My friend Reya posted a good blog entry today on pain. What John Friend says of pain is that it is nature’s way of showing that we are out of alignment. I am in full agreement with Reya that intentionally causing ourselves pain is not what brings the most gain.
We sometimes have to go into discomfort, though, to get out of pain, when we are practicing therapeutically. What I tell my students, when they are seeking to use the physical practice of yoga to heal injuries, is that they want to practice mindfully enough to notice and back away from stabbing, pinching, tearing, or cramping sensations (you might think of other words to add to the list, but you get the idea). On the other hand, intentionally embracing some level of therapeutic discomfort can be necessary to heal and grow. An obvious non-yoga example is getting an operation to remove a tumor or fix something that is broken. The operation is going to be a challenge, but it is better than not healing.
If we are not used to holding poses for a long time or balancing on one foot or on our hands, our muscles may think they would rather slouch on the couch–though slouching on the couch may be what precipitated injury or ill-health in the first place. The discomfort of working muscles more than we usually do, but to the right degree and in alignment, is radically different than the pain of forcing our body to do something beyond its current capacity that exacerbates existing injuries or causes new ones and does not sufficiently heed proper alignment.
I invite you to practice slowly and with sufficient attention to know deeply whether you are just bringing on discomfort from right effort and changing old patterns that no longer serve or whether you are making yourself suffer for no real purpose. No pose or distance or timing is worth injury, but healing and getting stronger and more flexible (as well as more courageous and expansive for what life brings to us) is most definitely worth some intentional discomfort.