Flintoff's action problems
1. His front foot is pointing towards fine leg rather than at the batsmen
2. The knee twists as the top half of the body rotates
3. Hips and shoulders need to be straighter towards the batsman
Former Australia bowler Damien Fleming believes Andrew Flintoff faces a tough challenge to modify his bowling action.
Flintoff has asked England fast bowling adviser Allan Donald to help him straighten his left foot at the point of delivery to avoid further injuries.
But Fleming, who was forced to change his action because of injury, said the lower body is more difficult to alter.
"He needs to get his hips and knee straighter to the target, but it will be tough at 29," he told BBC Sport.
"Fast bowlers have a higher injury rate compared to other sports. I found when I was coaching (at Australia's centre of excellence in Adelaide) bowlers seem to be able to change their top half of their action easier than their bottom half."
Flintoff recently resumed playing after a third operation on his left ankle and has since been named in England's one-day and ICC World Twenty20 squads.
The all-rounder bowled three overs and took 1-24 in Lancashire's eight-wicket defeat to Gloucestershire in the Twenty/20 Cup semi-final at Edgbaston without apparent discomfort.
But Donald is concerned Flintoff's current action, where his front foot points inwards rather than straight towards the batsman, is placing excessive stress on the bone and muscle.
"It is not something that I am going to start working on modifying," said Donald. "It would have to be done in the close season. It is up to Freddie to decide."
If his action gets streamlined too much, he may lose some of his main weapons
Biomechanical research has shown that a fast bowler's leading leg will absorb a downward force equivalent to 10 times their body weight at the point of delivery.
Therefore any misalignment in a bowler's action will add extra pressure on to an already overworked front leg.
However Fleming warned any change in action could potentially negate Flintoff's main strengths.
"When you talk to batsmen they say his (Flintoff's) arms and legs fly everywhere, taking a lot of focus away from the ball," said Fleming, who took 75 wickets in 20 Test matches for Australia in a seven-year span.
"If his action gets streamlined too much, he may lose some of his main weapons - his unpredictability and extra bounce because of his high arm action.
Fleming retired from cricket in 2003 to concentrate on coaching
"You tend to lose a lot of potency when you're injured and that's been the test for 'Freddie' over the last 12 to 18 months.
"However he could turn into a 'shock' bowler rather than the stock bowler he has been for the past few years."
Fleming's career was cut short by injury despite making significant modifications to his bowling action.
"I changed my action halfway through my career at 26," said Fleming, who is now working as a television commentator.
"I lost a fair bit of pace and bounce and had a lot of back knee collapse, so I had to straighten up my action a fair bit. It took me five to six months of the pre-season to do that.
"You start by running on a track and using straight lines to land your back and front feet in a straight line. It took a lot of repetition because I had trained myself with bad habits.
"So it was about training with the good habits and it took me a while to get used to it."