Tom Petranoff used hose drills to develop a great ability to run down the runway and keep his arm back during the crossteps. His ability to begin the throwing motion with the arm back has little to do with the ability to run crossteps while dragging a hose.
I have discussed resisted crosstep work with many international coaches and nobody does by pulling weight at the hand. Dragging 50 pounds or more with the hand behind you has very little relation to what actually happens in a real throw. The negatives are blazing, while the positives are hard to assess. Negatives being... Crosstepping while dragging a hose will definitely cause you to lean back and run out of balance. For the perceived affect of learning to keep your arm back while running sideways, the lack of balance in a run-up is so far more critical to a thrower it is impossible to express it. Now you are also running with the arm down. This is a problem every thrower will contend with all the time throughout their career. Don't add to the misery.
A run-up is all about balance and attack. Crossteps are even more critical to maintain balance and accelerate your attack. Balance means you are carrying your center of gravity forward without too much lean angle either way. So, to help you improve power in your ability to crosstep you use resistance at the center of gravity. This means some weight attached to your waist. When you need power and strength use resistance, when you need speed get assistance.
If you want to learn how to keep your arm back or at least improve this ability, then carry a javelin while you are working the crossteps with resistance. Want to relax your arm? Then open your hand and carry the javelin on your palm like a tray of drinks(Rum and Coke for Seppo). This will play a superior role in your ability to carry the javelin back.
By the way, if you have a problem in carrying the javelin back while doing a crosstep, then you shouldn't throw a javelin. I have never met anyone who couldn't do that. Throwing the javelin while starting the arm motion without it being back is the real issue. This comes from throwing balls, or footballs or any related round implement. Round implements allow you to cheat your arm because alignment can't be measured accurately. If you want to practice starting a throw with your arm back, throw a javelin itself, or a broomstick, or a Turbo-jav.
The bottom line is doing hose drags to get the feeling of keeping you arm back would be a waste of time, and it might even create more problems. Tom Petranoff did it and it worked but he had talent, and new how to differentiate the positive aspects of the drill without being affected by the negatives.
The big three you need to do. 5-7 sets of medballs up against wall stomach touchwall up on tippy toes and 20x 2 hand 20 x right hand 20 x left hand. work the shoulder. Get a 4 lb sledge and throw it from stand one step and three step. If you really want to work shoulder drills get a 10 lb and work multi range drill. email me direct or call me for what to do. To hard to explain in writing. Hose drags are the biggest single drill that helped me get leg drive and post over leg well. Most throwers don't get this drill and how much it will help them. It is about finding rhythm and leg drive while relaxing throwing arm.
Bill Webb and I came up with the drill to get me to run away from javelin and to get vertical left arm and shoulder drive while relaxing right side. You start with the hose over your cg and start to walk and build up speed to drive legs and arm in rhythm and then let gravity pull you back into c-position. Most people rotate the hose sideways or draw back and work the left arm low as you mention. They also tend to lean forward to get going and then lean to far back at the end while slowing down. Imagine you start running with hose and build up speed with good drive and at peak speed someone cuts the hose behind you. That is the whip your looking for. Obviously you can't do that but in essence that is javelin throwing. Run through the throw and keep throwing side relaxed
Hose drags!!!!!!!!!!!!!!!!!!!! I have told many throwers this is sooooooo important of all drills I did and NO ONE listens. Bill Webb and I started them in 1982 and a few thousand reps later 327 feet or 99.72 meters. One person who did them with me was Johan Oustheisen my training partner in South Africa. He went from 72 meters to 81 meters in one year. I asked him last week how many his son did and he said they did them almost every day. He threw 79.70 on Saturday with 700gram and he is 15 years old. The best drill to run away from javelin and learn to find rhythm and cadence in crossovers is hose drags. I did them every other day for 17 years, without fail. 10-20 reps, run, drawback hose slowly over the shoulder and drive the legs and bound with nice strides and build every drawback with more energy over two or three run throughs/ 50-70 meters. My run and drawback was 7 steps, drawback and 7 crossovers. Work on what feels best for you and add weight only when you have mastered hose only. You want more info email me firstname.lastname@example.org. Garden hose should be 20-25 feet long. 6-8 meters.
I prefer long hose and no weight to start. 100 ft is best. use the female end as the grip and hold like javelin grip.take most of hose 70-80feet and bundle up and duck tape it. now you have weight and drag..hose lasts longer on grass surfaces or wood indoors....the idea is to hold grip above cg and start to run and do not lean forward as you start to get momentum going. key is to stay tall and get deep leg drive from hips. hard to do at first. then build up your run up and slowly draw back and stay tall and behing cg....you will notice heavy fatigue at 30-40-50 meters in legs /hips.....exspecially after few sets....build up tolerance and then add weights. 5 lbs at a time. big mistake is too much weight and leaning forward or ahead of cg....in few months of this drill every other day ---- you can start to crack the whip drill which is second faze drill and depends on your progress. if you get good at hose drags and can stay back and hit block then you get the whip and pull to shoulder and you can feel the stretch reflex hit shoulder......if your out of balance you will feel it...most throwers have too narrow of block and hips have nowhere to go, look at the Pitman or Torkman (fin and norway dudes)the drift last 3-5 steps to the left so they get hips blocking over cg...they had some great video of meets this summer and show the whip they get from this action...leaving arm back and relaxed is hard to do when trying to throw far. take 10,000 run threws and hose drags to get on auto pilot and let throwing side go and focus on block,,,,,hose drags helped me and roggy get back and relaxed and driving legs with boundy rythem. getting cadence down of 4 left leg hits ---draw back and block on 4 left again is where I found my zone....whatever feels best --do good correct run ups and draw backs whith hose and javelin and heavy pole 10lbs or so and get that run ups so good --you don't have to think about it...
what do you do (in percentages) right hand versus left
for us it was 70-30% strong side weak side...also try doing run threws with javelin and do them backwards and forward.. great coordination drill and when you go backwards you will find you are in better layback position...do many and you will see improvement of balance and width of base at plant