Frank,   You should not be resting your elbow on the counter while 
sectioning.  The elbow on the counter will cause the wrist to bend back and 
forth and that causes discomfort and can lead to carpal tunnel.  Section with 
shoulders relaxed, head slightly forward, arm close to the body (no flying 
elbows), elbows bent, wrist straight.  Most of us cannot adjust the counter 
height, so maybe your chair needs to be adjusted higher so that your elbow 
does not rest on the counter.  Get up and stretch periodically, repetitive 
motion for long periods of time can increase risk for cumulative trauma 
disorders.  Stretch the shoulders, neck, arms and hand and fingers.  Or just 
get up and do something else.  
Consider an electronic microtome.   They are great.  Do you want me to send 
you some info?   I have a handout for a workshop in ergo that I will be 
giving in Providence.  Included are some source for ergo products.  
Pearl Gervais