INSTRUCTOR AND CFI STUDENT PLT DECLARE EMERGENCY WHEN PITCH CONTROL OF PA28 FEELS HEAVY AND EXCESSIVELY SLUGGISH IN RESPONSE.

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ON A CFI CANDIDATE TRAINING FLT; THE PITCH CTL OF THE ACFT BECAME NOTICEABLY HEAVIER FOR UNKNOWN REASONS. THIS WAS THE THIRD FLT OF THE DAY FOR THIS ACFT; WHICH HAD BEEN USED EARLIER IN THE DAY FOR PATTERN WORK FOR APPROX 2 HRS. UPON RECONFIGURING THE ACFT AFTER PRACTICING 'SLOW FLT;' THE ACFT PITCH CTL BECAME INCREASINGLY HEAVIER. WE THOUGHT THAT THE TRIM MIGHT HAVE BECOME STUCK IN A 'NOSE UP' POS. THE STUDENT STATED TO MYSELF (THE INSTRUCTOR) THAT THE CTLS FELT HVY AND THAT A LARGER THAN NORMAL AMOUNT OF FORWARD YOKE PRESSURE WAS NECESSARY TO MAINTAIN LEVEL FLT; EVEN THOUGH HE HAD ADJUSTED THE TRIM BACK TO A NORMAL POS FOR AN INCREASING AIRSPD. I FELT THE CTLS AND GLANCED AT THE TRIM WHICH WAS SET SLIGHTLY IN THE 'NOSE DOWN' POS AND CHKED THE CTLS AND ALSO AGREED THAT THE ACFT NEEDED MORE FORWARD PRESSURE THAN NORMAL. THE STUDENT (CFI CANDIDATE) AND I BOTH INITIALLY THOUGHT THAT THE ACFT TRIM MIGHT HAVE GOTTEN STUCK SLIGHTLY NOSE UP. UPON ADJUSTING THE TRIM MORE 'NOSE DOWN' THE ACFT CTLS STILL FELT HVY AND THE ACFT NEEDED FORWARD PRESSURE TO MAINTAIN LEVEL FLT. AT THIS POINT; I DECLARED AN EMER WITH ZZZ DEP AS I WAS UNSURE WHAT WAS CAUSING THE CTLS TO FEEL SUBSTANTIALLY HEAVIER; AND THE ACFT CTL PRESSURE SHOULD HAVE BEEN RELIEVED BY THE AMOUNT OF NOSE DOWN TRIM THAT WE HAD INPUTTED. I PROCEEDED TO THE ZZZ ARPT. AS THE ACFT SLOWED DOWN TO AN APCH SPD; IT WAS NOTED THAT THE CTL PRESSURES BEGAN TO FEEL NORMAL AND THE ACFT HANDLED NORMAL DURING THE LNDG FLARE. AFTER INITIAL INSPECTION FROM ACFT MAINT ON FIELD; THERE WAS NO APPARENT PROB WITH THE ACFT TRIM WHEEL OR TRIM TAB. MAINT WAS UNABLE TO DUPLICATE THE PROB. AS A PRECAUTION; MAINT FURTHER INVESTIGATED THE PROB AND NOTED THAT A FEW OF THE ELEVATOR PULLEYS WERE AGED. ALTHOUGH STILL FUNCTIONAL; THE MECH RECOMMENDED THAT THE PULLEYS BE REPLACED SINCE THEY APPEARED TO BE THE ORIGINAL ON THE 1976 ACFT. THE FLT SCHOOL CHOSE TO REPLACE THOSE PULLEYS.