Injuries to frontline contenders in the Terex Australian Supercross Championship were apparent at Phillip Island over the weekend, with just 10 riders completing Sunday’s SX-Open main event.

On the biggest stage of the year alongside the Tissot Australian Motorcycle Grand Prix, participation in the premier class final at round five was down by near 50 percent compared with 2012 when a full grid of 20 riders started the main event.

A total of 14 riders contested the opening Open practice session on Saturday, however Motorex KTM’s Kirk Gibbs was ruled out due to injuries sustained in South Australia the weekend prior after just three laps.

“My ribs were sore as expected but I thought they’d be right,” Gibbs explained. “I tried riding yesterday morning but as soon as I did a little double I got real weak.

“I went to RACESAFE and talked to them and they think there’s more going on than meets the eye, so we’ll look into it some more. There’s no point being out there if I can’t be competitive.”

Later that afternoon, CDR Yamaha’s Kade Mosig sustained a broken wrist, effectively sidelining CDR Yamaha as teammate Lawson Bopping had already opted out of the weekend with a knee injury from Mount Gambier.

American Weston Peick (Carlton Dry Honda) won on Saturday to take over the points lead, but suffered a broken collarbone in Sunday morning qualifying to further deplete the field.

A total of 11 riders started Sunday’s main event, however returnee Brett Metcalfe registered a DNF, resulting in the concerning 10-rider conclusion.

Prior to the season, Monster Energy Kawasaki rider Adam Monea suffered a dislocated shoulder, dashing his hopes of a maiden 450 supercross campaign. He won’t return until 2014.

The SX-Lites class was also thin throughout the weekend, with 16 riders qualifying for both days of competition. Kale Makeham (Tunetech Racing KTM) was declared out of the season remainder after also injuring his shoulder in round three.

Riders who gritted out the weekend through injury included Lites title contender Luke Styke (Serco Yamaha) despite a shoulder injury, as well as Daniel McCoy (Motorex KTM), whose dramatic start straight crash in the round four main event was a major talking point on Saturday.

Of the remaining championship categories, Under 19s featured 15 starters on Friday, while the Women and Junior Lites had six-rider fields apiece. All three were reduced by their final races of the weekend.

Rider numbers competing on a national level have been key in discussions for the sport’s future over recent months, the evident decline instrumental in developing ongoing structures for 2014 and beyond.

Darwin’s season-opening double-header last month featured 16 riders each across the Open and Lites fields, despite series promoter International Entertainment Group claiming “full grids” in the series lead-up (click here to view).

Earlier this year, the Monster Energy MX Nationals season started in April at Raymond Terrace with 29 riders completing the opening MX1 session, 47 in MX2 and 58 in MXD (Under 19s). Series promoter Williams Event Management (WEM) made an exception for the opening round to accept more than 40 entries, using a qualifying structure to decide the moto grids.

By Coolum’s ever-popular season finale, which fell just two weeks before International Entertainment Group (IEG) scheduled the supercross opener, those amounts were 29 (MX1), 26 (MX2) and 35 (MXD) respectively according to timing and scoring documentation.

Both series have experienced fluctuation at times during the course of their respective seasons.