Anaerobic threshold (AT) and VO2max have been used as endurance predictors (1). It is unclear that metabolic stress (MS) as indicated by ‘AT’ reflects more towards physiological fatigue or muscular fatigue. This is because of the contradictory research findings between lactate (La) and muscle fatigue (2,3) and ‘La’ kinetics with O2 transport system (4). Due to this complexity, this study will have three purposes. 1) To investigate if endurance time (ET) at individual’s anaerobic speed (vAT) will be similar between participants during a discontinuous constant speed and a continuous constant speed protocol. 2) To evaluate anaerobic fitness (%VO2max) effect on ET and oxygen reserve (ΔVO2 = VO2max – VO2). 3) To examine if running at ‘vAT’ stresses the physiological or muscular or both systems. 20 male recreational runners (age 23.2±1.42 years, BMI 21.67±2.16, VO2max 57.83±5.45 ml.kg-1.min-1) went through three test sessions, with recovery period of 5-7 days in-between. Session 1 included VO2submax followed by VO2max protocol (5) to determine vAT at lactate 4 m.mol.l-1 and VO2max. During session 2 & 3, the treadmill was programmed to run at individual’s vAT with 4 min run and 1 min rest intervals and at individual’s vAT without rest till volitional exhaustion respectively. For respiratory data, “ParvoMedics True One 2400” analyzer was used and for ‘La’, 20 ul blood samples were drawn from finger in all three sessions. Borg 10 point RPE scale was used to quantify volitional exhaustion factors (RPE chest, RPE muscular and RPE overall). Results indicated that the average duration to sustain running at vAT was 37±9.87 mins for session 2 and 23.4±9.74 mins for session 3. Participants also experienced higher MS (7.08±1.86 m.mol.l-1) in session 3 then in session 2 (5.74±1.14 m.mol.l-1). Descriptive statistics are summarized in table 1. For session 2, one-factor ANOVA reported significant difference for BLa (p=0.024), ΔVO2 (p=0.033), %VO2max (p=0.047) and ET (p=0.05) between these grouping factors but no significance was found in session 3. “Kendall’s Tau_b” correlation with significance p<0.05 reported a significant correlation (τb =-0.76) b/w ΔVO2 and %VO2max, (τb=0.449) b/w ΔVO2 and discontinuous ET, (τb=0.56) b/w ΔVO2 and continuous ET, (τb=-0.53) b/w %VO2max and ET, and (τb=0.452) b/w %VO2max and vAT. Findings suggests that at ‘vAT’, changes in %VO2max, VO2max and ΔVO2 resulted in different ET during session 2 & 3, shown in figure 1. One-minute rest interval, during session 2, resulted in higher MS for RPE chest than RPE muscular whereas session 3 did not have any significant difference. Increase in ΔVO2 and decrease in %VO2max were linked with better ET. Findings suggest that ΔVO2 along with AT and VO2max can be used for better endurance performance prediction.