Squats are an excellent home exercise but have the disadvantage of high joint forces. Squat-in-home exercises are performed with support and may help reduce joint loading. However, the extent to which knee joint loading is reduced remains unclear. This study aimed to compare joint and muscle forces during normal squats and squats with support. Ten healthy young males performed normal squats and squats with support by the right hand. The hand support and ground reaction forces of both the lower limbs were measured using force plates. The tibiofemoral and patellofemoral joint forces and muscle force of the lower extremities were estimated using a musculoskeletal model simulation based on motion capture data. The joint and muscle forces were normalised to the body weight (% BW) of each participant. The variables of normal squats and squats with support were tested using repeated-measures analysis of variance or the Friedman test. The hand support force in squats with support was 12 ± 5 % BW. By using a support, right tibiofemoral joint force was significantly reduced from 321 ± 38 % BW to 278 ± 42 % BW (p = 0.032) and right patellofemoral joint force decreased from 427 ± 46 % BW to 356 ± 61 % BW (p = 0.008). The right muscle forces in the vastus medialis, biceps femoris, and gluteus maximus decreased, whereas those in the rectus femoris increased. These findings suggest that squats with hand support can reduce joint force, offering safer exercise instruction for rehabilitation, particularly in telerehabilitation and home exercise settings.