Objective To investigate whether the addition of a swiss ball to a wall squat exercise has any effect on the levels of lower limb muscle activity at varying angles of knee flexion.

Design An observational study with repeated measures design.

Methods Measures were made of both legs of 14 healthy subjects (3 female, 11 male) mean height, age and weight were 31 years, 175 cm, 73 kg respectively. Each subject performed the wall squat exercise to 60°, 90° and 110° of knee flexion, with and without a swiss ball. Electromyographical (EMG) muscle activity was collected from vastus medialis, vastus lateralis, rectus femoris, semitendinosus, bicep femoris, internal oblique, gluteus maximus and gluteus medius. A pelvis and lower limb motion capture protocol was used to enable the EMG to be referenced to position. The EMG data was rectified and smoothed using a root mean square method. Analysis was made of the EMG data to determine whether the addition of the swiss ball resulted in any significant changes in muscle activity and also to identify whether there was a significant difference in muscle activity between the three angles of knee flexion used during the test.

Results The addition of the swiss ball to the wall squat exercise resulted in a significant increase in muscle activity of vastus medialis at 60° and 90° of knee flexion (Z=−4.053 and 3.643 respectively, p<0.002), vastus lateralis at 60°, 90° and 110° of knee flexion (Z=−3.142, −3.142, −3.142 respectively, p=0.002), semitendinosus at 60°, 90° and 110° of knee flexion(Z=−3.388, −3.075, −4.213, p=0.002) and internal oblique at 90°of knee flexion (Z=−3.074, p=0.002).

Conclusion The addition of the swiss ball to the wall squat exercise does increase muscle activity of the some of the lower limb muscles. However, the effects appear to be dependant on the muscles investigated and the angle of knee flexion to which the exercise is performed. The swiss ball cannot be generalised as a means of increasing lower limb muscle activity during the wall squat but the study indicates that it does play a role in increasing the muscle activity of specific muscles.