"medium" action bamboo rod may have a faster action than a "fast" fibreglass rod. Action is also subjectively used by anglers, as an angler might compare a given rod as "faster" or "slower" than a different rod. A rod's action and power may change when load is greater or lesser than the rod's specified casting weight. When the load used greatly exceeds a rod's specifications a rod may break during casting, if the line doesn't break first. When the load is significantly less than the rod's recommended range the casting distance is significantly reduced, as the rod's action cannot launch the load. It acts like a stiff pole. In fly rods, exceeding weight ratings may warp the blank or have casting difficulties when rods are improperly loaded. Rods with a fast action combined with a full progressive bending curve allows the fisherman to make longer casts, given that the cast weight and line diameter is correct. When a cast weight exceeds the specifications lightly, a rod becomes slower, slightly reducing the distance. When a cast weight is slightly less than the specified casting weight the distance is slightly reduced as well, as the rod action is only used partially. Bending curve and tapering A fishing rod's main function is to bend and deliver a certain resistance or power: While casting, the rod acts as a catapult: by moving the rod shaft forward, the inertia of the mass of the terminal tackles and the distal portion of rod itself will load (bend) the rod tip backward, and the subsequent elastic rebound forward will sling out the lure/bait. When a hook bite is registered and the fisherman pulls the line, the elasticity of the rod will dampen the shock to avoid line failure. When fighting a fish, the bending of the rod not only enables the fisherman to keep the line under tension, but the bending of the rod will also keep the fish under a constant tension which will exhaust the fish and enable the fisherman to reel it in. Also the bending lessens the effect of the leverage by shortening the distance of the lever (the rod). Stiff rods demand much power of the fisherman, while actually less power is put on the fish. In comparison, a deep bending rod will demand less power from the fisherman, but deliver more fighting power to the fish. In practice, this leverage effect