When I first started fly fishing, I hadn't a clue what the terms "fast action" or "moderate action" meant. It wasn't until I began working in the fly fishing industry as a shop employee that I learned these terms out of necessity. In simple terms, the action of the rod is essentially just describing the 'kick point' on the rod blank (the point at which the rod bends).
Slow action rods
Slower action rods will often see the kick point in the bottom third of the rod blank. In comparison to newer, ultra-fast action rods, rods with a slow action will feel like trying to cast a cooked spaghetti noodle at first. Though they take a bit to get used to, especially if you are used to modern equipment, slow action rods can be incredibly enjoyable to fish.
Slower action rods are favourable in situations that call for delicate delivery of the fly, and cater well to lines with a long front taper. Split cane, bamboo and glass rods are perfect examples of slower action rods that anglers favour due to their ability to deliver flies to spooky fish in a subtle manner.
Slow action rods are suited to anglers with slower, smoother casting strokes, and 'stepping on' your cast with a slow rod will often lead to throwing tailing loops. Though they take a bit of time to get used to, slower action rods undoubtedly have their time and place.
Fast action rods
Certainly the majority of fly rod manufacturers, and anglers alike, are leaning in the direction of lighter, faster, more responsive rods with a quicker recovery rate. Fast rods will have a kick point in the top two-thirds of the rod blank, and are excellent for delivering the fly quickly while generating immense line speed.
Though fast action rods are incredibly popular, there are still anglers that favour a slower action blank. Fast action rods are stiffer in the back end, therefore they do not soak up the weight of the fish on the end of your line and can result in broken tippets if fish are not played diligently. On the flip side, the backbone of fast action rods is favoured in fishing big game saltwater species due to their ability to fight fish quickly with the back end of the rod.
Listen to today's episode of the Fly Fish University Podcast below on rod action: