After teaching yoga classes where I hold postures longer than usual my students are surprised that they feel they worked even harder than when we do more of a flow.  The reason why it’s harder is you’re using multiple muscles to hold a posture.  Engaging multiple muscles means you’re increasing your muscle tone.  So don’t be surprised if you get sore after holding multiple postures in yoga.  A good instructor will mix up a class with multiple postures that you hold and or a flowing  sequence combining multiple postures. Enjoy the results! -Sara Holliday MFT, CPT