C172 PLT HAS RWY EXCURSION AT POU.

Narrative

I WAS WORKING IN THE PATTERN; PRACTICING TOUCH-AND-GO LNDGS. THIS WAS MY FIRST LNDG OF THE DAY. THE RWY IN USE WAS RWY 24; WHICH WAS THE USUAL RWY ASSIGNED BY ATC. THE WIND WAS VARIABLE AT 3-4 KTS; WHICH GENERALLY REQUIRES SOME CTL INPUTS ON SHORT FINAL DUE TO THERMALS. I HAD FLAPS AT 20%; AIRSPD WAS 68 KIAS; AND I WAS ON THE VASI. AFTER TOUCHDOWN; I RAISED THE FLAPS AND APPLIED FULL PWR. I APPLIED A SMALL AMOUNT OF R RUDDER (COMPENSATING FOR TORQUE). THE AIRPLANE FELT LIKE IT WASN'T HANDLING PROPERLY AND STARTED TO WEAVE L. AS I VEERED OFF THE L SIDE OF THE RWY; THE WEAVING GOT MORE AND MORE EXAGGERATED AND I PICKED UP SPD. I PUSHED IN THE THROTTLE. I DID NOT VERIFY MY AIRSPD INDICATOR; BUT IMAGINE I WAS DOING ABOUT 55 KIAS. I HAD ALL I COULD DO TO MAINTAIN A RELATIVELY STRAIGHT PATH ACROSS THE GRASS BTWN THE RWY AND TXWY. ATC DIVERTED A LNDG ACFT ON SHORT FINAL DURING THIS TIME AND ASKED IF I WAS OK. I HAD REGAINED CTL AND WAS MOVING ACROSS THE INFIELD; STILL IN A RELATIVE STRAIGHT LINE; MAKING FOR A TXWY TO GET BACK TO THE FBO. I DID NOT HIT ANYTHING DURING THE INCIDENT (LIGHTS; RWY SIGNS; ETC) BUT THE C172 TOOK SOME GOOD BUMPS. I BELIEVE THE CAUSE OF THE INCIDENT WAS; THE HEEL OF MY FEET NOT BEING ON THE FLOOR WHEN I BEGAN APPLYING RUDDER INPUT FOR THE TKOF. THIS WOULD HAVE ACTUATED THE BRAKES; AND MY ATTEMPTS INITIALLY TO CTL THE AIRPLANE ONLY MADE MATTERS WORSE. WHILE TAXIING BACK TO THE FBO; THE BRAKES WORKED FINE AND ALL CTL INPUTS FELT NORMAL. THE MECH CHKED OUT THE PLANE AND I RETURNED TO FINISH UP MY PRACTICE TOUCH-AND-GO'S WITHOUT FURTHER INCIDENT. I CAN'T EXPLAIN WHY I WENT OFF THE L SIDE OF THE RWY IF I WAS BRAKING R. UNLESS; I STARTED A SLIGHT MOVEMENT TO THE R AND APPLIED L RUDDER (BRAKE) TO COMPENSATE. THINKING BACK; THIS IS NOT TOO CLR.