Muscle force production is usually impaired in people with spinal cord injury (SCI). The use of high-intensity neuromuscular electrical stimulation (NMES) strength training can help promote metabolically active lean muscle mass and, thus, increase muscle mass and improve physical health and quality of life (QoL). Nonetheless, NMES is usually used at low-stimulation intensities, and there is limited evidence on the effects of high-intensity NMES strength training into improving muscle force and mass, symptoms of spasticity, or physical health and QoL in people with SCI. Five individuals with chronic SCI completed five 10-repetition sets of high-intensity knee extension NMES strength training sessions for 12 wk in both quadriceps muscles. Quadriceps femoris (QF) knee extensor torque was measured on a dynamometer, and cross-sectional area (CSAQF) was measured with extended field-of-view ultrasonography. Venous blood samples were collected for blood lipid profiling and C-reactive protein analyses. The Spinal Cord Injury Spasticity Evaluation Tool was used to assess symptoms of spasticity, and the QoL index SCI version III was used for QoL measures. QF tetanic knee extensor torque increased on average by 35% (2%-92%), and CSAQF increased by 47% (14%-145%). A significant increase in the HDL/LDL cholesterol ratio (P < 0.001) and a mean significant improvement of 4.8% ± 2.3% (absolute value = 0.26) in the Spinal Cord Injury Spasticity Evaluation Tool score was observed, whereas QoL showed a near-significant improvement in the health and functioning domain (15.0 ± 4.2 and 17.3 ± 5.1; P = 0.07). High-intensity NMES strength training in people with SCI may improve muscle strength, mass, physical health, and QoL. However, replication of these results is necessary before clinical implementation.