Adjustable office arm chair structure with articulation for the synchronous movement of the seat and the backrest

An office chair apparatus comprising:

• a seat;
• an adjustable backrest having a support frame;
• a swivelable movable base:
• a height-adjustable column extending upwardly from said base, said column supporting said seat and said backrest thereon;
• a headrest adjustably supported by said backrest, said backrest having an adjustable lumbar support thereon;
• a central support body anchored to a top of said column along a vertical axis thereof, said seat being frontally connected to a corresponding anterior side of said central support body;
• a pair of armrest stanchions having respective lower ends hingedly connected to a posterior side of said central support body, said pair of armrest stanchions being hingedly connected in a position intermediate said support frame of said backrest, said support frame of said backrest being hingedly connected at opposite sides thereof to a posterior portion of said seat;
• a compressed spring interposed between said central support body and said support frame of said backrest so as to allow an oscillating movement between said backrest and said seat;
• and
• a locking means cooperative with said backrest and said seat so as to fix a position of said backrest relative to said seat and for selectively preventing against the oscillating movement therebetween, said central support body comprising:
• a plate that is cantilevered and extends toward an anterior part of said seat;
• and
• a pair of parallel arms having an arched shape, each of said pair of parallel arms defining a hinged brace pivotally connected to said seat.