When a muscle contracts while it shortens (concentric), it consumes ATP I believe primarily due to cross-bridge shortening to remove the myosin head from it's attached state.
However, when a muscle contracts while it lengthens (eccentric), it must absorb negative mechanical energy. Is this negative mechanical energy absorbed used to disengage an attached cross bridge and thus doesn't require as much ATP?
If fatigue of concentric muscle contraction results from a shortage of ATP for contraction, is there a similar rule for eccentric contractions. Since it is known that eccentric contractions cost 5x less metabolically then concentric contractions, where do these savings come from?