The aim was to determine whether the intensity of unilateral standing on the T-board can be determined by muscle activation and the movement strategy. Twenty-four randomly selected healthy young adults, 13 males (23.3 ± 4.3 years; 182.6 ± 5.8 cm; 83.6 ± 4.8 kg) and 11 females (24.8) were freely participating in the study (24,8 ± 4,0 let; 168,5 ± 5,5 cm; 59,7 ± 8,8 kg). The subjects maintained their posture on the right leg on the T-board, which was unstable in the sagittal plane. The stability of the T-board was systematically reduced. While standing in equilibrium, we measured kinematic parameters of body segments and T-board oscillation, equlibrium time, number of lost equilibrium positions, CoP velocity, and surface electromyography signal of soleus, gastrocnemius, tibialis anterior, rectus femoris and biceps femoris. The results showed high and excellent repeatability of T-board oscillations. Furthermore, high and excellent repeatability was calculated for equilibrium time and centre of pressure velocity while standing on T-board under all stability conditions. The results confirmed that T-board oscillation was systematically magnified. To maintain equlibrium on T-board muscle activation of the thigh and shank was similar, as well as movement strategies. In all conditions, the tibialis anterior muscle was the most active. The effectiveness of maintaining unilateral standing on a less stable T-board was associated with greater activation of the biceps femoris and higher angular velocities in the ankle. The activation of the shank muscles does not change to a great extent with the lower stability of the T-board, while a greater change is reflected in the activation of the thigh muscles. We conclude that a change in movement strategy during unilateral posture is a better indicator of the relative intensity of the equilibrium task than the relative amplitude of the surface EMG signal of the shank and thigh muscles.
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