The purpose of this study was to compare trunk muscle activity, spinal decompression force, and trunk flexibility resulting from various protocols of spinal traction. Four experiments explored the effects of (1) sinusoidal, triangular, square, and continuous distraction-force waveforms, (2) 0, 10, 20, and 30 degrees of pull angle, (3) superimposed low, medium and high frequency force oscillations, and (4) sham traction. Nineteen healthy subjects volunteered for this study. Surface EMG was recorded during traction and later used in a biomechanical model to estimate spine decompression force. Trunk flexibility was measured before and after each treatment. There were no differences in muscle activity between any of the experimental conditions except the thoracic erector spinae muscle, which had lower EMG during continuous compared to sinusoidal distraction-force waveform (p=0.02). Thoracic and lumbar erector spinae muscles were significantly less active during sham than real traction (p=0.01 and p=0.04, respectively). The estimated L4-L5 spine compression force was 25N. Trunk flexibility decreased after each experimental session (p=0.01), and there were no differences between sessions. Our results suggest that the trunk muscle activity is minimal and point toward fluid exchange in the disc as one of the key biomechanical effects of spinal traction.