PURPOSE: Forward and side lunge exercises are frequently employed during patellofemoral joint syndrome rehabilitation. The purpose was to compare patellofemoral joint force and stress while performing the forward and side-lunge at ground level and up to a 10 cm platform. METHODS: Sixteen participants performed a forward and side lunge at ground level and up to a 10 cm platform. Electromyography, ground-reaction-force, and kinematic variables were collected and input into a biomechanical optimization model, and patellofemoral joint force and stress were calculated as a function of knee angle during the lunge descent and ascent and assessed with a repeated-measures 2-way analysis of variance (p<0.05). RESULTS: Collapsed across step-height, at 10° (p=0.003) knee angle during lunge descent and 10° and 30° (p<0.001) knee-angles during lunge ascent patellofemoral joint force and stress were greater in forward lunge than side lunge. At 40°(p=0.005), 50°(p=0.002), 60°(p<0.001), 70°(p=0.006), 80°(p=0.005), 90°(p=0.002), and 100°(p<0.001) knee angles during lunge descent and 50°(p=0.002), 60°(p<0.001), 70°(p<0.001), 80°(p<0.001), and 90°(p<0.001) knee angles during lunge ascent patellofemoral joint force and stress were greater in side lunge than forward lunge. Collapsed across lunge type, at 60° (p=0.009) knee angle during lunge descent and 40°(p=0.008), 50°(p=0.009), and 60°(p=0.007) knee angles during lunge ascent patellofemoral joint force and stress were greater lunging at ground level than up to 10 cm platform. No interactions occurred between lunge type and step height. CONCLUSIONS: Patellofemoral joint loading changed according to lunge type, step height, and knee angle. When the goal is to initially minimize and then gradually progress patellofemoral joint loading, the following may be a prudent lunging progression: 1) forward lunge at lower knee angles(0°-30°) at ground level or up to 10 cm platform; 2) forward lunge at middle knee angles(0°-60°) up to 10 cm platform and progressed to ground-level; 3) side lunge at middle knee angle(0°-60°) up to 10 cm platform and progressed to ground level; 4) forward lunge at higher knee angles(0°-100°) up to 10 cm platform and progressed to ground level; and 5) side lunge at higher-knee angle(0°-100°) up to 10 cm platform and progressed to ground level.