Players are now being set "targets" to reach rather than "restrictions" as part of a raft of changes in Australian cricket's new youth pace bowling guidelines. In some cases, juniors will be allowed to bowl more.

The management of the nation's fast bowlers has become a controversial topic with many old timers believing workload limits imposed by sports science were leading to more injuries rather than preventing them.

While there are still recommendations on how many balls a junior should deliver a week, new research has found the frequency of bowling had a greater bearing on a bowler's susceptibility to injury rather than volume.

Back stress fractures are an occupational hazard for fast bowlers until they reach the age of 24 when bones harden. Test quicks Mitchell Starc, Josh Hazlewood, Pat Cummins and James Pattinson have all suffered serious back injuries in their early years. Pattinson, 27, was forced out of the upcoming tour of Bangladesh due to a back issue.

CA believes the changes will improve the resilience of players entering elite ranks by narrowing the gap in workloads, prevent bone injuries later in their careers and help retain talent that would otherwise be lost due to injury.

Under the new measures, players are being advised to avoid bowling more than two days in a row and on no more than four days a week.

"We're thinking during that developmental stage if you give the bone a hint of loading on one day, we know physiologically it needs some hours, days to repair itself, just like muscles do," CA's sports science and sports medicine manager Alex Kountouris told Fairfax Media.

"When you go to a gym and feel sore the next day, that's the muscle repairing itself and making itself bigger and stronger for the next session. Bone does the same thing, you just don't get bone pain so you don't feel it.

"If you bowl 150 balls in a week, you're better off bowling them in three or four sessions rather than five or six. Having that time to recover between sessions is valuable.

"We're hoping the bones become stronger and more resilient by taking this approach."

In other changes:

• the change in age groups to align with pathway programs means under 14s, 16s and 18s, now competing with 15s, 17s and 19s respectively, can bowl an extra two overs a day.
• players will also be allowed to make up for overs they do not get in a game at training, which will help conditioning and skill development.

While Kountouris said players would still be vulnerable to injury until their bones matured, he believed CA's guidelines would create a "higher threshold" during that period.

"We're hoping you maximise the strength of the bone during the developmental phase," Kountouris said.

"That's the fundamental difference between a 17-year-old and a 28-year-old - their bones have hardened up and they can tolerate a lot more.

"If we get them as pristine as possible we'll get them through their whole career."