The M-D Line stands for maximum relief of sensitive areas and so the 621 M-D® active 2.1 offers the optimal pressure distribution according to medical criteria for city bikes with a slightly forward bent to very upright sitting position. This model has with 85% the highest relief for perineal area and prostate from the entire SQlab product range. Talk to your doctor to be on the safe side.  The 621 M-D active 2.1 offers the optimal pressure distribution according to medical aspects for trekking and touring bikes. The 621 M-D active 2.1 also gets an improved, lighter saddle shell, an increased adjustment range and the completely newly developed technology for the Comfort active system, which is now adjustable via a switch function. New are also integrated threads for the connection of bags. The new 621 M-D offers more comfort with the same relief and a slightly narrower saddle nose.  + maximum relief + high comfort + active Comfort with Switch-Function + relief according to medical aspects  active- Saddle technology comfort The proven SQlab active system the saddle follows the pedaling motion, the comfort increases, the intervertebral discs are mobilized and the pressure on the sit bones minimized. The active movement can be regulated via the new switch function, in two settings. M-D line  More relief - less pressure. The M-D Line was developed for maximum relief of sensitive areas and allows pressure to be distributed according to medical criteria. M-D stands for maximized dip and, in combination with the high classic step shape, distributes the body weight onto the sit bones. This shape in combination with the CrMo rails make the M-D Line suitable for heavy riders. The width of 24 cm in particular offers a very large contact surface for absorbing even heavy body weight. If for you the comfort on the sit bones is more important than the relief of the perineal area, we recommend the ERGOLUX® series.