Background and Aim: Given the biomechanical differences between over ground and treadmill walking, it is expected that the contraction of muscles should be also different, so exercise training in these scenarios may have various effects on trunk muscles. The aim of this study was to compare amplitude and duration of activation of trunk muscles during over ground and treadmill walking to prescribe a suitable exercise mode considering the special circumstances of each person.

Materials and Methods: Nineteen healthy 20-40 years old male with sedentary life style were selected via simple sampling. Surface electromyography of rectus abdominis, external oblique, longissimus and multifidus muscles were recorded.

 Results: In each gait cycle, there was not statistically significant differences on duration of trunk muscles activity between treadmill and over ground walking. The mean amplitude of these muscles was greater on treadmill in comparison with over ground and this difference was statistically significant for rectus abdominis (P=0.005), longissimus (P=0.018) and multifidus (P=0.044) muscles.

Conclusion: Stabilizing role of trunk muscles during walking causes them to be active throughout the entire gait cycle. The increased muscle amplitude on treadmill might show that more motor units may be recruited during the contraction, which is helpful in prescribing the appropriate type of exercise especially to patients who have trunk muscles weakness.