Home buyers refinancing their loans were the most active participants in the mortgage market during the September quarter, according to a leading aggregator group.AFG's latest Mortgage Index shows that refinancing accounted for 38 per cent of the applications lodged by AFG brokers in the September quarter.Investors accounted for 32 per cent of applications, "upgraders" for 34 per cent and first-home buyers for eight per cent.Refinancers have been the driving force behind AFG's business since the middle of last year, when the Australian Prudential Regulation Authority's crackdown on mortgage lending to investors started to bite.AFG brokers lodged 31,649 applications worth A$15.2 billion during the quarter - an eight per cent increase over the same period last year.The average loan size was $480,094 and the average loan-to-valuation ratio was 69.2 per cent - down from an average LVR of 69.3 per cent in the June quarter.Sixty-eight per cent of applications were for standard variable rate loans and 15.9 per cent were for fixed rates.