Loss of quadriceps strength after total knee arthroplasty (TKA) is most pronounced acutely but persists long-term, negatively impacting physical function in daily activities. Neuromuscular electrical stimulation (NMES) early after surgery is an effective adjuvant to standard of care rehabilitation (SOC) for attenuating strength loss following TKA, but the mechanisms whereby NMES maintains strength are unclear. This work aimed to determine the effects of early NMES on quadriceps strength and skeletal muscle fiber size 2 weeks after TKA compared to SOC. Patients scheduled for primary, unilateral TKA were enrolled and randomized into SOC (n = 9) or NMES plus SOC (n = 10) groups. NMES was started within 48 h of TKA, with 45-min sessions twice a day for 2 weeks. Isometric quadriceps strength was assessed preoperatively and 2 weeks following TKA. Vastus lateralis muscle biopsies of the involved leg were performed at the same time points and immunohistochemistry conducted to assess muscle fiber cross-sectional area and distinguish fiber types. Groups did not differ in age, body mass index, sex distribution, or preoperative strength. Both groups got weaker postoperatively, but the NMES group had higher normalized strength. After 2 weeks, the group receiving NMES and SOC had significantly greater MHC IIA and MHC IIA/IIX fiber size compared to SOC alone, with no group differences in MHC I fiber size. These results suggest that NMES mitigates early muscle weakness following TKA, in part, via effects on fast-twitch, type II muscle fiber size. This investigation advances our understanding of how adjuvant, early postoperative NMES aids muscle strength recovery.