2.2. Experimental Procedure

The study was designed to test six different exercises. The trial was designed to compare the quadriceps muscle activities during different leg exercises, including when combined with hip adductor co-contraction. The exercises followed the sequence; (1) squatting (SQ), (2) SQ with hip adduction (SQH), (3) knee extension (KE), (4) KE with hip adduction (KEH), (5) straight leg raising (SLR) and (6) SLR with hip adduction (SLRH) (see Figure 1).

Steps of performing each exercise.

Each participant was asked to practice before performing three tests of each exercise, with a 30 s rest between the trials and a five-minute rest between the exercise conditions (Figure 1). During each leg exercise, surface electromyography (sEMG) was used to determine the superficial quadriceps muscle activity in the rectus femoris (RF), vastus medialis oblique (VMO) and vastus lateralis (VL). The dominant leg of each participant (identified based on the preferred leg) was used for the EMG measurements. A researcher recorded the sEMG and scored the data. Muscle activities were compared between the different leg exercises both with and without hip adductor co-contraction.