Biomechanics FOR Fly Casting: Part 3

Meeting the Demands of Physics

As detailed in the Physic FOR Fly Casting series mechanical casting efficiency demands body movements which:

  1. Optimise the net Force applied in the intended direction of the cast, in other words its target bearing. (This applies to all casts, whether the target is in front or behind the caster, to back casts as much as to forward casts.)
  2. Generate line speed sufficient to overcome gravity and air resistance so that we reach our target. In others words, so we achieve the range to target. Range and bearing mark the exact position of your casting target which is especially important for the delivery. (Yes, we also need trajectory but for my purposes it would be an unnecessary complication to do more than note it as a variable.)
  3. Enable and compensate for the use of a bendy lever to achieve 1. and 2.

Using a lever which extends our casting arm is advantageous because it amplifies the speed of the rod hand. Speed is distance over time. During a casting stroke the rod tip, which tows the line, moves further than the rod hand. More distance over much the same time means more speed. This is basically good.

The bendiness of the lever also does useful things. It causes delays in acceleration and deceleration, respectively before the rod bends and then again as it unbends. Thus is softens both the stops and the starts. Lastly, this flexibility effectively changes the length of the lever, shortening and then lengthening it again during the stroke. These features are both the good and the bad news. The softer stops and starts are easier on the body. Length changes make the whole shebang harder to control as we try to keep everything travelling as straight as possible and our loops aerodynamically clean.

Adding Biomechanics to the Analytical Mix

I like Bruce Richards’ six step model for casting instruction because it demonstrates how in practice we can connect mechanics and biomechanics. As he puts it “The six steps analyse the cause of the problem from top to bottom, then produce the cure of the problem from bottom to top.” The six steps are line, rod, body then body, rod, line.. We look at the line to see what the rod is doing to see what the caster is doing to the rod. Correcting the body, we change what the rod is doing and therefore what the line is doing. Mechanics is concerned with what the rod and line are doing to each other. Biomechanics looks at what we are doing to make the rod do what it does to the line.

The Basic Casting Stroke

For much of our casting, short to medium length and maybe more, all we need is the basic or foundation casting stroke. This largely involves a proximal to distal movement sequence of the upper arm, forearm and hand using the shoulder, elbow and wrist joints. There is little if any weight transfer or rotation of the torso. So ideally the upper arm sets the line of the vertical plane. The elbow being a hinge joint, the forearm will follow the leader and if we don’t rotate the hand (further inwards or outwards) then it too will stay on track. Job done.

Accuracy casters and many anglers utilise the basic stroke because it is simple, repeatable and minimises tracking error. You face the forward target, keep your eyes on it and move in line with that target.

The basic stroke also allows for some translation of the rod together with the more apparent rotation of the rod. As a foundation stroke, it can be extended by some leaning of the upper body backwards and forwards. Leaning back for the back cast and forward for the forward cast will also involve weight transfer which adds momentum. Additionally it can be extended on the forward cast by a fuller extension of the arm into a thrusting finish.

Getting a Grip

The grip you choose will have significant biomechanical implications but I won’t be providing a separate analysis for all the possible grips. So instead of that here is a general rundown. There are three standard grips and, roughly in order of commonality, they are thumb on top, V grip, and index finger on top. They each affect the range of movement a hand can make at the wrist during a cast. This is because they effect how the hand is oriented during the cast.

The range of possible hand movements is conveniently extensive for a species that makes tools and likes throwing things. Hold your hand out as though about to shake hands and follow along.

We can bend the hand inwards and outwards using the wrist joint (flexion and extension) .
We can make the hand curve slightly down and slightly up at the wrist joint (ulna and radial deviation.)
We can rotate the hand (and wrist) inwards until the palm is facing down and outwards until the palm is facing up (pronation and supination).
We can variously combine all the above movements.

The thumb on top grip puts the hand in a vertical position as though shaking hands or hammering a nail. Strength clue. The V grip rotates the palm slightly inwards (pronation) as for inserting a key into a lock. Finger on top further pronates the hand and extends the index finger along the rod grip.

I’m not going to do the pros and cons because in the end it’s a personal choice. My personal choice is sometimes the thumb on top – heavier outfits and close in shots. Sometimes it’s the V grip especially when going long. It is the closest of the three to a natural throwing action and allows a good range of movement. Hint, hint. Never really got on with the finger on top grip but can see its usefulness for shorter casts.

One last thing about grips. We seem to be conditioned to exert greater grip pressure when trying to achieve greater casting force and/or control – the grip of death syndrome. As with casting force, grip force is a case of just enough. The rod is unlikely to fly out of your hand because you weren’t holding it securely ie too little grip force. Too much grip force restricts movement and can lead to overuse injuries like tennis elbow.

Casting Principles From General Theory

Here is where we try to bring together the casting knowledge given to us by mechanics, biomechanics and traditional trial and error experience. The big picture for fly casting technique is that we need both repeatability and adaptability.

Repeatability gives us consistency in achieving the required range and bearing to target.

Adaptability enables us to adjust our casting smoothly to different conditions and different gear combinations and to improvise casts to a fish that isn’t in a text book position.

Forced to make a choice between the two I’ll take adaptability every time because if you have the technique to adapt well and quickly then it is pretty likely that you have already achieved and surpassed repeatability.

These two abilities are what we recognise almost instinctively when watching great casters at work. The work of the master appears effortless because their technique is sustained and solid in all departments. The novice struggles because their technique is unsustainable and weak in many departments.

Elite golfers are better at getting out of trouble just as much as whacking the ball longer and/or closer to the pin. Their overall mastery of technique enables better performance in every aspect of the game. So it is in many sports, including fly casting whether for fish or in competitions. If you are fishing, improvisation and adaption to changing conditions are even more important. One cast might be very short, the next quite long. One cast goes straight out in front, the next is off to the side. Some fish tolerate repeated presentations and innumerable false casts much better than others. Like many anglers it is the hard fish I most want to catch, the ones that demand excellent casting and tolerate few mistakes – in casting or otherwise.

A grasp of general principles is a sound foundation for developing the ability to adjust our movements at will. It is a different path than rote learning to perform somewhat robotic overhead or other casts at a limited range of distances.

Proximal to Distal Throwing Sequence

We are anatomically designed to throw things using a proximal to distal sequence. As we have seen big muscles are for power and smaller ones are for finesse. The sensory motor system, as much as the muscles, bones and connective tissues, is laid out on this basis.

As we will see this design principle holds up for short casts, through medium casts and on to long casts. It holds up for side casts as much as overhead casts, for hauls as well as strokes. You get the picture. It is fundamental.

By understanding, accepting and consciously incorporating this anatomical and biomechanical reality we can optimise our casting technique. It is as useful in avoiding and curing movement errors as it is in increasing performance – achieving range and bearing to target.

Straight Lines Rule

As previously explored in depth [LINK], to optimise the net Force applied in the intended direction of the cast we need to stay straight. Staying straight means not making errors in either the vertical or the horizontal plane when casting forward or back.

The vertical plane is what we would see if looking down from above the caster – the drone or birds eye view. Rod movement away from a straight line in this plane is usually called a tracking error. Using a basic casting stroke reduces the risk of tracking errors. We can make controlled variations in the amount of force applied and the distance over which it is applied (stroke length) and all with comparatively less risk of movement away from the line to the target.

The issue of force application brings us to the horizontal plane in which we also need to stay as straight as possible. This is what we observe from side on to the caster and watching the path of the rod tip. It’s the tricky bit. In order to maintain a straight line (rod tip) path in the horizontal plane while using a bendy lever (that changes length) we have to make complex adjustments. These adjustments are more complex, in fact, than throwing just about anything else I can think of including spears using spear throwers. Let’s unpack the complexity but without forgetting that we manage all this stuff mostly without needing to think about it at all. Two million years of evolution has made us pretty handy at throwing things – even with a bendy lever.

Let’s consider a forward cast using the basic casting stroke. As we accelerate the rod it starts to bend and shorten. (The translation phase is relatively short so in the basic stroke most of the rod bending and all of the unbending happens during the rotation phase.) The rod will also want to rise above the horizontal plane as it moves toward the perpendicular and dip away again after passing through the 90deg point. That is, unless we do something about it the rod tip will describe an arc instead of a straight line. Our options are either to make the rod bend more or to change/curve the path of our rod hand to compensate. The third option is a combination of both.

You see a problem here, right? We cast to many different distances requiring different amounts of force. More acceleration during rotation will produce more rod bend. Less acceleration means less bend and more of a problem in keeping the rod tip tracking along a straight line and not rising above it. The tip of a straight rod or one bent to a particular length from our casting hand will travel upwards and then downwards in an arc instead of a straight line unless we do something about it. Too much or too little hand path curvature at the wrong time will spoil the party.

To adjust for the net effect of rod bend and the naturally curved path of the tip we have to progressively and accurately change the pace and track of our rod hand. No great problem really. We have a sensory motor system which can monitor and control the force being applied. That takes care of pace. The pivoting of the upper arm in the shoulder joint (the proximal section of the arm) will start the process of curving the rod hand path. The extension of the forearm carries it on, both increasing the speed of the hand movement and the length of its arc. The wrist action finishes it off. The alternative adjustment is to keep increasing the rod acceleration so that it bends more. But this tactic has it limits. Rods can only bend so much. Also, at some point we have to stop accelerating and start decelerating at which time the rod will start lengthening again.

In practice and ideally we use a variable combination of rod bend under acceleration and curved hand path to achieve the desired rod length and loop shape of any given cast. In my opinion the skill of a caster is fundamentally defined by their ability to adaptively control their movements thereby using rod bend and hand path combinations pretty much at will.

Let’s assume we choose to make a hard stop. As we decelerate the rod, it will unbend. This also needs to be managed, largely by timing. To keep the loop fairly narrow we don’t want the rod to dip too far below the horizontal before (or for a while after) the loop is formed but the rod still has to get out of the way of the line as it begins to overtake the rod tip. As the rod unbends it will lengthen but by the time we make the hard stop the rod should be well past the perpendicular so we don’t have to adjust the rod hand path as much, if at all. Stopping at the right point will take care of the tip path, and thus the loop shape. So we stop below the perpendicular by not too far towards the horizontal.

We achieve all this by using a proximal to distal movement sequence of the upper arm, forearm and hand. It isn’t necessary to finish one part completely before the next part of the sequence begins.That would ruin the flow of the movement. The job is rather to perform the sequence in its proper order while maintaining flow. Flow comes from some overlap between the movements of the body parts included in the sequence. We don’t get to start the wrist action before the upper arm has done its thing just because Mark said some overlap was permitted. Rather we start the forearm extension before the upper arm movement is completed and likewise the hand moves at the wrist before the forearm has done all of its work.

After all that, here is the biomechanical take away. I truly hope it was worth the wait.

We optimise the cumulative application of force to the rod by our body when and only if, we make the relevant movements in the proper order and with the flow that evolution has created – just for us. 

Throwing a fly line with a bendy lever does make the throwing action much harder to do well because of the adjustments we have to make. They demand exacting control of the power applied throughout the proximal to distal flow but hey, isn’t that what any experienced and competent fielder would say about a return throw? The benefits are why we accept the challenge and most of us can meet it. Evolution has made us damn good at controlling our throwing movements.

Longer Cast Longer Stroke

One of the famous Five Essentials of Fly Casting is that stroke length needs to vary with the amount of line being carried. The reason given is that the rod bends more when the mass of the line being accelerated increases. And, in a general sense that’s true (enough).

It is equally true that the same amount of line can be cast quite efficiently with strokes of different lengths, provided we make the necessary adjustments. Of course there are limits. Way too short and way too long a stroke will mess things up. Why is that so? Because the rate of acceleration affects rod bend and too much or too little bend will make it harder to manage the path of the rod tip. Our ingrained managerial competence and expectations will be thrown out of whack and that interrupts the flow of our movements. Co-ordination fails.

Likewise we can cast a fixed amount of line easily with the same stroke length but with less, more or far more power applied. Overpowering, using more power than we need to complete turnover, is very easy to do. Underpowering, however, is actually much harder to do, intentionally in a controlled way.

What I’m getting at here is that varying the stroke length with line length is not just about rod bend. It has to do with Work, which is multiple of the force applied to something by the distance that something is moved. We use the rod to put kinetic energy into the fly line. That is, we do Work on the rod and we can vary both the amount of force and the distance over which it is applied. This brings us to the next principle.

Smooth Power Application

I think smoothness of power application deserves far more prominence and more detailed attention than it has generally received. It’s true that we want to be smooth because it helps maintain the control needed to keep the tip as straight as we can – in both the vertical and horizontal planes. It is also true that it helps us to avoid the demons of a tailing loop. For my $0.02AUD, however, it means a whole lot more than that. We’ll get to that directly. First though, let’s recap the mechanics of Work and how they relate to smooth casting.

Work is about how power (force) is applied.
How much force we apply over what distance determines how smoothly or roughly we apply power. Smooth power application is what we need to optimise loop shape and net Force in the direction of the cast.

In short, smooth power application equals more net Force applied by the rod to the fly line in a straight(er) line. Lumpy power promotes tracking errors in the vertical plane and in the horizontal plane it causes dips and rises of the rod tip away from a straight line path.

What are the biomechanical implications of the task so defined? Easy question. We follow the proximal to distal sequence with a nice flow. We use the bigger muscles for power when it is needed – say at the beginning of the stroke to get things moving. We use smaller muscles for finesse, to complete the movement and stay on track despite the increasing speed of our movements.

How do we move smoothly? More difficult question. Smoothness is a demonstration of controlled and progressive power application and the very opposite of jerky, instant, maximum power application. It’s co-ordinated movement. Remember, even power lifters need to stay smooth, both to perform the task and to avoid injury.

Fly casters aren’t power athletes demonstrating strength. We are more like dancers trying to demonstrate grace. Graceful movement comes from fluid economy of effort. It looks elegant and effortless because nothing is being overpowered. It is no co-incidence that Joan Wulff and Christopher Rownes were both professional dancers before they became renowned and distinguished fly casters.

Controlled power is easier to produce and maintain when less effort is required from the muscles providing the power. We start the stroke with the bigger muscles and we go easy knowing we have more than enough power in reserve. As the sequence progresses the movements speed up. However, as the musculoskeletal structures get smaller we can get away with a bit more effort because we have finer control over them. That’s because the parts we use for finer motor skill have more sensory motor connections controlling them. Again, we can do it that way because that’s how we are built for the job.

In a sense then, smoothness is both a cause and an effect of mechanical and biomechanical casting efficiency. Honestly, I have thought about it a lot and still can’t decide which is the chicken and which the egg – smoothness or advanced technique. So I’ll put it this way. Whether you are a fly fisher or tournament caster, trust me, effective technique is built on efficiency and smoothness is essential to efficiency.


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