatigue development, as measured by slope analysis, was significantly accelerated in all BFR conditions compared to unrestricted circulation (p = 0.013). Pain scores were significantly higher under severe BFR pressure, with a dose-dependent relationship between NMES intensity and discomfort, where 75% of maximum tolerable intensity elicited significantly greater pain than 50% intensity (p = 0.001). Conclusions The combination of moderate-to-high NMES intensity with severe BFR pressure accelerates muscular fatigue while increasing pain perception. For clinical implementation, we recommend initiating protocols with 50% maximum tolerable NMES intensity combined with moderate BFR pressure (50 mmHg) to optimize therapeutic benefit while maintaining patient tolerability. Progression to higher intensities should be personalized based on the patient's response and level of adherence.