As a title-winning coach with Adelaide Strikers in the KFC Big Bash League and with Yorkshire in England's county championship, Jason Gillespie has witnessed cricket's contemporary evolution from a vantage point few can match.

And the former Australia fast bowler has noted a distinct shift in players' aspirations and expectations over recent years that are subtly shifting the game's demographics, and might potentially bring profound change to the Test format.

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With the Strikers finishing third in the BBL|09 regular season, and eyeing his third season in charge of Sussex in the UK after five years at the helm of Yorkshire, Gillespie can claim a rare breadth and depth of coaching experiences.

During that time, he has witnessed a growing number of senior cricketers keen to walk away from the first-class game upon passing age 30 with the aim of ending their careers in the shorter formats, a fact borne out even today by the news that New Zealand leg-spinner Todd Astle – a member of the Black Caps XI for the final Test of their recent Domain Series in Australia – was turning his back on red-ball cricket to concentrate on the shorter formats.

"As I've got to the back end of my career I've found it harder to maintain the level of commitment required to be fully invested in this (long-form) version of the game," 33-year-old Astle said in announcing his decision.

But while Gillespie expects that trend to continue growing among players of Astle's seniority, he also expects that ever more players will make choices much earlier in their careers to specialise in one-day (50-over) cricket and – potentially in even greater numbers – the 20-over format.

"I'm seeing players, and hearing of players, from all age groups who want to have conversations about the prospect of focusing on the shorter forms of the game," Gillespie told cricket.com.au recently.

"It's happening everywhere.

"Certainly, every county in England has at least one player who is having a conversation about potentially wanting to specialise in the shorter forms of the game."

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For many ageing stars the likes of South Africa duo AB de Villiers and Dale Steyn, who signed with the KFC Big Bash this season having called time on their international commitments, the appeal of short-format competition is often the smaller window it occupies in the annual playing schedule.

However, Gillespie believes that the ongoing growth of T20 franchise competitions around the globe means young players who doubt they will earn international playing honours also see those tournaments as a genuine opportunity to experience life as an international cricketer.

In addition to established series such as BBL, the Indian Premier League and T20 tournaments in Pakistan and the Caribbean, South Africa launched their domestic T20 event last year and England's franchise-based The Hundred – a new twist on the 20-over format – begins in mid-2020.

As a result, players who might have otherwise foreseen their futures confined to state or county teams now believe honing their short-form skills might offer a more realistic chance to strut their stuff on the world stage as professional cricketers.

"If you've never played international cricket, it's the next best thing," Gillespie said of the lure that T20 competitions now provide.

"To play in different countries, be exposed to different cultures, different team environments, with different teammates and coaches.

"While there's certainly a financial carrot being dangled to become a franchise T20 player, there's also the opportunity to learn and improve and develop your game in a different environment, with different coaches who have different ideas on the game.

"It's exciting, and I think a lot of players are seeing that as a career path, especially if they don't see a future representing their own country.

"So I think we'll see more and more players making that that choice."

Gillespie also challenges perceptions that 20-over cricket holds appeal for players entering their twilight on-field years because it takes a lesser toll on their bodies.

The former quick, who played 71 Tests and 97 one-day internationals for Australia as well as a stint in the ill-fated Indian Cricket League T20 competition, echoed the thoughts of fellow fast bowler Mitchell Johnson that 20-over cricket can be the most physically demanding.

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He claimed that was certainly the case for fast bowlers, who often take longer to recover from four overs at the crease and 16 overs in the field than they do to bounce back from a full ODI or four consecutive days of first-class cricket.

"It's because you're just not getting the volume and you're bowling in a high-intensity game," Gillespie said.

"So don't assume that T20 – because it's less overs – puts less stress on the body.

"I know players who pull up less sore from a 50-over game and from a day of (English county) Championship cricket than from a 20-over game."

Gillespie believes there will always be a strong core of players, particularly in Australia and the UK, who prioritise Test cricket over the shorter formats.

But as he's seen across almost a decade, since taking over as Yorkshire coach in late-2011, a Test cap is no longer the single, unifying ambition of a cricketer progressing through pathway programs into senior competitions.

"Ten years ago, that (Test ambition) was pretty exclusive, or it was very rare for someone to say, 'I prefer to play the shortest form of the game'," he said.

"But now, the players are increasingly looking at one-day and T20 as a genuine career option and foregoing the long form of the game."

Consequently, Gillespie admits to holding fears for the primacy of cricket's elite form among some of the 12 current Test-playing nations.

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Test cricket will long remain a cornerstone in Australia and the UK, and over the immediate-term in India where – despite the upsurge in support for the IPL – the patronage of current men's captain Virat Kohli (an avowed advocate for Tests) will ensure the longest format remains strong.

Global administrators also see Pakistan (where Test cricket has recently returned after a prolonged hiatus due to security concerns) and Bangladesh as future standard-bearers for the Test game on the back of their vast populations and resultant pools of player talent.

However, on their most recent Test visit to Australia last November, Pakistan fielded a fast-bowling attack featuring teenagers Shaheen Shah Afridi (19), Muhammad Musa Khan (19) and Naseem Shah (16) after left-arm strike bowler Mohammad Amir (27) quit Test cricket to pursue short-form opportunities.

It's a similar situation to which the West Indies Test outfit has found itself in recent years, and other small nations (such as Sri Lanka) plus those not blessed with hefty coffers (South Africa and New Zealand) have faced questions about the viability of Test cricket in their respective domains.

Gillespie, who began his coaching journey in Zimbabwe's domestic franchise competition in 2010 and has also served as head coach for Papua New Guinea's national men's team, acknowledges the gathering appeal and drawing power of T20 competitions presents challenges for the Test game.

"I've got concerns for Test cricket outside of Australia and England," he said.

"India, I think there is still the appetite for the game because Indians just love cricket even though 50-over and T20 still rule there, and it's encouraging to see that New Zealand still rate it.

"But I fear for Test cricket in places like the West Indies and Sri Lanka and South Africa.

"It will always have a place here and in England, but the rest of the world I'm not so sure about.

"I guess we just have to wait and see."