Fly Fishing for Pike from Float Tubes & Boats:

Casting heavy lines and flies with single handed rods - Avoiding fatigue

What are the Casting Weights Involved in Heavy Single Handed Fly Casting?
One thing about fishing a #10 line .... the weight of a length of aerialised fly line used in continuous fly casting must first be compared with a fixed weight of lead to be cast out by a bait or lure caster.
Then conclusions can be drawn after you know what the equivalent spinning lure weight would be:
     10 metres/30' of no 10 fly line weighs 20g/.75 oz.
     25 metres/75' of no 10 fly line weighs 50g/ almost 2oz.

So since it's casting these weights, this salt water fly / pike fly / big trout fly rod should really be regarded as just heavy spinning gear in another form. The weight is in the line instead of the lure. So the line acts as an elongated weight that requires a fly casting technique, but the load on the rod and on you the angler is similar to heavy spinning gear.

A salmon angler can throw 30 yards/metre of #10 line all day with less fatigue. This is due to the longer fly rod, and also the double handed operation. Also, the salmon river angler often does not retrieve the line, they let it swing downstream and in to the bank, and then lift it up put it all out again in one go. They have no need to extend a short line, into a long line for every cast. Theirs is a well organised, highly efficient, way of fishing a long range fly.
For piking, specimen trouting, and saltwater fly fishing much stripping in of line is required. This retrieve makes the whole operation different from salmon fishing. Every cast is beginning with a short line, and ends full distance. The rod must be single handed to free one hand for the stripping in retrieve. Therefore the rod must be capable of single hand casting, and it is therefore shorter. The way it works it is all much more like spinning than traditional fly fishing. The flies are sometimes a lot bulkier and can catch the air as they fly through it. This changes things a lot.

Fly Casting Frequency and the Tiring Effect compared with Spin Casting
Let's continue our spinning comparison a bit more. Fly casting frequency is obviously greater than spinning/baitcasting.
If we break it down into components the final cast is the same, (one final cast per retrieve) but there are extra false casting to lengthen line prior to a final shoot. These represent extra casts to be made.
Say you roll it onto the surface, false backcast back to aerialise it and shoot a bit out, and shoot hard on the forward cast out to the target fishing area. Let's count them -  that is one rollcast, one backcast and the final cast. Triple the casting work of a spinner/baitcaster.
If you need to make just one more false cast it is quadruple the casts of a spinning rod, EVERY TIME.

It is clear that developing the ability to shoot long lengths is highly desirable. It reduces false casting greatly. Since the false casts are all about getting more line aerialised, and if you can shoot line into the air both forwards, and backwards, then you do fewer false casts.
Double haul is the best casting style, because this casting technique shoots the most line out fastest. Learn to double haul, as soon as you have mastered a standard fly cast well.
Shooting head is the best casting line profile, because this line type gets the most line out fastest.
If you retrieve it in close, for following fish, a shorter no 12 shooting head could be better than a longer no 10 shooting head which weighs the same, because the shorter SH can be got outside the tip ring quicker, ready to shoot again.
A fast sinking line will be better than a thicker floating line with more air resistance, and fly streamlining assumes importance, from the point of view of conserving energy by less casting.

It's good to have a lower handle extension (below the reel)  so as to spread the work of all those casts, dividing it between both arms if one arm begins to tire, but the day is not yet over. It will also keep the rotating fly reel handle and spool clear of obstructions while fighting fish.

The extension could be removable, although on my rods it is fixed. That would be handy, just pop it on after you hook one, or when you want to do 10 mins double handed to give your arm a rest, but without stopping fishing.

 
David Norwich make extension Handle pieces

An Essential Trick that Eliminates Tires Arm/Wrists
Take a look at the saltwater fly rod handle on the left. The extension helps keep the reel away from clothing while fishing, but it can do another job too.

Now take a look at the fly rod reel fitting right lower. Notice how the reel screw locking device screws upwards away from the rod butt. In this type of reel fitting there will always be a little screw part sticking down below the reel. I use that as a small extension handle for wrist support during casting all day.

I velcro the storm cuffs of my jacket to make an instant wrist strap to grip onto the lower fly rod handle. This means that when I apply the forward power stroke during the forward cast, I have the power of my forearm applied to the rod, not just that power my wrist can apply. The result is I can drive the rod faster and compress it more using my supported wrist and forearm. this extra compression of the rod produces a faster more powerful forwards cast, and I can shoot a lot more line  to achieve greater distance. This works very well. Without it a small amount of give at the wrist at that moment will reduce distance.
The results of this trick are all good. The improved shoot of line reduces the number of false casts by at least 30% and I suspect by 50%, a major saving of effort, reduction of casting tangles, and more time with the lure in the water actually fishing.

This solution assumes a rod butt with a slight extension of handle/reel fitting below the the reel mount. So if the fly rod you are considering does not have a little bit of handle below the reel .... DON'T BUY IT ... unless it can have a handle extension added while casting bulky flies or playing a big fish. AT the very least you need a reel fitting that screws upwards under the reel to lock it on, leaving the exposed threaded portion as a "lower handle".

For medium range 15 - 25 metre/yrd casting, in summer where no jacket is worn, an alternative is to place a wrist strap around your wrist and the rod below the reel, and this moves leverage onto the forearm from the wrist and produces a faster forward power stroke, so important for shooting the maximum length of line, and reducing the need to back cast, a major improvement.

Wrap it round the end of butt of the rod handle below the reel and your lower arm just above your wrist. This will now take ALL the load off the wrist and moves it onto the forearm, which has far greater strength.
If you want a quick feel for how well this works do one of these tests:
   1 Tuck the rod butt into your jacket sleeve, if it has velcro storm cuffs, tighten them up to include the rod, and take 2 - 3 casts .
   2 Get a thick rubber band, double it and place on your arm above the wrist. insert the rod butt. Cast.

Try it once. You will have your eyes opened and never forget the size of the advantage this produces.

In the past, when casting into a wind with stiff rods I have even used shoelaces as a wrist brace. They work too.

Don't make it too tight. When we backcast stopping the power stroke abruptly at 1:00, and then pause for the line to extend out and back, while the line is extending in the air we drift the rod back to 2:00, usually by "opening the wrist" slightly. There should be just enough free room in your wrist strap to allow this flex and no more. This is coincidentally about the space that a velcroed tight parka sleeve will allow. The best amount will be clear when you try it for yourself.

Learn to cast using the double haul style If you use a single hand fly rod nothing gets so much distance, or power into a head wind, as double haul casting.