Could I even do 108 Sun Salutations? Would it feel like running a marathon or a 3K? Would the shoulder-stressing downward-dogs become unbearable after, say, round 36? Or round five? And, most importantly, would it quiet my mind?
Core training within the yoga tradition doesn't focus on the muscles contracting; the emphasis is on openness. Instead of putting your attention on what's being tightened or clamped down, consider the places on your body that are allowed to stretch in new ways.