I have often come across, in writing on cross-country skiing, the importance of the compression phase of poling. One is advised, on pole plant, to compress, contracting the abdominals to initiate the action of poling. Let’s compare the action of poling with the action of the arm against the trunk in free-style swimming. The latissimi dorsi (lats) are the primary muscles that extend the shoulder against the trunk in swimming and in cross-country skiing. In swimming, it is essential to lengthen the trunk while pulling oneself through the water with the hands/arms. First, because it is important to keep the trunk long and hydrodynamic, secondly, because the powerful lats must be opposed by the muscles which extend the spine to utilize their full potential. To compress and contract the abdominals would take the lats out of action, and would transfer the work of shoulder extension to anterior muscles and arm rotators, so the work of shoulder extension would be limited by the relatively small mass of muscles like pectorals and teres major. In other words, the work of the abdominal muscles would be limited by the mass and strength of muscles that connect them to the shoulder for extension. In order for the lats to be effectively engaged, it is important to lengthen the trunk on pole plant, so that the spinal extensors support and oppose the action of the powerful latissimi dorsi.
As much as possible, arm recovery in skiing should follow arm extension. In running, the actions of extending a leg lead to recovery of the other leg – spinal extension and rotation lead to rotation and inclination of the pelvis, which initiates leg recovery. This is trickier in poling, because one must have some hold on the pole, so letting the wrist extend, so that arm recovery does not begin from the hand, is not obvious. A good strap, one that velcros around the hand, seems essential. One can extend the wrist and keep some fingers on the pole grip, because just releasing the hand, as one does the foot in running and skiing, results in the pole dragging. At any rate, allowing full arm extension and allowing arm recovery, rather than reaching out with the recovering arm, results in more powerful arm extension, as the muscles activated by trying to reach with an arm will work against those (lats, primarily) that extend it.
Today I worked on arm extension and recovery, trying to make it as much like those actions in the leg — that is, letting the arm release in extension, and not pulling it in to recover. I imagine pulling a heavy sled — doing it with my whole body, not trying to do it with the arm. Just like in leg extension, where one shouldn’t lift the toes to bring the leg forward, one shouldn’t flex the wrist to recover the arm. I wind up opening my hand on pole plant, so that pole plant is not led by the heel of the hand, which is like heel-striking in running. With a good grip strap, one can begin arm extension with an open hand. It feels really good to do this, but takes constant intention to keep it going.
As in leg extension, arm extension in poling can begin with the hand “landing” on the outer metacarpals, then pronating towards the thumb, so that the arm rotates inward against the counter-rotation of the shoulder girdle, just like an extending leg rotates inward against the counter-rotation of the pelvis.
Here is a photo of a skier beautifully extending her body from head to toe, and poling without compression: