In young, healthy adults, early phase (i.e., 0-50 ms) rate of torque development (RTD) is primarily determined by neural characteristics. However, it is unclear if this remains the case in older adults. PURPOSE: To examine the physiological characteristics of early phase RTD in older men. METHODS: Seventeen older males (age = 73 ± 6 y) completed 2 maximal (MVIC) and 2 rapid (rMVIC) isometric knee extensions. Early phase RTD values were calculated from the first 50 ms (aRTD50) of the rapid contractions and normalized (nRTD50) to maximal torque (%MVIC/s). Muscle activation amplitude (EMG) was calculated during the first 50 ms (nEMG50) of EMG onset and was normalized to the peak-to-peak M-wave amplitude (%MPP) of the vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF). Evoked peak twitch torque (PTT) was determined as the maximal torque (Nm) produced from a single electrical stimulus. Motor unit number estimation (MUNE) was calculated as a ratio of the ensemble average of the single MU potential amplitude to the compound muscle action potential amplitude and was corrected for alteration. Muscle quality (MQ) was determined by examining the average muscle cross-sectional area relative to the average muscle echo intensity for each muscle using an ultrasound. Relationships between the predictor variables (nEMG50, MUNE, PTT, MQ) and RTD (aRTD50 and nRTD50) were analyzed via Pearson’s correlation coefficients. Stepwise multiple regression was used to examine the amount of variance in aRTD50 and nRTD50 accounted for by each of the predictor variables. RESULTS: aRTD50 (577.8 ± 241.0 Nm/s-1) was related to MUNE (144.1 ± 47.1, r = .549, p = .023), nEMG (137.5 ± 97.7 %MPP, r = .673, p = .003), and PTT (20.34 ± 12.5 Nm, r = .504, p = .039). nRTD50 (433.2 ± 175.4 %MVIC/s) was related to MUNE (r = .531, p = .028) and nEMG50 (r = .604, p = .010). nEMG50 and PTT were significant determinants (p = .001) that accounted for 45.3% and 15.5% of the variance in aRTD50, respectively. nEMG50 was the only significant predictor (p = .01), explaining 36.4% of the variance in nRTD50. CONCLUSIONS: These pilot data support the notion that early phase RTD is primarily determined by neural factors, even in older adults. These data also suggest that possessing a higher number of viable MUs may influence early phase absolute RTD in older men.