This has been an interesting discussion. The original question was barbells or kettlebells to prepare for British Army parachute training.
Which branch of Service and at which Selection are you aiming?
British Army Pre Parachute (P-Company). Very ruck and running heavy.
Here is a video that gives a good idea of what to expect.
Note: There is a lot of running and it is in military boots. The course is heavy on obstacle course training. The ruck marches are fast and you can expect them to be on hilly trails.
Below are a couple of pages on the selection and training. The first page states a 6-week basic fitness program is available upon request.
The second page has this recommendation.
To get fit, and stay that way, we suggest that recruits put an exercise programme together. The programme needs to combine stamina exercises – such as running and swimming – and strength exercises like press-ups.
I would add rope climbing in a gym. It is good exercise and you can expect it at some point of your training.
I am retired from the US Army and my opinion is kettlebells are the best option this point of your training. You will get them most result for the time spent. Barbells could be used for an area that needs improvement. I didn't see a post that said where you currently are in S&S other than practicing six days a week. You may need to adjust this if you add other demanding physical training. You need to do press-ups/sit-ups/pull-ups as other training can help with the numbers there is no substitute for doing them.
The Parachute Regiment Assessment Course
You will need to attend a Parachute Regiment Assessment Course which is held at The Parachute Regiment Assessment Centre (PRAC) at Catterick. The course comprises of a series of physical tests to examine your durability and physical fitness. The assessment covers three days and upon successful completion you will be given a start date to join a platoon in PARA Company. (click here to download the PRAC course program) Individuals should ensure that prior to attending PRAC they have conditioned themselves to hill running to improve basic stamina and fitness.
Frequently Asked Questions
What is PRAC?
The Parachute Regiment Assessment Course.
Where does Parachute Regiment training take place?
At the Infantry Training Centre, Helles Barracks, Catterick.
What sort of fitness training should I do?
Potential recruits can contact us for a 6-week basic fitness programme.
http://www.army.mod.uk/infantry/regiments/parachute/24313.aspx
Combat Infantryman's Course - PARA
Much is demanded of recruits at ITC Catterick, both mentally and physically. All recruits must be prepared, arrive with a positive attitude and be ready to learn a lot. Recruits usually find that Army life is different from anything they have experienced, and they need to adjust quickly to the Army’s discipline and rules.
Course overview
The Combat Infantryman’s Course – PARA builds up recruits’ skills and fitness bit by bit. In rough order, this involves learning individual skills first, followed by team/section skills and then platoon skills, ending with an assessment.
During training, recruits are taught the importance of discipline, integrity, loyalty and respect for others. They learn that being a soldier is about putting others first and having the courage to do the right thing in any given situation.
This version of the CIC is two weeks longer than the Line Infantry version. Greater emphasis is placed on fitness, bearing in mind the higher fitness standards of the Parachute Regiment.
Fitness
There's lots of exercise in the course including sports, running, gym work, swimming, the assault course and general physical training. Fitness is very important. The training is tough, so it’s important that recruits get in shape before they arrive at ITC Catterick. The fitter they are, the easier it is. It’s vital that recruits don't let their fitness slip between selection and arrival at ITC Catterick.
To get fit, and stay that way, we suggest that recruits put an exercise programme together. The programme needs to combine stamina exercises – such as running and swimming – and strength exercises like press-ups. Recruits should spend between 40 and 60 minutes exercising, four days a week. Recruits due to arrive at ITC Catterick will find the Army Fitness site useful – click ‘Fitness’ on the right.
Combat Infantryman's Course - PARA - British Army Website