The exercise works the best when performed with light loads and higher number of repetitions (15 - 20)-- Contract the abs during the motion. (fitnessandpower.com)
Also, there appears to be no difference in muscle activity between vertical and horizontal pulling exercises performed with similar loads. (strengthandconditioningresearch.com)
Although lifting heavy is not always hazardous for your body, some exercises are better performed with lighter weights. (fitnessandpower.com)