meaning of isotonic contraction/movement

[sarahjay8]

Question: some definitions of isotonic movement say it means equal tension while others same it’s the muscle shortening as the tension increases: what is it? Can the tension increase over time even know the weight remains the same?
thanks

[mith]

http://en.wikipedia.org/wiki/Isotonic_( ... physiology)

So tension is the reaction force on the muscle fiber. Assume a tension force equal to the weight if you're just holding it. However if you're trying to lift it, you have a tension force equal to the weight plus the acceleration upwards(the force of lifting). Therefore the tension force is higher. Draw a force diagram if this is unclear.