Heart contractility

["guest@endurance.net" <guest@endurance.net>]

beth Glace lb@nismat.org
Hi Frank,
the response of cardiac muscle depends upon the type of training.
Strength-trained individuals, ie weight lifters, have enlarged hearts due to an increase in wall thickness: muscular hypertrophy.  The chambers are made smaller due to this hypertrophy.  The contractile force does increase with this type of training, but the volume of blood ejected from the heart is decreased due to reduced chamber size.
Endurance training results in larger chambers, but not thickened walls, resulting in overall enlargement of the heart.  Stroke volume increases, thus increasing cardiac capacity:  a larger volume can be circulated per beat of the heart making the heart more efficient.  
Christine Murphy, PAC
Department of Cardiology/Orthopedics
Lenox Hill Hospital

Beth Glace, MS
Sports Medicine
Lenox Hill Hospital
NY, NY



<<If the heart actually increases in size, is it's "increase" in all areas? 
 Wouldn't the THICKNESS of the chamber walls increase as well?  And if so, 
wouldn't the contractile strength actually be DECREASED rather than the 
"desired" increase?
    I don't know, but the effect of a "thickness" increase could affect all 
cardio-pulmonary efficiency and seriously endanger the horse.
    I'm not a vet, I'm barely literate, but if anyone knows if the phenomenon 
described could happen, I sure would be interested in knowing.

Thanks,
   Frank.